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Green Biosynthesis of Tin Oxide Nanomaterials Mediated by Agro-Waste Cotton Boll Peel Extracts for the Remediation of Environmental Pollutant Dyes
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  • Boya Palajonnala Narasaiah
    Boya Palajonnala Narasaiah
    CASEST, School of Physics, University of Hyderabad, Prof. C. R Rao Road, Gachibowli, Hyderabad 500046, Telangana, India
    Laboratorio de Cerámicos y Nanomateriales, Facultad de Ciencias Físicas, Universidad Nacional Mayor de San Marcos, Ap. Postal 14-0149, Lima 14, Peru
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  • Pravallika Banoth
    Pravallika Banoth
    CASEST, School of Physics, University of Hyderabad, Prof. C. R Rao Road, Gachibowli, Hyderabad 500046, Telangana, India
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  • Arya Sohan
    Arya Sohan
    CASEST, School of Physics, University of Hyderabad, Prof. C. R Rao Road, Gachibowli, Hyderabad 500046, Telangana, India
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  • Badal Kumar Mandal
    Badal Kumar Mandal
    Department of Chemistry, School of Advanced Sciences, Vellore Institute of Technology, Vellore 632014, Tamil Nadu, India
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  • Angel G. Bustamante Dominguez
    Angel G. Bustamante Dominguez
    Laboratorio de Cerámicos y Nanomateriales, Facultad de Ciencias Físicas, Universidad Nacional Mayor de San Marcos, Ap. Postal 14-0149, Lima 14, Peru
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  • Luis De Los Santos Valladares*
    Luis De Los Santos Valladares
    Laboratorio de Cerámicos y Nanomateriales, Facultad de Ciencias Físicas, Universidad Nacional Mayor de San Marcos, Ap. Postal 14-0149, Lima 14, Peru
    Cavendish Laboratory, Department of Physics, University of Cambridge, J.J. Thomson Avenue, Cambridge CB3 OHE, U.K.
    School of Materials Science and Engineering, Northeastern University, No 11, Lane 3, Wenhua Road, Heping District, Shenyang 110819, Liaoning, People’s Republic of China
    *Email: [email protected]
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    Orcidhttps://orcid.org/0000-0001-5930-9916
  • Pratap Kollu*
    Pratap Kollu
    CASEST, School of Physics, University of Hyderabad, Prof. C. R Rao Road, Gachibowli, Hyderabad 500046, Telangana, India
    *Email: [email protected]
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    Orcidhttps://orcid.org/0000-0001-6250-9396
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ACS Omega

Cite this: ACS Omega 2022, 7, 18, 15423–15438
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https://doi.org/10.1021/acsomega.1c07099
Published April 26, 2022

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Abstract

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The sustainable synthesis of metal oxide materials provides an ecofriendly and more exciting approach in the domain of a clean environment. Besides, plant extracts to synthesize nanoparticles have been considered one of the more superior ecofriendly methods. This paper describes the biosynthetic preparation route of three different sizes of tetragonal structure SnO2 nanoparticles (SNPs) from the agro-waste cotton boll peel aqueous extract at 200, 500, and 800 °C for 3 h and represents a low-cost and alternative preparation method. The samples were characterized by X-ray diffraction, Fourier transform infrared spectrophotometry, ultraviolet–visible absorption spectroscopy, high-resolution transmission electron microscopy (HR-TEM), and energy-dispersive X-ray spectroscopy. Surface area and porosity size distribution were identified by nitrogen adsorption–desorption isotherms and Brunauer–Emmett–Teller analysis. The photocatalytic properties of the SNP samples were studied against methylene blue (MB) and methyl orange (MO), and the degradation was evaluated with three different size nanomaterials of 3.97, 8.48, and 13.43 nm. Photocatalytic activities were carried out under a multilamp (125 W Hg lamps) photoreactor. The smallest size sample exhibited the highest MB degradation efficiency within 30 min than the most significant size sample, which lasted 80 min. Similarly, in the case of MO, the smallest sample showed a more superior degradation efficiency with a shorter period (40 min) than the large-size samples (100 min). Therefore, our studies suggested that the developed SNP nanomaterials could be potential, promising photocatalysts against the degradation of industrial effluents.

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1. Introduction

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Over the last years, the novel synthesis of nanomaterials such as metal, metal oxide, and metal sulfide nanoparticles have gained much attention. Metal, metal oxide, and their composites have become an exciting area in nanoscience and technology due to the many applications in versatile fields and even proven promise in human life aspects. (1) Synthesis of nanoparticles through eco-friendly routes attracted much awareness in recent years because of its environment friendly nature, that is, nontoxic to the environment, reaction process, short time, low temperature, and safe, mild reaction conditions. (2) However, modifying the surface area of the nanoparticles through the natural reducing and capping agents remains challenging. Nevertheless, nanoparticles can be generated by green chemical agents that are plant extracts that possess even higher stability. (3) The green process synthesis of metal oxide nanoparticles, particularly tin oxide nanomaterials using plant extract, is an alternative method to the chemical synthesis that could control the chemical toxicity to the environment and control the size and shape of the nanomaterials. (4) State of the art shows the possibilities of synthesis nanomaterials in an aqueous medium with reducing agents that counts the hydroxyl group of polyphenols that possess the stabilizing/capping agents without using hazardous chemicals. (5) Moreover, green synthesized nanomaterials are gaining interest in the research fields, environmental sciences, synthetic chemistry, nanobiotechnology, and material chemistry, respectively. (6) Among various nanomaterials, SnO2 nanomaterials are considered an alternative source for degradation of water purification/environmental pollutants because they possess outstanding UV light absorption and generate reactive oxygen species (ROS) that lead to the degradation of environment pollutant dye molecules. (7,8)
Tin oxide nanoparticles (SnO2 NPs) are widely used in several fields such as photocatalytic activity, energy storage application, and organic transformation used as catalysts in various fields. (9) The literature reports the synthesis of SnO2 NPs (SNPs) through multiple methods. Nejati-Moghadam et al. (2015) reported the production of SnO2 nanostructures by the precipitation method, (10) Ling Zhang et al. (2018) reported cubic sub-micron SnO2 particles for the reduction of nitrogen to sustainable process for scalable NH3 synthesis with less energy consumption, (11) and Haspulat et al. (2020) have synthesized SnO nanoparticles in the presence of Triton-X 100 (TX-100) surfactant assisted via the hydrothermal method. (12) Maharajan et al. (2020) reported a nano-Rattle SnO2@carbon composite by melt diffusion method/thermal decomposition methods for the material for high-energy Li-ion batteries. (13) Karmaoui et al. (2018) studied the band gap properties and structural study of SNPs and synthesized a one-step process by the sol gel method. (14) Zhu et al. (2019) reported ultrafine SNPs (diameter 2–4 nm) fabricated on the surfaces of g-C3N4 material through the combination of the hydrothermal method and ball milling in order to improve the dispersion of SnO2 NPs as well as to strengthen the bonding between SnO2 and g-C3N4. (15) These methods are reported to be effective for controlling the shape and size of the nanoparticles. However, all these methods require high temperature, high cost, and environmentally hazardous chemical precursors during synthesis processes. Therefore, environmentally friendly, low-cost, and straightforward production is preferred.
The potential nanomaterials synthesizing through physical and chemical methods are expensive and require high pressure, temperature, and energy. They include prolonged reactions and required toxic reactants and solvents, which are potentially hazardous to the environment. Hence, there is a continuous demand for developing new techniques for nanomaterials synthesis without the above drawbacks. Green synthesis has been adopted nowadays as the best alternative way to overcome the methods mentioned above to synthesize nanomaterials because of several advantages such as a fast and straightforward reaction process, inexpensive approach, environmentally ecofriendly to nature, reduction of metal ions to metal nano, and use of less toxic and hazardous chemicals. The synthesis of metal oxide nanomaterials through plant extracts has turned very promising because it allows both reducing and capping agents. (16) In fact, plant extracts have various phytochemical constituents, that is, secondary metabolites such as alkaloids, terpenoids, flavonoids, antioxidants, and amino acids, respectively, which exist in fruits, peels, seeds, and leaves that permit the replacement of the traditional toxic chemicals for the synthesis of nanomaterials. (17) Diallo et al. (2016) reported the preparation of n-type SNPs by a green chemistry process using Aspalathus linear natural extract as an effective chelating agent. The obtained SNPs exhibited photocatalytic degradation of methylene blue (MB), Congo red, and Eosin Y. (18) Matussin et al. (2020) also reported plant-extract-mediated SNPs. (19) Singh et al. (2019) synthesized SnO2 NPs through pomegranate leaves (Punica Granatum), and the obtained SnO2 NPs (20 nm) showed 91.5% photodegradation efficiency of MB dye under direct sunlight within 240 min. (20) Bhattacharjee et al. (2015) developed a green process of SnO2 quantum dots using the amino acids aspartic and glutamic as reducing agents and used for the photocatalyst in the degradation of Rose Bengal and Eosin Y dye under direct sunlight. (21) Sinha et al. (2017) green fabricated sphere-shaped Ag–SnO2 nanocomposites (9 nm) employing stem extracts of saccharin officinarum and used as a photocatalyst and prospective antibacterial and antioxidant agents. (22) Sudhaparimala et al. (2016) reported coupled semiconductor SnO2–ZnO NPs using the assisted gel of aloe vera plants as the medium. They studied the photocatalytic activity of the organic dye methyl orange (MO) degradation in the presence of visible light. They also studied the antibacterial activity of staphylococcus aureus and Escherichia Coli growth at the microgram level. (23)
Currently, photocatalysis applications for addressing environmental issues such as environmental pollution and energy crises have attracted more and more attention and gradually become a research hotspot. The most common pollutants identified in urban and industrial areas are volatile organic compounds such as toluene, benzaldehyde, benzyl alcohol, and chlorinated derivatives. (24) Volatile organic compounds are dangerous for human health, and they are toxic, mutagenic, and carcinogenic to all human beings. Nowadays, research has mostly been focused on the toxicity of volatile organic compounds sources or the degradation conditions rather than the byproducts generated during the treatment procedures. (25) The drawback of traditional methods such as absorption, incineration, and condensation used for removing volatile organic compounds from pollutants is that they are costly, have a short life, and lead to the production of secondary pollutants. (26) Some approaches have been devised recently to solve the problem. Photocatalysis is a promising technology for purifying wastewater and textile dyes under visible/ultraviolet light irradiation. For example, Cu–Fe2O3/Ni–ZnO nanoplate is an excellent photocatalyst for the degradation of environmental pollutants in visible light. It allows the mineralization of CO2 and water molecules. (27) The photocatalyst activity of nanoparticles mainly depends on their high surface area, size, shape, and less band gap energy. (28) Tuan et al. (2019) noticed that the photocatalyst activity of SnO2/rGO nanocomposites depends on their morphology, structure, and size. (29) Jiang et al. (2021) studied the anode materials for the degradation of organic pollutants by anodic oxidation. (30) Yuanyuan et al. (2018) estimated the degradation of methyl blue (MB) and Rhodamine B (RhB) by the SnO2 nanoparticle photocatalyst in more than 90% for under UV light irradiation within 50 min and 270 min. (31) Huang et al. (2018) prepared a tetragonal phase Bi2O2CO3 catalyst and reported its photocatalytic behavior with the degradation of MO dye under visible light conditions. (32) They also prepared Cerium-based hybrid nanorods (CN-600 to CN-800) photocatalyst; however, the CN-700 catalyst displays a degradation efficiency of 100% for MB in aqueous solution in 90 min. (33)
The present work reports the green production of photocatalyst of tetragonal structure SNPs of different sizes (2–13 nm) from eco-friendly nature, cost effective manner using Agro-waste cotton boll peels with tin Chloride di-hydrate as a precursor. The prepared tetragonal structure SnO2 photocatalyst nanoparticles were characterized by X-ray diffraction (XRD) technique, high-resolution transmission electron microscopy (HR-TEM), UV–visible diffuse reflectance spectroscopy (UV–vis DRS), and surface area analyzed by Brunauer–Emmett–Teller (BET). The tetragonal structure SnO2 photocatalyst offered an enhanced catalytic activity to degrade MB and MO dyes under UV light irradiation.

2. Experimental Procedure

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2.1. Material and Methods

Tin chloride di-hydrate (SnCl2·2H2O), MB, and MO were purchased from Sigma Aldrich to synthesize the SNP samples. All other chemicals and reagents used analytical grade with no purification, and double-distilled water was used as a solvent. Agro-waste cotton peels were collected near the Tungabhadra River, Mantralayam Road, Kurnool District, Andhra Pradesh, India.

2.2. Preparation of Agro-Waste Cotton Peel Extracts

Freshly collected peels were washed 2–3 times under running tap water, followed by sanitizing with Milli-Q water one time and then dried at room temperature under dust-free conditions for 1 week. The preparation followed a similar way reported by Balaji Reddy et al. (2017) to synthesize metal oxide nanoparticles using Eucalyptus globulus leaf. (34) The dried peels were ground into powder through an electric mixer and sieved by a 100 mesh sieving net. About 3 g of powder was added to 100 mL of de-ionized water and kept for boiling on a water bath at 80 °C for 30 min to prepare the aqueous extract. Eventually, the extract was cooled at room temperature, filtered through a Whatman no.1 filter paper, and stored at 4 °C in a refrigerator.

2.3. Synthesis of Tin Oxide (SnO2 NPs) from Agro-Waste Cotton Peel Extract

About 0.329 g of Tin chloride di-hydrate (SnCl2·2H2O) (0.05 M) was dissolved in 30 mL of double-distilled water and subsequently 30 mL of agro-waste cotton peel aqueous extract was added drop-wise while thoroughly stirring at 80 °C for 3 h. The color of the solution changed from light yellow to brown color after 30 min because of the heating process. Then, the mixture was cooled at room temperature and subsequently centrifuged for 30 min at 6000 rpm. The residue was carefully collected and washed three times with absolute ethanol, following washing with double-distilled water and eventually dried on the hot plate at 60 °C. The resulting dried powder followed calcination at 200 °C for 3 h inside a muffle furnace. That sample was labeled as tin oxide (SnO2) nanoparticles (SNPs-2). A similar procedure was used to prepare additional samples, once synthesized and calcined at 500 °C, labeled as SNPs-5, and another at 800 °C (labeled as sample SNPs-8) for 3 h inside a muffle furnace.

2.4. Characterization of the SnO2 Nanoparticles

A X-ray powder diffractometer, Bruker D8, was used to measure the SNPs samples by X-ray diffraction. The data were recorded in the range of 2θ values from 10 to 90° with a scanning rate of 4° min–1 by using the Cu-Kα radiation with a λmax of 1.54 Å. The morphology and size of the synthesized SNPs were inspected by dispersing the SNP samples onto Cu grids through HR-TEM (Model: JEM 2100 USA JEOL) with 0.1 nm resolution and an acceleration voltage of 200 keV. The TEM equipment also provided information about the elemental composition of the samples by energy-dispersive X-ray (EDX) analysis. The optical properties of the synthesized SNP samples were also analyzed by using a Shimadzu (model UV-2450) UV–visible spectrophotometer at room temperature. The bang gap calculations assumed the absorption band. The functional groups in the cotton peel agro-waste aqueous extract SNP samples were analyzed using FT-IR (Fourier transform infrared) spectroscopy. Functional groups determined in purified dried SNP samples using a Shimadzu IR AFFINITY-1 against the agro-waste cotton peel aqueous extract. However, pelted took control under similar instrumental conditions using JASCO FT-IR in the wavenumber range 500–4000 cm–1 at a resolution of 4 cm–1 using potassium bromide pellets in the diffuse reflectance mode. Quanta chrome nova-1000 autosorb-1 instrument was used to determine the surface area and pore diameter through nitrogen adsorption–desorption isotherms.

2.5. Photocatalytic Activity of SNP Samples

The SNP samples were used as a photocatalyst to degrade the MB and MO dyes under UV light irradiation. The present investigation was performed with a Heber photoreactor having multilamp UV lamps (254 nm) with a low pressure of 125 W under continuous stirring. The experiment was carried out by loading 0.02 g of SNP samples with 60 mL of MB dye solution (concentration 10 mg/L) into a quartz tube (100 mL capacity) and then followed by continuous stirring, without disturbance, under the dark condition for 50 min without UV-light exposure to obtain the constant equilibrium. After getting the stable equilibrium, the final solution was exposed with UV light radiations at 125 W, 254 nm, and regular time intervals. The sample was collected in an Eppendorf tube (2 mL capacity) and centrifuged. The degraded de-colorization solution was monitored by UV–vis spectro-photometer analysis to record the de-colorization solution’s absorbance, scanned at 200–800 nm. The catalyst was then recollected after complete de-colorization of MB dye molecules through centrifugation. We also recycled it to check the stability and reusability of the SNP catalyst. The same procedure was repeated for the MO dye degradation and all other samples (SNPs-5 and SNPs-8) to degrade MB and MO dyes. We also studied the effects of varying catalysts and dye concentration for MB and MO degradation of dyes. Thus, the degradation of the samples was recorded by UV–vis spectroscopy.

3. Results and Discussion

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3.1. Determination of Crystalline Nature from XRD-Analysis of SNP Samples

XRD patterns of the samples SNPs-2, SNPs-5, and SNPs-8 are shown in Figure 1 and analyzed to estimate the crystal structure and crystallinity of the nanomaterials. The diffraction pattern of sample SNPs-2 represents reflections at 2θ = 26.53, 34.38, 52.12, and 65.27° which correspond to the diffraction peaks hkl values of lattice planes (110), (101), (211), and (220), respectively (see Figure 1A). The confirmed diffraction pattern corresponds to the tetragonal structure of SnO2 NPs at 200 °C, which matches the standard Match3 software (JCPDS card no: 96-210-4744). Because the XRD pattern presents monophasic diffraction, that confirms the purity of the SNP-2 nanomaterials. Figure 1B presents the XRD pattern of the SNP-5 sample with 2θ reflections at 26.96, 34.52, 38.22, 52.16, 65.68, 71.53, and 78.72° which attributes to the Miller indices reflecting planes (110), (101), (200), (211), (301), (112), and (321), respectively, and with the tetragonal structure after annealing at 500 °C (JCPDS card no: 96-210-4744). However, there are no impurity peaks in the RDX pattern, which indicates the purity of SNP-5.

Figure 1

Figure 1. XRD pattern of sample SNPs: SNPs-200 °C (A), SNPs-500 °C (B), and SNPs-800 °C (C).

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The XRD pattern for sample SNPs-8, shown in Figure 1C, presents 2θ reflections at 26.82, 34.29, 38.26, 52.27, 54.77, 62.11, 65.78, 71.49, 78.86, and 83.69° which are characteristic diffraction peaks of hkl planes (110), (101), (200), (211), (220), (311), (301), (112), (321), and (222), respectively. Therefore, the noticed XRD patterns confirm the tetragonal structure of the SNPs-8 sample and match the standard Match3 software (JCPDS card no: 96-210-4755). The results concluded that all the SNP samples are tetragonal structures in pure phase so that the activity of SNP samples depends on its crystallinity nature.
Table 1 summarizes the results given by XRD: the full width at half-maximum (fwhm), inter-planar distance (d) values, and crystallite sizes. The crystallite sizes were calculated to be 4.7, 9.7, and 14 nm for the SNPs 2, 5, and 8, respectively, meaning that the annealing process plays a significant role in the crystallization and changes the fwhm values. The increase of temperature influences in the diffraction intensity and reduces the fwhm values, attributed to the systematic arrangement of atoms on the crystal system. Therefore, increasing the annealing temperature gradually increases the particle size because of oxygen vacancies, originated by atomic diffusion, lattice strains, and crystal lattice defects, which causes the crystallite size to increase. The SNP samples crystallite size could be calculated according to the following Scherrer formula equation I
(I)
Here, D is the crystallite size, k is the Scherrer’s coefficient (0.891), λ is the X-ray wavelength, θ is the Bragg angle, and β is the fwhm intensity (in radians). Note that the crystallite size is obtained or defined as the measurement of the diffracting crystallite size of the samples that are not equal to the particle size because they exhibit polycrystalline aggregates. Estimation of the crystallite sizes and interplanar distance (d) values of the SNP samples planes fitted with Scherrer’s equation are listed in Table 1. Therefore, calculated average crystallite sizes of sample SNPs-2 at 200 °C, sample SNPs-5 at 500 °C, and sample SNPs-8 at 800 °C are 4, 9, and 14 nm, respectively. Similar results have been obtained by Osuntokun et al. (2017) using the leaf extract of Brassica oleracea L. var. botrytis which results in SNPs with crystallite sizes 3.6–6.3 nm. (35)
Table 1. Structure and Geometric Parameters of SNP Samples of Diffraction Study
SNPslattice plane2θfwhm valued-spacing (Å)Cos(θ)crystallite size (nm)
SnO2 NPs at 200 °C(110)26.532.0443.460.97334.2
 (101)34.382.5572.630.95533.4
 (211)52.122.5871.840.89833.6
 (220)65.271.2731.450.84217.8
average size4.7
SnO2 NPs at 500 °C(110)26.961.7543.370.97244.9
 (101)34.520.7172.680.954912.1
 (200)38.220.7482.430.944811.8
 (211)52.160.9721.860.89819.5
 (220)65.680.9701.410.840110.2
average size9.7
SnO2 NPs at 800 °C(110)26.820.8573.350.972710
 (101)34.290.6702.670.955513
 (200)38.260.4932.480.944717.8
 (211)52.270.9361.750.89779.9
 (220)54.770.6471.790.887914.5
 (311)62.110.6061.540.856616
 (301)65.780.5261.470.839718.8
 (321)78.860.8471.260.772412.7
average size14

3.2. Size and Morphology Identified by HR-TEM Analysis

The size, morphology, d-spacing, elemental composition, and crystalline/amorphous nature of the SnO2 samples were inspected by HR-TEM as shown in Figures 2–4. The HR-TEM images of sample SNPs-2 at different magnifications, selected area electron diffraction pattern (SAED), particle size distribution, and EDX spectra are presented in Figure 2A–F. Figure 2A,B displays the micrographs of sample SNPs-2 at different magnifications, and the size identified by the Image J software ranges 2.92–4.59 nm so that the average diameter (AD) is 3.97 nm. Moreover, the interplanar distance representing the d-spacing is 0.262 nm which is characteristic for the reflection plane (101), as shown in Figure 2C. The diffraction rings in the SAED pattern shown in Figure 2D expose the amorphous nature, corresponding to the amorphous SnO2 component of the SNPs-2 noticed from the respective XRD background above. The identified elemental composition of the SNPs-2 sample, determined by the EDX spectrum in Figure 2E, reveals weight % and atomic % of tin and oxygen: 86.59 and 13.41 weight % and 46.53 and 53.47 atomic %, respectively, and no other impurities are found. Therefore, the obtained results confirm that the SNPs-2 sample also contains amorphous SnO2 without impurity. Figure 2F presents the particle size histogram, where the particle size distribution is around 2.92–4.59 nm with an AD of 3.97 nm and the standard deviation (SD) is approximately 0.07 nm.

Figure 2

Figure 2. HR-TEM of sample SNPs-2 at annealing at 200 °C; (A,B) different scale magnifications (20 and 10 nm), (C) inter planar d-spacing, (D) SEAD pattern, (E) EDX micrograph, and (F) particle size distribution of the histogram.

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Figure 3

Figure 3. HR-TEM of sample SNPs-5 at annealing at 500 °C; (A) 10 nm scale magnification, (B) 20 nm scale magnification, (C) inter planar d-spacing, (D) SEAD pattern, (E) EDX micrograph, and (F) particle size distribution of the histogram.

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Figure 4

Figure 4. HR-TEM of sample SNPs-8 at annealing at 800 °C; (A) 20 nm scale magnification, (B) 50 nm scale magnification, (C) inter planar d-spacing, (D) SEAD pattern, (E) EDX micrograph, and (F) particle size distribution of the histogram.

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Figure 3A–F shows the HR-TEM, EDX spectrum, SAED pattern, and particle size distribution of the SNPs-5 samples. Figure 3A,B presents TEM micrographs at different magnifications showing that the size of the particles ranges from 5.2 to 12.8 nm, and the AD is 8.4 nm. The interplane distance is around 0.27 nm, characteristic of the reflection plane (101) as represented in (Figure 3C). The circular rings existing in the SAED pattern (see Figure 3D) correspond to the poly-crystallinity nature of the SNPs-5 sample. The elemental composition of the SNPS-5 sample from the EDX spectrum (see Figure 3E) reveal tin and oxygen in atomic % and weight % are as follows: 48.76, 51.24 and 87.60, 12.40% respectively, which indicates that the polycrystalline SNPs-5 sample has no impurities. The particle size distribution is shown in Figure 3F, where particles range from 5.2 to 12.9 nm. The average particle size diameter is 8.5 nm, and the SD is around 0.4 nm.
Figure 4A–F displays the HR-TEM, SAED pattern, EDX spectrum, and particle size distribution of the SNPs-8 sample. Figure 4A,B presents different magnification TEM micrographs showing particle sizes between 15.6 and 7.7 nm with an AD of 13.4 nm. Figure 4C reveals that the inter plane distance (d) is 0.27 nm, which agrees with the respective XRD results and corresponds to the diffraction reflection plane (101). The circular radiant spots in the SAED pattern (see Figure 4D) confirms the poly-crystallinity nature of the sample. Figure 4E shows the EDX spectrum revealing the elemental composition as tin and oxygen in atomic % and weight %: 53.84, 46.16 and 89.87, 10.13%, respectively, which leads to the purity of the SNPs-8 sample. The histogram of the particle size distribution is shown in Figure 4F, where particles range around 15.6–7.7 nm, giving the average particle size diameter (AD) of 13.4 nm and SD is 0.8 nm. Similarly, Ma et al. (2020) reported SNPs obtained by the precipitation method to be in the range of 20–80 nm and an average particle size around 40 nm. (36)
The TEM results of three samples (SNPs-2, SNPs-5, and SNPs-8) demonstrate the strong influence of the temperature on the size of the SnO2 nanomaterials. Increasing the annealing temperature may lead to defects in the crystal system and subsequently regulate the arrangement of atoms in the unit cell resulting in the rise of the size of the nanoparticles and the crystallinity, as confirmed by XRD above. From the results, we concluded that the annealing process could control the size of the NPs.

3.3. Identification of Functional Groups on the Surface of the SNPs by FTIR Analysis

FTIR analysis is a well-known technique to determine the functional groups in the cotton peel aqueous extract and the capping of biomolecules on the surfaces of the SNPs based on the vibrational stretching of functional groups. Figure 5A describes the FTIR spectrum of the agro-waste cotton peel aqueous extract recorded in the range 4000–500 cm–1. In the defined spectrum, the bands located around 3346.78, 3257.63, 1737.86, 1606.64, 13346.78, 1105.97, and 921.58 cm–1 are associated with the stretching vibration of the hydroxyl (−OH) group (indicating the existence of polyphenols in the plant extract); stretching vibration of the aromatic amine (−N–H) group; stretching vibration of the carbonyl (−C═O) group; bending vibration of the amide (−N–H) group corresponding to nitrogen and hydrogen vibrations; vibration of the nitro (−N–O) group; ether group of (−C–O–C−); and bending vibration of aliphatic carbon and hydrogen (−C–H) groups, respectively. Similarly, Arumugam et al. (2021) reported various biomolecules in Syzygium cumini (Java plum) aqueous extract detected from the FTIR technique. (37)

Figure 5

Figure 5. FT-IR analysis of cotton peel aqueous extract (A), sample SNPs-2 at 200 °C, (B), sample SNPs-5 at 500 °C (C), and sample SNPs-8 at 800 °C (D).

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Figure 5B displays the FTIR spectrum of the SNP sample at 200 °C. The absorption bands at 3321.25, 1639.13, and 518.44 cm–1 could be assigned to stretching vibrations of the hydroxyl (−OH) group, alkene (−C═C−) group, and oxygen (O–Sn–O), respectively. Figure 5C presents the FTIR spectrum of the SNPs at 500 °C where the bands located at 3329.98, 1627.29, and 548.87 cm–1 correspond to hydroxyl (−OH) group stretching vibrations of phenols present in the extract; stretching vibration of alkene (−C═C−) group and oxygen/metal/oxygen (O–Sn–O) stretching vibrations, respectively. The FTIR spectrum of the SNPs obtained at 800 °C is shown in Figure 5D. The band at 592.34 cm–1 corresponds to the oxygen–metal–oxygen (O–Sn–O) stretching vibration group. Both samples, SNPs-2 and SNPs-5, contain stretching and bending vibrations of biomolecules on their surface, but the SNPs-8 sample does not exhibit those bonds. This suggests that annealing at higher temperatures decomposes the bio-molecules on the surface of the SNPs. Therefore, the O–Sn–O stretching vibration bands in the SNPs annealed at 200 and 800 °C increases with the increase in the annealing temperature caused by higher atomic diffusion in the crystal system that possesses size enhancement nanomaterials. Our current results resemble recently reported results: stretching vibration of oxygen and metal, oxygen of SNPs in the range of 540–660 cm–1, which indicates O–Sn–O and Sn–O stretching vibration modes reported by Paramarta et al. (2016). (38)

3.4. UV–Visible Analysis

As mentioned in the Experimental section, in the present investigation, crystalline SnO2 nanomaterials are synthesized without using any commercial reducing or surfactant chemicals. Instead, the synthesis of the nanoparticles was performed by reducing agents that possess the cotton peel extracts that act as a capping/size controlling agent. Figure 6 represents the characteristic UV–vis absorption spectrum of the SNP samples in the band range 200–800 nm. Figure 6A–C demonstrates absorption bands at around λmax = 275, 263, and 244 nm for the SNPs-2, SNPs-5, and SNPs-8, respectively. Note that the λmax value shifts toward to the UV region when increasing the size of the particles. However, the maximum absorbance for sample SNPs-2 is in the visible region, and the maximum absorbance for sample SNPs-5 lies in both UV and visible regions.

