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Ternary Photodegradable Nanocomposite (BiOBr/ZnO/WO3) for the Degradation of Phenol Pollutants: Optimization and Experimental Design
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  • Hager R. Ali
    Hager R. Ali
    Spectroscopic Division, Analysis and Evaluation Department, Egyptian Petroleum Research Institute (EPRI), Nasr City 11727 Cairo, Egypt
    More by Hager R. Ali
  • Eman A. Motawea*
    Eman A. Motawea
    Spectroscopic Division, Analysis and Evaluation Department, Egyptian Petroleum Research Institute (EPRI), Nasr City 11727 Cairo, Egypt
    *Email: [email protected]. Phone: 002-01227024388.
    More by Eman A. Motawea
    Orcidhttps://orcid.org/0000-0003-4028-3909
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ACS Omega

Cite this: ACS Omega 2021, 6, 34, 22047–22064
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https://doi.org/10.1021/acsomega.1c02644
Published August 17, 2021

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Abstract

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The degradation of environmental contaminants with photocatalysts has bright prospects for application in the control of pollution. In this study, BiOBr/ZnO/WO3 heterojunctions have been documented to be reliable visible-light photocatalysts for phenol deterioration. X-ray diffraction, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, photoluminescence spectral analysis, electrochemical impedance spectroscopy (EIS), EIS Bode plots, linear sweep voltammetry, and UV–visible diffuse reflectance spectroscopy were employed to describe the heterojunction’s structure in addition to its optical features. The results revealed that the BiOBr/ZnO/WO3 ternary photocatalyst displayed more degradation activity in comparison to single-phase ZnO, WO3, or BiOBr, which is also higher than that of binary mixture photocatalysts with a phenol degradation efficiency of 90%. The influence of degradation variables, for instance, the potential of hydrogen (pH) and the initial organic contaminant content besides the heterojunction dose, on the deterioration efficiency was optimized using the response surface methodology. The degradation efficiency reached 95% under the optimal conditions of 0.08 g/0.03 L catalyst dose, a pH of 9, and an initial organic contaminant content of 10 mg L–1. However, the optimal phenol degradation efficiency of 39.37 mg g–1 was achieved under the conditions of 0.08 g/0.03 L catalyst dose, pH of 9, and 200 mg L–1 initial phenol concentration.