Figure 6

Figure 6. UV–vis absorption spectra of SNP sample at 200 °C (A), SNP sample at 500 °C (B), SNP sample at 800 °C (C), band gap energy of SNPs-2 (D), band gap energy of SNPs-5 (E), and band gap energy of SNPs-8 (F).

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In contrast, sample SNPs-8 has an absorption in the UV region. In this manner, the λmax absorption value depends upon the size of the nanomaterials. With the increase in size, the maximum absorption band shifted toward the UV region. The band gap/energy gap (Eg), one of the optical properties that demonstrate the semiconducting nature of nanomaterials and the absorption coefficients for the tin oxide samples, was determined by the following II.
(II)
where Eg is the energy band gap, hυ is the photon energy, and α is the optical absorption coefficient. Figure 6 also shows the energy band gaps of the SNPs-2, SNPs-5, and SNPs-8 samples, obtained by extrapolating the Tauc plot (αhυ)1/2 of the tin oxide nanomaterials versus the photon energy (hυ). Note that the band gap values depend on the sintering sample. The band gap energy values are 2.68 eV (Figure 6D), 2.92 eV (Figure 6E), and 3.14 eV (Figure 6F) for the samples annealed at 200, 500, and 800 °C, respectively. Therefore, the above observation suggests that increasing the annealing process increases the band gap of the tin oxide nanomaterials. However, it has been indicated that a decrease in the band gap value is attributed to crystal defects in the material, leading to new energy levels that decrease. (39) Thus, not only the Fermi energy level but also the temperature influences the band gap of the material. The present study reveals that the material’s band gap increased with the increase in sintering temperature, which might influence the decrease of crystal defects.

3.5. Surface Area and Porosity Identification by BET Analysis

BET technique was used to identify the pore diameter, specific surface area, pore volume, and size distribution of the SNP samples by possessing adsorption–desorption nitrogen isotherms. Figure 7A represents the adsorption–desorption of nitrogen isotherms of the SNPs-2 samples measured at 77 K. The BET surface area is around 153.20 m2/g, and the pore size distribution Barrett–Joyner–Halenda (BJH) exhibits a narrow curve of calculated pore size diameter ∼ 3.10 nm, as shown in Figure 7B. Similarly, the SNPs-5 sample exhibits a BET surface area ∼ 90.34 m2/g, with pore diameter 4.95 nm denoted in Figure 7C,D. In the case of the sample calcined at 800 °C (SNPs-8), it possesses a specific surface area ∼43.72 m2/g and pore diameter 5.41 nm, which is displayed in Figure 7E,F.

Figure 7

Figure 7. BET analysis of sample SNPs at 200 °C total surface area (A), pore diameter (B), at 500 °C total surface area (C), pore diameter (D), and at 800 °C total surface area (E), pore diameter (F).

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These results reveal that the sample SNPs-2 has the highest surface area compared to samples SNPs-5 and SNPs-8. From the point of view of the size and higher surface area, this material (SNPs-2) is more promising than the others to show excellent photocatalytic activity for the remediation of organic pollutants. Our results are analogous to that one reported by Ullah et al. (2017), (40) where the SNP surface area was reported to be 47.85 m2/g for samples calcined at 600 °C and the BJH curve is narrow. However, the pore diameter was noticed to be 10.5 nm.

4. Photocatalytic Activity for the Remediation of Organic Pollutants

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The release of excess dyes from the industry may cause environmental effects. From this point of view, nowadays, there is more and more interest in the remediation of MB and MO dyes by semiconducting materials. Thus, SNPs were tested for the photodegradation of MB and MO dyes widely used in textiles and paper. In the present work, the photocatalytic degradation of MB and MO dyes and reaction were performed under UV light exposure.

4.1. Photocatalytic Activity of SNPs for the Degradation of MB Dye

The photocatalytic activity of cotton peel extract-mediated SNPs-3, SNPs-5, and SNPs-8 nanoparticles in remediation of MB dye was carried out in the presence of UV light (λmax = 254 nm) irradiation. Figure 8 shows the MB dye’s absorbance spectra under regular intervals recorded in the range 200–800 nm. Strong absorption bands arise at 663 nm, representing the maximum wavelength of the MB dye, and gradually decrease intensity in the absorbance spectrum concerning time in the presence of samples SNPs-2, SNPs-5, and SNPs-8. These results are similar to those reported by Huang et al. (2018) for the degradation of MB 98.7% within 120 min using the Pd/BiOI/MnOx hollow sphere catalyst. (41) The synthesized SNP samples in the present work show a remarkable decrease of MB dye degradation in the UV–vis spectra.

Figure 8

Figure 8. Photocatalytic activity of SNPs-2 for the degradation of MB dye (A), SNPs-5 for the degradation of MB dye (B), SNPs-8 for the degradation of MB dye (C), SNPs-2 percentage of MB dye degradation (D), SNPs-5 percentage of MB dye degradation (E), and SNPs-8 percentage of MB dye degradation (F).

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The degradation was calculated using III.
(III)
where C0 is the MB concentration of absorbance and Ct is the degradation time taken for the MB absorbance. The results indicate that in the case of the SNPs-2 sample, the MB dye degradation represents 98.56% within 30 min, as shown in Figure 8A. In the case of sample SNPs-5, the MB degradation is 97.84% within 50 min, as shown in Figure 8B. However, in the case of sample SNPs-8, the degradation is 97.12% within 80 min in the presence of UV light, as shown in Figure 8C. The obtained degradation study is compared to other results reported in the literature in Table 2. In the beginning, the MB dye degradation was monitored without the catalyst. The results show that the degradation of MB without a catalyst for sample SNPs-2 is 9.35%, as shown in Figure 8D. In the case of sample SNPs-5, the degradation is 7.91%, as represented in Figure 8E, whereas in the case of sample SNPs-8, a 7.17% degradation occurs, as shown in Figure 8F. A previous study by Elango et al. (2016) reported that MB 85% degrades in 70 min of spherical shape SNPs. (42) However, there are no similar studies using SNPs.
Table 2. Comparison of Photocatalytic Activity of SNP Samples to the Degradation of MB and MO Dyes by Different Nanocatalysts
Rmaterial usedNPs dose/dye dosesize/shapetimedegradation efficiency (%)refs
MBSnO2/SnO NPs50.0014–70 nm/spherical shape180 min90.28% MB (46)
 Sr-doped ZnO nanocatalyst33.3325–45 nm/hexagonal120 min78.50% MB (47)
 spindle-like TiO2100.0050–70 nm/spindle-like120 min62.70% MB (48)
 Cu/MMT nanocatalyst31.268 nm/spherical shape120 min95.06% MB (49)
 SNPs-2 at 200 °C33.333.97 nm/spherical shape30 min98.56% MBPresent Work
 SNPs-5 at 500 °C33.338.48 nm/spherical shape50 min97.84% MBPresent Work
 SNPs-8 at 800 °C33.3313.43 nm/spherical shape80 min97.12% MBPresent Work
MOZnO nanocatalyst100.0040 nm/spherical shape120 min83.99% MO (50)
 SnO2 nanocatalyst100.0010–42 nm/spherical shape120 min94.00% MO (51)
 NiFe2O4 nanocatalyst50.0034.74 nm/quasi globular-shaped300 min72.66% MO (52)
 Fe nanocatalyst12.007–14 nm/tetragonal shaped100 min95.00% MO (53)
 SNPs-2 at 200 °C33.333.97 nm/spherical shape40 min98.26% MOPresent Work
 SNPs-5 at 500 °C33.338.48 nm/spherical shape70 min97.39% MOPresent Work
 SNPs-8 at 800 °C33.3313.43 nm/spherical shape100 min96.52% MOPresent Work

4.2. Photocatalytic Activity for the MO Dye Degradation

The photocatalytic activity analysis was performed to evaluate the efficiency of the green synthesized SNPs in the degradation of MO under UV light irradiation. Figure 9 shows the absorbance spectra of MO dye degradation noticed between 200 and 800 nm with time intervals. The maximum absorbance occurs at λmax ∼ 464 nm in the UV–vis spectra. In the case of the catalyst, the degradation of MO dye in sample SNPs-2 drastically reached up to 98.26% in 40 min under UV light exposure in the UV–vis spectrum; no intermediate peaks are detected in Figure 9A. In the case of sample SNPs-5, the MO dye degradation reaches up to 97.39% within 70 min, as shown in Figure 9B, and in the case of sample SNPs-8, the degradation significantly reaches 96.52% within 100 min in the presence of UV light irradiation as represented in Figure 9C.

Figure 9

Figure 9. Photocatalytic activity of SNPs-2 for the degradation of MO dye (A), SNPs-5 for the degradation of MO dye (B), SNPs-8 for the degradation of MO dye (C), SNPs-2 percentage of MO dye degradation (D), SNPs-5 percentage of MO dye degradation (E), and SNPs-8 percentage of MO dye degradation (F).

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However, the degradation of MO dye does not change significantly without a catalyst; only 9.56% degrades under UV light irradiation, as represented in Figure 9D. Similarly, the degradation of MO in the case of sample SNPs-5 is around 8.69%, as illustrated in Figure 9E. In contrast, for sample SNPs-8, the 10.43% degradation occurs within 100 min, as shown in Figure 9F. Our results are pretty similar to those reported by Yao et al. (2021), which report MO dye degradation 91.3% after 14 h in the presence of visible light irradiation. (43) Hence, the above III determined well the % of MO dye degradation and the effectiveness of the photocatalytic treatment process. The obtained results of photodegradation of MB and MO were compared with the degradation time and the % of degradation reported literature (see Table 2).

4.3. Effect of Catalyst Dose on MO/Methyl Blue Degradation

MO/MB dye degradation was tested with 10, 20, and 30 mg catalyst sample SNPs-2 at a constant concentration of MB and MO pollutants (10 mg/L). The photodegradation efficiency of MB gradually increased from 96.42 to 99.28%, while under the same condition, the MO dye degradation efficiency increased from 96.61 to 99.15%, as indicated in Table 3. The photocatalytic of MB/MO dyes remediation was estimated from the pseudo-first-order kinetics, as follow (IV).
(IV)
where r is the MB and MO dye degradation rate, C is the concentration of MB and MO dye solution, K is the absorption coefficient of MB and MO, t is the degradation time taken for MB/MO, and k is the constant rate reaction of MB/MO. Because the initial concentration of MB/MO is C0 = 10 mg/L, the above equation can be approximated to a pseudo-first-order model. For MB dye photodegradation, a similar procedure was previously employed to the GO/TiO2 nanocomposite loading by Kurniawan et al. (2020). (44) The degradation of MB/MO dye by photocatalyst increased, leading to more and more active sites generated, particularly on the photocatalyst surface, increasing the number of radicals. Therefore, the amount of catalyst enormously increased the rate constant, and consequently, the degradation time was reduced for completing the reaction as noticed and represented in Table 3. The results concluded that at the high dosage catalyst improves the MO/MB dye degradation efficiency, as is represented in Figure 10A,B. However, from the results, the amount of catalyst (mg) increases the rate constant (k) and decreases the degradation duration time (t), as shown in Table 3. From the result, we concluded that the photocatalytic properties of the SNP samples exhibited against the MB and MO dye degradation. However, the degradation efficiency depends on the smaller size SNP samples (3.97, 8.48, and 13.43 nm, respectively), lower band gap energies (2.68, 2.92, and 3.14 eV, respectively), and surface area (153.20, 90.34, and 43.72 m2/g, respectively), which play a key role in the photocatalytic dye degradation.

Figure 10

Figure 10. Kinetic plots of MB and MO dye degradation, (A) MB degradation kinetics curves for varying catalyst doses (10–30 mg), (B) MO degradation kinetics curves for varying catalyst doses (10–30 mg), (C) effect of dye concentration (5–15 mg/L) on the degradation of MB dye, and (D) effect of dye concentration (5–15 mg/L) on the degradation of MO dye.

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Table 3. Degradation (%) and with Ratio of Catalyst Dose (mg) to Dye Dose (mg) and Rate Constant of MB and MO Dye
dye nameNPs dose (mg)/dye dose (mg)time (min)degradation (%)rate constant (k) min–1
MB16.666096.420.0858
 33.333098.560.2053
 50.002099.280.3316
 66.661599.590.3408
 33.333098.560.2053
 22.227097.910.1211
MO16.667096.610.1082
 33.334098.260.2025
 50.003099.150.3174
 66.662098.480.3783
 33.334098.260.2025
 22.228096.960.1355

4.4. Effect of MO/MB Dye Concentration

The effect of MO/MB dye concentration on the degradation of MO and MB at different dye concentrations (5, 10, and 15 mg/L) is analyzed at a particular constant catalyst dose (20 mg) of photocatalyst sample SNPs-2. Figure 10C,D shows that the degradation efficiency of MB and MO dyes gradually decreased, resulting in longer degradation times. The MB and MO pollutant concentrations 5 to 15 mg/L were tested with 20 mg of SNPs-2 sample photocatalyst under UV light exposure. Table 3 shows that the MB and MO dye photodegradation rate decreased while the MB and MO dye concentration increased from 5 to 15 mg/L. However, the MB and MO dye photodegradation efficiency rate did not increase significantly. It is at a constant rate even upon increasing the concentration of the MB and MO dye solution. Similarly, Chen et al. (2017) reported the effect of dye solution concentration at a particular constant catalyst (ZnO NPs) for Congo red, MO, and DB38 dye degradation efficiency in the presence of photoirradiation. (45)

4.5. Degradation Efficiency Comparison with Published Reports

The results for the degradation efficiency of MB and MO dyes providing the corresponding ratio of SNP samples nanocatalyst dose (mg) to dye concentration (mg/mg), size, surface area, shape, band gap energy of the NPs, degradation efficiency, and time (min) are listed in Table 2. Our results are compared to similar reported works, including the photocatalyst SnO/SnO2 hybrids, spindle-like TiO2 nanocatalysts, Sr-doped ZnO nanocatalysts, as well as copper nanoparticles supported with montmorillonite clays nanocatalyzed for the degradation efficiency of MB dye. (46−49) Moreover, ZnO nanocatalysts, SnO2 nanocatalysts, and Fe nanocatalyst degradation of MO dye reported in references (50)– () () (53) and degradation efficiencies are compared in the table.
It is noticed that the degradation time depends on the ratio of the SNP photocatalyst dose to dye concentration (mg/mg), shape, surface area, and particle size of the NPs, as represented in Table 2. However, there have been recent studies that report that during the degradation of MB and MO by nano photocatalysts, massive free radicals that represent ROS are released, reacting with the dye molecules and leading to nontoxic products such as mineral acids, water molecules (H2O), and carbon dioxide (CO2), which support our observation. Thus, the synthesized SNP samples exhibit extremely enhanced degradation efficiency summarized to the recently reported literature given in Table 2. However, it strongly depends on the smaller particle size and uniform spherical shape of the nanoparticles. The MB degradation 98.56 percentage degraded within 30 min for a rate constant (k) 0.2053 min–1, similar to MO 98.26 percentage degradation within 40 min concerning rate constant (k) 0.2025 min–1. However, the SNP sample photocatalyst dye degradation reaction experiment was processed at a particular constant (20 mg) photocatalyst and 60 mL of volume of dye solution at a specific dye concentration (10 mg/L) under UV light exposure. Similar experimental studies of the effect of photocatalytic at varied catalyst doses and concentrations of dye solution and that provide results of rate constant (k), degradation efficiency, and degradation time are tabulated in Table 2. Therefore, the synthesized SNP samples exhibited extraordinary photocatalytic activity performance and could be promising materials utilized in degradation water purification and toxic and hazardous organic pollutant dyes.

4.6. Possible Mechanism of MB and MO Dye Degradation

The reasonable possible mechanism of MB and MO dye degradation demonstrated by the obtained semiconductor SnO2 nanomaterials in the present work is represented in Scheme 1. Photocatalyst semiconductors have many characteristics and properties (such as small size, high surface area, low band gap energy, tetragonal structure, and so forth), which can influence the removal of MB and MO dyes. For example, the tetragonal structure of tin oxide nanomaterials has shown high photocatalytic activity and feasibility in dye removal. (54) The photocatalytic activity described in Scheme 1 is carried out in two steps. The first step includes the absorbance of dye molecules on the surface of the SNP sample during the constant stirring process without UV light exposure. The second step consists of forming electron–hole pairs, which generates superoxide radicals and hydroxide radicals in the SNP matrix, which degrade the dye molecules to complete mineralization (H2O and CO2) of the pollutant molecules.

Scheme 1

Scheme 1. Possible Mechanism of MB and MO Dye Degradation by SNPs Obtained in This Work
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The feasible mechanism describes the various reaction succession steps occurring during the degradation of MB and MO dyes in the presence of SnO2 nanomaterials under UV light irradiation and assumes the excess of highly ROS in the solution. Vidya et al. (2017) proposed a similar mechanism for the ZnO NP photocatalytic activity of Cong red dye degradation in the presence of UV light exposure. (55) The possible mechanism involves sequence steps described by the following equations. UV light bombarding the SNP nanomaterials generates electrons and transfers electrons from the valence band to the conduction band with corresponding energy higher than the band gap energy of the SNP nanomaterials that should promote holes in the valence band and generate electrons in the conduction band. This process might generate high ROS species that are reactive with MB and MO dye molecules such as successive carbon dioxide and water molecules. At the beginning, under UV light irradiation, electrons moved from the valence band to the conduction band on the surface of the SNPs, which is represented in eq 1. In this way, conduction band electrons (eCB–) readily react with oxygen to generate superoxide (O2–•) ions, as shown in eq 2, and subsequently, these highly reactive oxide ions react with hydrogen (H+) ions to release the −OOH, as represented in eq 3, whereas in the valence band, (hvVB+) holes readily contact with water molecules to produce hydroxide (−OH–) ions which in turn generate highly active hydroxide radicals (−•OH), as represented in eqs 4 and 5. The produced −OOH can readily react with conduction-band electrons and hydrogen ions to produce highly active superoxide (H2O2) molecules. Eventually, the cleavage of hydrogen peroxide (H2O2) molecules occurs to produce the highly active hydroxyl radical (−•OH), and also, the photoelectrons diminish the oxygen molecules (O2) adsorbed on the SNP catalyst surface generating superoxide (O2–•) radicals. Eventually, MB and MO dye molecules are decomposed by the formed highly active hydroxyl (•OH) radicals and superoxide (O2–•) radicals to produce mineral acids, H2O, and CO2, as shown in eqs 6–11. This mechanism is similar to that proposed by Zangeneh et al., (2015), which assumes the formation of radicals during dyes’ degradation. (56)
Liu et al., (2021) reported charge-carrier trapping on the surface of the materials based on the band gap energy. The higher level of energy than the band gap of the materials leads to electron transfer from the conduction band to the valence band and generating hydroxide and superoxide radical’s degradation of the dye molecules. (57) The photocatalytic reactions take place provided that the semiconductor receives irradiation photons with energy greater than the band gap. An irradiating photon with insufficient energy leads to the failure of electron transition and then degradation is not possible to carbon dioxide and water molecules. Li et al. (2021) reported reactive species scavenging experiments and electron spin resonance which revealed that hydroxyl radicals (•OH), superoxide radical anions (O2–•), and photogenerated holes (h+) played critical roles for the photocatalytic degradation. (58)
Recent reports discussed the effect of the pH for the degradation of MB and MO dyes. Alkaykh et al. (2020) reported the effect of pH for the MB dye degradation, where at pH2, it shows the 15% removal of MB dyes; however, at pH 9, it shows 60% MB dye removal. (59) Wu et al. (2022) studied the effect of pH from 4 to 9 for the methylene dye degradation that possesses under acidic condition pH 4 is 63.88% degradation of the MB dye; however, at pH 9 basic condition, it shows 60.73% degradation, but at pH 6 neutral condition, it shows the 95.94% degradation of MB dye removal. (60) Abbasi and Hasanpour, (2017) studied the effect of pH from 4 to 10 that shows at pH 7 its higher efficiency of 99% MO dye removal than at pH 4 and pH 10. (61) Cai et al. (2017) studied the effect of pH at 3–9 that represents that at pH 3 and 5, it shows the higher decolorization efficiency of MO at 99 and 98%; however, at pH 9 alkaline medium, it shows 88% of MO decolorization efficiency. (62) Adeel et al. (2021) studied the effect of pH at 2–10; however, at pH 4 and 2, the highest photodegradation of MO rate constant was reported, that is, 0.0144 and 0.0099 min–1, but in the case of at pH 10, 0.0043 min–1 degradation efficiency was reported. (63)

4.7. Reusability of the SNP Sample

The reusability stability of the synthesized photocatalyst sample SNPs-2 has been studied. The SNPs-2 sample residue was collected after the degradation of MB and MO under UV-light exposure, centrifugated, washed, and then reused five consecutive cycles under identical conditions. The removal of MB and MO using the SNPs-2 sample offer after the firstt cycle the highest photodegradation 98.56% for MB and 98.26% for MO. After that, the second cycle removal for MB and MO was 97.84 and 96.52%, respectively. In the case of the third cycle, the MB and MO degradations were 97.12 and 95.65%, respectively. In the case of the fourth cycle, the MB and MO degradation reached 96.54 and 93.91%, respectively. Eventually, in the fifth cycle, the photocatalytic activity gradually decreased to 95.82% for MB and 92.17% for MO. The degradation versus cycle plot is shown in Figure 11A. Thus, sample SNPs-2 exhibits excellent reusability for the photodegradation of MB and MO pollutant dyes. Moreover, to authenticate the stability of sample SNPs-2 after five cycles, any phase change was analyzed by powder XRD (see Figure 11B). Based on the results, the crystallization of the recovered catalyst remains unchanged even after five cycles of use when compared to the as synthesized SNPs-2 sample. Therefore, we concluded that the synthesized SNPs-2 sample is stable and maintains its outstanding photocatalytic activity for consecutive cycles.

Figure 11

Figure 11. Recyclability check of biosynthesized sample SNPs-3 for the degradation of MB and MO under identical experimental conditions (A) and XRD pattern after five consecutive cycles for sample SNPs-3 (B).

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5. Conclusions

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The present study carried out a simple, nontoxic, eco-friendly, and cost-effective method to produce SNP nanomaterials through the agro-waste cotton boll peel aqueous extract. SNPs were successfully synthesized at different temperatures of 200, 500, and 800 °C without involving toxic chemicals or solvents. XRD patterns confirmed that the crystal structure is tetragonal, and the average crystallite sizes for the SNP samples obtained after 200, 500, and 800 °C are 4.72, 9.68, and 14.06 nm, respectively. HR-TEM images manifested spherical shaped samples with sizes 3.79, 8.48, and 13.43 nm for SNP-2, SNP-5, and SNP-8, respectively. The samples were further analyzed by FT-IR, UV–vis spectroscopy, and BET analysis, and their photocatalytic activity for the degradation of MB and MO was inspected. From the result, we concluded that the smaller size of the SNPs-2 sample (3.79 nm), the lower band gap energy (2.68 eV) and higher the surface area (153.20 m2/g) exhibited superior performance of photocatalytic efficiency for the degradation of MB/MO. Therefore, MB dye 98.56% degradation within 30 min and MO dye 98.26% degradation within 40 min, respectively, under UV light exposure. Moreover, we have also studied the effect of catalyst and the effect of dye concentration. As the amount of catalyst (10 mg to 30 mg) increases, the rate constant increases and decreases the degradation duration time. However, when the dye concentration (5–15 mg/L) increases, the rate constant decreases, and the degradation duration time increases. Consequently, the synthesized SNP samples are promising materials to be used as a photocatalyst for the remediation of pollutant dyes.

Author Information

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  • Corresponding Authors
    • Luis De Los Santos Valladares - Laboratorio de Cerámicos y Nanomateriales, Facultad de Ciencias Físicas, Universidad Nacional Mayor de San Marcos, Ap. Postal 14-0149, Lima 14, Peru;  Cavendish Laboratory, Department of Physics, University of Cambridge, J.J. Thomson Avenue, Cambridge CB3 OHE, U.K.;  School of Materials Science and Engineering, Northeastern University, No 11, Lane 3, Wenhua Road, Heping District, Shenyang 110819, Liaoning, People’s Republic of China;  Orcidhttps://orcid.org/0000-0001-5930-9916;  Email: [email protected]
    • Pratap Kollu - CASEST, School of Physics, University of Hyderabad, Prof. C. R Rao Road, Gachibowli, Hyderabad 500046, Telangana, India;  Orcidhttps://orcid.org/0000-0001-6250-9396;  Email: [email protected]
  • Authors
    • Boya Palajonnala Narasaiah - CASEST, School of Physics, University of Hyderabad, Prof. C. R Rao Road, Gachibowli, Hyderabad 500046, Telangana, India;  Laboratorio de Cerámicos y Nanomateriales, Facultad de Ciencias Físicas, Universidad Nacional Mayor de San Marcos, Ap. Postal 14-0149, Lima 14, Peru
    • Pravallika Banoth - CASEST, School of Physics, University of Hyderabad, Prof. C. R Rao Road, Gachibowli, Hyderabad 500046, Telangana, India
    • Arya Sohan - CASEST, School of Physics, University of Hyderabad, Prof. C. R Rao Road, Gachibowli, Hyderabad 500046, Telangana, India
    • Badal Kumar Mandal - Department of Chemistry, School of Advanced Sciences, Vellore Institute of Technology, Vellore 632014, Tamil Nadu, India
    • Angel G. Bustamante Dominguez - Laboratorio de Cerámicos y Nanomateriales, Facultad de Ciencias Físicas, Universidad Nacional Mayor de San Marcos, Ap. Postal 14-0149, Lima 14, Peru
  • Author Contributions

    B.P.N. and P.B. are equally contributing first authors.

  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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This work was supported by the “Incorporation de Investigadores program” CONCYTEC─FONDECYT. UNMSM (contrat no. 12-2019-FONDECYT-BM-INC.INV.). P.K., P.B., and A.S. thank the Institute of Eminence (IoE), Ministry of Human Resource Development (MHRD), Grant number: UoH-IoE-RC2-21-017 at University of Hyderabad, India.