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Introduction

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Treatment of water contaminated with industrial effluents is a persistent global problem today. Several related bodies have raised concerns about the green technology and energy efficiency in wastewater treatment in recent years to reduce the current environmental problems. Phenol is present in the industrial synthesis of adhesive and antiseptic products as an intermediate. (1) An innate deterioration rate of monophenol can happen depending on a condition through various processes. In water bodies, the acceptable limit for phenol is 0.1–1.0 mg L–1. Owing to its toxicity, genotoxicity, and exceptionally high endocrine-disrupting potency, phenol remediation therapies are becoming problems despite the low concentration limit. (2) One of the best approaches is producing a photocatalyst and its use in process treatment. Some of the rare-earth semiconductors such as BiOBr and ZnO besides WO3 are used during photocatalytic processes. To start the photocatalytic reaction and ultimately degrade the contaminant, these semiconductors will use sunlight. (3) Recently, due to their peculiar properties and possible uses, BiO halogenides (BiOX, where X = Cl, Br, and I) were studied. Bismuth oxybromide is a positive-category semiconductor that has a band gap of 2.80 eV and an enticing photocatalyst for contaminant deterioration under solar light illumination. (4,5) Some researchers have reported that photocatalytic activity is strongly dependent on the size, diameter, and structure of catalysts. Nanophotocatalysts’ shape, scale, and structure have therefore been tuned to enhance their activity. (4,6) Recently, due to their high crystallinity and ultrathin thickness, the lamellar nanostructures have been gaining greater attention. It is well known that this structure could help in reducing the recombination possibilities of the illumination-created free charge carriers, so that they can easily move toward the surface to degrade the organic molecules. (5,7) Fabricating a blend of different p–n types through integrating different transistors with suitable band models is the most efficient way. Besides, an n-type may be generated by hybridizing ZnO with WO3, which could facilitate the isolation of illumination-produced carriers. Tungsten(VI) oxide (WO3) nanoparticles (NPs) have attracted particular interest among researchers in the domain of illumination catalysts owing to their heavy sorption in the presence of solar spectra (almost 500 nm), their sustainable physical and chemical properties, and their resistance toward photocorrosion. (8) Tungstic anhydride (WO3) has exceptional electrical illumination characteristics of a small band gap of 2.40–2.80 eV with a favorable hole dispersion width that may potentially use ∼12% solar light. (9−11) However, because of stagnant kinetics and low charge transfer at the transistor–electrolyte system, WO3 demonstrates a fair photocatalytic activity toward the deterioration of phenolic contaminants. (12,13) Several techniques have been employed to decorate WO3 to solve these problems, including metal implantation (14,15) and coupling with other semiconductors. (6,16) ZnO, additionally defined as the II–IV transistor, contains a broadband energy band gap (3.3 eV), high photosensitivity, and stability. (17,18) Also, at room temperature, ZnO possessed good heat sustainability (19) and is relatively inexpensive. The variables of a process can be developed, improved, and optimized by the response surface methodology (RSM), which is an assimilation of theoretical and numerical tools used for assessing the significance of deferential process factors in the presence of different correlations. RSM is a viable procedure for optimizing responses that are modeled by process parameters. (20) To our knowledge, no previous research has focused on the fabrication of a BiOBr/WO3/ZnO p–n heterojunction and its phenol degradation performance. We present a simple and cost-effective solvothermal synthesis technique for fabricating a unique hybrid BiOBr/WO3/ZnO p–n heterojunction. In the current work, we discuss the effects of p–n heterojunction formation on the visible-light photodegradation properties of phenol and its mechanisms.

Results and Discussion

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Characterization of NPs

X-ray Diffraction

To characterize the synthesized NPs, various techniques were used. X-ray diffraction (XRD) was used to describe the crystal structure and primary crystal scale. XRD analysis was used to analyze the BiOBr/WO3/ZnO phase and crystalline composition (Figure 1). XRD detected the pure WO3 as well. The sharp diffraction peaks may be well ascribed to the WO3 phase (JCPDS card no. 024-0747) with 2θ values of 24.35, 26.56, 33.23, 34.15, 35.50, 45.70, and 49.90° and a crystallinity of 79.03%. XRD peaks of the as-prepared ZnO (JCPDS card no. 01-081-8838) were observed at angles of 31.80, 34.46, 36.27, 47.50, 56.60, 62.89, 67.97, 69.11, 72.59, and 76.97o (2θ). The most common diffraction peaks of BiOBr were observed at 2θ angles of 25.16, 31.80, 32.17, 46.16, and 57.17° with a crystallinity of 59.35% and indexed to BiOBr according to JCPDS card no. 52-0084 with a crystallinity of 81.63%. The BiOBr/WO3 XRD pattern (JCPDS file no. 52-0084) and of BiOBr/ZnO (JCPDS file no. 09-0393) corresponded to JCPDS file no. 52-0084; ZnO- and WO3-related peaks were not identified due to the presence of low BiOBr-related ZnO and WO3 amounts. In the BiOBr/WO3/ZnO composites, the XRD pattern corresponded to JCPDS file no. 52-0084. This may be due to the great dispersion of ZnO and WO3 in BiOBr; the position of the peaks showed some changes suggesting the formation of a new compound. Besides, the presence of BiOBr limited the growth of ZnO and WO3 NPs.

Figure 1

Figure 1. XRD spectra of the synthesized WO3, ZnO, BiOBr, BiOBr/WO3, BiOBr/ZnO, and BiOBr/WO3/ZnO.