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    A review. In recent years, the development of efficient green chem. methods for synthesis of metal nanoparticles has become a major focus of researchers. They have investigated in order to find an eco-friendly technique for prodn. of well-characterized nanoparticles. One of the most considered methods is prodn. of metal nanoparticles using organisms. Among these organisms plants seem to be the best candidates and they are suitable for large-scale biosynthesis of nanoparticles. Nanoparticles produced by plants are more stable and the rate of synthesis is faster than in the case of microorganisms. Moreover, the nanoparticles are more various in shape and size in comparison with those produced by other organisms. The advantages of using plant and plant-derived materials for biosynthesis of metal nanoparticles have interested researchers to investigate mechanisms of metal ions uptake and bioredn. by plants, and to understand the possible mechanism of metal nanoparticle formation in plants. In this review, most of the plants used in metal nanoparticle synthesis are shown.
  4. 4
    Shamaila, S.; Sajjad, A. K. L.; Ryma, N.-u. -A.; Farooqi, S. A.; Jabeen, N.; Majeed, S.; Farooq, I. Advancements in nanoparticle fabrication by hazard free eco-friendly green routes. Appl. Mater. Today 2016, 5, 150– 199,  DOI: 10.1016/j.apmt.2016.09.009
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    Kumar, K. M.; Mandal, B. K.; Tammina, S. K. Green synthesis of nano platinum using naturally occurring polyphenols. RSC Adv. 2013, 3, 4033– 4039,  DOI: 10.1039/c3ra22959a
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    Green synthesis of nano platinum using naturally occurring polyphenols
    Kumar, Kesarla Mohan; Mandal, Badal Kumar; Tammina, Sai Kumar
    RSC Advances (2013), 3 (12), 4033-4039CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)
    The authors report a simple one step green synthesis of platinum nanoparticles using naturally occurring plant polyphenols obtained from an aq. ext. of Terminalia chebula. No surfactant/stabilizing agent was employed in this method. All the platinum nanoparticles obtained were in the size range of <4 nm. The polyphenols responsible for redn. were identified using HPLC. The authors demonstrated redn. of Pt+4 to Pt0 and also how the oxidized polyphenols were responsible for stabilizing platinum nanoparticles.
  6. 6
    Mazari, S. A.; Ali, E.; Abro, R.; Khan, F. S. A.; Ahmed, I.; Ahmed, M.; Nizamuddin, S.; Siddiqui, T. H.; Hossain, N.; Mubarak, N. M.; Shah, A. Nanomaterials: Applications, waste-handling, environmental toxicities, and future challenges - A review. J. Environ. Chem. Eng. 2021, 9, 105028,  DOI: 10.1016/j.jece.2021.105028
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    Nanomaterials: Applications, waste-handling, environmental toxicities, and future challenges - A review
    Mazari, Shaukat Ali; Ali, Esfandyar; Abro, Rashid; Khan, Fahad Saleem Ahmed; Ahmed, Israr; Ahmed, Mushtaq; Nizamuddin, Sabzoi; Siddiqui, Tahir Hussain; Hossain, Nazia; Mubarak, Nabisab Mujawar; Shah, Asif
    Journal of Environmental Chemical Engineering (2021), 9 (2), 105028CODEN: JECEBG; ISSN:2213-3437. (Elsevier Ltd.)
    A review. Currently, nanotechnol. is referred to be one of the attractive research sectors in several countries because of its vast potential and com. impact. Nanotechnol. includes the investigation, development, fabrication, and processing of structures and materials on a nanoscale in various fields of science, health care, agriculture, technol., and industries. As such, it has provided a steady restructuring of related technologies. However, the irregularities and uncertainties in dimensions and chem. compns., makes the viability of such materials questionable. Concerns have been inclined about the transport, destiny, and transformation of nanomaterials discharged into the environment. A crit. anal. of the present phase of knowledge concerning the exposure and effects of nanomaterials has been discussed in-depth. In this review, different nanomaterials along with their applications have also been reviewed, that include graphene-based nanomaterials, carbon nanotubes, and their composites, nanoclay composites, nanostructured thin films, metal-org. frameworks, conducting polymers and their composites, MXenes, chalcogenide nanocrystals, and quantum dots. Besides, a few of the groundbreaking applications of nanomaterials for different sectors like human health, processes, photochem. process, energy conversion and energy storage, sepn. and purifn. processes, optoelectronics, etc. are discussed in detail with their chem. Moreover, the unique characteristics and applications of nanomaterials, they inherently introduce challenges for their applications and large-scale prodn. Acknowledgment of the potential benefits and unknown dangers of nanomaterials is critically is critically analyzed and discussed in the manuscript.
  7. 7
    Palanisamy, G.; Bhuvaneswari, K.; Srinivasan, M.; Vignesh, S.; Elavarasan, N.; Venkatesh, G.; Pazhanivel, T.; Ramasamy, P. Two-dimensional g-C3N4 nanosheets supporting Co3O4-V2O5 nanocomposite for remarkable photodegradation of mixed organic dyes based on a dual Z-scheme photocatalytic system. Diamond Relat. Mater. 2021, 118, 108540,  DOI: 10.1016/j.diamond.2021.108540
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    7
    Two-dimensional g-C3N4 nanosheets supporting Co3O4-V2O5 nanocomposite for remarkable photodegradation of mixed organic dyes based on a dual Z-scheme photocatalytic system
    Palanisamy, G.; Bhuvaneswari, K.; Srinivasan, M.; Vignesh, S.; Elavarasan, N.; Venkatesh, G.; Pazhanivel, T.; Ramasamy, P.
    Diamond and Related Materials (2021), 118 (), 108540CODEN: DRMTE3; ISSN:0925-9635. (Elsevier B.V.)
    A dual Z-scheme g-C3N4-Co3O4-V2O5 nanocomposite was synthesized through a simple wet impregnation technique. The phase purity and optical behavior of the synthesized samples were characterized by various anal. techniques. The morphol. consequences indicated that Co3O4 nanorods and V2O5 nanoparticles were effectively embedded on the exterior of g-C3N4 nanosheets. The emission properties and energy band gap measurement of g-C3N4-Co3O4-V2O5 nanocomposite reveal suppression of e--h+ recombination and the optical absorption are red shifted to the visible region. The photodegrdn. capability of the prepd. samples was assessed against mixed org. dyes (methylene blue (MB) and methyl yellow (MY)) under visible light illumination. The g-C3N4-Co3O4-V2O5 nanocomposite established that the enhanced photocatalytic properties in the photodegrdn. of mixed dyes compared to bare and hybrid samples. The as-prepd. g-C3N4-Co3O4-V2O5 nanocomposite shows the enhanced degrdn. efficiency for 93.8 and 93.2% over the MY and MB aq. dyes under the visible light irradn. Notably, the g-C3N4-Co3O4-V2O5 photocatalyst was recycled in four consecutive runs with no noticeable loss of catalytic performance. A synergistic dual Z-scheme g-C3N4-Co3O4-V2O5 photocatalyst could be constructed based on the energy band matching within g-C3N4, Co3O4 and V2O5 NPs.
  8. 8
    Choi, E.; Lee, D.; Shin, H. J.; Kim, N.; Valladares, L. D. L. S.; Seo, J. Role of oxygen vacancy sites on the temperature-dependent photoluminescence of SnO2 nanowires. J. Phys. Chem. C 2021, 125, 14974– 14978,  DOI: 10.1021/acs.jpcc.1c02937
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    8
    Role of Oxygen Vacancy Sites on the Temperature-Dependent Photoluminescence of SnO2 Nanowires
    Choi, Euiyoung; Lee, Dongwook; Shin, Hyun-Joon; Kim, Namdong; Valladares, L. De Los Santos; Seo, Jiwon
    Journal of Physical Chemistry C (2021), 125 (27), 14974-14978CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    The role of oxygen vacancies in temp.-dependent photoluminescence of SnO2 nanowires was investigated by X-ray absorption spectroscopy. Two types of oxygen vacancies are present in the nanowires: at out-of-plane sites and at in-plane sites; both play crucial roles in the temp. dependence of the photoluminescence. Oxygen vacancies at in-plane sites participate in photon emission at low temp., whereas those at out-of-plane sites result in photoluminescence at room temp. Accordingly, the luminescence color changes from orange (630 nm, 1.93 eV) to green (515 nm, 2.4 eV) at 100 K. The color change is accompanied with a notable change in the oxygen K-edge X-ray absorption spectra. The scanning transmission X-ray microscopy results indicate that more oxygen vacancies at in-plane sites are present in the surface region than in the bulk region, whereas more oxygen vacancies at out-of-plane sites are present in the bulk region than in the surface region. Overall, the results demonstrate that oxygen-vacancy-mediated fluorescence properties of SnO2 nanowires are temp.-dependent; i.e., the photoluminescence mechanisms of the nanowires are mediated by oxygen vacancies at different sites, and the bicolor fluorescence originates from charge transfer between the states.
  9. 9
    Suthakaran, S.; Dhanapandian, S.; Krishnakumar, N.; Ponpandian, N. Hydrothermal synthesis of SnO2 nanoparticles and its photocatalytic degradation of methyl violet and electrochemical performance. Mater. Res. Express 2019, 6, 0850i3,  DOI: 10.1088/2053-1591/ab29c2
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    Nejati-Moghadam, L.; Esmaeili, B. K. A.; Salavati, N. M.; Safardoust, H. Synthesis and characterisation of SnO2 nanostructures prepared by a facile precipitation method. J. Nanostruct. 2015, 5, 47– 53,  DOI: 10.7508/JNS.2015.01.007
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    Zhang, L.; Ren, X.; Luo, Y.; Shi, X.; Asiri, A. M.; Li, T.; Sun, X. Ambient NH3 synthesis via electrochemical reduction of N2 over cubic sub-micron SnO2 particles. Chem. Commun. 2018, 54, 12966– 12969,  DOI: 10.1039/C8CC06524A
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    11
    Ambient NH3 synthesis via electrochemical reduction of N2 over cubic sub-micron SnO2 particles
    Zhang, Ling; Ren, Xiang; Luo, Yonglan; Shi, Xifeng; Asiri, Abdullah M.; Li, Tingshuai; Sun, Xuping
    Chemical Communications (Cambridge, United Kingdom) (2018), 54 (92), 12966-12969CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
    Electrochem. N2-to-NH3 fixation under ambient conditions is emerging as a promising alternative to the energy-intensive and CO2-emitting Haber-Bosch process. However, this process involves difficulty in N2 activation, underlining the demand of electrocatalysts for the N2 redn. reaction (NRR). Cubic sub-micron SnO2 particles on C cloth (SnO2/CC) are proposed as an efficient NRR electrocatalyst for ambient N2 conversion to NH3 with excellent selectivity. Electrochem. tests reveal that SnO2/CC attains a large NH3 yield of 1.47 × 10-10 mol s-1 cm-2 at -0.8 V vs. reversible H electrode (RHE) and a high faradaic efficiency of 2.17% at -0.7 V vs. RHE in 0.1M Na2SO4, outperforming most reported aq.-based NRR electrocatalysts. Notably, it also shows strong electrochem. stability.
  12. 12
    Haspulat, B.; Sarıbel, M.; Kamış, H. Surfactant assisted hydrothermal synthesis of SnO nanoparticles with enhanced photocatalytic activity. Arab. J. Chem. 2020, 13, 96– 108,  DOI: 10.1016/j.arabjc.2017.02.004
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    Maharajan, S.; Kwon, N. H.; Brodard, P.; Fromm, K. M. A Nano-Rattle SnO2@carbon Composite Anode Material for High-Energy Li-ion Batteries by Melt Diffusion Impregnation. Nanomaterials 2020, 10, 804,  DOI: 10.3390/nano10040804
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    13
    A nano-rattle SnO2/carbon composite anode material for high-energy Li-ion batteries by melt diffusion impregnation
    Maharajan, Sivarajakumar; Kwon, Nam Hee; Brodard, Pierre; Fromm, Katharina M.
    Nanomaterials (2020), 10 (4), 804CODEN: NANOKO; ISSN:2079-4991. (MDPI AG)
    The huge vol. expansion in Sn-based alloy anode materials (up to 360%) leads to a dramatic mech. stress and breaking of particles, resulting in the loss of cond. and thereby capacity fading. To overcome this issue, SnO2@C nano-rattle composites based on <10 nm SnO2 nanoparticles in and on porous amorphous carbon spheres were synthesized using a silica template and tin melting diffusion method. Such SnO2@C nano-rattle composite electrodes provided two electrochem. processes: a partially reversible process of the SnO2 redn. to metallic Sn at 0.8 V vs. Li+/Li and a reversible process of alloying/dealloying of LixSny at 0.5 V vs. Li+/Li. Good performance could be achieved by controlling the particle sizes of SnO2 and carbon, the pore size of carbon, and the distribution of SnO2 nanoparticles on the carbon shells. Finally, the areal capacity of SnO2@C prepd. by the melt diffusion process was increased due to the higher loading of SnO2 nanoparticles into the hollow carbon spheres, as compared with Sn impregnation by a reducing agent.
  14. 14
    Karmaoui, M.; Jorge, A. B.; McMillan, P. F.; Aliev, A. E.; Pullar, R. C.; Labrincha, J. A.; Tobaldi, D. M. One-Step Synthesis, Structure, and Band Gap Properties of SnO2 Nanoparticles Made by a Low Temperature Nonaqueous Sol-Gel Technique. ACS Omega 2018, 3, 13227– 13238,  DOI: 10.1021/acsomega.8b02122
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    14
    One-Step Synthesis, Structure, and Band Gap Properties of SnO2 Nanoparticles Made by a Low Temperature Nonaqueous Sol-Gel Technique
    Karmaoui, Mohamed; Jorge, Ana Belen; McMillan, Paul F.; Aliev, Abil E.; Pullar, Robert C.; Labrincha, Joao Antonio; Tobaldi, David Maria
    ACS Omega (2018), 3 (10), 13227-13238CODEN: ACSODF; ISSN:2470-1343. (American Chemical Society)
    Due to its elec. conducting properties combined with excellent thermal stability and transparency throughout the visible spectrum, tin oxide (SnO2) is extremely attractive as a transparent conducting (TCO) material for applications in low emission window coating process materials and solar cells, as well as in lithium-ion batteries and gas sensors. It is also an important catalyst and catalyst support for oxidn. reactions. Here we describe a novel non-aq. sol-gel synthesis approach to produce tin oxide nanoparticles (NPs) with a low NP size dispersion. The success of this method lies in the non-hydrolytic pathway that involves the reaction between tin chloride and an oxygen donor, 1-hexanol, without the need for a surfactant or subsequent thermal treatment. This one-pot procedure is carried out at relatively low temps. in the 160 to 260 °C range, compatible with coating process processes on flexible plastic supports. The nanoparticle size distribution, shape and dislocation d. were studied by powder X-ray powder diffraction (XRPD) analyzed using the method of whole powder pattern simulation, physicochem., physicochem. (WPPM), as well as high-resoln. transmission electron microscopy (HRTEM). The SnO2 NPs were detd. to have particle sizes between 3.4 and 7.7 nm. The reaction products were characterized using liq. state 13C and 1H NMR (NMR) that confirmed the formation of dihexyl ether and 1-chlorohexane. The NPs were studied by a combination of 13C, 1H and 119Sn solid state NMR as well as Fourier transform IR (FTIR) and Raman spectroscopy. The 13C SSNMR, FTIR and Raman data showed the presence of org. species derived from the 1-hexanol reactant remaining within the samples. The optical absorption studied using UV-visible spectroscopy indicated that the band gap (Eg) shifted systematically to lower energy with decreasing NP sizes. This unusual result could be due to mech. strains present within the smallest NPs perhaps assocd. with the org. ligands decorating the NP surface. As the size increased we obsd. a correlation with an increased d. of screw dislocations present within the NPs that could indicate relaxation of the stress. We suggest that this could provide a useful method for band gap control within SnO2 NPs in the absence of chem. dopants.
  15. 15
    Zhu, K.; Lv, Y.; Liu, J.; Wang, W.; Wang, C.; Li, S.; Wang, P.; Zhang, M.; Meng, A.; Li, Z. Facile fabrication of g-C3N4/SnO2 composites and ball milling treatment for enhanced photocatalytic performance. J. Alloys Compd. 2019, 802, 13– 18,  DOI: 10.1016/j.jallcom.2019.06.193
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    15
    Facile fabrication of g-C3N4/SnO2 composites and ball milling treatment for enhanced photocatalytic performance
    Zhu, Kaixing; Lv, Yang; Liu, Jing; Wang, Wenjun; Wang, Chunping; Li, Songmei; Wang, Peng; Zhang, Meng; Meng, Alan; Li, Zhenjiang
    Journal of Alloys and Compounds (2019), 802 (), 13-18CODEN: JALCEU; ISSN:0925-8388. (Elsevier B.V.)
    Ultrafine SnO2 nanoparticles (NPs) with diams. of 2-4 nm were in situ fabricated on the surfaces of g-C3N4 material through a hydrothermal method. Ball milling was then applied to treat the obtained g-C3N4/SnO2 composites in order to improve the dispersion of SnO2 NPs as well as to strengthen the bonding between SnO2 and g-C3N4. The enhanced sepn. efficiency of photogenerated carriers, as indicated by the photoluminescence spectrum, was achieved after the ball milling treatment. Consequently, the ball milled g-C3N4/SnO2 composite demonstrated significantly improved photocatalytic performance when degrading crystal violet, as evidenced by photodegrdn. efficiency enhancements of 5.06 and 3.23 times, resp., when compared with bulk g-C3N4 and the in situ synthesized g-C3N4/SnO2 composite; these improvements were due to more useable and accessible electronic transport sites at the interfaces of the composites.
  16. 16
    Chavali, M. S.; Nikolova, M. P. Metal oxide nanoparticles and their applications in nanotechnology. SN Appl. Sci. 2019, 1, 607,  DOI: 10.1007/s42452-019-0592-3
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    Metal oxide nanoparticles and their applications in nanotechnology
    Chavali, Murthy S.; Nikolova, Maria P.
    SN Applied Sciences (2019), 1 (6), 607CODEN: SASNBO; ISSN:2523-3971. (Springer International Publishing AG)
    A review. Considering metal oxide nanoparticles as important technol. materials, authors provide a comprehensive of researches on metal oxide nanoparticles, their synthetic strategies, and techniques, nanoscale physicochem. properties, defining specific industrial applications in the various fields of applied nanotechnol. This work expansively s the recent developments of semiconducting metal oxide gas sensors for environmental gases including CO2, O2, O3, and NH3; highly toxic gases including CO, H2S, and NO2; combustible gases such as CH4, H2, and liquefied petroleum gas; and volatile org. compds. gases. The gas sensing properties of different metal oxides nanoparticles towards specific target gases have been individually discussed. Promising metal oxide nanoparticles for sensitive and selective detection of each gas have been identified. This also categorizes metal oxides sensors by analyte gas and also summarizes the major techniques and synthesis strategies used in nanotechnol. Addnl., strategies, sensing mechanisms and related applications of semiconducting metal oxide materials are also discussed in detail. Related applications are innumerable trace to ultratrace-level gas sensors, batteries, magnetic storage media, various types of solar cells, metal oxide nanoparticles applications in catalysis, energy conversion, and antennas (including microstrip and patch-type optically transparent antennas), rectifiers, optoelectronic, and electronics.
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    Yuliarto, B.; Septiani, N. L. W.; Kaneti, Y. V.; Iqbal, M.; Gumilar, G.; Kim, M.; Na, J.; Wu, K. C.-W.; Yamauchi, Y. Green synthesis of metal oxide nanostructures using naturally occurring compounds for energy, environmental, and bio-related applications. New J. Chem. 2019, 43, 15846– 15856,  DOI: 10.1039/c9nj03311d
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    17
    Green synthesis of metal oxide nanostructures using naturally occurring compounds for energy, environmental, and bio-related applications
    Yuliarto, Brian; Septiani, Ni Luh Wulan; Kaneti, Yusuf Valentino; Iqbal, Muhammad; Gumilar, Gilang; Kim, Minjun; Na, Jongbeom; Wu, Kevin C.-W.; Yamauchi, Yusuke
    New Journal of Chemistry (2019), 43 (40), 15846-15856CODEN: NJCHE5; ISSN:1144-0546. (Royal Society of Chemistry)
    A review. In recent years, naturally occurring compds. found in plants (also known as phytochems.) found increasing application in the synthesis of metal oxide nanostructures due to their multi-role as reducing agents, capping agents, and/or complexing agents. Also, the use of natural agents, such as phytochems. provide a green and sustainable way for fabricating metal oxide nanostructures compared to conventional chem. methods. This perspective will cover various types of plant-derived phytochems. which have been employed in the prepn. of metal oxide nanostructures, including their roles and the assocd. formation mechanisms. This review will also discuss some prospective applications of phytochem.-derived metal oxide nanostructures for energy storage, environmental remediation, and bio-related applications. Finally, some perspectives on the future direction of the synthesis of metal oxide nanostructures via green chem. will be provided.
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    Diallo, A.; Manikandan, E.; Rajendran, V.; Maaza, M. Physical & enhanced photocatalytic properties of green synthesized SnO2 nanoparticles via Aspalathus linearis. J. Alloys Compd. 2016, 681, 561– 570,  DOI: 10.1016/j.jallcom.2016.04.200
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    18
    Physical & enhanced photocatalytic properties of green synthesized SnO2 nanoparticles via Aspalathus linearis
    Diallo, A.; Manikandan, E.; Rajendran, V.; Maaza, M.
    Journal of Alloys and Compounds (2016), 681 (), 561-570CODEN: JALCEU; ISSN:0925-8388. (Elsevier B.V.)
    This contribution reports on the synthesis and the main phys. properties of n-type SnO2 nanoparticles synthesized for the first time by a completely green chem. process using Aspalathus linearis's natural ext. as an effective chelating agent. Their surface/interface and vol. properties by X-rays diffraction, Raman, X-rays photoemission and photoluminescence spectroscopies are reported. Their av. diam. ranging from 2.1 to 19.3 nm follows a thermal governed equation of 〈Oparticles〉 = 1.048 10-5 T2 - 4.92 10-3 T + 2.84. The smallest SnO2 nanoparticles exhibit effective photocatalytic responses to Methylene blue, Congo red and Eosin Y.
  19. 19
    Matussin, S.; Harunsani, M. H.; Tan, A. L.; Khan, M. M. Plant-Extract-Mediated SnO2 Nanoparticles: Synthesis and Applications. ACS Sustain. Chem. Eng. 2020, 8, 3040– 3054,  DOI: 10.1021/acssuschemeng.9b06398
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    Singh, J.; Kaur, H.; Kukkar, D.; Mukamia, V. K.; Kumar, S.; Rawat, M. Green synthesis of SnO2 NPs for solar light induced photocatalytic applications. Mater. Res. Express 2019, 6, 115007,  DOI: 10.1088/2053-1591/ab4412
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    20
    Green synthesis of SnO2 NPs for solar light induced photocatalytic applications
    Singh, Jagpreet; Kaur, Harpreet; Kukkar, Deepak; Mukamia, Vineet Kumar; Kumar, Sanjeev; Rawat, Mohit
    Materials Research Express (2019), 6 (11), 115007CODEN: MREAC3; ISSN:2053-1591. (IOP Publishing Ltd.)
    The present work emphasis on the eco-friendly and inexpensive approach for the synthesis of SnO2 NPs using pomegranate (Punica Granatum) leaves. The as-synthesized SnO2 NPs were confirmed by various electron and spectroscopic characterization techniques. FTIR study confirms the strong reducing and capping potential of SnO2 NPs by biomols. present in the plant ext. The successfully synthesized SnO2 NPs with a particle size of 20 nm were used as an efficient photocatalyst for the photo degrdn. of methylene blue (MB) dye under direct sunlight. The degrdn. efficiency was calcd. to be 91.5% at 240 min with the rate const. of 6.86x10-3 min-1.
  21. 21
    Bhattacharjee, A.; Ahmaruzzaman, M. A novel and green process for the production of tin oxide quantum dots and its application as a photocatalyst for the degradation of dyes from aqueous phase. J. Colloid Interface Sci. 2015, 448, 130– 139,  DOI: 10.1016/j.jcis.2015.01.083
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    A novel and green process for the production of tin oxide quantum dots and its application as a photocatalyst for the degradation of dyes from aqueous phase
    Bhattacharjee, Archita; Ahmaruzzaman, M.
    Journal of Colloid and Interface Science (2015), 448 (), 130-139CODEN: JCISA5; ISSN:0021-9797. (Elsevier B.V.)
    Green synthesis of SnO2 quantum dots (QDs) was developed by microwave heating method using the amino acids, namely, aspartic and glutamic acid. This method gave spherical SnO2 quantum dots with an av. diam. less than the exciton Bohr radius of SnO2. The av. diam. of SnO2 quantum dots formed using glutamic acid is ∼1.6 nm and is smaller than that formed using aspartic acid (∼2.6 nm). In the electronic spectra, a clear blue shift in the band gap energy from 4.33 to 4.4 eV is obsd. with a decrease in particle size (2.6-1.6 nm) due to 3 dimensional quantum confinement effects. The synthesized SnO2 QDs were characterized by TEM, selected area electron diffraction (SAED), XRD and Fourier transformed IR spectroscopy (FTIR). The optical properties were studied using UV-visible spectroscopy. The synthesized SnO2 QDs act as an efficient photocatalyst in the degrdn. of Rose Bengal and Eosin Y dye under direct sunlight. For the 1st time, Rose Bengal dye was degraded using SnO2 QDs as a photocatalyst by solar irradn.
  22. 22
    Sinha, T.; Ahmaruzzaman, M.; Adhikari, P. P.; Bora, R. Green and Environmentally Sustainable Fabrication of Ag-SnO2 Nanocomposite and Its Multifunctional Efficacy As Photocatalyst and Antibacterial and Antioxidant Agent. ACS Sustain. Chem. Eng. 2017, 5, 4645– 4655,  DOI: 10.1021/acssuschemeng.6b03114
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    22
    Green and Environmentally Sustainable Fabrication of Ag-SnO2 Nanocomposite and Its Multifunctional Efficacy As Photocatalyst and Antibacterial and Antioxidant Agent
    Sinha, Tanur; Ahmaruzzaman, Md.; Adhikari, Partha Pradip; Bora, Rekha
    ACS Sustainable Chemistry & Engineering (2017), 5 (6), 4645-4655CODEN: ASCECG; ISSN:2168-0485. (American Chemical Society)
    Herein, we describe a phytosynthetic, additive-free, economically viable, environmentally sustainable and rapid methodol. for the formation of sphere-shaped Ag-SnO2 nanocomposites of 9 nm av. particle size employing the stem exts. of Saccharum officinarum. Employing various spectroscopic techniques, the morphol., size, crystallinity, elemental conformation, and functional groups liable for surface stabilization as well as capping were depicted. Considerably, the Ag-SnO2 nanocomposite in aq. phase revealed excellent removal efficiency for the abatement of four industrially emerging pollutants (Methylene Blue, Rose Bengal, Methyl violet 6B, and 4-nitrophenol) and probable mechanisms were also suggested. Nearly, 99.1, 99.6, 99.5, and 98.4% of Methylene Blue, Rose Bengal, Methyl violet 6B, and 4-nitrophenol were eradicated resp., within 60, 75, 75, and 58.3 min using the synthesized nanocomposite. Moreover, the spent nanocomposites were renewed and their photocatalytic proficiencies were assessed for three consecutive cycles. The spent nanocomposite and the degraded products were resp. analyzed using X-ray diffraction and liq. chromatog.-mass spectrometry spectroscopic methods. Addnl., the nanocomposite displayed comparative antimicrobial action against Pseudomonas aeruginosa, Escherichia coli, and Bacillus subtilis and indicated fair activity on 2,2-diphenyl-1-picrylhydrazyl scavenging with IC50 values 0.73 mM depicting its efficient antimicrobial and antioxidant activity. Thus, the present article has disclosed a revolutionary way for fabricating Ag-SnO2 nanocomposites and depicted their multifunctional efficacy as photocatalysts and reducing and prospective antibacterial and antioxidant agents.
  23. 23
    Sudhaparimala, S.; Vaishnavi, M. Biological synthesis of nano composite SnO2- ZnO - Screening for efficient photocatalytic degradation and antimicrobial activity. Mater. Today Proc. 2016, 3, 2373– 2380,  DOI: 10.1016/j.matpr.2016.04.150
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    Li, A. J.; Pal, V. K.; Kannan, K. A review of environmental occurrence, toxicity, biotransformation and biomonitoring of volatile organic compounds. Environ. Chem. Ecotoxicol. 2021, 3, 91– 116,  DOI: 10.1016/j.enceco.2021.01.001
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    24
    A review of environmental occurrence, toxicity, biotransformation and biomonitoring of volatile organic compounds
    Li, Adela Jing; Pal, Vineet Kumar; Kannan, Kurunthachalam
    Environmental Chemistry and Ecotoxicology (2021), 3 (), 91-116CODEN: ECENAH; ISSN:2590-1826. (Elsevier B.V.)
    Volatile org. compds. (VOCs) encompass hundreds of high prodn. vol. chems. that have been used in a wide range of household and industrial products. Widespread use of products that contain VOCs resulted in their ubiquitous occurrence in the environment, with elevated concns. frequently found in indoor environments. Human exposure to VOCs is pervasive and has been a topic of concern, due to the mutagenic, neurotoxic, genotoxic, and carcinogenic potentials of these chems. Although several previous articles described toxic effects of VOCs, relatively less is known on their human exposure and body burdens. VOCs have been detd. in human breath condensate, blood, feces, and urine. This review updates the information on the environmental occurrence, toxicity, sources and pathways of human exposure, metab. and elimination, and biomonitoring of exposure to VOCs. Indoor air is a major source of human exposure to VOCs. Higher atm. concns. of VOCs have been reported in Asian countries than in North American and European countries. Elevated concns. of four widely studied VOCs namely, benzene, toluene, ethylbenzene and xylene (BTEX) were reported in air from newly constructed or renovated homes (1.3-350 μg/m3) and e-waste workshops (2.45-3,10,000 μg/m3). BTEX were also found in consumer products such as shoe polish, whiteout, leather cleaner and ink at notable concns. (e.g., ∼92,600 μg/g). Traditional methods of exposure assessment of VOCs entailed measurement of these chems. in indoor air and detn. of inhalation exposure dose. SStudies on VOC exposure assessment mainly focused on occupationally exposed individuals. Recent developments in biomonitoring of urinary metabolites of VOCs present accurate assessment of exposures and internal body burdens. Biomonitoring studies of VOCs offer novel biomarkers for the assessment of airway inflammation, lung injury, neurol. disorders, immune dysfunction and cancers in populations. Considering the very high prodn. vol. (at billions of pounds annually), known toxicity, and widespread human exposures, significance of VOCs in eliciting adverse health effects in populations will be a subject of increasing public health concern for years to come.