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Fourier-Transform Infrared Spectroscopy

To evaluate the composition, Fourier-transform infrared (FTIR) spectroscopy was performed. Figure 2 presents the contrast of FTIR spectra for all the prepared photocatalysts; the FTIR spectrum of the synthesized BiOBr/WO3/ZnO composite shows a high peak of absorption at 3508 cm–1 owing to the stretching vibration of nonchemical bond association of OH groups, while a peak at 1637 cm–1 was observed for H–O–H bending vibrations. The peaks are observed due to the existence of CO2 at 2390 cm–1. For Zn–O, the most characteristic peak at 514 cm–1 is observed, while for the bending vibration of C–H stretching, an absorption peak at about 1392 cm–1 is attributed. The findings mentioned above are in line with the results of XRD. The peak at a lower frequency of 810.84 cm–1 is the product of W–O–W bond stretching vibrations. The presence of W–O–W/O–W–O (842— and 781 cm–1, respectively) and also a further peak at 507 cm–1 is due to the Bi-O bond that is observed in the FTIR spectra of binary and ternary nanocomposites. (21) These findings further show that the preparation of the ternary nanocomposite BiOBr/WO3/ZnO has been effectively done.

Figure 2

Figure 2. FTIR patterns of WO3, ZnO, BiOBr, BiOBr/WO3, BiOBr/ZnO, and BiOBr/WO3/ZnO.

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X-ray Photoelectron Spectroscopy

The electronic states and the chemical composition of BiOBr/ZnO/WO3 were examined by X-ray photoelectron spectroscopy (XPS), and the results are given in Figure 3. It can be observed from the survey spectrum in Figure 3a that the characteristic peaks of Zn, Bi, Br, O, and W are present, indicating their coexistence on the surface of the BiOBr/ZnO/WO3 sample. As for the high-resolution Bi 4f spectrum in Figure 3b, two significant peaks are observed at 159 and 164.5 eV, corresponding to Bi 4f5/2 and Bi 4f7/2, respectively, due to the spin–orbital component of Bi3+ in BiOBr. (22) Moreover, as shown in Figure 3c, the XPS spectra of Br 3d consisted of Br 3d5/2 at 68.2 eV and Br 3d3/2 at 69.5 eV attributed to Br in the monovalent oxidation state. (22) Also, the high-resolution spectrum of W 4f depicted in Figure 3d shows that W 4f7/2 at 35.4 eV and W 4f 5/2 at 37.5 eV are ascribed to W6+ species. (23) From the Zn 2p XPS spectrum in Figure 3e, the fitted peaks at 1045 and 1022 eV can be observed, which were attributed to 2p1/2 and 2p3/2 of Zn2+, respectively, in ZnO. (24) The O 1s spectrum in Figure 3f could be resolved into four individual peaks, which indicated the presence of four different kinds of O species in the sample. The main peak at 530.4 eV was assigned to O2 ions that are in oxygen-deficient regions. The peak at 533.9 eV was attributed to the crystal lattice O atom in WO3. (23) Also, the peak at 531.9 eV was related to the crystal lattice O atom in BiOBr, (24) while the peak at 530.6 eV could be attributed to the O atom in ZnO. (24) The XPS analysis proves the existence of the BiOBr/ZnO/WO3 composite.

Figure 3

Figure 3. XPS spectrum of BiOBr/ZnO/WO3: (a) survey spectrum, (b) Bi 4f spectrum, (c) Br 3d spectrum, (d) W 4f spectrum, (e) Zn 2p spectrum, and (f) O 1s spectrum.

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Optical Properties of Photocatalysts

UV–visible diffuse reflection spectroscopy (UV–vis DRS) and photoluminescence (PL) spectroscopy were utilized to identify the optical characteristics of pure ZnO, WO3, BiOBr, and binary and ternary composites (Figure 4). As shown in Figure 4A, the neat BiOBr, ZnO, and WO3 display absorption edges at 425, 420, and 450 nm, respectively, while the binary BiOBr/ZnO and BiOBr/WO3 exhibit absorption edges at 428 and 470 nm, respectively; additionally, BiOBr/ZnO/WO3 shows the highest visible-light absorption edge at 485 nm, confirming the existence of additional energy levels of metal ions in the forbidden gap of BiOBr. The band gap of the prepared photocatalysts was calculated according to the classical equation of Taucʼs plot (Figure 4B,C)
(1)

Figure 4

Figure 4. Optical properties of the prepared photocatalysts: (A) UV–vis DRS spectra, (B) Taucʼs plots [(αhv)2 vs Hv] for WO3 and ZnO photocatalysts, (C) Taucʼs plots [(αhv)1/2vs Hv] for BiOBr, BiOBr/ZnO, BiOBr/WO3, and BiOBr/ZnO/WO3, and (D) PL spectra.