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    Rueda-Marquez, J. J.; Levchuk, I.; Fernández Ibañez, P.; Sillanpää, M. A critical review on application of photocatalysis for toxicity reduction of real wastewaters. J. Clean. Prod. 2020, 258, 120694,  DOI: 10.1016/j.jclepro.2020.120694
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    Li, Y.; Chang, H.; Yan, H.; Tian, S.; Jessop, P. G. Reversible Absorption of Volatile Organic Compounds by Switchable-Hydrophilicity Solvents: A Case Study of Toluene with N,N-Dimethylcyclohexylamine. ACS Omega 2020, 6, 253– 264,  DOI: 10.1021/acsomega.0c04443
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    Li, Y.; Liu, K.; Zhang, J.; Yang, J.; Huang, Y.; Tong, Y. Engineering the Band-Edge of Fe2O3/ZnO Nanoplates via Separate Dual Cation Incorporation for Efficient Photocatalytic Performance. Ind. Eng. Chem. Res. 2020, 59, 18865– 18872,  DOI: 10.1021/acs.iecr.0c03388
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    Engineering the Band-Edge of Fe2O3/ZnO Nanoplates via Separate Dual Cation Incorporation for Efficient Photocatalytic Performance
    Li, Ya; Liu, Kuiliang; Zhang, Jingnan; Yang, Jingdong; Huang, Yongchao; Tong, Yexiang
    Industrial & Engineering Chemistry Research (2020), 59 (42), 18865-18872CODEN: IECRED; ISSN:0888-5885. (American Chemical Society)
    Engineering the band-edge of photocatalysts is one of the important strategies to adjust the photocatalytic performance. Herein, we successfully prep. Cu-Fe2O3/Ni-ZnO nanoplate photocatalysts and confirm by a series of materials characterization. The prepd. Cu-Fe2O3/Ni-ZnO nanoplate exhibits the highest photodegrdn. performance of tetracycline among all the prepd. samples. The exptl. results demonstrate that introducing elements into Fe2O3/ZnO regulates the potentials of the conduction band and valence band, accelerating the recombination of Cu-Fe2O3 photogenerated electrons with Ni-ZnO holes. Furthermore, ESR (ESR) spectroscopy reveals that rapid prodn. of reactive oxygen species (ROS) such as •O2- and •OH can improve the photodegrdn. activity of Cu-Fe2O3/Ni-ZnO. This work reveals that engineering the band-edge of photocatalysts can be considered as an effective method to improve the photocatalytic activity.
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    Li, D.; Song, H.; Meng, X.; Shen, T.; Sun, J.; Han, W.; Wang, X. Effects of Particle Size on the Structure and Photocatalytic Performance by Alkali-Treated TiO2. Nanomaterials 2020, 10, 546,  DOI: 10.3390/nano10030546
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    Effects of particle size on the structure and photocatalytic performance by alkali-treated TiO2
    Li, Danqi; Song, Hongchen; Meng, Xia; Shen, Tingting; Sun, Jing; Han, Wenjia; Wang, Xikui
    Nanomaterials (2020), 10 (3), 546CODEN: NANOKO; ISSN:2079-4991. (MDPI AG)
    Particle size of nanomaterials has significant impact on their photocatalyst properties. In this paper, TiO2 nanoparticles with different cryst. sizes were prepd. by adjusting the alkali-hydrothermal time (0-48 h). An annealing in N2 atm after hydrothermal treatment caused TiO2 redn. and created defects, resulting in the visible light photocatalytic activity. The evolution of physicochem. properties along with the increase of hydrothermal time at a low alkali concn. has been revealed. Compared with other TiO2 samples, TiO2-24 showed higher photocatalytic activity toward degrading Rhodamine B and Sulfadiazine under visible light. The radical trapping and ESR expts. revealed that O2·- is the main reactive specie in TiO2-24. Large sp. surface areas and rapid transfer of photogenerated electrons are responsible for enhancing photocatalytic activity. The above findings clearly demonstrate that particle size and surface oxygen defects can be regulated by alkali-hydrothermal method. This research will deepen the understanding of particle size on the nanomaterials performance and provide new ideas for designing efficient photocatalysts.
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    Tuan, P. V.; Hieu, L. T.; Tan, V. T.; Phuong, T. T.; Tran Thi Quýnh, H.; Khiem, T. N. The dependence of morphology, structure, and photocatalytic activity of SnO2/rGO nanocomposites on hydrothermal temperature. Mater. Res. Express 2019, 6, 106204,  DOI: 10.1088/2053-1591/ab1e12
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    Jiang, Y.; Zhao, H.; Liang, J.; Yue, L.; Li, T.; Luo, Y.; Liu, Q.; Lu, S.; Asiri, A. M.; Gong, Z.; Sun, X. Anodic oxidation for the degradation of organic pollutants: anode materials, operating conditions and mechanisms. A mini review. Electrochem. Commun. 2021, 123, 106912,  DOI: 10.1016/j.elecom.2020.106912
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    Anodic oxidation for the degradation of organic pollutants: Anode materials, operating conditions and mechanisms. A mini review
    Jiang, Yingying; Zhao, Haitao; Liang, Jie; Yue, Luochao; Li, Tingshuai; Luo, Yonglan; Liu, Qian; Lu, Siyu; Asiri, Abdullah M.; Gong, Zhengjun; Sun, Xuping
    Electrochemistry Communications (2021), 123 (), 106912CODEN: ECCMF9; ISSN:1388-2481. (Elsevier B.V.)
    A review. Org. pollutants in domestic sewage, agricultural runoff, industrial wastewater, and contaminated land pose a serious threat to human beings as well as to ecosystems. Anodic oxidn. is one of the technologies most commonly used for the degrdn. of org. pollutants. In this review, we present the current status of promising anodic oxidn. technologies for the degrdn. of org. pollutants, with fundamental insights into anode materials, operating conditions and mechanisms. Firstly, anodes based on metallic Pt, metal oxides (RuO2, IrO2, PbO2 and SnO2), and carbon (BDD and others) are critically reviewed. Secondly, strategies for the effective removal of org. pollutants in wastewater under appropriate operating conditions are systematically investigated. Thirdly, the anodic oxidn. mechanism is comprehensively summarized with illustrations of how the org. pollutants can be broken down into small mols. of low or zero toxicity. Finally, we conclude with some future perspectives for application of anodic oxidn.
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    Li, Y.; Yang, Q.; Wang, Z.; Wang, G.; Zhang, B.; Zhang, Q.; Yang, D. Rapid fabrication of SnO2 nanoparticle photocatalyst: computational understanding and photocatalytic degradation of organic dye. Inorg. Chem. Front. 2018, 5, 3005– 3014,  DOI: 10.1039/C8QI00688A
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    Rapid fabrication of SnO2 nanoparticle photocatalyst: computational understanding and photocatalytic degradation of organic dye
    Li, Yuanyuan; Yang, Qimei; Wang, Zhongming; Wang, Guoyu; Zhang, Bin; Zhang, Qian; Yang, Dingfeng
    Inorganic Chemistry Frontiers (2018), 5 (12), 3005-3014CODEN: ICFNAW; ISSN:2052-1553. (Royal Society of Chemistry)
    Metal oxides have attracted an increasing attention for the photo-degrdn. of org. containments. Deep understanding of the phys. parameters correlated with the photocatalytic process is crit. and beneficial for finding an efficient and robust photocatalyst. Herein, by taking SnO2 as a prototypical model, we systematically study exciton energy, effective mass, carrier mobility and partial charge d. based on the d. functional theory (DFT). We demonstrate that the obtained exciton energy is quite low and can be effectively dissocd. into charge carriers at room temp. The estd. carrier mobility of electrons is about 50 times greater than that of holes. More interestingly, analyzing partial charge d. on the top of the valence band reveals that the photocatalytic oxidn. reaction site would occur on the O-p state. Exptl., SnO2 nanoparticles have been synthesized by a simple method and characterized by Powder XRD and TEM. With the photocatalyst SnO2, more than 90% methyl blue (MB) and Rhodamine B (RhB) are degraded under the UV light irradn. within 50 min and 270 min, resp. Trapping expts. reveal thaṫ OH are the main active species to oxidize the org. dye and mainly originate through the oxidn. of holes (h+). This study establishes an in-depth understanding of electronic structure and photocatalysis and provides insights into the designing of new photocatalytic materials.
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    Huang, Y.; Li, K.; Lin, Y.; Tong, Y.; Liu, H. Enhanced Efficiency of Electron-Hole Separation in Bi2 O2 CO3 for Photocatalysis via Acid Treatment. ChemCatChem 2018, 10, 1982– 1987,  DOI: 10.1002/cctc.201800101
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    Enhanced efficiency of electron-hole separation in Bi2O2CO3 for photocatalysis via acid treatment
    Huang, Yongchao; Li, Kunshan; Lin, Ying; Tong, Yexiang; Liu, Hong
    ChemCatChem (2018), 10 (9), 1982-1987CODEN: CHEMK3; ISSN:1867-3880. (Wiley-VCH Verlag GmbH & Co. KGaA)
    We herein prepd. defective Bi2O2CO3 microspheres via a simple nitric acid treatment method. Upon generation from Bi2O2CO3, electrons and holes were superbly sepd. with the existence of defects. Combined with the advantages of multiple scattering and reflection, a large surface area and increased range of visible-light absorption, the defective Bi2O2CO3 displayed a high efficiency for the photodegrdn. of HCHO gases and methyl orange. The defective Bi2O2CO3 also possessed a superior stability, which is important for practical applications. This work opens up new opportunities for the design and fabrication of high-activity Bi-based photocatalysts for environmental protection.
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    Huang, Y.; Lu, Y.; Lin, Y.; Mao, Y.; Ouyang, G.; Liu, H.; Zhang, S.; Tong, Y. Cerium-based hybrid nanorods for synergetic photo-thermocatalytic degradation of organic pollutants. J. Mater. Chem. A 2018, 6, 24740– 24747,  DOI: 10.1039/c8ta06565a
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    Cerium-based hybrid nanorods for synergetic photo-thermocatalytic degradation of organic pollutants
    Huang, Yongchao; Lu, Yirui; Lin, Ying; Mao, Yanchao; Ouyang, Gangfeng; Liu, Hong; Zhang, Shanqing; Tong, Yexiang
    Journal of Materials Chemistry A: Materials for Energy and Sustainability (2018), 6 (48), 24740-24747CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)
    In this work, phase boundary engineered cerium oxide-cerium nitride (CeO2/CeN) is synthesized and used as a high performance photocatalyst for photo-thermocatalytic degrdn. of org. pollutants in wastewater. A CeO2/CeN composite is obtained through simply annealing CeO2 nanowires under an ammonia atm. Both theor. and exptl. analyses are used to study the interfacial interaction between CeO2 and CeN crystallites. Benefiting from the interface engineering, the as-prepd. CeO2/CeN composite exhibits higher photo-thermocatalytic performance than pristine CeO2 for the removal of org. pollutants. ESR (ESR) spectroscopy and liq. chromatog. tandem mass spectrometry anal. of intermediates and products are used to further confirm the synergetic effect and degrdn. mechanism of the photo-thermocatalysis reactions. The results of this work suggest that the synergetic effect of the photo-thermal reaction can be considered as one of the most efficient strategies for environmental pollution remediation.
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    Siripireddy, B.; Mandal, B. K. Facile green synthesis of zinc oxide nanoparticles by Eucalyptus globulus and their photocatalytic and antioxidant activity. Adv. Powder Technol. 2017, 28, 785– 797,  DOI: 10.1016/j.apt.2016.11.026
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    Facile green synthesis of zinc oxide nanoparticles by Eucalyptus globulus and their photocatalytic and antioxidant activity
    Siripireddy, Balaji; Mandal, Badal Kumar
    Advanced Powder Technology (2017), 28 (3), 785-797CODEN: APTEEE; ISSN:0921-8831. (Elsevier B.V.)
    Eucalyptus globulus leaf ext. mediated synthesis of spherical zinc oxide nanoparticles (ZnO NPs) was carried out under ambient conditions. UV-Visible studies of the synthesized nanoparticles revealed the characteristic peak at 361 nm indicating the formation of ZnO nanoparticles. Powder X-ray Diffractometric (XRD) study showed the strong, intense and narrow-width diffraction peaks indicating the formation of cryst. nanoparticles with most stable hexagonal phase. Field emission-SEM (FE-SEM) and high resoln.-transmission electron microscopic (HR-TEM) results confirmed the formation of spherical ZnO NPs with mean particle size of 11.6 nm which is in close agreement with XRD pattern. Further, energy dispersive X-ray diffraction anal. (EDAX) revealed the formation of highly pure ZnO NPs with the peaks of Zn and O atoms. ZnO NPs exhibited effective photocatalytic activity in degrading Methylene blue and Methyl orange with max. degrdn. efficiency up to 98.3% at 30 mg of catalyst doses. In addn., ZnO NPs exhibited high antioxidant activity against DPPH free radicals scavenger.
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    Osuntokun, J.; Onwudiwe, D. C.; Ebenso, E. E. Biosynthesis and Photocatalytic Properties of SnO2 Nanoparticles Prepared Using Aqueous Extract of Cauliflower. J. Cluster Sci. 2017, 28, 1883– 1896,  DOI: 10.1007/s10876-017-1188-y
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    Biosynthesis and Photocatalytic Properties of SnO2 Nanoparticles Prepared Using Aqueous Extract of Cauliflower
    Osuntokun, Jejenija; Onwudiwe, Damian C.; Ebenso, Eno E.
    Journal of Cluster Science (2017), 28 (4), 1883-1896CODEN: JCSCEB; ISSN:1040-7278. (Springer)
    This work reports the biosynthesis of Sn(OH)2 using aq. ext. of fresh cauliflower (Brassica oleracea L. var. botrytis), and the subsequent prepn. of SnO2 nanoparticles at two different annealing temps. of 300 and 450°C for 2 h. The obtained SnO2 nanoparticles were denoted as S1 and S2 for the samples prepd. at 300 and 450°C, resp. XRD anal. identified rutile tetragonal phase of SnO2 nanoparticles and TEM results gave a quasispherical and spherical morphologies for S1 and S2 resp. of the size range 3.62-6.34 nm. The optical properties were studied with UV-vis and photoluminescence (PL) spectroscopies, and the nanoparticles showed blue shift in their absorption edges. The obsd. emission peak in the PL spectra found around 419 nm is attributable to oxygen vacancies and defects. Photocatalytic activities of the nanoparticles (S1 and S2) were studied using methylene blue (MB) under UV light irradn. and the results reveal 91.89 and 88.23% degrdn. efficiency of MB by S1 and S2 resp. over a period of 180 min.
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    Ma, C. M.; Hong, G. B.; Lee, S. C. Facile Synthesis of Tin Dioxide Nanoparticles for Photocatalytic Degradation of Congo Red Dye in Aqueous Solution. Catalysts 2020, 10, 792,  DOI: 10.3390/catal10070792
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    Facile synthesis of tin dioxide nanoparticles for photocatalytic degradation of Congo red dye in aqueous solution
    Ma, Chih Ming; Hong, Gui Bing; Lee, Shang Chieh
    Catalysts (2020), 10 (7), 792CODEN: CATACJ; ISSN:2073-4344. (MDPI AG)
    This research work reports an approach used to prep. a SnO2 photocatalyst by pptn. and calcination pathways and describes an investigation of the effects of prepn. parameters on SnO2 yield. The SnO2 photocatalyst was further used for the photocatalytic degrdn. of Congo red (CR) dye, and the removal efficiency was optimized using response surface methodol. The results indicate that the SnO2 photocatalyst yield was the highest in 0.05 M of the precursor, stannous chloride and 28 wt% ammonia as the precipitant, pH 10, at 30 °C. The transmission electron microscopy results of the SnO2 photocatalyst illustrate that the av. particle size was mainly around 30-50 nm and had a solid spherical shape. The X-ray diffraction results reveal that the prepd. sample had a highly cryst. SnO2 rutile crystal structure. The prediction and exptl. results of the Response surface methodol. (RSM) indicate that, when the reaction time was 97 min, the operating temp. was 47 °C, the photocatalyst dosage was 751 mg/L, and the optimal degrdn. rate of the CR dye was 100%. After five consecutive photodegrdn. reactions, the degrdn. rate remained at 100%. The results demonstrated that the SnO2 photocatalyst prepd. in this study possesses excellent reusability.
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    Arumugam, M.; Manikandan, D. B.; Dhandapani, E.; Sridhar, A.; Balakrishnan, K.; Markandan, M.; Ramasamy, T. Green synthesis of zinc oxide nanoparticles (ZnO NPs) using Syzygium cumini: Potential multifaceted applications on antioxidants, cytotoxic and as nanonutrient for the growth of Sesamum indicum. Environ. Technol. Innovation 2021, 23, 101653,  DOI: 10.1016/j.eti.2021.101653
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    Green synthesis of zinc oxide nanoparticles (ZnO NPs) using Syzygium cumini: Potential multifaceted applications on antioxidants, cytotoxic and as nanonutrient for the growth of Sesamum indicum
    Arumugam, Manikandan; Manikandan, Dinesh Babu; Dhandapani, Elayaraja; Sridhar, Arun; Balakrishnan, Karthiyayini; Markandan, Manickavasagam; Ramasamy, Thirumurugan
    Environmental Technology & Innovation (2021), 23 (), 101653CODEN: ETINBL; ISSN:2352-1864. (Elsevier B.V.)
    The green synthesis of nanoparticles using plant exts. attracts considerable interest from researchers as an eco-friendly alternative methods to conventional phys. and chem. approaches to avoid toxic chems. for the development of modern nanotechnol. resources. In this study, Syzygium cumini (Java plum) aq. leaf ext. was used as a stabilizing and reducing agent to synthesize zinc oxide nanoparticles (ZnO NPs) and analyzed its in vitro antioxidant and cytotoxic potential. The beneficial effect of ZnO NPs on the growth dynamics of Sesamum indicum (sesame) plant was investigated. The formation of the ZnO NPs was characterized by UV-Visible spectroscopy, Field emission SEM (FE-SEM) coupled with energy dispersive X-ray (EDX) spectrometer, Zeta potential, Fourier transform IR spectroscopy (FT-IR), X-ray diffraction (XRD) techniques. In vitro antioxidants of DPPH and H2O2 radical scavenging action of ZnO NPs exhibited moderate activity. Significant finding of the research was nuclear damage and cellular level modification in the human lung cancer cell line A549 by the ZnO NPs with respect to the concn. Green synthesized ZnO NPs were given as the nutrient source for the growth of the sesame plant with different concns. (1, 3, 5, 7, 9 mg/mL). At the concn. of 5 mg/mL of ZnO NPs reveals significant (p < 0.05) growth in root and shoot development of the plant when compared to the control. In conclusion, the overall study suggests the facet of ZnO NPs in the field of nanomedicine and nanonutrient.
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    Paramarta, V.; Taufik, A.; Saleh, R. Better adsorption capacity of SnO2 nanoparticles with different graphene addition. J. Phys.: Conf. Ser. 2016, 776, 012039,  DOI: 10.1088/1742-6596/776/1/012039
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    Better adsorption capacity of SnO2 nanoparticles with different graphene addition
    Paramarta, V.; Taufik, A.; Saleh, R.
    Journal of Physics: Conference Series (2016), 776 (8th International Conference on Physics and Its Applications, 2016), 012039/1-012039/6CODEN: JPCSDZ; ISSN:1742-6588. (IOP Publishing Ltd.)
    The adsorption capacity of SnO2 nanoparticle has been studied by graphene and nanographene platelets (NGP) addns. using co-pptn. method. The cryst. phase, compn., and morphol. of the samples are analyzed using X-ray diffraction (XRD), energy dispersive X-ray (EDX), Fourier-transform IR spectroscopy (FT-IR), and transmission electron microscope (TEM). Tetragonal structure of SnO2 is shown for the nanoparticle and its composites. The presence of graphene and NGP is also confirmed. The adsorption capacity of the nanoparticle and its composites are analyzed by observing the degrdn. of methylene blue (MB) as the org. dye model using UV-Vis Spectroscopy. The result shows that SnO2 composite with graphene achieves higher adsorption capacity of about 20% than the composite with NGP. The fitting of equil. adsorption capacity result indicates that the adsorption mechanism of SnO2 composite with graphene tends to follow the Langmuir adsorption-isotherm model.
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    Haq, S.; Rehman, W.; Waseem, M.; Javed, R.; Mahfooz-ur-Rehman, M.; Shahid, M. Effect of heating on the structural and optical properties of TiO2 nanoparticles: antibacterial activity. Appl. Nanosci. 2018, 8, 11– 18,  DOI: 10.1007/s13204-018-0647-6
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    Effect of heating on the structural and optical properties of TiO2 nanoparticles: antibacterial activity
    Haq, Sirajul; Rehman, Wajid; Waseem, Muhammad; Javed, Rehan; Mahfooz-ur-Rehman; Shahid, Muhammad
    Applied Nanoscience (2018), 8 (1-2), 11-18CODEN: ANPACY; ISSN:2190-5517. (Springer GmbH)
    TiO2 nanoparticles were synthesized at room temp. by chem. pptn. method and were then heated at 120, 300, 600 and 900°C temps. The phase transition and crystallite size variation were detd. by X-rays diffraction (XRD) anal. The surface area, pore vol. and pore size were measured using Brunauer-Emmet-Teller (BET) and Barrett-Joyner-Halenda (BJH) methods. The optical activity of heat treated and non-heat treated samples were carried out by diffuse reflectance (DR) spectroscopy. Four different methods were used to calc. band gap energy. The results obtained from thermogravimetric and differential thermal gravimetric (TG/TDG) analyses and Fourier transform infra-red (FTIR) spectroscopy agreed with each other. Agar well diffusion method has been applied to explore the antibacterial activity of nanoparticles against different bacterial strains such as Bacillus subtilis, Staphylococcus Aureus, Escherichia coli and Pseudomonas Aeruginosa. It was obsd. that TiO2 nanoparticles heated at 120°C displayed max. antibacterial activity while those heated at higher temp. showed no activity against the examd. bacteria.
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    Ullah, H.; Khan, I.; Yamani, Z. H.; Qurashi, A. Sonochemical-driven ultrafast facile synthesis of SnO2 nanoparticles: Growth mechanism structural electrical and hydrogen gas sensing properties. Ultrason. Sonochem. 2017, 34, 484– 490,  DOI: 10.1016/j.ultsonch.2016.06.025
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    Sonochemical-driven ultrafast facile synthesis of SnO2 nanoparticles: Growth mechanism structural electrical and hydrogen gas sensing properties
    Ullah, Hafeez; Khan, Ibrahim; Yamani, Zain H.; Qurashi, Ahsanulhaq
    Ultrasonics Sonochemistry (2017), 34 (), 484-490CODEN: ULSOER; ISSN:1350-4177. (Elsevier B.V.)
    Synthesis of SnO2 nanoparticles have been successfully accomplished moderately at lower temp. by facile, rapid, efficient and mild ultrasonic irradn. method. The as-grown SnO2 nanoparticles are investigated by various characterization techniques in terms of structural, optical, elec. and gas sensing properties. XRD investigation has shown that the SnO2 nanoparticles materials exhibit single rutile crystal phase with high crystallinity. FESEM studies showed uniform and monodisperse morphol. of SnO2 nanoparticles. The chem. compn. of SnO2 was systematically studied by EDX measurements. Addnl. confirmation of three Raman shifts (432, 630, 772 cm-1) indicated the characteristic properties of the rutile phase of the as-grown SnO2 nanoparticles. The optical properties of SnO2 nanoparticles were examd. by DRS, and the electronic band gap of SnO2 nanoparticles were around 3.6 eV. Elec. properties of the SnO2 nanoparticles measured at various temps. have shown the semiconducting properties. Surface area and pore size of synthesized nanoparticles were analyzed from BET. It has been revealed that SnO2 nanoparticles have surface area is 47.8574 m2/g and the pore size is 10.5 nm. Moreover, hydrogen gas sensor made of SnO2 nanoparticles showed good sensitivity and faster response for the hydrogen gas.
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    Huang, Y.; Xu, H.; Yang, H.; Lin, Y.; Liu, H.; Tong, Y. Efficient charges separation using advanced BiOI-based hollow spheres decorated with palladium and manganese dioxide nanoparticles. ACS Sustainable Chem. Eng. 2018, 6, 2751– 2757,  DOI: 10.1021/acssuschemeng.7b04435
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    Efficient Charges Separation Using Advanced BiOI-Based Hollow Spheres Decorated with Palladium and Manganese Dioxide Nanoparticles
    Huang, Yongchao; Xu, Huimin; Yang, Haojie; Lin, Ying; Liu, Hong; Tong, Yexiang
    ACS Sustainable Chemistry & Engineering (2018), 6 (2), 2751-2757CODEN: ASCECG; ISSN:2168-0485. (American Chemical Society)
    Multishell hollow structures have attracted tremendous attention due to their outstanding properties for application on photocatalysis. In this work, we demonstrated a straightforward and general method to construct BiOI-based core-double shell hollow spheres for the first time. The core-double shell hollow spheres consist of Pd particles and MnOx loaded onto the inner and outer surfaces of BiOI hollow spheres, resp. (Pd/BiOI/MnOx), and utilized them as an advanced photocatalyst for photocatalytic oxidn. of formaldehyde gases and methyl blue. The hollow spheres structure could provide a large sp. surface area, exposing a large no. of catalytic active sites. Addnl., the Pd particles and MnOx serve the function of sepg. the redn. and oxidn. reactive sites. The unique morphol. combined with enhanced light-absorption provided the Pd/BiOI/MnOx core-double shell hollow spheres with high efficiency for the photocatalytic oxidn. of formaldehyde gases and methyl blue. In situ diffuse reflectance IR Fourier transform and ESR measurement were performed to study the mechanism of photocatalytic degrdn., which revealed the important role of h+ and ·O2- during the photocatalytic reaction. These findings shed some light on the design of highly efficient photocatalysts for environmental protection.
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    Elango, G.; Roopan, S. M. Efficacy of SnO 2 nanoparticles toward photocatalytic degradation of methylene blue dye. J. Photochem. Photobiol., B 2016, 155, 34– 38,  DOI: 10.1016/j.jphotobiol.2015.12.010
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    Efficacy of SnO2 nanoparticles toward photocatalytic degradation of methylene blue dye
    Elango, Ganesh; Roopan, Selvaraj Mohana
    Journal of Photochemistry and Photobiology, B: Biology (2016), 155 (), 34-38CODEN: JPPBEG; ISSN:1011-1344. (Elsevier B.V.)
    Maximum pollutants in the industrial and domestic waste water effluents from any sources include pathogens and org. chems., which can be removed before discharging into the water bodies. Methylene blue has been considered as one of the major water contaminated pollutants. Such pollutant is dominant in surface water and groundwater. It will cause irreversible hazards to human and aquatic life. Nanotechnol. plays a major role in degrading such type of pollutant. In order to fulfill today's requirement, we have decided to handle the green synthesis of nanoparticles and its application by merging important fields like chem., environmental science, and biotechnol. Here our work emphasizes on the biol. synthesis of SnO2 nanoparticles (SnO2 NPs) using the methanolic ext. of Cyphomandra betacea (C.betacea), and it was confirmed by various characterization techniques such as UV-visible spectroscopy, FT-IR, XRD, SEM, particle size analyzer, zeta potential, and TEM. The obtained results stated that the synthesized SnO2 NPs were in rod shape with an av. size of 21 nm, which resulted in a product of nanobiotechnol. Further, we have utilized the environmental-friendly synthesized SnO2 NPs photocatalytic degrdn. of environmental concern methylene blue with first-order kinetics. In this paper, we have attempted to prove that secondary metabolite-entrapped SnO2 NPs are non-toxic to the environment.
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    Yao, X.; Zhang, B.; Cui, S.; Yang, S.; Tang, X. Fabrication of SnSO4-modified TiO2 for enhance degradation performance of methyl orange (MO) and antibacterial activity. Appl. Surf. Sci. 2021, 551, 149419,  DOI: 10.1016/j.apsusc.2021.149419
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    Fabrication of SnSO4-modified TiO2 for enhance degradation performance of methyl orange (MO) and antibacterial activity
    Yao, Xiyan; Zhang, Bin; Cui, Shuai; Yang, Sue; Tang, Xiaoning
    Applied Surface Science (2021), 551 (), 149419CODEN: ASUSEE; ISSN:0169-4332. (Elsevier B.V.)
    SnSO4-modified TiO2 nanoparticles with different SnSO4 contents were prepd., and their morphol., light absorption properties and photocatalytic degrdn. and antibacterial activities were detd. The results revealed that the samples had mesoporous structures consisting of anatase phase, and their surface area increased with increasing SnSO4 content. The XPS anal. showed that Sn had the valence state of + 4 and existed as SnO2; and S existed on the surface as sulfate. The photocatalytic degrdn. assay showed that SnSO4-modified TiO2 shifted the absorption peak of methyl orange (MO), and gradually changed its structure from azo structure to quinone structure. Compared with that of pure TiO2, SnSO4-modified TiO2 had higher MO degrdn. activity under UV irradn. and visible light irradn. and had higher antibacterial activity against Escherichia coli and Staphylococcus aureus under visible light and dark conditions. The expts. on MO degrdn. in the presence of scavengers also showed that ·O2- was the predominant radicals generated during degrdn. under visible light irradn. The data also indicated that the SnSO4-modified TiO2 nanoparticles could produce reactive oxygen species (ROS) under visible light and dark conditions, and the produced ROS, esp. for ·OH radicals, significantly play roles in their antibacterial activity under visible light.
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    Kurniawan, T. A.; Mengting, Z.; Fu, D.; Yeap, S. K.; Othman, M. H. D.; Avtar, R.; Ouyang, T. Functionalizing TiO2 with graphene oxide for enhancing photocatalytic degradation of methylene blue (MB) in contaminated wastewater. J. Environ. Manage. 2020, 270, 110871,  DOI: 10.1016/j.jenvman.2020.110871
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    Functionalizing TiO2 with graphene oxide for enhancing photocatalytic degradation of methylene blue (MB) in contaminated wastewater
    Kurniawan, Tonni Agustiono; Zhu, Mengting; Fu, Dun; Yeap, Swee Keong; Othman, Mohd Hafiz Dzarfan; Avtar, Ram; Ouyang, Tong
    Journal of Environmental Management (2020), 270 (), 110871CODEN: JEVMAW; ISSN:0301-4797. (Elsevier Ltd.)