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It should be noted that the absorption coefficient per unit length (4,17) is expressed as α, Eg represents the band gap energy, h refers to Planck’s constant, v is the frequency of vibration, hv implies the incident photon energy, A refers to the proportional constant, and n is 0.50 for the indirect band-gap semiconductor and 2 for the direct band-gap semiconductor. ZnO and WO3 have been reported to be attributed, as shown in Figure 4B, to the n-type direct band-gap semiconductor (5) and BiOBr to the p-type indirect band-gap semiconductor (7) (Figure 4C). The band gaps of the synthesized ZnO and WO3 were estimated to be 3.20 and 2.85 eV, respectively, and that of BiOBr was 2.80 eV. By doping BiOBr with ZnO and WO3, the band gap was reduced to approximately 2.75 and 2.70 eV, respectively, while the band gap was reduced to approximately 2.60 eV for the BiOBr/WO3/ZnO composite. This confirms that BiOBr/WO3/ZnO exhibits the narrowest band gap, and this reduction in energy value is due to excessive absorption in the visible region due to the energy level existing in the forbidden gap through the doping of ZnO and WO3. Furthermore, the conduction band (CB) and valence band (VB) edges of ZnO, BiOBr, and WO3 that are depicted in Table 1 have been studied more as a result of their significant roles in assessing the heterojunction flowchart of photogenerated electrons and holes. WO3 (band gap: 2.85 eV), ZnO (band gap: 3.20 eV), and BiOBr (band gap: 2.80 eV) band-edge positions have been assessed according to the following equations
(2)
(3)
where the VB edge potential is expressed as EVB and X is the semiconductor electronegativity, which is the geometric mean of electronegativity for constituent atoms. The X values are determined as 6.18, 5.79 and 6.49 eV, respectively, for BiOBr, ZnO, and WO3. E0 is the free electron energy of the hydrogen scale (∼4.5 eV) and Eg is the semiconductor’s band gap energy. The EVB and ECB values of BiOBr are calculated as 3.16 and 0.20 eV, respectively, while those of WO3 are calculated as 3.365 and 0.615 eV and of ZnO are 2.89 and −0.31 eV, respectively.
Table 1. Values of Calculated ECB and EVB for ZnO, WO3, and BiOBr
semiconductor absolute electronegativityX (eV)ECB (eV)EVB (eV)Eg (eV)
ZnO5.790–0.312.893.2
BiOBr6.1800.23.162.8
WO36.490.6153.362.85
PL is an efficient tool for investigating the performance of charge carrier transfer, trapping, and separation of photogenerated electrons and holes in heterojunctions. (7)Figure 4D displays the PL spectra of all samples, where the main emission peak is located at 430 nm. The PL spectrum of composite photocatalysts is similar to that of pure BiOBr, while the intensity emission is reduced in the BiOBr/WO3/ZnO photocatalyst. Generally, the intensity of PL emission is derived from free charge carrier recombination, so the lower emission intensity of the BiOBr/WO3/ZnO heterojunction implies a lower electron and hole recombination rate under visible light irradiation. PL results prove that WO3 and ZnO are favorable for charge separation in BiOBr/WO3/ZnO photocatalysts as a result of the lower recombination rate of photogenerated charge carriers.