    Methylene blue is a refractory pollutant commonly present in textile wastewater. This study tests the feasibility of TiO2/graphene oxide (GO) composite in enhancing photocatalytic degrdn. of MB in synthetic wastewater with respect to scientific and engineering aspects. To enhance its removal, we vary the compn. of the composite based on the TiO2 wt. Under UV-vis irradn., the effects of photocatalyst's dose, pH, and reaction time on MB removal by the composites are evaluated under optimum conditions, while any changes in their physico-chem. properties before and after treatment are analyzed by using TEM, SEM, XRD, FTIR and BET. The photodegrdn. pathways of the target pollutant by the composite and its removal mechanisms are also elaborated. It is found that the same composite with a 1:2 wt ratio of GO/TiO2 has the largest surface area of 104.51 m2/g. Under optimum reactions (0.2 g/L of dose, pH 10, and 5 mg/L of pollutant's concn.), an almost complete MB removal could be attained within 4 h. This result is higher than that of the TiO2 alone (30%) under the same conditions. Since the treated effluents could meet the strict discharge std. limit of ≤0.2μg/L set by China's regulation, subsequent biol. treatments are unnecessary for completing biodegrdn. of remaining oxidn. byproducts in the wastewater effluents.
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    Chen, X.; Wu, Z.; Liu, D.; Gao, Z. Preparation of ZnO photocatalyst for the efficient and rapid photocatalytic degradation of azo dyes. Nanoscale Res. Lett. 2017, 12, 143,  DOI: 10.1186/s11671-017-1904-4
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    Preparation of ZnO Photocatalyst for the Efficient and Rapid Photocatalytic Degradation of Azo Dyes
    Chen Xiaoqing; Wu Zhansheng; Liu Dandan; Gao Zhenzhen
    Nanoscale research letters (2017), 12 (1), 143 ISSN:1931-7573.
    Zinc oxide (ZnO) photocatalysts were synthesized by sol-gel method using zinc acetate as precursor for degradation of azo dyes under UV irradiation. The resultant samples were characterized by different techniques, such as XRD, SEM, and EDX. The influence of preparation conditions such as calcination temperature and composite ratio on the degradation of methyl orange (MO) was investigated. ZnO prepared with a composite ratio of 4:1 and calcination temperature of 400 °C exhibited 99.70% removal rate for MO. The effect of operation parameters on the degradation was also studied. Results showed that the removal rate of azo dyes increased with the increased dosage of catalyst and decreased initial concentration of azo dyes and the acidic condition is favorable for degradation. Furthermore, the kinetics and scavengers of the reactive species during the degradation were also investigated. It was found that the degradation of azo dyes fitted the first-order kinetics and superoxide ions were the main species. The proposed photocatalyst can efficiently and rapidly degrade azo dyes; thus, this economical and environment-friendly photocatalyst can be applied to the treatment of wastewater contaminated with synthetic dyes.
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    Santhi, K.; Rani, C.; Karuppuchamy, S. Synthesis and characterisation of a novel SnO/SnO2 hybrid photocatalyst. J. Alloys Compd. 2016, 662, 102– 107,  DOI: 10.1016/j.jallcom.2015.12.007
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    Synthesis and characterization of a novel SnO/SnO2 hybrid photocatalyst
    Santhi, K.; Rani, C.; Karuppuchamy, S.
    Journal of Alloys and Compounds (2016), 662 (), 102-107CODEN: JALCEU; ISSN:0925-8388. (Elsevier B.V.)
    Nanostructured SnO/SnO2 hybrid material was successfully synthesized by microwave irradn. method. X-ray diffraction spectroscopy shows the formation of SnO/SnO2 nanocomposite material. Nanosphere morphol. of the nanocomposite was obsd. by SEM. UV-visible diffuse reflectance spectra demonstrate that the light absorption capacity of SnO/SnO2 nanocomposite was extended to the visible region. The photocatalytic activity of SnO/SnO2 nanocomposite was investigated by the degrdn. of Methylene blue under UV light irradn. The effect of SnO/SnO2 nanocomposite dose, dye concn., pH and irradn. time for photodegrdn. of Methylene blue dye was also studied. SnO/SnO2 nanocomposite exhibits higher photocatalytic activity in neutral pH.
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    Yousefi, R.; Jamali-Sheini, F.; Cheraghizade, M.; Khosravi-Gandomani, S.; Sáaedi, A.; Huang, N. M.; Basirun, W. J.; Azarang, M. Enhanced visible-light photocatalytic activity of strontium-doped zinc oxide nanoparticles. Mater. Sci. Semicond. Process. 2015, 32, 152– 159,  DOI: 10.1016/j.mssp.2015.01.013
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    Enhanced visible-light photocatalytic activity of strontium-doped zinc oxide nanoparticles
    Yousefi, Ramin; Jamali-Sheini, Farid; Cheraghizade, Mohsen; Khosravi-Gandomani, Sara; Saaedi, Abdolhossein; Huang, Nay Ming; Basirun, Wan Jefrey; Azarang, Majid
    Materials Science in Semiconductor Processing (2015), 32 (), 152-159CODEN: MSSPFQ; ISSN:1369-8001. (Elsevier Ltd.)
    Strontium-doped zinc oxide nanoparticles (Zn1-xSrxO NPs; x=0, 0.02, 0.04, and 0.06) were synthesized by a sol-gel method. Transmission electron microscopy (TEM) and SEM (SEM) images showed NPs with nearly spherical shapes, with sizes from 27 to 41 nm for high Sr concn. and undoped ZnO NPs, resp. X-ray diffraction (XRD) patterns, selected area electron diffraction (SAED) patterns, and Raman spectra indicated that the undoped and Sr-doped ZnO NPs were crystd. in a hexagonal wurtzite structure. However, the Raman results revealed a decrease in the cryst. quality with an increase in the Sr concn. in the ZnO structure. Evidence of dopant incorporation is demonstrated by XPS of the Sr-doped ZnO NPs. From the results of optical characterizations, the band-gap values of the Zn0.98Sr0.02O and Zn0.96Sr0.04O NPs decreased, while the band-gap value of the Zn0.94Sr0.06O NPs increased in comparison to the band-gap value of the undoped ZnO NPs. Finally, the obtained NPs were used as a photocatalyst to remove methylene blue (MB). Observations showed that the efficiency of the photocatalyst activity of the ZnO NPs was significantly increased by increasing the Sr, but until an optimum concn.
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    Arunkumar, S.; Alagiri, M. Synthesis and Characterization of Spindle-Like TiO2 Nanostructures and Photocatalytic Activity on Methyl Orange and Methyl Blue Dyes Under Sunlight Radiation. J. Cluster Sci. 2017, 28, 2635– 2643,  DOI: 10.1007/s10876-017-1245-6
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    Synthesis and Characterization of Spindle-Like TiO2 Nanostructures and Photocatalytic Activity on Methyl Orange and Methyl Blue Dyes Under Sunlight Radiation
    Arunkumar, S.; Alagiri, M.
    Journal of Cluster Science (2017), 28 (5), 2635-2643CODEN: JCSCEB; ISSN:1040-7278. (Springer)
    Spindle-like TiO2 nanostructures was prepd. by a simple one pot solvothermal method followed by calcination at 400°C for 3 h. The sample was characterized using various techniques such as X-ray diffractometer, transmission electron microscopy, Fourier transform IR spectroscopy and UV-Vis absorption spectroscopy. The crystal structure of TiO2 nanostructure was measured by X-ray diffractometer. According to the XRD result, the peaks in the sample can be indexed to anatase phase of TiO2. The morphol. characterization of TiO2 sample was examd. by transmission electron microscopy. The synthesized sample consisted of spindle-like shape with size in the range of 50-70 nm. The band gap value of Spindle-like TiO2 nanostructures is 2.92 eV, which is lower than that of bulk TiO2 of 3.2 eV. The FTIR bands obsd. at 493, 443 and 428 cm-1 confirms the presence of TiO2. The Spindle-like TiO2 nanostructures showed photodegrdn. ability for methyl orange and methyl blue dye. The reuse evaluation of the Spindle-like TiO2 nanostructures showed that their photocatalytic activity had good durability.
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    Mekewi, M. A.; Darwish, A. S.; Amin, M. S.; Eshaq, G.; Bourazan, H. A. Copper nanoparticles supported onto montmorillonite clays as efficient catalyst for methylene blue dye degradation. Egypt. J. Pet. 2016, 25, 269– 279,  DOI: 10.1016/j.ejpe.2015.06.011
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    Karnan, T.; Selvakumar, S. A. S. Biosynthesis of ZnO nanoparticles using rambutan (Nephelium lappaceumL.) peel extract and their photocatalytic activity on methyl orange dye. J. Mol. Struct. 2016, 1125, 358– 365,  DOI: 10.1016/j.molstruc.2016.07.029
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    Biosynthesis of ZnO nanoparticles using rambutan (Nephelium lappaceum L.) peel extract and their photocatalytic activity on methyl orange dye
    Karnan, Thenmozhi; Selvakumar, Stanly Arul Samuel
    Journal of Molecular Structure (2016), 1125 (), 358-365CODEN: JMOSB4; ISSN:0022-2860. (Elsevier B.V.)
    In the present study, describes the synthesis of ZnO nanoparticles from rambutan (Nephelium lappaceum L.) peel ext. via bio synthesis method and developed a new low cost technol. to prep. ZnO nanoparticles. During the synthesis, fruit peel ext. act as a natural ligation agent. The successfully prepd. product was analyzed with some std. characterization studies like X-Ray Diffraction (XRD), UV-VIS Diffuse reflectance spectra (UV-Vis DRS), Field Emission Scanning Electron Microscope (FESEM), High resoln. transmittance electron microscope (HR-TEM), N2 adsorption-desorption isotherm and UV-Vis absorption Spectroscopy. The photocatalytic activity of ZnO nanoparticles was evaluated by photodegrdn. of methyl orange (MO) dye under UV light and the result depicts around 83.99% decolorisation efficiency at 120 min of illumination. In addn. with photodecolorization, mineralization was also achieved. The mineralization has been confirmed by measuring COD (COD) values.
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    Srivastava, N.; Mukhopadhyay, M. Biosynthesis of SnO2 Nanoparticles Using Bacterium Erwinia herbicola and Their Photocatalytic Activity for Degradation of Dyes. Ind. Eng. Chem. Res. 2014, 53, 13971– 13979,  DOI: 10.1021/ie5020052
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    Biosynthesis of SnO2 Nanoparticles Using Bacterium Erwinia herbicola and Their Photocatalytic Activity for Degradation of Dyes
    Srivastava, Nishant; Mukhopadhyay, Mausumi
    Industrial & Engineering Chemistry Research (2014), 53 (36), 13971-13979CODEN: IECRED; ISSN:0888-5885. (American Chemical Society)
    Tetragonal SnO2 nanoparticles (15-40 nm) were synthesized according to a green biol. synthesis technique using Gram-neg. bacteria Erwinia herbicola followed by an annealing treatment over 425 K. The SnO2 nanoparticles were characterized by dynamic light scattering (DLS), transmission electron microscopy (TEM), X-ray diffraction spectroscopy (XRD), and SEM with energy dispersive X-ray (SEM-EDX). The zeta potential of biosynthesized SnO2 nanoparticles was 7.53 mV. A biosynthesis mechanism for SnO2 nanoparticles was also proposed. In the biosynthesis, the bacterial protein and biomols. served as the template for redn. and stabilization of SnO2 nanoparticles. These biomols. also helped in controlling SnO2 nanoparticle size and aggregation. The SnO2 nanoparticles exhibited excellent photocatalytic activity for photodegrdn. of org. dyes such as methylene blue, methyl orange, and erichrome black T. Approx. 93.3, 97.8, and 94.0% degrdns. of methylene blue, erichrome black T, and methyl orange were obsd. with biosynthesized SnO2 nanoparticles in the photocatalytic degrdn. process, resp.
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    Hirthna; Sendhilnathan, S.; Rajan, P. I.; Adinaveen, T. Synthesis and Characterization of NiFe2O4 Nanoparticles for the Enhancement of Direct Sunlight Photocatalytic Degradation of Methyl Orange. J. Supercond. Novel Magn. 2018, 31, 3315– 3322,  DOI: 10.1007/s10948-018-4601-3
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    Synthesis and Characterization of NiFe2O4 Nanoparticles for the Enhancement of Direct Sunlight Photocatalytic Degradation of Methyl Orange
    Hirthna; Sendhilnathan, S.; Rajan, P. Iyyappa; Adinaveen, T.
    Journal of Superconductivity and Novel Magnetism (2018), 31 (10), 3315-3322CODEN: JSNMBN; ISSN:1557-1939. (Springer)
    The current investigation shows the simple and direct sunlight-mediated photocatalytic degrdn. of methyl orange dye by quasi globular NiFe2O4 nanocrystals synthesized from the high-temp. chem. co-pptn. method. The expt. was carried out under direct sunlight which shows significant degrdn. results lead to the practical possibility of heterogeneous photocatalysis towards environmental remediation. The as-synthesized quasi globular NiFe2O4 nanocrystals also were characterized by well-known anal. measurements of their structural, morphol., bonding, surface area, band gap and magnetic properties prior to the photocatalytic expts. The presence of active free radicals formed during the photocatalytic reaction was confirmed from the EPR signals recorded for the soln. contg. the photocatalyst and dye soln., and accordingly, the photocatalytic degrdn. mechanism was discussed.
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    Radini, I. A.; Hasan, N.; Malik, M. A.; Khan, Z. Biosynthesis of iron nanoparticles using Trigonella foenum-graecum seed extract for photocatalytic methyl orange dye degradation and antibacterial applications. J. Photochem. Photobiol., B 2018, 183, 154– 163,  DOI: 10.1016/j.jphotobiol.2018.04.014
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    Biosynthesis of iron nanoparticles using Trigonella foenum-graecum seed extract for photocatalytic methyl orange dye degradation and antibacterial applications
    Radini, Ibrahim Ali; Hasan, Nazim; Malik, Maqsood Ahmad; Khan, Zaheer
    Journal of Photochemistry and Photobiology, B: Biology (2018), 183 (), 154-163CODEN: JPPBEG; ISSN:1011-1344. (Elsevier B.V.)
    Trigonella foenum-graecum is the source of various biol. and chem. constituents with a wide area of applications, esp in the treatment/prevention of diabetes and other chronic diseases such as cancer. Multiple biol and org moieties in the aq or the org phase of Trigonella foenum-graecum carry soft redn. properties to reduce the metal cations to nanoparticles. In this investigation, the Trigonella foenum-graecum was found in the seed ext for the first time in an aq medium. We successfully synthesized zero-valent iron nanoparticles (Fe0) (ZV-Fe NPs) and stabilized these nanoparticles in an aq. medium. The stabilization mechanism of Fe NPs by Trigonella foenum-graecum in an aq. ext. was investigated. Further, Fe NPs were characterized by UV-visible spectrometry, x-ray diffraction (XRD), thermogravimetric anal.-deriv. thermogravimetric (TGA/DTG), magnetization, Fourier-transform IR (FTIR) spectroscopy, and transmission electron microscopy (TEM) images. The size of the nanoparticles, calcd using the Debye-Scherer equation and TEM, was found to be approx. 11 nm with the highest particle distribution no.
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    Najjar, M.; Hosseini, H. A.; Masoudi, A.; Sabouri, Z.; Mostafapour, A.; Khatami, M.; Darroudi, M. Green chemical approach for the synthesis of SnO2 nanoparticles and its application in photocatalytic degradation of Eriochrome Black T dye. Optik 2021, 242, 167152,  DOI: 10.1016/j.ijleo.2021.167152
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    Green chemical approach for the synthesis of SnO2 nanoparticles and its application in photocatalytic degradation of Eriochrome Black T dye
    Najjar, Morvarid; Hosseini, Hasan Ali; Masoudi, Abdolhossein; Sabouri, Zahra; Mostafapour, Asma; Khatami, Mehrdad; Darroudi, Majid
    Optik (Munich, Germany) (2021), 242 (), 167152CODEN: OTIKAJ; ISSN:0030-4026. (Elsevier GmbH)
    In this paper, SnO2 nanoparticles (SnO2-NPs) were synthesized by a simple and green sol-gel route which had involved the usage of chitosan at different temps. for performing polymn. and proceed with certain factors such as increasing the stability, preventing aggregation, and reducing the toxicity of particles. The obtained SnO2-NPs have been investigated through the means of FTIR, TGA/DTA, XRD, EDX/FESEM, TEM, and UV-Vis anal. The spherical shape of these nanoparticles has been exhibited by the FESEM images, while the XRD studies have confirmed their tetragonal cryst. structure that had contained an av. size of 25.6 nm. As the next steps, the photocatalytic activity of SnO2-NPs was evaluated the in regards to the degrdn. of Eriochrome Black T (EBT) dye under irradn. of mercury vapor lamp (500 W) for 270 min and degrdn. percentage has been estd. about 77%.
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    Vidya, C.; Manjunatha, C.; Chandraprabha, M. N.; Rajshekar, M.; Raj M.A.L, A. Hazard free green synthesis of ZnO nano-photo-catalyst using Artocarpus Heterophyllus leaf extract for the degradation of Congo red dye in water treatment applications. J. Environ. Chem. Eng. 2017, 5, 3172– 3180,  DOI: 10.1016/j.jece.2017.05.058
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    Hazard free green synthesis of ZnO nano-photo-catalyst using Artocarpus Heterophyllus leaf extract for the degradation of Congo red dye in water treatment applications
    Vidya., C.; Manjunatha., C.; Chandraprabha., M. N.; Rajshekar, Megha; Raj. M. A. L, Antony
    Journal of Environmental Chemical Engineering (2017), 5 (4), 3172-3180CODEN: JECEBG; ISSN:2213-3437. (Elsevier Ltd.)
    The present study describes the use Artocarpus Heterophyllus leaves ext. for the synthesis of Zinc oxide nanoparticles (ZnO NPs). The particles were calcined at 400, 600 and 800°C for 1 h. Powder X-Ray Diffraction (PXRD) results showed the ZnO NPs calcined at different temp. to be cryst. with hexagonal wurtzite phase. The morphol. was studied using SEM (SEM) and elemental compn. investigated using energy dispersive spectroscopy (EDS) showed peaks for Zn and O only. The exact size of ZnO particles and its cryst. nature were investigated from transmission electron microscopy (TEM),High resoln. transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED). The TEM showed the size range of the ZnO NPs to be ∼10-15 nm at 400°C, ∼15-25 nm at 600°C and ∼25-30 at 800°C which are in good agreement with the SEM observation. The band gap energy was calcd. from UV diffuse reflectance spectra and found to be 3.42, 3.38 and 3.35 eV for 400, 600 and 800°C resp. The fourier transform infra-red spectroscopy (FTIR) spectra of leaf ext. confirmed the presence of phyto constituents such as amines, amides, quinines and ketones in the leaf ext. The ZnO NPs calcined at 400°C having higher band gap energy and smaller size was used for photocatalytic degrdn. The studies showed the efficiency greater than 90% towards degrdn. of 20 ppm Congo red dye soln. at 0.24 g/L ZnO NPs in 1 h at pH 9.
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    Zangeneh, H.; Zinatizadeh, A. A. L.; Habibi, M.; Akia, M.; Hasnain Isa, M. Photocatalytic oxidation of organic dyes and pollutants in wastewater using different modified titanium dioxides: A comparative review. J. Ind. Eng. Chem. 2015, 26, 1– 36,  DOI: 10.1016/j.jiec.2014.10.043
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    Photocatalytic oxidation of organic dyes and pollutants in wastewater using different modified titanium dioxides: A comparative review
    Zangeneh, H.; Zinatizadeh, A. A. L.; Habibi, M.; Akia, M.; Hasnain Isa, M.
    Journal of Industrial and Engineering Chemistry (Amsterdam, Netherlands) (2015), 26 (), 1-36CODEN: JIECFI; ISSN:1226-086X. (Elsevier B.V.)
    This article compares the effectiveness of pure and modified TiO2 for photocatalytic degrdn. of different org. matters and clarifies the advantages of the modified TiO2 with photoactivity under visible light. Photocatalytic degrdn. technique with titanium dioxide is generally applied for treating wastewater contg. refractory org. contaminants with the purpose of reuse due to its ability to achieve complete mineralization of the compds. under mild conditions such as ambient temp. and pressure. Performance of different types of photocatalytic reactors, effects of important parameters on the reactors performance, effect of various methods used to enhance the photocatalytic activity of TiO2 including doping, sensitization of TiO2 and surface modification are discussed in details. So far, a few review papers have been published and extensive information have been reported on the structure and electronic properties of TiO2, difference between TiO2 with other common semiconductors used for photocatalytic applications, various methods used to enhance the photocatalytic characteristics of TiO2 including dye sensitization, doping, coupling, the effects of various operating parameters on the photocatalytic degrdn. of phenols and dyes and types of reactors, comparison between effective modes of TiO2 application as immobilized on surface or as suspension, and photocatalytic hybrid membrane system are presented. However, in the published review papers, performance of the different modified photocatalysts is rarely compared quant. Therefore, in order to provide an inclusive and effective comparison among the studies, specific removal rate (SRR) (mg compd.removed/g cat. h) was calcd. as a response.
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    Liu, J.; Zhang, Q.; Tian, X.; Hong, Y.; Nie, Y.; Su, N.; Jin, G.; Zhai, Z.; Fu, C. Highly efficient photocatalytic degradation of oil pollutants by oxygen deficient SnO2 quantum dots for water remediation. Chem. Eng. J. 2021, 404, 127146,  DOI: 10.1016/j.cej.2020.127146
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    Photocatalytic degradation of oil pollutants by oxygen deficient SnO2 quantum dots for water remediation
    Liu, Jianqiao; Zhang, Qianru; Tian, Xinyue; Hong, Ye; Nie, Yichen; Su, Ningning; Jin, Guohua; Zhai, Zhaoxia; Fu, Ce
    Chemical Engineering Journal (Amsterdam, Netherlands) (2021), 404 (), 127146CODEN: CMEJAJ; ISSN:1385-8947. (Elsevier B.V.)
    The oil spill pollution has become one of the most significant threats to the marine environment and coastal ecol. An efficient way is urgently expected to remove the oil pollutants at this last stage of the petroleum age. In this work, the oxygen vacancy-rich SnO2 quantum dots (QDs) are prepd. in aq. soln. via a facile bottom-up self-assembly route. The QDs are applied to the photocatalytic degrdn. of oil pollutants in water. A high degrdn. efficiency of 91.9% for octane is obtained within 48 h under the UV-visible irradn. and the excellent performance is able to be maintained within a period of 90 days. The primary reactive radical is superoxide anion (O•-2) in the degrdn. process, where the oxygen supply is essential to the photocatalytic removal of oil pollutants. The optical characterizations conclude that the QDs have 16.7% of oxygen vacancies and a band gap of 4.2 eV. Based on these characteristics, a computational model is established for the first principle-based simulation, which reveals the elec. properties and demonstrates a deep energy level of oxygen vacancies at 1.4 eV below the conduction band. The proficient photocatalytic degrdn. efficiency is ascribed to the inherent oxygen vacancies, which build an internal Z-scheme mechanism for the electron transition. A novel strategy is therefore proposed that the deep energy levels in low dimensional semiconductors are beneficial to the enhancement of photocatalytic activity. The present oxygen vacancy-rich SnO2 QDs are prospective candidates for mass degrdn. of org. oil pollutants in water and they are of great significance to the development of semiconductor photocatalysts as well as the remediation of marine environment.
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    Li, Li.; Huang, J.; Li, R.; Chen, P.; Chen, D.; Cai, M.; Liu, G.; Feng, Y.; Lv, W.; Liu, G. Synthesis of a carbon dots modified g-C3N4/SnO2 Z-scheme photocatalyst with superior photocatalytic activity for PPCPs degradation under visible light irradiation. J. Hazard. Mater. 2021, 401, 123257,  DOI: 10.1016/j.jhazmat.2020.123257
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    Synthesis of a carbon dots modified g-C3N4/SnO2 Z-scheme photocatalyst with superior photocatalytic activity for PPCPs degradation under visible light irradiation
    Li, Daguang; Huang, Jiaxing; Li, Ruobai; Chen, Ping; Chen, Danni; Cai, Meixuan; Liu, Haijin; Feng, Yiping; Lv, Wenying; Liu, Guoguang
    Journal of Hazardous Materials (2021), 401 (), 123257CODEN: JHMAD9; ISSN:0304-3894. (Elsevier B.V.)
    As an emerging carbon nanomaterial, carbon dots (CDs) have superior prospects for applications in the area of photocatalysis due to their unique optical and electronic properties. In this study, a novel CDs modified g-C3N4/SnO2 photocatalyst (CDs/g-C3N4/ SnO2) was successfully synthesized by the thermal polymn. Under visible light irradn., the resulting CDs/g-C3N4/SnO2 photocatalyst exhibited excellent photocatalytic activity for the degrdn. of indomethacin (IDM). It was demonstrated that a 0.5% loading content of CDs led to the highest IDM degrdn. rate, which was 5.62 times higher than that of pristine g-C3N4. This improved photocatalytic activity might have been attributed to the unique up-conversion photoluminescence (PL) properties and efficient charge sepn. capacities of the CDs. Reactive species (RSs) scavenging expts. and ESR (ESR) revealed that superoxide radical anions (O·-2) and photogenerated holes (h+) played crit. roles during the photocatalytic process. The results of the detection of H2O2 and ESR confirmed that CDs/g-C3N4/ SnO2 was a Z-scheme heterojunction photocatalyst. Further, HRAM LC-MS/MS was employed to identify the byproducts of IDM, and the major IDM degrdn. pathways of the CDs/g-C3N4/SnO2 photocatalyst were proposed. This study provides new ideas for the design of novel CDs modified photocatalysts for environmental remediation.
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    Alkaykh, S.; Mbarek, A.; Ali-Shattle, E. E. Photocatalytic degradation of methylene blue dye in aqueous solution by MnTiO3 nanoparticles under sunlight irradiation. Heliyon 2020, 6, e03663  DOI: 10.1016/j.heliyon.2020.e03663
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    Wu, K.; Shi, M.; Pan, X.; Zhang, J.; Zhang, X.; Shen, T.; Tian, Y. Decolourization and biodegradation of methylene blue dye by a ligninolytic enzyme-producing Bacillus thuringiensis: degradation products and pathway. Enzyme Microb. Technol. 2022, 156, 109999,  DOI: 10.1016/j.enzmictec.2022.109999
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    Decolourization and biodegradation of methylene blue dye by a ligninolytic enzyme-producing Bacillus thuringiensis: Degradation products and pathway
    Wu, Kangli; Shi, Meiling; Pan, Xiaomei; Zhang, Jianqiang; Zhang, Xiaomeng; Shen, Tong; Tian, Yongqiang
    Enzyme and Microbial Technology (2022), 156 (), 109999CODEN: EMTED2; ISSN:0141-0229. (Elsevier Inc.)
    In this study, a ligninolytic enzyme-producing strain F5 was isolated and identified as Bacillus thuringiensis, which can efficiently degrade methylene blue (MB) dye. The optimal pH, temp., rotation speed, NaCl concn., and inoculum of strain F5 for MB degrdn. were pH 6.0, 30°C, 140 rpm, 10 g/L NaCl, 4% inoculum (vol./vol.), and the strain F5 had salt tolerance, the MB decolorization rate reached 95% after 12 h. The degraded products were characterized by UV-vis, FT-IR, and GC-MS. Based on products anal., four different intermediates were identified, and a new pathway for the degrdn. of MB was proposed. The degrdn. of MB by strain F5 was due to the synergistic effects of laccase (Lac), manganese peroxidase (MnP), lignin peroxidase (LiP), and NADH-DCIP reductase; among them, Lac and MnP were the key enzymes. The phytotoxicity results showed that MB degraded metabolites' toxicity was lower than that of the parent compd., indicating that the strain F5 had a detoxification effect on MB dyes.
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    Abbasi, S.; Hasanpour, M. The effect of pH on the photocatalytic degradation of methyl orange using decorated ZnO nanoparticles with SnO2 nanoparticles. J. Mater. Sci.: Mater. Electron. 2017, 28, 1307– 1314,  DOI: 10.1007/s10854-016-5660-5
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    The effect of pH on the photocatalytic degradation of methyl orange using decorated ZnO nanoparticles with SnO2 nanoparticles
    Abbasi, Sedigheh; Hasanpour, Maryam
    Journal of Materials Science: Materials in Electronics (2017), 28 (2), 1307-1314CODEN: JSMEEV; ISSN:0957-4522. (Springer)
    In this study we investigate for the first time the effect of pH on the photocatalytic activity of SnO2 nanoparticles, ZnO nanoparticles and hybrids contg. decorated ZnO nanoparticles with difference amt. of SnO2 nanoparticles (ZnO-SnO2 (1-0.5) and ZnO-SnO2 (1-2)). The exptl. results show that the removal efficiency of methyl orange increases with respect to the irradn. time in all of the tested suspensions. Meanwhile, the effect of pH confirm that the removal efficiency of pollutant in the suspension with natural pH (pH = 7) is higher than that of acidic (pH = 4) and alk. condition (pH = 10). The results of statistical anal. reveal that the irradn. time and pH have significant impact on the photocatalytic activity of all nanoparticles and hybrids. The coeff. of detn. of all proposed models justify that the proposed models can be successfully predicted the removal efficiency of methyl orange in the all suspensions. The results of Duncan's multiple range test (α = 0.05) demonstrate that there is a significant difference between different levels of pH. Also, the photocatalytic activity of hybrid increase by increasing the decorated SnO2 nanoparticles content.
  62. 62
    Cai, R.; Zhang, B.; Shi, J.; Li, M.; He, Z. Rapid Photocatalytic Decolorization of Methyl Orange under Visible Light Using VS4/Carbon Powder Nanocomposites. ACS Sustain. Chem. Eng. 2017, 5, 7690– 7699,  DOI: 10.1021/acssuschemeng.7b01137
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    Adeel, M.; Saeed, M.; Khan, I.; Muneer, M.; Akram, N. Synthesis and Characterization of Co-ZnO and Evaluation of Its Photocatalytic Activity for Photodegradation of Methyl Orange. ACS Omega 2021, 6, 1426– 1435,  DOI: 10.1021/acsomega.0c05092
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    Synthesis and Characterization of Co-ZnO and Evaluation of Its Photocatalytic Activity for Photodegradation of Methyl Orange
    Adeel, Muhammad; Saeed, Muhammad; Khan, Iltaf; Muneer, Majid; Akram, Nadia
    ACS Omega (2021), 6 (2), 1426-1435CODEN: ACSODF; ISSN:2470-1343. (American Chemical Society)
    Photocatalysis is one of the techniques used for the eradication of org. pollutants from wastewater. In this study, Co-ZnO was tested as a photocatalyst for the degrdn. of methyl orange under irradn. of visible light. Co-ZnO loaded with 5%, 10%, and 15% Co was prepd. by the pptn. method. The advanced techniques including X-ray diffraction, XPS, diffuse reflectance UV-visible spectroscopy, photoelectrochem. measurements, temp.-programmed desorption, photoluminescence, and fluorescence spectroscopy related to OH• measurements were used for characterization of prepd. Co-ZnO. Expts. showed that 10% Co-ZnO was a highly efficient catalyst for the photodegrdn. of methyl orange as compared to ZnO. The enhanced photocatalytic activity of Co-ZnO is attributed to the implantation of Co which inhibits the electron-hole recombination. A 100 mg/L soln. of methyl orange dye was completely degraded within 130 min. The reaction kinetics has been described in terms of the Eley-Rideal mechanism.

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  • Abstract

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    Figure 1

    Figure 1. XRD pattern of sample SNPs: SNPs-200 °C (A), SNPs-500 °C (B), and SNPs-800 °C (C).

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    Figure 2

    Figure 2. HR-TEM of sample SNPs-2 at annealing at 200 °C; (A,B) different scale magnifications (20 and 10 nm), (C) inter planar d-spacing, (D) SEAD pattern, (E) EDX micrograph, and (F) particle size distribution of the histogram.

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    Figure 3

    Figure 3. HR-TEM of sample SNPs-5 at annealing at 500 °C; (A) 10 nm scale magnification, (B) 20 nm scale magnification, (C) inter planar d-spacing, (D) SEAD pattern, (E) EDX micrograph, and (F) particle size distribution of the histogram.

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    Figure 4

    Figure 4. HR-TEM of sample SNPs-8 at annealing at 800 °C; (A) 20 nm scale magnification, (B) 50 nm scale magnification, (C) inter planar d-spacing, (D) SEAD pattern, (E) EDX micrograph, and (F) particle size distribution of the histogram.

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    Figure 5

    Figure 5. FT-IR analysis of cotton peel aqueous extract (A), sample SNPs-2 at 200 °C, (B), sample SNPs-5 at 500 °C (C), and sample SNPs-8 at 800 °C (D).

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    Figure 6

    Figure 6. UV–vis absorption spectra of SNP sample at 200 °C (A), SNP sample at 500 °C (B), SNP sample at 800 °C (C), band gap energy of SNPs-2 (D), band gap energy of SNPs-5 (E), and band gap energy of SNPs-8 (F).

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    Figure 7

    Figure 7. BET analysis of sample SNPs at 200 °C total surface area (A), pore diameter (B), at 500 °C total surface area (C), pore diameter (D), and at 800 °C total surface area (E), pore diameter (F).

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    Figure 8

    Figure 8. Photocatalytic activity of SNPs-2 for the degradation of MB dye (A), SNPs-5 for the degradation of MB dye (B), SNPs-8 for the degradation of MB dye (C), SNPs-2 percentage of MB dye degradation (D), SNPs-5 percentage of MB dye degradation (E), and SNPs-8 percentage of MB dye degradation (F).

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    Figure 9

    Figure 9. Photocatalytic activity of SNPs-2 for the degradation of MO dye (A), SNPs-5 for the degradation of MO dye (B), SNPs-8 for the degradation of MO dye (C), SNPs-2 percentage of MO dye degradation (D), SNPs-5 percentage of MO dye degradation (E), and SNPs-8 percentage of MO dye degradation (F).

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    Figure 10

    Figure 10. Kinetic plots of MB and MO dye degradation, (A) MB degradation kinetics curves for varying catalyst doses (10–30 mg), (B) MO degradation kinetics curves for varying catalyst doses (10–30 mg), (C) effect of dye concentration (5–15 mg/L) on the degradation of MB dye, and (D) effect of dye concentration (5–15 mg/L) on the degradation of MO dye.

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    Scheme 1

    Scheme 1. Possible Mechanism of MB and MO Dye Degradation by SNPs Obtained in This Work
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    Figure 11

    Figure 11. Recyclability check of biosynthesized sample SNPs-3 for the degradation of MB and MO under identical experimental conditions (A) and XRD pattern after five consecutive cycles for sample SNPs-3 (B).