Photoelectrochemical Measurements

The charge generation, migration, and recombination processes in photocatalysts were investigated by electrochemical impedance spectroscopy (EIS Nyquist spectra); it is evident that the higher the electron and hole separation efficiency, the better the photocatalytic performance. Figure 5a demonstrates that compared to BiOBr, BiOBr/ZnO/WO3 has a much lower impedance, as evidenced by the smaller arc radius in the EIS Nyquist plots, implying that BiOBr/ZnO/WO3 has a lower interfacial layer resistance, beneficial to a faster interfacial transfer of electron–hole pairs and thus a more effective separation. For better analysis of the EIS data, the corresponding Bode phase plot is presented in Figure 5b; a characteristic of the Bode phase plot is its ability to identify the predominant electrical behavior of the system in a given frequency range. The maximum oscillation frequency (fmax) of the impedance semicircle of BiOBr/ZnO/WO3 is less than that of BiOBr. Thus, the corresponding lifetime of photoelectrons in BiOBr/ZnO/WO3 increases. This can be ascribed to the efficient separation of light-generated electrons and holes in BiOBr/ZnO/WO3. In other words, the electrons transferred from the CB of BiOBr to that of ZnO and WO3, while the holes were transported to the VB of BiOBr. Therefore, the recombination of electron–hole pairs was inhibited, and the lifetime of photoelectrons was prolonged. Figure 5c shows the linear sweep voltammetry (LSV) measurements under visible-light irradiation for the BiOBr and BiOBr/ZnO/WO3 electrodes. The photocurrent values of both electrodes increased with the upgrade of the applied potential. The photocurrent densities of BiOBr/ZnO/WO3 were much higher than that of bare BiOBr at the same applied potential, which further indicated that BiOBr/ZnO/WO3 has higher charge separation and migration.

Figure 5

Figure 5. Photoelectrochemical measurements: (a) Nyquist plots of EIS, (b) EIS Bode plots, and (c) LSV curves for BiOBr and BiOBr/ZnO/WO3.

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Scanning Electron Microscopy, Transmission Electron Microscopy, and Energy-Dispersive X-ray spectroscopy and Electron Microscopy Studies

The size and morphologies of the prepared BiOBr/ZnO/WO3 nanocomposite were investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). For comparison, Figure 6A,E displays the SEM and TEM photos of ZnO NPs; the particles clearly show the spherical structural composition, also nearly spongy-like structural NPs were observed with an average size of 122–193 nm; however, Figure 6B,F shows disc-shaped of agglomerated WO3 plates and also confirms the orthorhombic shapes of different dimensions with an average size of 71.9–168 nm. Evidently, it is clear that the prepared BiOBr, as shown in Figure 6C,G, contained ultrathin nanocrystals of irregular-shaped nanoplates with an average width of 50–122 nm, whereas ZnO and WO3 can be observed deposited on the surface of flakes/plates of BiOBr, as shown in Figure 6D,H, and such a structure is expected to provide abundant heterojunction interfaces between BiOBr, ZnO, and WO3.

Figure 6

Figure 6. SEM images of the synthesized (A) ZnO NPs, (B) WO3NPs, (C) BiOBr NPs, and (D) BiOBr/ZnO/WO3 nanocomposites, TEM images of (E) ZnO NPs, (F) WO3NPs, (G) BiOBr NPs, and (H) BiOBr/ZnO/WO3, and (I) EDX spectra of BiOBr/ZnO/WO3.

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Energy-dispersive X-ray spectroscopy (EDX) analysis was utilized to explore the surface chemical composition of ternary BiOBr/ZnO/WO3. As per Figure 6I, the constituents of Bi, Br, O, Zn, and W were revealed in the spectrum of BiOBr/ZnO/WO3, implying that the ternary nanocomposite was successfully formed.