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      Choi, Euiyoung; Lee, Dongwook; Shin, Hyun-Joon; Kim, Namdong; Valladares, L. De Los Santos; Seo, Jiwon
      Journal of Physical Chemistry C (2021), 125 (27), 14974-14978CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      The role of oxygen vacancies in temp.-dependent photoluminescence of SnO2 nanowires was investigated by X-ray absorption spectroscopy. Two types of oxygen vacancies are present in the nanowires: at out-of-plane sites and at in-plane sites; both play crucial roles in the temp. dependence of the photoluminescence. Oxygen vacancies at in-plane sites participate in photon emission at low temp., whereas those at out-of-plane sites result in photoluminescence at room temp. Accordingly, the luminescence color changes from orange (630 nm, 1.93 eV) to green (515 nm, 2.4 eV) at 100 K. The color change is accompanied with a notable change in the oxygen K-edge X-ray absorption spectra. The scanning transmission X-ray microscopy results indicate that more oxygen vacancies at in-plane sites are present in the surface region than in the bulk region, whereas more oxygen vacancies at out-of-plane sites are present in the bulk region than in the surface region. Overall, the results demonstrate that oxygen-vacancy-mediated fluorescence properties of SnO2 nanowires are temp.-dependent; i.e., the photoluminescence mechanisms of the nanowires are mediated by oxygen vacancies at different sites, and the bicolor fluorescence originates from charge transfer between the states.
    9. 9
      Suthakaran, S.; Dhanapandian, S.; Krishnakumar, N.; Ponpandian, N. Hydrothermal synthesis of SnO2 nanoparticles and its photocatalytic degradation of methyl violet and electrochemical performance. Mater. Res. Express 2019, 6, 0850i3,  DOI: 10.1088/2053-1591/ab29c2
      There is no corresponding record for this reference.
    10. 10
      Nejati-Moghadam, L.; Esmaeili, B. K. A.; Salavati, N. M.; Safardoust, H. Synthesis and characterisation of SnO2 nanostructures prepared by a facile precipitation method. J. Nanostruct. 2015, 5, 47– 53,  DOI: 10.7508/JNS.2015.01.007
      There is no corresponding record for this reference.
    11. 11
      Zhang, L.; Ren, X.; Luo, Y.; Shi, X.; Asiri, A. M.; Li, T.; Sun, X. Ambient NH3 synthesis via electrochemical reduction of N2 over cubic sub-micron SnO2 particles. Chem. Commun. 2018, 54, 12966– 12969,  DOI: 10.1039/C8CC06524A
      11
      Ambient NH3 synthesis via electrochemical reduction of N2 over cubic sub-micron SnO2 particles
      Zhang, Ling; Ren, Xiang; Luo, Yonglan; Shi, Xifeng; Asiri, Abdullah M.; Li, Tingshuai; Sun, Xuping
      Chemical Communications (Cambridge, United Kingdom) (2018), 54 (92), 12966-12969CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
      Electrochem. N2-to-NH3 fixation under ambient conditions is emerging as a promising alternative to the energy-intensive and CO2-emitting Haber-Bosch process. However, this process involves difficulty in N2 activation, underlining the demand of electrocatalysts for the N2 redn. reaction (NRR). Cubic sub-micron SnO2 particles on C cloth (SnO2/CC) are proposed as an efficient NRR electrocatalyst for ambient N2 conversion to NH3 with excellent selectivity. Electrochem. tests reveal that SnO2/CC attains a large NH3 yield of 1.47 × 10-10 mol s-1 cm-2 at -0.8 V vs. reversible H electrode (RHE) and a high faradaic efficiency of 2.17% at -0.7 V vs. RHE in 0.1M Na2SO4, outperforming most reported aq.-based NRR electrocatalysts. Notably, it also shows strong electrochem. stability.
    12. 12
      Haspulat, B.; Sarıbel, M.; Kamış, H. Surfactant assisted hydrothermal synthesis of SnO nanoparticles with enhanced photocatalytic activity. Arab. J. Chem. 2020, 13, 96– 108,  DOI: 10.1016/j.arabjc.2017.02.004
      There is no corresponding record for this reference.
    13. 13
      Maharajan, S.; Kwon, N. H.; Brodard, P.; Fromm, K. M. A Nano-Rattle SnO2@carbon Composite Anode Material for High-Energy Li-ion Batteries by Melt Diffusion Impregnation. Nanomaterials 2020, 10, 804,  DOI: 10.3390/nano10040804
      13
      A nano-rattle SnO2/carbon composite anode material for high-energy Li-ion batteries by melt diffusion impregnation
      Maharajan, Sivarajakumar; Kwon, Nam Hee; Brodard, Pierre; Fromm, Katharina M.
      Nanomaterials (2020), 10 (4), 804CODEN: NANOKO; ISSN:2079-4991. (MDPI AG)
      The huge vol. expansion in Sn-based alloy anode materials (up to 360%) leads to a dramatic mech. stress and breaking of particles, resulting in the loss of cond. and thereby capacity fading. To overcome this issue, SnO2@C nano-rattle composites based on <10 nm SnO2 nanoparticles in and on porous amorphous carbon spheres were synthesized using a silica template and tin melting diffusion method. Such SnO2@C nano-rattle composite electrodes provided two electrochem. processes: a partially reversible process of the SnO2 redn. to metallic Sn at 0.8 V vs. Li+/Li and a reversible process of alloying/dealloying of LixSny at 0.5 V vs. Li+/Li. Good performance could be achieved by controlling the particle sizes of SnO2 and carbon, the pore size of carbon, and the distribution of SnO2 nanoparticles on the carbon shells. Finally, the areal capacity of SnO2@C prepd. by the melt diffusion process was increased due to the higher loading of SnO2 nanoparticles into the hollow carbon spheres, as compared with Sn impregnation by a reducing agent.
    14. 14
      Karmaoui, M.; Jorge, A. B.; McMillan, P. F.; Aliev, A. E.; Pullar, R. C.; Labrincha, J. A.; Tobaldi, D. M. One-Step Synthesis, Structure, and Band Gap Properties of SnO2 Nanoparticles Made by a Low Temperature Nonaqueous Sol-Gel Technique. ACS Omega 2018, 3, 13227– 13238,  DOI: 10.1021/acsomega.8b02122
      14
      One-Step Synthesis, Structure, and Band Gap Properties of SnO2 Nanoparticles Made by a Low Temperature Nonaqueous Sol-Gel Technique
      Karmaoui, Mohamed; Jorge, Ana Belen; McMillan, Paul F.; Aliev, Abil E.; Pullar, Robert C.; Labrincha, Joao Antonio; Tobaldi, David Maria
      ACS Omega (2018), 3 (10), 13227-13238CODEN: ACSODF; ISSN:2470-1343. (American Chemical Society)
      Due to its elec. conducting properties combined with excellent thermal stability and transparency throughout the visible spectrum, tin oxide (SnO2) is extremely attractive as a transparent conducting (TCO) material for applications in low emission window coating process materials and solar cells, as well as in lithium-ion batteries and gas sensors. It is also an important catalyst and catalyst support for oxidn. reactions. Here we describe a novel non-aq. sol-gel synthesis approach to produce tin oxide nanoparticles (NPs) with a low NP size dispersion. The success of this method lies in the non-hydrolytic pathway that involves the reaction between tin chloride and an oxygen donor, 1-hexanol, without the need for a surfactant or subsequent thermal treatment. This one-pot procedure is carried out at relatively low temps. in the 160 to 260 °C range, compatible with coating process processes on flexible plastic supports. The nanoparticle size distribution, shape and dislocation d. were studied by powder X-ray powder diffraction (XRPD) analyzed using the method of whole powder pattern simulation, physicochem., physicochem. (WPPM), as well as high-resoln. transmission electron microscopy (HRTEM). The SnO2 NPs were detd. to have particle sizes between 3.4 and 7.7 nm. The reaction products were characterized using liq. state 13C and 1H NMR (NMR) that confirmed the formation of dihexyl ether and 1-chlorohexane. The NPs were studied by a combination of 13C, 1H and 119Sn solid state NMR as well as Fourier transform IR (FTIR) and Raman spectroscopy. The 13C SSNMR, FTIR and Raman data showed the presence of org. species derived from the 1-hexanol reactant remaining within the samples. The optical absorption studied using UV-visible spectroscopy indicated that the band gap (Eg) shifted systematically to lower energy with decreasing NP sizes. This unusual result could be due to mech. strains present within the smallest NPs perhaps assocd. with the org. ligands decorating the NP surface. As the size increased we obsd. a correlation with an increased d. of screw dislocations present within the NPs that could indicate relaxation of the stress. We suggest that this could provide a useful method for band gap control within SnO2 NPs in the absence of chem. dopants.
    15. 15
      Zhu, K.; Lv, Y.; Liu, J.; Wang, W.; Wang, C.; Li, S.; Wang, P.; Zhang, M.; Meng, A.; Li, Z. Facile fabrication of g-C3N4/SnO2 composites and ball milling treatment for enhanced photocatalytic performance. J. Alloys Compd. 2019, 802, 13– 18,  DOI: 10.1016/j.jallcom.2019.06.193
      15
      Facile fabrication of g-C3N4/SnO2 composites and ball milling treatment for enhanced photocatalytic performance
      Zhu, Kaixing; Lv, Yang; Liu, Jing; Wang, Wenjun; Wang, Chunping; Li, Songmei; Wang, Peng; Zhang, Meng; Meng, Alan; Li, Zhenjiang
      Journal of Alloys and Compounds (2019), 802 (), 13-18CODEN: JALCEU; ISSN:0925-8388. (Elsevier B.V.)
      Ultrafine SnO2 nanoparticles (NPs) with diams. of 2-4 nm were in situ fabricated on the surfaces of g-C3N4 material through a hydrothermal method. Ball milling was then applied to treat the obtained g-C3N4/SnO2 composites in order to improve the dispersion of SnO2 NPs as well as to strengthen the bonding between SnO2 and g-C3N4. The enhanced sepn. efficiency of photogenerated carriers, as indicated by the photoluminescence spectrum, was achieved after the ball milling treatment. Consequently, the ball milled g-C3N4/SnO2 composite demonstrated significantly improved photocatalytic performance when degrading crystal violet, as evidenced by photodegrdn. efficiency enhancements of 5.06 and 3.23 times, resp., when compared with bulk g-C3N4 and the in situ synthesized g-C3N4/SnO2 composite; these improvements were due to more useable and accessible electronic transport sites at the interfaces of the composites.
    16. 16
      Chavali, M. S.; Nikolova, M. P. Metal oxide nanoparticles and their applications in nanotechnology. SN Appl. Sci. 2019, 1, 607,  DOI: 10.1007/s42452-019-0592-3
      16
      Metal oxide nanoparticles and their applications in nanotechnology
      Chavali, Murthy S.; Nikolova, Maria P.
      SN Applied Sciences (2019), 1 (6), 607CODEN: SASNBO; ISSN:2523-3971. (Springer International Publishing AG)
      A review. Considering metal oxide nanoparticles as important technol. materials, authors provide a comprehensive of researches on metal oxide nanoparticles, their synthetic strategies, and techniques, nanoscale physicochem. properties, defining specific industrial applications in the various fields of applied nanotechnol. This work expansively s the recent developments of semiconducting metal oxide gas sensors for environmental gases including CO2, O2, O3, and NH3; highly toxic gases including CO, H2S, and NO2; combustible gases such as CH4, H2, and liquefied petroleum gas; and volatile org. compds. gases. The gas sensing properties of different metal oxides nanoparticles towards specific target gases have been individually discussed. Promising metal oxide nanoparticles for sensitive and selective detection of each gas have been identified. This also categorizes metal oxides sensors by analyte gas and also summarizes the major techniques and synthesis strategies used in nanotechnol. Addnl., strategies, sensing mechanisms and related applications of semiconducting metal oxide materials are also discussed in detail. Related applications are innumerable trace to ultratrace-level gas sensors, batteries, magnetic storage media, various types of solar cells, metal oxide nanoparticles applications in catalysis, energy conversion, and antennas (including microstrip and patch-type optically transparent antennas), rectifiers, optoelectronic, and electronics.
    17. 17
      Yuliarto, B.; Septiani, N. L. W.; Kaneti, Y. V.; Iqbal, M.; Gumilar, G.; Kim, M.; Na, J.; Wu, K. C.-W.; Yamauchi, Y. Green synthesis of metal oxide nanostructures using naturally occurring compounds for energy, environmental, and bio-related applications. New J. Chem. 2019, 43, 15846– 15856,  DOI: 10.1039/c9nj03311d
      17
      Green synthesis of metal oxide nanostructures using naturally occurring compounds for energy, environmental, and bio-related applications
      Yuliarto, Brian; Septiani, Ni Luh Wulan; Kaneti, Yusuf Valentino; Iqbal, Muhammad; Gumilar, Gilang; Kim, Minjun; Na, Jongbeom; Wu, Kevin C.-W.; Yamauchi, Yusuke
      New Journal of Chemistry (2019), 43 (40), 15846-15856CODEN: NJCHE5; ISSN:1144-0546. (Royal Society of Chemistry)
      A review. In recent years, naturally occurring compds. found in plants (also known as phytochems.) found increasing application in the synthesis of metal oxide nanostructures due to their multi-role as reducing agents, capping agents, and/or complexing agents. Also, the use of natural agents, such as phytochems. provide a green and sustainable way for fabricating metal oxide nanostructures compared to conventional chem. methods. This perspective will cover various types of plant-derived phytochems. which have been employed in the prepn. of metal oxide nanostructures, including their roles and the assocd. formation mechanisms. This review will also discuss some prospective applications of phytochem.-derived metal oxide nanostructures for energy storage, environmental remediation, and bio-related applications. Finally, some perspectives on the future direction of the synthesis of metal oxide nanostructures via green chem. will be provided.
    18. 18
      Diallo, A.; Manikandan, E.; Rajendran, V.; Maaza, M. Physical & enhanced photocatalytic properties of green synthesized SnO2 nanoparticles via Aspalathus linearis. J. Alloys Compd. 2016, 681, 561– 570,  DOI: 10.1016/j.jallcom.2016.04.200
      18
      Physical & enhanced photocatalytic properties of green synthesized SnO2 nanoparticles via Aspalathus linearis
      Diallo, A.; Manikandan, E.; Rajendran, V.; Maaza, M.
      Journal of Alloys and Compounds (2016), 681 (), 561-570CODEN: JALCEU; ISSN:0925-8388. (Elsevier B.V.)
      This contribution reports on the synthesis and the main phys. properties of n-type SnO2 nanoparticles synthesized for the first time by a completely green chem. process using Aspalathus linearis's natural ext. as an effective chelating agent. Their surface/interface and vol. properties by X-rays diffraction, Raman, X-rays photoemission and photoluminescence spectroscopies are reported. Their av. diam. ranging from 2.1 to 19.3 nm follows a thermal governed equation of 〈Oparticles〉 = 1.048 10-5 T2 - 4.92 10-3 T + 2.84. The smallest SnO2 nanoparticles exhibit effective photocatalytic responses to Methylene blue, Congo red and Eosin Y.
    19. 19
      Matussin, S.; Harunsani, M. H.; Tan, A. L.; Khan, M. M. Plant-Extract-Mediated SnO2 Nanoparticles: Synthesis and Applications. ACS Sustain. Chem. Eng. 2020, 8, 3040– 3054,  DOI: 10.1021/acssuschemeng.9b06398
      There is no corresponding record for this reference.
    20. 20
      Singh, J.; Kaur, H.; Kukkar, D.; Mukamia, V. K.; Kumar, S.; Rawat, M. Green synthesis of SnO2 NPs for solar light induced photocatalytic applications. Mater. Res. Express 2019, 6, 115007,  DOI: 10.1088/2053-1591/ab4412
      20
      Green synthesis of SnO2 NPs for solar light induced photocatalytic applications
      Singh, Jagpreet; Kaur, Harpreet; Kukkar, Deepak; Mukamia, Vineet Kumar; Kumar, Sanjeev; Rawat, Mohit
      Materials Research Express (2019), 6 (11), 115007CODEN: MREAC3; ISSN:2053-1591. (IOP Publishing Ltd.)
      The present work emphasis on the eco-friendly and inexpensive approach for the synthesis of SnO2 NPs using pomegranate (Punica Granatum) leaves. The as-synthesized SnO2 NPs were confirmed by various electron and spectroscopic characterization techniques. FTIR study confirms the strong reducing and capping potential of SnO2 NPs by biomols. present in the plant ext. The successfully synthesized SnO2 NPs with a particle size of 20 nm were used as an efficient photocatalyst for the photo degrdn. of methylene blue (MB) dye under direct sunlight. The degrdn. efficiency was calcd. to be 91.5% at 240 min with the rate const. of 6.86x10-3 min-1.
    21. 21
      Bhattacharjee, A.; Ahmaruzzaman, M. A novel and green process for the production of tin oxide quantum dots and its application as a photocatalyst for the degradation of dyes from aqueous phase. J. Colloid Interface Sci. 2015, 448, 130– 139,  DOI: 10.1016/j.jcis.2015.01.083
      21
      A novel and green process for the production of tin oxide quantum dots and its application as a photocatalyst for the degradation of dyes from aqueous phase
      Bhattacharjee, Archita; Ahmaruzzaman, M.
      Journal of Colloid and Interface Science (2015), 448 (), 130-139CODEN: JCISA5; ISSN:0021-9797. (Elsevier B.V.)
      Green synthesis of SnO2 quantum dots (QDs) was developed by microwave heating method using the amino acids, namely, aspartic and glutamic acid. This method gave spherical SnO2 quantum dots with an av. diam. less than the exciton Bohr radius of SnO2. The av. diam. of SnO2 quantum dots formed using glutamic acid is ∼1.6 nm and is smaller than that formed using aspartic acid (∼2.6 nm). In the electronic spectra, a clear blue shift in the band gap energy from 4.33 to 4.4 eV is obsd. with a decrease in particle size (2.6-1.6 nm) due to 3 dimensional quantum confinement effects. The synthesized SnO2 QDs were characterized by TEM, selected area electron diffraction (SAED), XRD and Fourier transformed IR spectroscopy (FTIR). The optical properties were studied using UV-visible spectroscopy. The synthesized SnO2 QDs act as an efficient photocatalyst in the degrdn. of Rose Bengal and Eosin Y dye under direct sunlight. For the 1st time, Rose Bengal dye was degraded using SnO2 QDs as a photocatalyst by solar irradn.
    22. 22
      Sinha, T.; Ahmaruzzaman, M.; Adhikari, P. P.; Bora, R. Green and Environmentally Sustainable Fabrication of Ag-SnO2 Nanocomposite and Its Multifunctional Efficacy As Photocatalyst and Antibacterial and Antioxidant Agent. ACS Sustain. Chem. Eng. 2017, 5, 4645– 4655,  DOI: 10.1021/acssuschemeng.6b03114
      22
      Green and Environmentally Sustainable Fabrication of Ag-SnO2 Nanocomposite and Its Multifunctional Efficacy As Photocatalyst and Antibacterial and Antioxidant Agent
      Sinha, Tanur; Ahmaruzzaman, Md.; Adhikari, Partha Pradip; Bora, Rekha
      ACS Sustainable Chemistry & Engineering (2017), 5 (6), 4645-4655CODEN: ASCECG; ISSN:2168-0485. (American Chemical Society)
      Herein, we describe a phytosynthetic, additive-free, economically viable, environmentally sustainable and rapid methodol. for the formation of sphere-shaped Ag-SnO2 nanocomposites of 9 nm av. particle size employing the stem exts. of Saccharum officinarum. Employing various spectroscopic techniques, the morphol., size, crystallinity, elemental conformation, and functional groups liable for surface stabilization as well as capping were depicted. Considerably, the Ag-SnO2 nanocomposite in aq. phase revealed excellent removal efficiency for the abatement of four industrially emerging pollutants (Methylene Blue, Rose Bengal, Methyl violet 6B, and 4-nitrophenol) and probable mechanisms were also suggested. Nearly, 99.1, 99.6, 99.5, and 98.4% of Methylene Blue, Rose Bengal, Methyl violet 6B, and 4-nitrophenol were eradicated resp., within 60, 75, 75, and 58.3 min using the synthesized nanocomposite. Moreover, the spent nanocomposites were renewed and their photocatalytic proficiencies were assessed for three consecutive cycles. The spent nanocomposite and the degraded products were resp. analyzed using X-ray diffraction and liq. chromatog.-mass spectrometry spectroscopic methods. Addnl., the nanocomposite displayed comparative antimicrobial action against Pseudomonas aeruginosa, Escherichia coli, and Bacillus subtilis and indicated fair activity on 2,2-diphenyl-1-picrylhydrazyl scavenging with IC50 values 0.73 mM depicting its efficient antimicrobial and antioxidant activity. Thus, the present article has disclosed a revolutionary way for fabricating Ag-SnO2 nanocomposites and depicted their multifunctional efficacy as photocatalysts and reducing and prospective antibacterial and antioxidant agents.
    23. 23
      Sudhaparimala, S.; Vaishnavi, M. Biological synthesis of nano composite SnO2- ZnO - Screening for efficient photocatalytic degradation and antimicrobial activity. Mater. Today Proc. 2016, 3, 2373– 2380,  DOI: 10.1016/j.matpr.2016.04.150
      There is no corresponding record for this reference.
    24. 24
      Li, A. J.; Pal, V. K.; Kannan, K. A review of environmental occurrence, toxicity, biotransformation and biomonitoring of volatile organic compounds. Environ. Chem. Ecotoxicol. 2021, 3, 91– 116,  DOI: 10.1016/j.enceco.2021.01.001
      24
      A review of environmental occurrence, toxicity, biotransformation and biomonitoring of volatile organic compounds
      Li, Adela Jing; Pal, Vineet Kumar; Kannan, Kurunthachalam
      Environmental Chemistry and Ecotoxicology (2021), 3 (), 91-116CODEN: ECENAH; ISSN:2590-1826. (Elsevier B.V.)
      Volatile org. compds. (VOCs) encompass hundreds of high prodn. vol. chems. that have been used in a wide range of household and industrial products. Widespread use of products that contain VOCs resulted in their ubiquitous occurrence in the environment, with elevated concns. frequently found in indoor environments. Human exposure to VOCs is pervasive and has been a topic of concern, due to the mutagenic, neurotoxic, genotoxic, and carcinogenic potentials of these chems. Although several previous articles described toxic effects of VOCs, relatively less is known on their human exposure and body burdens. VOCs have been detd. in human breath condensate, blood, feces, and urine. This review updates the information on the environmental occurrence, toxicity, sources and pathways of human exposure, metab. and elimination, and biomonitoring of exposure to VOCs. Indoor air is a major source of human exposure to VOCs. Higher atm. concns. of VOCs have been reported in Asian countries than in North American and European countries. Elevated concns. of four widely studied VOCs namely, benzene, toluene, ethylbenzene and xylene (BTEX) were reported in air from newly constructed or renovated homes (1.3-350 μg/m3) and e-waste workshops (2.45-3,10,000 μg/m3). BTEX were also found in consumer products such as shoe polish, whiteout, leather cleaner and ink at notable concns. (e.g., ∼92,600 μg/g). Traditional methods of exposure assessment of VOCs entailed measurement of these chems. in indoor air and detn. of inhalation exposure dose. SStudies on VOC exposure assessment mainly focused on occupationally exposed individuals. Recent developments in biomonitoring of urinary metabolites of VOCs present accurate assessment of exposures and internal body burdens. Biomonitoring studies of VOCs offer novel biomarkers for the assessment of airway inflammation, lung injury, neurol. disorders, immune dysfunction and cancers in populations. Considering the very high prodn. vol. (at billions of pounds annually), known toxicity, and widespread human exposures, significance of VOCs in eliciting adverse health effects in populations will be a subject of increasing public health concern for years to come.
    25. 25
      Rueda-Marquez, J. J.; Levchuk, I.; Fernández Ibañez, P.; Sillanpää, M. A critical review on application of photocatalysis for toxicity reduction of real wastewaters. J. Clean. Prod. 2020, 258, 120694,  DOI: 10.1016/j.jclepro.2020.120694
      There is no corresponding record for this reference.
    26. 26
      Li, Y.; Chang, H.; Yan, H.; Tian, S.; Jessop, P. G. Reversible Absorption of Volatile Organic Compounds by Switchable-Hydrophilicity Solvents: A Case Study of Toluene with N,N-Dimethylcyclohexylamine. ACS Omega 2020, 6, 253– 264,  DOI: 10.1021/acsomega.0c04443
      There is no corresponding record for this reference.
    27. 27
      Li, Y.; Liu, K.; Zhang, J.; Yang, J.; Huang, Y.; Tong, Y. Engineering the Band-Edge of Fe2O3/ZnO Nanoplates via Separate Dual Cation Incorporation for Efficient Photocatalytic Performance. Ind. Eng. Chem. Res. 2020, 59, 18865– 18872,  DOI: 10.1021/acs.iecr.0c03388
      27
      Engineering the Band-Edge of Fe2O3/ZnO Nanoplates via Separate Dual Cation Incorporation for Efficient Photocatalytic Performance
      Li, Ya; Liu, Kuiliang; Zhang, Jingnan; Yang, Jingdong; Huang, Yongchao; Tong, Yexiang
      Industrial & Engineering Chemistry Research (2020), 59 (42), 18865-18872CODEN: IECRED; ISSN:0888-5885. (American Chemical Society)
      Engineering the band-edge of photocatalysts is one of the important strategies to adjust the photocatalytic performance. Herein, we successfully prep. Cu-Fe2O3/Ni-ZnO nanoplate photocatalysts and confirm by a series of materials characterization. The prepd. Cu-Fe2O3/Ni-ZnO nanoplate exhibits the highest photodegrdn. performance of tetracycline among all the prepd. samples. The exptl. results demonstrate that introducing elements into Fe2O3/ZnO regulates the potentials of the conduction band and valence band, accelerating the recombination of Cu-Fe2O3 photogenerated electrons with Ni-ZnO holes. Furthermore, ESR (ESR) spectroscopy reveals that rapid prodn. of reactive oxygen species (ROS) such as •O2- and •OH can improve the photodegrdn. activity of Cu-Fe2O3/Ni-ZnO. This work reveals that engineering the band-edge of photocatalysts can be considered as an effective method to improve the photocatalytic activity.
    28. 28
      Li, D.; Song, H.; Meng, X.; Shen, T.; Sun, J.; Han, W.; Wang, X. Effects of Particle Size on the Structure and Photocatalytic Performance by Alkali-Treated TiO2. Nanomaterials 2020, 10, 546,  DOI: 10.3390/nano10030546
      28
      Effects of particle size on the structure and photocatalytic performance by alkali-treated TiO2
      Li, Danqi; Song, Hongchen; Meng, Xia; Shen, Tingting; Sun, Jing; Han, Wenjia; Wang, Xikui
      Nanomaterials (2020), 10 (3), 546CODEN: NANOKO; ISSN:2079-4991. (MDPI AG)
      Particle size of nanomaterials has significant impact on their photocatalyst properties. In this paper, TiO2 nanoparticles with different cryst. sizes were prepd. by adjusting the alkali-hydrothermal time (0-48 h). An annealing in N2 atm after hydrothermal treatment caused TiO2 redn. and created defects, resulting in the visible light photocatalytic activity. The evolution of physicochem. properties along with the increase of hydrothermal time at a low alkali concn. has been revealed. Compared with other TiO2 samples, TiO2-24 showed higher photocatalytic activity toward degrading Rhodamine B and Sulfadiazine under visible light. The radical trapping and ESR expts. revealed that O2·- is the main reactive specie in TiO2-24. Large sp. surface areas and rapid transfer of photogenerated electrons are responsible for enhancing photocatalytic activity. The above findings clearly demonstrate that particle size and surface oxygen defects can be regulated by alkali-hydrothermal method. This research will deepen the understanding of particle size on the nanomaterials performance and provide new ideas for designing efficient photocatalysts.
    29. 29
      Tuan, P. V.; Hieu, L. T.; Tan, V. T.; Phuong, T. T.; Tran Thi Quýnh, H.; Khiem, T. N. The dependence of morphology, structure, and photocatalytic activity of SnO2/rGO nanocomposites on hydrothermal temperature. Mater. Res. Express 2019, 6, 106204,  DOI: 10.1088/2053-1591/ab1e12
      There is no corresponding record for this reference.
    30. 30
      Jiang, Y.; Zhao, H.; Liang, J.; Yue, L.; Li, T.; Luo, Y.; Liu, Q.; Lu, S.; Asiri, A. M.; Gong, Z.; Sun, X. Anodic oxidation for the degradation of organic pollutants: anode materials, operating conditions and mechanisms. A mini review. Electrochem. Commun. 2021, 123, 106912,  DOI: 10.1016/j.elecom.2020.106912
      30
      Anodic oxidation for the degradation of organic pollutants: Anode materials, operating conditions and mechanisms. A mini review
      Jiang, Yingying; Zhao, Haitao; Liang, Jie; Yue, Luochao; Li, Tingshuai; Luo, Yonglan; Liu, Qian; Lu, Siyu; Asiri, Abdullah M.; Gong, Zhengjun; Sun, Xuping
      Electrochemistry Communications (2021), 123 (), 106912CODEN: ECCMF9; ISSN:1388-2481. (Elsevier B.V.)
      A review. Org. pollutants in domestic sewage, agricultural runoff, industrial wastewater, and contaminated land pose a serious threat to human beings as well as to ecosystems. Anodic oxidn. is one of the technologies most commonly used for the degrdn. of org. pollutants. In this review, we present the current status of promising anodic oxidn. technologies for the degrdn. of org. pollutants, with fundamental insights into anode materials, operating conditions and mechanisms. Firstly, anodes based on metallic Pt, metal oxides (RuO2, IrO2, PbO2 and SnO2), and carbon (BDD and others) are critically reviewed. Secondly, strategies for the effective removal of org. pollutants in wastewater under appropriate operating conditions are systematically investigated. Thirdly, the anodic oxidn. mechanism is comprehensively summarized with illustrations of how the org. pollutants can be broken down into small mols. of low or zero toxicity. Finally, we conclude with some future perspectives for application of anodic oxidn.
    31. 31
      Li, Y.; Yang, Q.; Wang, Z.; Wang, G.; Zhang, B.; Zhang, Q.; Yang, D. Rapid fabrication of SnO2 nanoparticle photocatalyst: computational understanding and photocatalytic degradation of organic dye. Inorg. Chem. Front. 2018, 5, 3005– 3014,  DOI: 10.1039/C8QI00688A
      31
      Rapid fabrication of SnO2 nanoparticle photocatalyst: computational understanding and photocatalytic degradation of organic dye
      Li, Yuanyuan; Yang, Qimei; Wang, Zhongming; Wang, Guoyu; Zhang, Bin; Zhang, Qian; Yang, Dingfeng
      Inorganic Chemistry Frontiers (2018), 5 (12), 3005-3014CODEN: ICFNAW; ISSN:2052-1553. (Royal Society of Chemistry)
      Metal oxides have attracted an increasing attention for the photo-degrdn. of org. containments. Deep understanding of the phys. parameters correlated with the photocatalytic process is crit. and beneficial for finding an efficient and robust photocatalyst. Herein, by taking SnO2 as a prototypical model, we systematically study exciton energy, effective mass, carrier mobility and partial charge d. based on the d. functional theory (DFT). We demonstrate that the obtained exciton energy is quite low and can be effectively dissocd. into charge carriers at room temp. The estd. carrier mobility of electrons is about 50 times greater than that of holes. More interestingly, analyzing partial charge d. on the top of the valence band reveals that the photocatalytic oxidn. reaction site would occur on the O-p state. Exptl., SnO2 nanoparticles have been synthesized by a simple method and characterized by Powder XRD and TEM. With the photocatalyst SnO2, more than 90% methyl blue (MB) and Rhodamine B (RhB) are degraded under the UV light irradn. within 50 min and 270 min, resp. Trapping expts. reveal thaṫ OH are the main active species to oxidize the org. dye and mainly originate through the oxidn. of holes (h+). This study establishes an in-depth understanding of electronic structure and photocatalysis and provides insights into the designing of new photocatalytic materials.
    32. 32
      Huang, Y.; Li, K.; Lin, Y.; Tong, Y.; Liu, H. Enhanced Efficiency of Electron-Hole Separation in Bi2 O2 CO3 for Photocatalysis via Acid Treatment. ChemCatChem 2018, 10, 1982– 1987,  DOI: 10.1002/cctc.201800101
      32
      Enhanced efficiency of electron-hole separation in Bi2O2CO3 for photocatalysis via acid treatment
      Huang, Yongchao; Li, Kunshan; Lin, Ying; Tong, Yexiang; Liu, Hong
      ChemCatChem (2018), 10 (9), 1982-1987CODEN: CHEMK3; ISSN:1867-3880. (Wiley-VCH Verlag GmbH & Co. KGaA)
      We herein prepd. defective Bi2O2CO3 microspheres via a simple nitric acid treatment method. Upon generation from Bi2O2CO3, electrons and holes were superbly sepd. with the existence of defects. Combined with the advantages of multiple scattering and reflection, a large surface area and increased range of visible-light absorption, the defective Bi2O2CO3 displayed a high efficiency for the photodegrdn. of HCHO gases and methyl orange. The defective Bi2O2CO3 also possessed a superior stability, which is important for practical applications. This work opens up new opportunities for the design and fabrication of high-activity Bi-based photocatalysts for environmental protection.
    33. 33
      Huang, Y.; Lu, Y.; Lin, Y.; Mao, Y.; Ouyang, G.; Liu, H.; Zhang, S.; Tong, Y. Cerium-based hybrid nanorods for synergetic photo-thermocatalytic degradation of organic pollutants. J. Mater. Chem. A 2018, 6, 24740– 24747,  DOI: 10.1039/c8ta06565a
      33
      Cerium-based hybrid nanorods for synergetic photo-thermocatalytic degradation of organic pollutants
      Huang, Yongchao; Lu, Yirui; Lin, Ying; Mao, Yanchao; Ouyang, Gangfeng; Liu, Hong; Zhang, Shanqing; Tong, Yexiang
      Journal of Materials Chemistry A: Materials for Energy and Sustainability (2018), 6 (48), 24740-24747CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)
      In this work, phase boundary engineered cerium oxide-cerium nitride (CeO2/CeN) is synthesized and used as a high performance photocatalyst for photo-thermocatalytic degrdn. of org. pollutants in wastewater. A CeO2/CeN composite is obtained through simply annealing CeO2 nanowires under an ammonia atm. Both theor. and exptl. analyses are used to study the interfacial interaction between CeO2 and CeN crystallites. Benefiting from the interface engineering, the as-prepd. CeO2/CeN composite exhibits higher photo-thermocatalytic performance than pristine CeO2 for the removal of org. pollutants. ESR (ESR) spectroscopy and liq. chromatog. tandem mass spectrometry anal. of intermediates and products are used to further confirm the synergetic effect and degrdn. mechanism of the photo-thermocatalysis reactions. The results of this work suggest that the synergetic effect of the photo-thermal reaction can be considered as one of the most efficient strategies for environmental pollution remediation.
    34. 34
      Siripireddy, B.; Mandal, B. K. Facile green synthesis of zinc oxide nanoparticles by Eucalyptus globulus and their photocatalytic and antioxidant activity. Adv. Powder Technol. 2017, 28, 785– 797,  DOI: 10.1016/j.apt.2016.11.026
      34
      Facile green synthesis of zinc oxide nanoparticles by Eucalyptus globulus and their photocatalytic and antioxidant activity
      Siripireddy, Balaji; Mandal, Badal Kumar
      Advanced Powder Technology (2017), 28 (3), 785-797CODEN: APTEEE; ISSN:0921-8831. (Elsevier B.V.)
      Eucalyptus globulus leaf ext. mediated synthesis of spherical zinc oxide nanoparticles (ZnO NPs) was carried out under ambient conditions. UV-Visible studies of the synthesized nanoparticles revealed the characteristic peak at 361 nm indicating the formation of ZnO nanoparticles. Powder X-ray Diffractometric (XRD) study showed the strong, intense and narrow-width diffraction peaks indicating the formation of cryst. nanoparticles with most stable hexagonal phase. Field emission-SEM (FE-SEM) and high resoln.-transmission electron microscopic (HR-TEM) results confirmed the formation of spherical ZnO NPs with mean particle size of 11.6 nm which is in close agreement with XRD pattern. Further, energy dispersive X-ray diffraction anal. (EDAX) revealed the formation of highly pure ZnO NPs with the peaks of Zn and O atoms. ZnO NPs exhibited effective photocatalytic activity in degrading Methylene blue and Methyl orange with max. degrdn. efficiency up to 98.3% at 30 mg of catalyst doses. In addn., ZnO NPs exhibited high antioxidant activity against DPPH free radicals scavenger.
    35. 35
      Osuntokun, J.; Onwudiwe, D. C.; Ebenso, E. E. Biosynthesis and Photocatalytic Properties of SnO2 Nanoparticles Prepared Using Aqueous Extract of Cauliflower. J. Cluster Sci. 2017, 28, 1883– 1896,  DOI: 10.1007/s10876-017-1188-y
      35
      Biosynthesis and Photocatalytic Properties of SnO2 Nanoparticles Prepared Using Aqueous Extract of Cauliflower
      Osuntokun, Jejenija; Onwudiwe, Damian C.; Ebenso, Eno E.
      Journal of Cluster Science (2017), 28 (4), 1883-1896CODEN: JCSCEB; ISSN:1040-7278. (Springer)
      This work reports the biosynthesis of Sn(OH)2 using aq. ext. of fresh cauliflower (Brassica oleracea L. var. botrytis), and the subsequent prepn. of SnO2 nanoparticles at two different annealing temps. of 300 and 450°C for 2 h. The obtained SnO2 nanoparticles were denoted as S1 and S2 for the samples prepd. at 300 and 450°C, resp. XRD anal. identified rutile tetragonal phase of SnO2 nanoparticles and TEM results gave a quasispherical and spherical morphologies for S1 and S2 resp. of the size range 3.62-6.34 nm. The optical properties were studied with UV-vis and photoluminescence (PL) spectroscopies, and the nanoparticles showed blue shift in their absorption edges. The obsd. emission peak in the PL spectra found around 419 nm is attributable to oxygen vacancies and defects. Photocatalytic activities of the nanoparticles (S1 and S2) were studied using methylene blue (MB) under UV light irradn. and the results reveal 91.89 and 88.23% degrdn. efficiency of MB by S1 and S2 resp. over a period of 180 min.
    36. 36
      Ma, C. M.; Hong, G. B.; Lee, S. C. Facile Synthesis of Tin Dioxide Nanoparticles for Photocatalytic Degradation of Congo Red Dye in Aqueous Solution. Catalysts 2020, 10, 792,  DOI: 10.3390/catal10070792
      36
      Facile synthesis of tin dioxide nanoparticles for photocatalytic degradation of Congo red dye in aqueous solution
      Ma, Chih Ming; Hong, Gui Bing; Lee, Shang Chieh
      Catalysts (2020), 10 (7), 792CODEN: CATACJ; ISSN:2073-4344. (MDPI AG)
      This research work reports an approach used to prep. a SnO2 photocatalyst by pptn. and calcination pathways and describes an investigation of the effects of prepn. parameters on SnO2 yield. The SnO2 photocatalyst was further used for the photocatalytic degrdn. of Congo red (CR) dye, and the removal efficiency was optimized using response surface methodol. The results indicate that the SnO2 photocatalyst yield was the highest in 0.05 M of the precursor, stannous chloride and 28 wt% ammonia as the precipitant, pH 10, at 30 °C. The transmission electron microscopy results of the SnO2 photocatalyst illustrate that the av. particle size was mainly around 30-50 nm and had a solid spherical shape. The X-ray diffraction results reveal that the prepd. sample had a highly cryst. SnO2 rutile crystal structure. The prediction and exptl. results of the Response surface methodol. (RSM) indicate that, when the reaction time was 97 min, the operating temp. was 47 °C, the photocatalyst dosage was 751 mg/L, and the optimal degrdn. rate of the CR dye was 100%. After five consecutive photodegrdn. reactions, the degrdn. rate remained at 100%. The results demonstrated that the SnO2 photocatalyst prepd. in this study possesses excellent reusability.
    37. 37
      Arumugam, M.; Manikandan, D. B.; Dhandapani, E.; Sridhar, A.; Balakrishnan, K.; Markandan, M.; Ramasamy, T. Green synthesis of zinc oxide nanoparticles (ZnO NPs) using Syzygium cumini: Potential multifaceted applications on antioxidants, cytotoxic and as nanonutrient for the growth of Sesamum indicum. Environ. Technol. Innovation 2021, 23, 101653,  DOI: 10.1016/j.eti.2021.101653
      37
      Green synthesis of zinc oxide nanoparticles (ZnO NPs) using Syzygium cumini: Potential multifaceted applications on antioxidants, cytotoxic and as nanonutrient for the growth of Sesamum indicum
      Arumugam, Manikandan; Manikandan, Dinesh Babu; Dhandapani, Elayaraja; Sridhar, Arun; Balakrishnan, Karthiyayini; Markandan, Manickavasagam; Ramasamy, Thirumurugan
      Environmental Technology & Innovation (2021), 23 (), 101653CODEN: ETINBL; ISSN:2352-1864. (Elsevier B.V.)
      The green synthesis of nanoparticles using plant exts. attracts considerable interest from researchers as an eco-friendly alternative methods to conventional phys. and chem. approaches to avoid toxic chems. for the development of modern nanotechnol. resources. In this study, Syzygium cumini (Java plum) aq. leaf ext. was used as a stabilizing and reducing agent to synthesize zinc oxide nanoparticles (ZnO NPs) and analyzed its in vitro antioxidant and cytotoxic potential. The beneficial effect of ZnO NPs on the growth dynamics of Sesamum indicum (sesame) plant was investigated. The formation of the ZnO NPs was characterized by UV-Visible spectroscopy, Field emission SEM (FE-SEM) coupled with energy dispersive X-ray (EDX) spectrometer, Zeta potential, Fourier transform IR spectroscopy (FT-IR), X-ray diffraction (XRD) techniques. In vitro antioxidants of DPPH and H2O2 radical scavenging action of ZnO NPs exhibited moderate activity. Significant finding of the research was nuclear damage and cellular level modification in the human lung cancer cell line A549 by the ZnO NPs with respect to the concn. Green synthesized ZnO NPs were given as the nutrient source for the growth of the sesame plant with different concns. (1, 3, 5, 7, 9 mg/mL). At the concn. of 5 mg/mL of ZnO NPs reveals significant (p < 0.05) growth in root and shoot development of the plant when compared to the control. In conclusion, the overall study suggests the facet of ZnO NPs in the field of nanomedicine and nanonutrient.
    38. 38
      Paramarta, V.; Taufik, A.; Saleh, R. Better adsorption capacity of SnO2 nanoparticles with different graphene addition. J. Phys.: Conf. Ser. 2016, 776, 012039,  DOI: 10.1088/1742-6596/776/1/012039
      38
      Better adsorption capacity of SnO2 nanoparticles with different graphene addition
      Paramarta, V.; Taufik, A.; Saleh, R.