Evaluation of Photocatalytic Activity

The efficiency of the prepared photocatalyst toward organic pollutant photocatalytic degradation was investigated by conducting phenol removal. Adsorptive and photocatalytic activities were assessed individually for evaluating and comparing the performance. To screen the best catalyst that can be included in the upcoming experiments and achieve the highest removal of monophenol under visible-light irradiation, the photocatalytic performance of ZnO, WO3, BiOBr, BiOBr/ZnO, BiOBr/WO3, and BiOBr/ZnO/WO3 photocatalysts was evaluated. To attain adsorption–desorption equilibrium, the phenol samples with photocatalysts were shaken in the dark for 1 h. Due to its significant role in the polluted water-treatment process, sorption kinetics was evaluated. At an initial concentration of 50 mg/L, time-dependent phenol adsorption/degradation on the prepared catalysts was evaluated and is presented in Figure 7A as a function of adsorption/degradation capacity and in Figure 7B as a function of adsorption/degradation efficiency. As a result, in the dark, all catalysts reached the adsorption equilibrium after 60 min, while in the presence of visible light, catalysts reached degradation equilibrium after 300 min. From Figure 7A, it can be observed that the maximum phenol degradation capacity reached 27 mg/g with BiOBr/ZnO/WO3 photocatalysts. In the dark, the phenol removal percent was negligible, as depicted in Figure 7B, and decreased in the order of BiOBr/ZnO/WO3 (25%) > BiOBr/WO3 (22%) > BiOBr/ZnO (18%) > BiOBr (17.6%) > ZnO (16%) > WO3 (14%). This may be due to the high surface acidity of ZnO and WO3 (29,30) that increases the positive charge on the surface of the catalyst and also the repulsion forces between the catalyst and the cationic adsorbents. However, the efficiency of phenol photodegradation under visible light enhanced and is in the order of ZnO (50%) < WO3 (60%) < BiOBr (66.5%) < BiOBr/ZnO (73%) < BiOBr/WO3 (81%) < BiOBr/ZnO/WO3 (90%), which may be attributed to ZnO and WO3 photocatalysts operating as an acceptor of the electron, which is helpful for the efficient isolation of electron–hole pairs generated in the system and prevent their recombination. (27)

Figure 7

Figure 7. (A) Degradation capacity of phenol vs time with different catalysts, (B) degradation percentage at an equilibrium time of 300 min, and (C) kinetics of the photodegradation of phenol using different photocatalysts at the initial concentration of 50 mg/L, dose of 0.05 g/0.03 L, and a pH of 6.