      Journal of Physics: Conference Series (2016), 776 (8th International Conference on Physics and Its Applications, 2016), 012039/1-012039/6CODEN: JPCSDZ; ISSN:1742-6588. (IOP Publishing Ltd.)
      The adsorption capacity of SnO2 nanoparticle has been studied by graphene and nanographene platelets (NGP) addns. using co-pptn. method. The cryst. phase, compn., and morphol. of the samples are analyzed using X-ray diffraction (XRD), energy dispersive X-ray (EDX), Fourier-transform IR spectroscopy (FT-IR), and transmission electron microscope (TEM). Tetragonal structure of SnO2 is shown for the nanoparticle and its composites. The presence of graphene and NGP is also confirmed. The adsorption capacity of the nanoparticle and its composites are analyzed by observing the degrdn. of methylene blue (MB) as the org. dye model using UV-Vis Spectroscopy. The result shows that SnO2 composite with graphene achieves higher adsorption capacity of about 20% than the composite with NGP. The fitting of equil. adsorption capacity result indicates that the adsorption mechanism of SnO2 composite with graphene tends to follow the Langmuir adsorption-isotherm model.
    39. 39
      Haq, S.; Rehman, W.; Waseem, M.; Javed, R.; Mahfooz-ur-Rehman, M.; Shahid, M. Effect of heating on the structural and optical properties of TiO2 nanoparticles: antibacterial activity. Appl. Nanosci. 2018, 8, 11– 18,  DOI: 10.1007/s13204-018-0647-6
      39
      Effect of heating on the structural and optical properties of TiO2 nanoparticles: antibacterial activity
      Haq, Sirajul; Rehman, Wajid; Waseem, Muhammad; Javed, Rehan; Mahfooz-ur-Rehman; Shahid, Muhammad
      Applied Nanoscience (2018), 8 (1-2), 11-18CODEN: ANPACY; ISSN:2190-5517. (Springer GmbH)
      TiO2 nanoparticles were synthesized at room temp. by chem. pptn. method and were then heated at 120, 300, 600 and 900°C temps. The phase transition and crystallite size variation were detd. by X-rays diffraction (XRD) anal. The surface area, pore vol. and pore size were measured using Brunauer-Emmet-Teller (BET) and Barrett-Joyner-Halenda (BJH) methods. The optical activity of heat treated and non-heat treated samples were carried out by diffuse reflectance (DR) spectroscopy. Four different methods were used to calc. band gap energy. The results obtained from thermogravimetric and differential thermal gravimetric (TG/TDG) analyses and Fourier transform infra-red (FTIR) spectroscopy agreed with each other. Agar well diffusion method has been applied to explore the antibacterial activity of nanoparticles against different bacterial strains such as Bacillus subtilis, Staphylococcus Aureus, Escherichia coli and Pseudomonas Aeruginosa. It was obsd. that TiO2 nanoparticles heated at 120°C displayed max. antibacterial activity while those heated at higher temp. showed no activity against the examd. bacteria.
    40. 40
      Ullah, H.; Khan, I.; Yamani, Z. H.; Qurashi, A. Sonochemical-driven ultrafast facile synthesis of SnO2 nanoparticles: Growth mechanism structural electrical and hydrogen gas sensing properties. Ultrason. Sonochem. 2017, 34, 484– 490,  DOI: 10.1016/j.ultsonch.2016.06.025
      40
      Sonochemical-driven ultrafast facile synthesis of SnO2 nanoparticles: Growth mechanism structural electrical and hydrogen gas sensing properties
      Ullah, Hafeez; Khan, Ibrahim; Yamani, Zain H.; Qurashi, Ahsanulhaq
      Ultrasonics Sonochemistry (2017), 34 (), 484-490CODEN: ULSOER; ISSN:1350-4177. (Elsevier B.V.)
      Synthesis of SnO2 nanoparticles have been successfully accomplished moderately at lower temp. by facile, rapid, efficient and mild ultrasonic irradn. method. The as-grown SnO2 nanoparticles are investigated by various characterization techniques in terms of structural, optical, elec. and gas sensing properties. XRD investigation has shown that the SnO2 nanoparticles materials exhibit single rutile crystal phase with high crystallinity. FESEM studies showed uniform and monodisperse morphol. of SnO2 nanoparticles. The chem. compn. of SnO2 was systematically studied by EDX measurements. Addnl. confirmation of three Raman shifts (432, 630, 772 cm-1) indicated the characteristic properties of the rutile phase of the as-grown SnO2 nanoparticles. The optical properties of SnO2 nanoparticles were examd. by DRS, and the electronic band gap of SnO2 nanoparticles were around 3.6 eV. Elec. properties of the SnO2 nanoparticles measured at various temps. have shown the semiconducting properties. Surface area and pore size of synthesized nanoparticles were analyzed from BET. It has been revealed that SnO2 nanoparticles have surface area is 47.8574 m2/g and the pore size is 10.5 nm. Moreover, hydrogen gas sensor made of SnO2 nanoparticles showed good sensitivity and faster response for the hydrogen gas.
    41. 41
      Huang, Y.; Xu, H.; Yang, H.; Lin, Y.; Liu, H.; Tong, Y. Efficient charges separation using advanced BiOI-based hollow spheres decorated with palladium and manganese dioxide nanoparticles. ACS Sustainable Chem. Eng. 2018, 6, 2751– 2757,  DOI: 10.1021/acssuschemeng.7b04435
      41
      Efficient Charges Separation Using Advanced BiOI-Based Hollow Spheres Decorated with Palladium and Manganese Dioxide Nanoparticles
      Huang, Yongchao; Xu, Huimin; Yang, Haojie; Lin, Ying; Liu, Hong; Tong, Yexiang
      ACS Sustainable Chemistry & Engineering (2018), 6 (2), 2751-2757CODEN: ASCECG; ISSN:2168-0485. (American Chemical Society)
      Multishell hollow structures have attracted tremendous attention due to their outstanding properties for application on photocatalysis. In this work, we demonstrated a straightforward and general method to construct BiOI-based core-double shell hollow spheres for the first time. The core-double shell hollow spheres consist of Pd particles and MnOx loaded onto the inner and outer surfaces of BiOI hollow spheres, resp. (Pd/BiOI/MnOx), and utilized them as an advanced photocatalyst for photocatalytic oxidn. of formaldehyde gases and methyl blue. The hollow spheres structure could provide a large sp. surface area, exposing a large no. of catalytic active sites. Addnl., the Pd particles and MnOx serve the function of sepg. the redn. and oxidn. reactive sites. The unique morphol. combined with enhanced light-absorption provided the Pd/BiOI/MnOx core-double shell hollow spheres with high efficiency for the photocatalytic oxidn. of formaldehyde gases and methyl blue. In situ diffuse reflectance IR Fourier transform and ESR measurement were performed to study the mechanism of photocatalytic degrdn., which revealed the important role of h+ and ·O2- during the photocatalytic reaction. These findings shed some light on the design of highly efficient photocatalysts for environmental protection.
    42. 42
      Elango, G.; Roopan, S. M. Efficacy of SnO 2 nanoparticles toward photocatalytic degradation of methylene blue dye. J. Photochem. Photobiol., B 2016, 155, 34– 38,  DOI: 10.1016/j.jphotobiol.2015.12.010
      42
      Efficacy of SnO2 nanoparticles toward photocatalytic degradation of methylene blue dye
      Elango, Ganesh; Roopan, Selvaraj Mohana
      Journal of Photochemistry and Photobiology, B: Biology (2016), 155 (), 34-38CODEN: JPPBEG; ISSN:1011-1344. (Elsevier B.V.)
      Maximum pollutants in the industrial and domestic waste water effluents from any sources include pathogens and org. chems., which can be removed before discharging into the water bodies. Methylene blue has been considered as one of the major water contaminated pollutants. Such pollutant is dominant in surface water and groundwater. It will cause irreversible hazards to human and aquatic life. Nanotechnol. plays a major role in degrading such type of pollutant. In order to fulfill today's requirement, we have decided to handle the green synthesis of nanoparticles and its application by merging important fields like chem., environmental science, and biotechnol. Here our work emphasizes on the biol. synthesis of SnO2 nanoparticles (SnO2 NPs) using the methanolic ext. of Cyphomandra betacea (C.betacea), and it was confirmed by various characterization techniques such as UV-visible spectroscopy, FT-IR, XRD, SEM, particle size analyzer, zeta potential, and TEM. The obtained results stated that the synthesized SnO2 NPs were in rod shape with an av. size of 21 nm, which resulted in a product of nanobiotechnol. Further, we have utilized the environmental-friendly synthesized SnO2 NPs photocatalytic degrdn. of environmental concern methylene blue with first-order kinetics. In this paper, we have attempted to prove that secondary metabolite-entrapped SnO2 NPs are non-toxic to the environment.
    43. 43
      Yao, X.; Zhang, B.; Cui, S.; Yang, S.; Tang, X. Fabrication of SnSO4-modified TiO2 for enhance degradation performance of methyl orange (MO) and antibacterial activity. Appl. Surf. Sci. 2021, 551, 149419,  DOI: 10.1016/j.apsusc.2021.149419
      43
      Fabrication of SnSO4-modified TiO2 for enhance degradation performance of methyl orange (MO) and antibacterial activity
      Yao, Xiyan; Zhang, Bin; Cui, Shuai; Yang, Sue; Tang, Xiaoning
      Applied Surface Science (2021), 551 (), 149419CODEN: ASUSEE; ISSN:0169-4332. (Elsevier B.V.)
      SnSO4-modified TiO2 nanoparticles with different SnSO4 contents were prepd., and their morphol., light absorption properties and photocatalytic degrdn. and antibacterial activities were detd. The results revealed that the samples had mesoporous structures consisting of anatase phase, and their surface area increased with increasing SnSO4 content. The XPS anal. showed that Sn had the valence state of + 4 and existed as SnO2; and S existed on the surface as sulfate. The photocatalytic degrdn. assay showed that SnSO4-modified TiO2 shifted the absorption peak of methyl orange (MO), and gradually changed its structure from azo structure to quinone structure. Compared with that of pure TiO2, SnSO4-modified TiO2 had higher MO degrdn. activity under UV irradn. and visible light irradn. and had higher antibacterial activity against Escherichia coli and Staphylococcus aureus under visible light and dark conditions. The expts. on MO degrdn. in the presence of scavengers also showed that ·O2- was the predominant radicals generated during degrdn. under visible light irradn. The data also indicated that the SnSO4-modified TiO2 nanoparticles could produce reactive oxygen species (ROS) under visible light and dark conditions, and the produced ROS, esp. for ·OH radicals, significantly play roles in their antibacterial activity under visible light.
    44. 44
      Kurniawan, T. A.; Mengting, Z.; Fu, D.; Yeap, S. K.; Othman, M. H. D.; Avtar, R.; Ouyang, T. Functionalizing TiO2 with graphene oxide for enhancing photocatalytic degradation of methylene blue (MB) in contaminated wastewater. J. Environ. Manage. 2020, 270, 110871,  DOI: 10.1016/j.jenvman.2020.110871
      44
      Functionalizing TiO2 with graphene oxide for enhancing photocatalytic degradation of methylene blue (MB) in contaminated wastewater
      Kurniawan, Tonni Agustiono; Zhu, Mengting; Fu, Dun; Yeap, Swee Keong; Othman, Mohd Hafiz Dzarfan; Avtar, Ram; Ouyang, Tong
      Journal of Environmental Management (2020), 270 (), 110871CODEN: JEVMAW; ISSN:0301-4797. (Elsevier Ltd.)
      Methylene blue is a refractory pollutant commonly present in textile wastewater. This study tests the feasibility of TiO2/graphene oxide (GO) composite in enhancing photocatalytic degrdn. of MB in synthetic wastewater with respect to scientific and engineering aspects. To enhance its removal, we vary the compn. of the composite based on the TiO2 wt. Under UV-vis irradn., the effects of photocatalyst's dose, pH, and reaction time on MB removal by the composites are evaluated under optimum conditions, while any changes in their physico-chem. properties before and after treatment are analyzed by using TEM, SEM, XRD, FTIR and BET. The photodegrdn. pathways of the target pollutant by the composite and its removal mechanisms are also elaborated. It is found that the same composite with a 1:2 wt ratio of GO/TiO2 has the largest surface area of 104.51 m2/g. Under optimum reactions (0.2 g/L of dose, pH 10, and 5 mg/L of pollutant's concn.), an almost complete MB removal could be attained within 4 h. This result is higher than that of the TiO2 alone (30%) under the same conditions. Since the treated effluents could meet the strict discharge std. limit of ≤0.2μg/L set by China's regulation, subsequent biol. treatments are unnecessary for completing biodegrdn. of remaining oxidn. byproducts in the wastewater effluents.
    45. 45
      Chen, X.; Wu, Z.; Liu, D.; Gao, Z. Preparation of ZnO photocatalyst for the efficient and rapid photocatalytic degradation of azo dyes. Nanoscale Res. Lett. 2017, 12, 143,  DOI: 10.1186/s11671-017-1904-4
      45
      Preparation of ZnO Photocatalyst for the Efficient and Rapid Photocatalytic Degradation of Azo Dyes
      Chen Xiaoqing; Wu Zhansheng; Liu Dandan; Gao Zhenzhen
      Nanoscale research letters (2017), 12 (1), 143 ISSN:1931-7573.
      Zinc oxide (ZnO) photocatalysts were synthesized by sol-gel method using zinc acetate as precursor for degradation of azo dyes under UV irradiation. The resultant samples were characterized by different techniques, such as XRD, SEM, and EDX. The influence of preparation conditions such as calcination temperature and composite ratio on the degradation of methyl orange (MO) was investigated. ZnO prepared with a composite ratio of 4:1 and calcination temperature of 400 °C exhibited 99.70% removal rate for MO. The effect of operation parameters on the degradation was also studied. Results showed that the removal rate of azo dyes increased with the increased dosage of catalyst and decreased initial concentration of azo dyes and the acidic condition is favorable for degradation. Furthermore, the kinetics and scavengers of the reactive species during the degradation were also investigated. It was found that the degradation of azo dyes fitted the first-order kinetics and superoxide ions were the main species. The proposed photocatalyst can efficiently and rapidly degrade azo dyes; thus, this economical and environment-friendly photocatalyst can be applied to the treatment of wastewater contaminated with synthetic dyes.
    46. 46
      Santhi, K.; Rani, C.; Karuppuchamy, S. Synthesis and characterisation of a novel SnO/SnO2 hybrid photocatalyst. J. Alloys Compd. 2016, 662, 102– 107,  DOI: 10.1016/j.jallcom.2015.12.007
      46
      Synthesis and characterization of a novel SnO/SnO2 hybrid photocatalyst
      Santhi, K.; Rani, C.; Karuppuchamy, S.
      Journal of Alloys and Compounds (2016), 662 (), 102-107CODEN: JALCEU; ISSN:0925-8388. (Elsevier B.V.)
      Nanostructured SnO/SnO2 hybrid material was successfully synthesized by microwave irradn. method. X-ray diffraction spectroscopy shows the formation of SnO/SnO2 nanocomposite material. Nanosphere morphol. of the nanocomposite was obsd. by SEM. UV-visible diffuse reflectance spectra demonstrate that the light absorption capacity of SnO/SnO2 nanocomposite was extended to the visible region. The photocatalytic activity of SnO/SnO2 nanocomposite was investigated by the degrdn. of Methylene blue under UV light irradn. The effect of SnO/SnO2 nanocomposite dose, dye concn., pH and irradn. time for photodegrdn. of Methylene blue dye was also studied. SnO/SnO2 nanocomposite exhibits higher photocatalytic activity in neutral pH.
    47. 47
      Yousefi, R.; Jamali-Sheini, F.; Cheraghizade, M.; Khosravi-Gandomani, S.; Sáaedi, A.; Huang, N. M.; Basirun, W. J.; Azarang, M. Enhanced visible-light photocatalytic activity of strontium-doped zinc oxide nanoparticles. Mater. Sci. Semicond. Process. 2015, 32, 152– 159,  DOI: 10.1016/j.mssp.2015.01.013
      47
      Enhanced visible-light photocatalytic activity of strontium-doped zinc oxide nanoparticles
      Yousefi, Ramin; Jamali-Sheini, Farid; Cheraghizade, Mohsen; Khosravi-Gandomani, Sara; Saaedi, Abdolhossein; Huang, Nay Ming; Basirun, Wan Jefrey; Azarang, Majid
      Materials Science in Semiconductor Processing (2015), 32 (), 152-159CODEN: MSSPFQ; ISSN:1369-8001. (Elsevier Ltd.)
      Strontium-doped zinc oxide nanoparticles (Zn1-xSrxO NPs; x=0, 0.02, 0.04, and 0.06) were synthesized by a sol-gel method. Transmission electron microscopy (TEM) and SEM (SEM) images showed NPs with nearly spherical shapes, with sizes from 27 to 41 nm for high Sr concn. and undoped ZnO NPs, resp. X-ray diffraction (XRD) patterns, selected area electron diffraction (SAED) patterns, and Raman spectra indicated that the undoped and Sr-doped ZnO NPs were crystd. in a hexagonal wurtzite structure. However, the Raman results revealed a decrease in the cryst. quality with an increase in the Sr concn. in the ZnO structure. Evidence of dopant incorporation is demonstrated by XPS of the Sr-doped ZnO NPs. From the results of optical characterizations, the band-gap values of the Zn0.98Sr0.02O and Zn0.96Sr0.04O NPs decreased, while the band-gap value of the Zn0.94Sr0.06O NPs increased in comparison to the band-gap value of the undoped ZnO NPs. Finally, the obtained NPs were used as a photocatalyst to remove methylene blue (MB). Observations showed that the efficiency of the photocatalyst activity of the ZnO NPs was significantly increased by increasing the Sr, but until an optimum concn.
    48. 48
      Arunkumar, S.; Alagiri, M. Synthesis and Characterization of Spindle-Like TiO2 Nanostructures and Photocatalytic Activity on Methyl Orange and Methyl Blue Dyes Under Sunlight Radiation. J. Cluster Sci. 2017, 28, 2635– 2643,  DOI: 10.1007/s10876-017-1245-6
      48
      Synthesis and Characterization of Spindle-Like TiO2 Nanostructures and Photocatalytic Activity on Methyl Orange and Methyl Blue Dyes Under Sunlight Radiation
      Arunkumar, S.; Alagiri, M.
      Journal of Cluster Science (2017), 28 (5), 2635-2643CODEN: JCSCEB; ISSN:1040-7278. (Springer)
      Spindle-like TiO2 nanostructures was prepd. by a simple one pot solvothermal method followed by calcination at 400°C for 3 h. The sample was characterized using various techniques such as X-ray diffractometer, transmission electron microscopy, Fourier transform IR spectroscopy and UV-Vis absorption spectroscopy. The crystal structure of TiO2 nanostructure was measured by X-ray diffractometer. According to the XRD result, the peaks in the sample can be indexed to anatase phase of TiO2. The morphol. characterization of TiO2 sample was examd. by transmission electron microscopy. The synthesized sample consisted of spindle-like shape with size in the range of 50-70 nm. The band gap value of Spindle-like TiO2 nanostructures is 2.92 eV, which is lower than that of bulk TiO2 of 3.2 eV. The FTIR bands obsd. at 493, 443 and 428 cm-1 confirms the presence of TiO2. The Spindle-like TiO2 nanostructures showed photodegrdn. ability for methyl orange and methyl blue dye. The reuse evaluation of the Spindle-like TiO2 nanostructures showed that their photocatalytic activity had good durability.
    49. 49
      Mekewi, M. A.; Darwish, A. S.; Amin, M. S.; Eshaq, G.; Bourazan, H. A. Copper nanoparticles supported onto montmorillonite clays as efficient catalyst for methylene blue dye degradation. Egypt. J. Pet. 2016, 25, 269– 279,  DOI: 10.1016/j.ejpe.2015.06.011
      There is no corresponding record for this reference.
    50. 50
      Karnan, T.; Selvakumar, S. A. S. Biosynthesis of ZnO nanoparticles using rambutan (Nephelium lappaceumL.) peel extract and their photocatalytic activity on methyl orange dye. J. Mol. Struct. 2016, 1125, 358– 365,  DOI: 10.1016/j.molstruc.2016.07.029
      50
      Biosynthesis of ZnO nanoparticles using rambutan (Nephelium lappaceum L.) peel extract and their photocatalytic activity on methyl orange dye
      Karnan, Thenmozhi; Selvakumar, Stanly Arul Samuel
      Journal of Molecular Structure (2016), 1125 (), 358-365CODEN: JMOSB4; ISSN:0022-2860. (Elsevier B.V.)
      In the present study, describes the synthesis of ZnO nanoparticles from rambutan (Nephelium lappaceum L.) peel ext. via bio synthesis method and developed a new low cost technol. to prep. ZnO nanoparticles. During the synthesis, fruit peel ext. act as a natural ligation agent. The successfully prepd. product was analyzed with some std. characterization studies like X-Ray Diffraction (XRD), UV-VIS Diffuse reflectance spectra (UV-Vis DRS), Field Emission Scanning Electron Microscope (FESEM), High resoln. transmittance electron microscope (HR-TEM), N2 adsorption-desorption isotherm and UV-Vis absorption Spectroscopy. The photocatalytic activity of ZnO nanoparticles was evaluated by photodegrdn. of methyl orange (MO) dye under UV light and the result depicts around 83.99% decolorisation efficiency at 120 min of illumination. In addn. with photodecolorization, mineralization was also achieved. The mineralization has been confirmed by measuring COD (COD) values.
    51. 51
      Srivastava, N.; Mukhopadhyay, M. Biosynthesis of SnO2 Nanoparticles Using Bacterium Erwinia herbicola and Their Photocatalytic Activity for Degradation of Dyes. Ind. Eng. Chem. Res. 2014, 53, 13971– 13979,  DOI: 10.1021/ie5020052
      51
      Biosynthesis of SnO2 Nanoparticles Using Bacterium Erwinia herbicola and Their Photocatalytic Activity for Degradation of Dyes
      Srivastava, Nishant; Mukhopadhyay, Mausumi
      Industrial & Engineering Chemistry Research (2014), 53 (36), 13971-13979CODEN: IECRED; ISSN:0888-5885. (American Chemical Society)
      Tetragonal SnO2 nanoparticles (15-40 nm) were synthesized according to a green biol. synthesis technique using Gram-neg. bacteria Erwinia herbicola followed by an annealing treatment over 425 K. The SnO2 nanoparticles were characterized by dynamic light scattering (DLS), transmission electron microscopy (TEM), X-ray diffraction spectroscopy (XRD), and SEM with energy dispersive X-ray (SEM-EDX). The zeta potential of biosynthesized SnO2 nanoparticles was 7.53 mV. A biosynthesis mechanism for SnO2 nanoparticles was also proposed. In the biosynthesis, the bacterial protein and biomols. served as the template for redn. and stabilization of SnO2 nanoparticles. These biomols. also helped in controlling SnO2 nanoparticle size and aggregation. The SnO2 nanoparticles exhibited excellent photocatalytic activity for photodegrdn. of org. dyes such as methylene blue, methyl orange, and erichrome black T. Approx. 93.3, 97.8, and 94.0% degrdns. of methylene blue, erichrome black T, and methyl orange were obsd. with biosynthesized SnO2 nanoparticles in the photocatalytic degrdn. process, resp.
    52. 52
      Hirthna; Sendhilnathan, S.; Rajan, P. I.; Adinaveen, T. Synthesis and Characterization of NiFe2O4 Nanoparticles for the Enhancement of Direct Sunlight Photocatalytic Degradation of Methyl Orange. J. Supercond. Novel Magn. 2018, 31, 3315– 3322,  DOI: 10.1007/s10948-018-4601-3
      52
      Synthesis and Characterization of NiFe2O4 Nanoparticles for the Enhancement of Direct Sunlight Photocatalytic Degradation of Methyl Orange
      Hirthna; Sendhilnathan, S.; Rajan, P. Iyyappa; Adinaveen, T.
      Journal of Superconductivity and Novel Magnetism (2018), 31 (10), 3315-3322CODEN: JSNMBN; ISSN:1557-1939. (Springer)
      The current investigation shows the simple and direct sunlight-mediated photocatalytic degrdn. of methyl orange dye by quasi globular NiFe2O4 nanocrystals synthesized from the high-temp. chem. co-pptn. method. The expt. was carried out under direct sunlight which shows significant degrdn. results lead to the practical possibility of heterogeneous photocatalysis towards environmental remediation. The as-synthesized quasi globular NiFe2O4 nanocrystals also were characterized by well-known anal. measurements of their structural, morphol., bonding, surface area, band gap and magnetic properties prior to the photocatalytic expts. The presence of active free radicals formed during the photocatalytic reaction was confirmed from the EPR signals recorded for the soln. contg. the photocatalyst and dye soln., and accordingly, the photocatalytic degrdn. mechanism was discussed.
    53. 53
      Radini, I. A.; Hasan, N.; Malik, M. A.; Khan, Z. Biosynthesis of iron nanoparticles using Trigonella foenum-graecum seed extract for photocatalytic methyl orange dye degradation and antibacterial applications. J. Photochem. Photobiol., B 2018, 183, 154– 163,  DOI: 10.1016/j.jphotobiol.2018.04.014
      53
      Biosynthesis of iron nanoparticles using Trigonella foenum-graecum seed extract for photocatalytic methyl orange dye degradation and antibacterial applications
      Radini, Ibrahim Ali; Hasan, Nazim; Malik, Maqsood Ahmad; Khan, Zaheer
      Journal of Photochemistry and Photobiology, B: Biology (2018), 183 (), 154-163CODEN: JPPBEG; ISSN:1011-1344. (Elsevier B.V.)
      Trigonella foenum-graecum is the source of various biol. and chem. constituents with a wide area of applications, esp in the treatment/prevention of diabetes and other chronic diseases such as cancer. Multiple biol and org moieties in the aq or the org phase of Trigonella foenum-graecum carry soft redn. properties to reduce the metal cations to nanoparticles. In this investigation, the Trigonella foenum-graecum was found in the seed ext for the first time in an aq medium. We successfully synthesized zero-valent iron nanoparticles (Fe0) (ZV-Fe NPs) and stabilized these nanoparticles in an aq. medium. The stabilization mechanism of Fe NPs by Trigonella foenum-graecum in an aq. ext. was investigated. Further, Fe NPs were characterized by UV-visible spectrometry, x-ray diffraction (XRD), thermogravimetric anal.-deriv. thermogravimetric (TGA/DTG), magnetization, Fourier-transform IR (FTIR) spectroscopy, and transmission electron microscopy (TEM) images. The size of the nanoparticles, calcd using the Debye-Scherer equation and TEM, was found to be approx. 11 nm with the highest particle distribution no.
    54. 54
      Najjar, M.; Hosseini, H. A.; Masoudi, A.; Sabouri, Z.; Mostafapour, A.; Khatami, M.; Darroudi, M. Green chemical approach for the synthesis of SnO2 nanoparticles and its application in photocatalytic degradation of Eriochrome Black T dye. Optik 2021, 242, 167152,  DOI: 10.1016/j.ijleo.2021.167152
      54
      Green chemical approach for the synthesis of SnO2 nanoparticles and its application in photocatalytic degradation of Eriochrome Black T dye
      Najjar, Morvarid; Hosseini, Hasan Ali; Masoudi, Abdolhossein; Sabouri, Zahra; Mostafapour, Asma; Khatami, Mehrdad; Darroudi, Majid
      Optik (Munich, Germany) (2021), 242 (), 167152CODEN: OTIKAJ; ISSN:0030-4026. (Elsevier GmbH)
      In this paper, SnO2 nanoparticles (SnO2-NPs) were synthesized by a simple and green sol-gel route which had involved the usage of chitosan at different temps. for performing polymn. and proceed with certain factors such as increasing the stability, preventing aggregation, and reducing the toxicity of particles. The obtained SnO2-NPs have been investigated through the means of FTIR, TGA/DTA, XRD, EDX/FESEM, TEM, and UV-Vis anal. The spherical shape of these nanoparticles has been exhibited by the FESEM images, while the XRD studies have confirmed their tetragonal cryst. structure that had contained an av. size of 25.6 nm. As the next steps, the photocatalytic activity of SnO2-NPs was evaluated the in regards to the degrdn. of Eriochrome Black T (EBT) dye under irradn. of mercury vapor lamp (500 W) for 270 min and degrdn. percentage has been estd. about 77%.
    55. 55
      Vidya, C.; Manjunatha, C.; Chandraprabha, M. N.; Rajshekar, M.; Raj M.A.L, A. Hazard free green synthesis of ZnO nano-photo-catalyst using Artocarpus Heterophyllus leaf extract for the degradation of Congo red dye in water treatment applications. J. Environ. Chem. Eng. 2017, 5, 3172– 3180,  DOI: 10.1016/j.jece.2017.05.058
      55
      Hazard free green synthesis of ZnO nano-photo-catalyst using Artocarpus Heterophyllus leaf extract for the degradation of Congo red dye in water treatment applications
      Vidya., C.; Manjunatha., C.; Chandraprabha., M. N.; Rajshekar, Megha; Raj. M. A. L, Antony
      Journal of Environmental Chemical Engineering (2017), 5 (4), 3172-3180CODEN: JECEBG; ISSN:2213-3437. (Elsevier Ltd.)
      The present study describes the use Artocarpus Heterophyllus leaves ext. for the synthesis of Zinc oxide nanoparticles (ZnO NPs). The particles were calcined at 400, 600 and 800°C for 1 h. Powder X-Ray Diffraction (PXRD) results showed the ZnO NPs calcined at different temp. to be cryst. with hexagonal wurtzite phase. The morphol. was studied using SEM (SEM) and elemental compn. investigated using energy dispersive spectroscopy (EDS) showed peaks for Zn and O only. The exact size of ZnO particles and its cryst. nature were investigated from transmission electron microscopy (TEM),High resoln. transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED). The TEM showed the size range of the ZnO NPs to be ∼10-15 nm at 400°C, ∼15-25 nm at 600°C and ∼25-30 at 800°C which are in good agreement with the SEM observation. The band gap energy was calcd. from UV diffuse reflectance spectra and found to be 3.42, 3.38 and 3.35 eV for 400, 600 and 800°C resp. The fourier transform infra-red spectroscopy (FTIR) spectra of leaf ext. confirmed the presence of phyto constituents such as amines, amides, quinines and ketones in the leaf ext. The ZnO NPs calcined at 400°C having higher band gap energy and smaller size was used for photocatalytic degrdn. The studies showed the efficiency greater than 90% towards degrdn. of 20 ppm Congo red dye soln. at 0.24 g/L ZnO NPs in 1 h at pH 9.
    56. 56
      Zangeneh, H.; Zinatizadeh, A. A. L.; Habibi, M.; Akia, M.; Hasnain Isa, M. Photocatalytic oxidation of organic dyes and pollutants in wastewater using different modified titanium dioxides: A comparative review. J. Ind. Eng. Chem. 2015, 26, 1– 36,  DOI: 10.1016/j.jiec.2014.10.043
      56
      Photocatalytic oxidation of organic dyes and pollutants in wastewater using different modified titanium dioxides: A comparative review
      Zangeneh, H.; Zinatizadeh, A. A. L.; Habibi, M.; Akia, M.; Hasnain Isa, M.
      Journal of Industrial and Engineering Chemistry (Amsterdam, Netherlands) (2015), 26 (), 1-36CODEN: JIECFI; ISSN:1226-086X. (Elsevier B.V.)
      This article compares the effectiveness of pure and modified TiO2 for photocatalytic degrdn. of different org. matters and clarifies the advantages of the modified TiO2 with photoactivity under visible light. Photocatalytic degrdn. technique with titanium dioxide is generally applied for treating wastewater contg. refractory org. contaminants with the purpose of reuse due to its ability to achieve complete mineralization of the compds. under mild conditions such as ambient temp. and pressure. Performance of different types of photocatalytic reactors, effects of important parameters on the reactors performance, effect of various methods used to enhance the photocatalytic activity of TiO2 including doping, sensitization of TiO2 and surface modification are discussed in details. So far, a few review papers have been published and extensive information have been reported on the structure and electronic properties of TiO2, difference between TiO2 with other common semiconductors used for photocatalytic applications, various methods used to enhance the photocatalytic characteristics of TiO2 including dye sensitization, doping, coupling, the effects of various operating parameters on the photocatalytic degrdn. of phenols and dyes and types of reactors, comparison between effective modes of TiO2 application as immobilized on surface or as suspension, and photocatalytic hybrid membrane system are presented. However, in the published review papers, performance of the different modified photocatalysts is rarely compared quant. Therefore, in order to provide an inclusive and effective comparison among the studies, specific removal rate (SRR) (mg compd.removed/g cat. h) was calcd. as a response.
    57. 57
      Liu, J.; Zhang, Q.; Tian, X.; Hong, Y.; Nie, Y.; Su, N.; Jin, G.; Zhai, Z.; Fu, C. Highly efficient photocatalytic degradation of oil pollutants by oxygen deficient SnO2 quantum dots for water remediation. Chem. Eng. J. 2021, 404, 127146,  DOI: 10.1016/j.cej.2020.127146
      57
      Photocatalytic degradation of oil pollutants by oxygen deficient SnO2 quantum dots for water remediation
      Liu, Jianqiao; Zhang, Qianru; Tian, Xinyue; Hong, Ye; Nie, Yichen; Su, Ningning; Jin, Guohua; Zhai, Zhaoxia; Fu, Ce
      Chemical Engineering Journal (Amsterdam, Netherlands) (2021), 404 (), 127146CODEN: CMEJAJ; ISSN:1385-8947. (Elsevier B.V.)
      The oil spill pollution has become one of the most significant threats to the marine environment and coastal ecol. An efficient way is urgently expected to remove the oil pollutants at this last stage of the petroleum age. In this work, the oxygen vacancy-rich SnO2 quantum dots (QDs) are prepd. in aq. soln. via a facile bottom-up self-assembly route. The QDs are applied to the photocatalytic degrdn. of oil pollutants in water. A high degrdn. efficiency of 91.9% for octane is obtained within 48 h under the UV-visible irradn. and the excellent performance is able to be maintained within a period of 90 days. The primary reactive radical is superoxide anion (O•-2) in the degrdn. process, where the oxygen supply is essential to the photocatalytic removal of oil pollutants. The optical characterizations conclude that the QDs have 16.7% of oxygen vacancies and a band gap of 4.2 eV. Based on these characteristics, a computational model is established for the first principle-based simulation, which reveals the elec. properties and demonstrates a deep energy level of oxygen vacancies at 1.4 eV below the conduction band. The proficient photocatalytic degrdn. efficiency is ascribed to the inherent oxygen vacancies, which build an internal Z-scheme mechanism for the electron transition. A novel strategy is therefore proposed that the deep energy levels in low dimensional semiconductors are beneficial to the enhancement of photocatalytic activity. The present oxygen vacancy-rich SnO2 QDs are prospective candidates for mass degrdn. of org. oil pollutants in water and they are of great significance to the development of semiconductor photocatalysts as well as the remediation of marine environment.
    58. 58
      Li, Li.; Huang, J.; Li, R.; Chen, P.; Chen, D.; Cai, M.; Liu, G.; Feng, Y.; Lv, W.; Liu, G. Synthesis of a carbon dots modified g-C3N4/SnO2 Z-scheme photocatalyst with superior photocatalytic activity for PPCPs degradation under visible light irradiation. J. Hazard. Mater. 2021, 401, 123257,  DOI: 10.1016/j.jhazmat.2020.123257
      58
      Synthesis of a carbon dots modified g-C3N4/SnO2 Z-scheme photocatalyst with superior photocatalytic activity for PPCPs degradation under visible light irradiation
      Li, Daguang; Huang, Jiaxing; Li, Ruobai; Chen, Ping; Chen, Danni; Cai, Meixuan; Liu, Haijin; Feng, Yiping; Lv, Wenying; Liu, Guoguang
      Journal of Hazardous Materials (2021), 401 (), 123257CODEN: JHMAD9; ISSN:0304-3894. (Elsevier B.V.)
      As an emerging carbon nanomaterial, carbon dots (CDs) have superior prospects for applications in the area of photocatalysis due to their unique optical and electronic properties. In this study, a novel CDs modified g-C3N4/SnO2 photocatalyst (CDs/g-C3N4/ SnO2) was successfully synthesized by the thermal polymn. Under visible light irradn., the resulting CDs/g-C3N4/SnO2 photocatalyst exhibited excellent photocatalytic activity for the degrdn. of indomethacin (IDM). It was demonstrated that a 0.5% loading content of CDs led to the highest IDM degrdn. rate, which was 5.62 times higher than that of pristine g-C3N4. This improved photocatalytic activity might have been attributed to the unique up-conversion photoluminescence (PL) properties and efficient charge sepn. capacities of the CDs. Reactive species (RSs) scavenging expts. and ESR (ESR) revealed that superoxide radical anions (O·-2) and photogenerated holes (h+) played crit. roles during the photocatalytic process. The results of the detection of H2O2 and ESR confirmed that CDs/g-C3N4/ SnO2 was a Z-scheme heterojunction photocatalyst. Further, HRAM LC-MS/MS was employed to identify the byproducts of IDM, and the major IDM degrdn. pathways of the CDs/g-C3N4/SnO2 photocatalyst were proposed. This study provides new ideas for the design of novel CDs modified photocatalysts for environmental remediation.
    59. 59
      Alkaykh, S.; Mbarek, A.; Ali-Shattle, E. E. Photocatalytic degradation of methylene blue dye in aqueous solution by MnTiO3 nanoparticles under sunlight irradiation. Heliyon 2020, 6, e03663  DOI: 10.1016/j.heliyon.2020.e03663
      There is no corresponding record for this reference.
    60. 60
      Wu, K.; Shi, M.; Pan, X.; Zhang, J.; Zhang, X.; Shen, T.; Tian, Y. Decolourization and biodegradation of methylene blue dye by a ligninolytic enzyme-producing Bacillus thuringiensis: degradation products and pathway. Enzyme Microb. Technol. 2022, 156, 109999,  DOI: 10.1016/j.enzmictec.2022.109999
      60
      Decolourization and biodegradation of methylene blue dye by a ligninolytic enzyme-producing Bacillus thuringiensis: Degradation products and pathway
      Wu, Kangli; Shi, Meiling; Pan, Xiaomei; Zhang, Jianqiang; Zhang, Xiaomeng; Shen, Tong; Tian, Yongqiang
      Enzyme and Microbial Technology (2022), 156 (), 109999CODEN: EMTED2; ISSN:0141-0229. (Elsevier Inc.)
      In this study, a ligninolytic enzyme-producing strain F5 was isolated and identified as Bacillus thuringiensis, which can efficiently degrade methylene blue (MB) dye. The optimal pH, temp., rotation speed, NaCl concn., and inoculum of strain F5 for MB degrdn. were pH 6.0, 30°C, 140 rpm, 10 g/L NaCl, 4% inoculum (vol./vol.), and the strain F5 had salt tolerance, the MB decolorization rate reached 95% after 12 h. The degraded products were characterized by UV-vis, FT-IR, and GC-MS. Based on products anal., four different intermediates were identified, and a new pathway for the degrdn. of MB was proposed. The degrdn. of MB by strain F5 was due to the synergistic effects of laccase (Lac), manganese peroxidase (MnP), lignin peroxidase (LiP), and NADH-DCIP reductase; among them, Lac and MnP were the key enzymes. The phytotoxicity results showed that MB degraded metabolites' toxicity was lower than that of the parent compd., indicating that the strain F5 had a detoxification effect on MB dyes.
    61. 61
      Abbasi, S.; Hasanpour, M. The effect of pH on the photocatalytic degradation of methyl orange using decorated ZnO nanoparticles with SnO2 nanoparticles. J. Mater. Sci.: Mater. Electron. 2017, 28, 1307– 1314,  DOI: 10.1007/s10854-016-5660-5
      61
      The effect of pH on the photocatalytic degradation of methyl orange using decorated ZnO nanoparticles with SnO2 nanoparticles
      Abbasi, Sedigheh; Hasanpour, Maryam
      Journal of Materials Science: Materials in Electronics (2017), 28 (2), 1307-1314CODEN: JSMEEV; ISSN:0957-4522. (Springer)
      In this study we investigate for the first time the effect of pH on the photocatalytic activity of SnO2 nanoparticles, ZnO nanoparticles and hybrids contg. decorated ZnO nanoparticles with difference amt. of SnO2 nanoparticles (ZnO-SnO2 (1-0.5) and ZnO-SnO2 (1-2)). The exptl. results show that the removal efficiency of methyl orange increases with respect to the irradn. time in all of the tested suspensions. Meanwhile, the effect of pH confirm that the removal efficiency of pollutant in the suspension with natural pH (pH = 7) is higher than that of acidic (pH = 4) and alk. condition (pH = 10). The results of statistical anal. reveal that the irradn. time and pH have significant impact on the photocatalytic activity of all nanoparticles and hybrids. The coeff. of detn. of all proposed models justify that the proposed models can be successfully predicted the removal efficiency of methyl orange in the all suspensions. The results of Duncan's multiple range test (α = 0.05) demonstrate that there is a significant difference between different levels of pH. Also, the photocatalytic activity of hybrid increase by increasing the decorated SnO2 nanoparticles content.
    62. 62
      Cai, R.; Zhang, B.; Shi, J.; Li, M.; He, Z. Rapid Photocatalytic Decolorization of Methyl Orange under Visible Light Using VS4/Carbon Powder Nanocomposites. ACS Sustain. Chem. Eng. 2017, 5, 7690– 7699,  DOI: 10.1021/acssuschemeng.7b01137
      There is no corresponding record for this reference.
    63. 63
      Adeel, M.; Saeed, M.; Khan, I.; Muneer, M.; Akram, N. Synthesis and Characterization of Co-ZnO and Evaluation of Its Photocatalytic Activity for Photodegradation of Methyl Orange. ACS Omega 2021, 6, 1426– 1435,  DOI: 10.1021/acsomega.0c05092
      63
      Synthesis and Characterization of Co-ZnO and Evaluation of Its Photocatalytic Activity for Photodegradation of Methyl Orange
      Adeel, Muhammad; Saeed, Muhammad; Khan, Iltaf; Muneer, Majid; Akram, Nadia
      ACS Omega (2021), 6 (2), 1426-1435CODEN: ACSODF; ISSN:2470-1343. (American Chemical Society)
      Photocatalysis is one of the techniques used for the eradication of org. pollutants from wastewater. In this study, Co-ZnO was tested as a photocatalyst for the degrdn. of methyl orange under irradn. of visible light. Co-ZnO loaded with 5%, 10%, and 15% Co was prepd. by the pptn. method. The advanced techniques including X-ray diffraction, XPS, diffuse reflectance UV-visible spectroscopy, photoelectrochem. measurements, temp.-programmed desorption, photoluminescence, and fluorescence spectroscopy related to OH• measurements were used for characterization of prepd. Co-ZnO. Expts. showed that 10% Co-ZnO was a highly efficient catalyst for the photodegrdn. of methyl orange as compared to ZnO. The enhanced photocatalytic activity of Co-ZnO is attributed to the implantation of Co which inhibits the electron-hole recombination. A 100 mg/L soln. of methyl orange dye was completely degraded within 130 min. The reaction kinetics has been described in terms of the Eley-Rideal mechanism.