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The kinetics of the photodegradation of phenol illustrated in Figure 7C implies that the lowest deterioration performance that may be due to the unsuitable band gap under visible-light-induced conditions was shown by pure ZnO and WO3. Under visible-light irradiation, these photocatalysts were hard to be simulated. (26) The deterioration activity of ZnO and WO3 was drastically improved by doping with BiOBr and it reached 90% for BiOBr/ZnO/WO3. We conclude according to the above results that BiOBr/ZnO/WO3 p–n heterojunctions display a high photocatalytic activity rather than the solitary phases of ZnO, WO3, and BiOBr, which is also higher than that of the two component mixture photocatalyst. Compared to an individual or binary components, the improvement of the deterioration activity of the BiOBr/ZnO/WO3 p–n heterojunctions could be related to the creation of heterojunctions through n-type ZnO, WO3, and p-type BiOBr, enabling the interface isolation of electron–hole pairs.
Pseudo-first-order and pseudo-second-order models were utilized to evaluate the kinetics of phenol sorption onto photocatalysts, and the values were calculated according to eqs 3 and 4, respectively, whose data are depicted in Table 2. The regression results predicted (R2) demonstrate that, in all cases, the pseudo-first-order model defines phenol sorption rather than the pseudo-second-order model, indicating that phenol degradation depends on the catalyst used. Therefore, the rate of phenol sorption process depending on the pseudo-first-order kinetic model increases in the order of WO3 (0.0014 min–1) < ZnO (0.0019 min–1) < BiOBr (0.0023 min–1) < BiOBr/ZnO (0.0024 min–1) < BiOBr/WO3 (0.0040 min–1) < BiOBr/ZnO/WO3 (0.0062 min–1). BiOBr/ZnO/WO3 was found to be the best catalyst with the best sorption capacity (7.5 mg/g) and a maximum sorption rate (0.0062 min–1) among all catalysts. Experimental data were applied to the pseudo-first-order (eq 3) to obtain more information on the kinetics of phenol deterioration catalyzed by different photocatalysts, where the rate constant K value generally provides an estimate about photocatalyst’s efficiency. (28) The dark and visible-light irradiation catalytic efficiencies of the prepared catalysts are illustrated in Figure 7C. Due to the high band gap of ZnO and WO3 (3.20 and 2.85 eV, respectively), their catalytic efficiencies were significantly limited under visible-light irradiation with nearly 50 and 60 percent, respectively, for monophenol deterioration after 5 h. In the case of BiOBr/ZnO/WO3, the efficiency of removal (R = 90%, k = 0.0065 min–1, and capacity = 27 mg/g) was significantly more than that of ZnO and WO3, indicating that the combination of BiOBr increased the catalytic activity. The p–n heterojunction semiconductor is a convenient system for relatively reliable charge collection and isolation. Typically, the generated electron–hole pairs could be rapidly isolated by the electric field in the charge carriers when the p–n heterojunction was irradiated by photons. Electrons were diverted to the CB of negative-type semiconductors, driven by an electric field, and holes were diverted to the VB of the positive-type transistors. (29) The Fermi level of positive-type BiOBr moved up when positive-type BiOBr and negative-type ZnO and WO3 were in contact, while that of n-type ZnO and WO3 moved down until the balance state was established. The entire energy band of positive-type BiOBr increased, compatible with the motion of the Fermi level, whereas that of negative-type ZnO and WO3 reduced. Consequently, a charging area was formed in functionalities from negative-type ZnO and WO3 to positive-type BiOBr. Both ZnO and WO3 may simulate to create electron–hole pairs during visible-light irradiation. BiOBrʼs photogenerated electrons in the CB would be transported to ZnO and WO3, whereas the holes of ZnO and WO3 in the VB would be transported to BiOBr. The built-in electrical field can endorse such transfers of photogenerated carriers. Therefore, as a consequence of the development of positive–negative heterojunction among positive-type BiOBr and negative-type ZnO and WO3 interfaces, the photogenerated electrons and holes split up successfully. This BiOBr/ZnO/WO3 p–n heterojunction can therefore create VB holes (ZnO and WO3) with a high oxidation activity and CB electrons (BiOBr) with a high reduction activity sequentially and effectively. Photocatalytic reactions may be involved in a greater amount of electrons on the BiOBr surface and holes on the ZnO and WO3 surface, leading to the understanding of the visible-light photocatalytic activity of the BiOBr/ZnO/WO3 p–n heterojunction. (30) From the above results, it can be concluded that BiOBr/ZnO/WO3 is an excellent catalyst for further experimental analysis of degradation.
Table 2. Kinetic Parameters and Correlation Coefficients for the Pseudo-First-Order and Pseudo-Second-Order Models
  Pseudo-first-order modelPseudo-second-order model
 catalystK1 (min–1)R2K2 (g mg–1 min–1)R2
dark studyZnO0.00190.9980.000040.729
 WO30.00140.9850.001900.282
 BiOBr0.00230.9750.002330.788
 BiOBr/ZnO0.00240.9730.003500. 882
 BiOBr/WO30.00400.9670.007910.946
 BiOBr/ZnO/WO30.00620.9770.000960.945
light studyZnO0.00250.9700.001970.945
 WO30.00150.9800.000770.883
 BiOBr0.00290.9600.001140.927
 BiOBr/ZnO0.00370.9900.001010.976
 BiOBr/WO30.00460.9900.000950.939
 BiOBr/ZnO/WO30.00650.9950.001030.972

Optimization Analysis and Design of Experiments

The central composite design, CCD, is a scientific and computational technique that is suitable for modeling tests, multivariate modeling with visual aspect measurements of deferent parameters. Herein, the impact of degradation variables, for instance, the potential of hydrogen (pH), initial monophenol concentration, and BiOBr/ZnO/WO3 dose, on the deterioration efficiency of phenol has been analyzed. The real benefit of CCD is to minimize the number of tests to be held on, also specifying the correlation of operational conditions in addition to maximizing the parameters of degradation.

Combined Influence of Initial Monophenol Concentration and pH on the Deterioration Activity

The initial reactant concentration is recognized as one of the significant parameters of photodegradation of organic compounds. Figure 8A shows how the photodegradation efficiency is affected by the combined effect of initial phenol concentration and solution pH. Evidently, with the increase of the initial phenol concentration from 10 to 200 mgL–1, the degradation efficiency reduced; the degradation efficiency reached 95 percent at an initial concentration of 10 mg L–1 of phenol and a pH of 9, which is ascribed to the existence of adequate surface area of the catalyst employed, and the reaction of phenol molecules with •OH increased. (31) At an initial concentration of 200 mg L–1 and a pH of 9, the degradation efficiency dropped to 52.50 percent. Such related to the possibility of monophenol molecules interacting with •OH declines; therefore, excessive oxidant radicals involving •OH and •O2 have been needed for improving the oxidation procedure and a lower efficiency of degradation is identified. (32) In the photocatalytic process, pH is the core parameter that influences the charging characteristics of the surface of the catalyst, followed by the effects of the sorption activity that influences the photocatalytic degradation. (27,36) As seen in Figure 8A, as the pH value increased, there is a clear increase in phenol photodegradation. At a pH of 9 with an initial monophenol concentration of 10 mg L–1, the optimum degradation value (95%) was obtained, although the minimal degradation value (42.80%) was achieved at a pH of 3 with an initial phenol concentration of 200 mg L–1. This is related to the greater H+ content that in the case of lower pH, it improves the functional protonation of the catalyst surface. In the meantime, a massive amount of H+ competes for the catalyst binding site with phenol. (28) The efficiency of phenol removal steadily increased once the concentration of H+ in the solution declined. Therefore, the favorite pH for phenol degradation was found to be 9. (33,34)

Figure 8

Figure 8. (A) 3D diagram of the combined effect of pH and the initial concentration of phenol for the degradation efficiency of phenol at a BiOBr/ZnO/WO3 dose of 0.08 g/0.03 L, (B) 3D diagram of the combined effect of pH and dose of BiOBr/ZnO/WO3 for the degradation efficiency of phenol at an initial phenol concentration of 10 mg L–1 and a contact time of 300 min, (C) proposed photocatalytic degradation pathway of phenol under visible light irradiation, and (D) total organic carbon (TOC) content in phenol suspension vs visible light irradiation time after degradation with BiOBr/ZnO/WO3 at the initial phenol concentration of 50 mg/L, catalyst dose of 0.08 g/0.03 L, and a pH of 9.

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Combined Effect of BiOBr/ZnO/WO3 Dose and pH on the Degradation Efficiency

Photocatalytic studies with various BiOBr/ZnO/WO3 photocatalyst doses of 0.02, 0.05, and 0.08 g per 0.03 L were carried out. An increase in the photocatalytic dose showed a significant enhancement in the photocatalytic degradation efficiency (Figure 8B), reaching an optimum of 95% degradation at 0.08 g/0.03 L catalyst dose, the pH of 9, and an initial monophenol concentration of 10 mg L–1. The improvement of photocatalytic efficiency with the increase of the BiOBr/ZnO/WO3 photocatalyst dose may be attributed to the fact that the increase of the photocatalyst’s available surface area and the creation of more OH radicals at the active sites would be sufficient to degrade and mineralize the organic pollutant. (31,35,37)
The photocatalytic degradation pathway for phenol under visible-light irradiation in the presence of BiOBr/ZnO/WO3 is depicted in Figure 8C, showing the complete degradation process of phenol. The radical produced on the surface of the BiOBr/ZnO/WO3 photocatalyst reacts with phenol to produce intermediates, and with continuous photo-oxidation, the benzene ring can open, leading to the formation of an aliphatic compound that mineralized into carbon dioxide and water.

TOC Content

The degradation of the organic molecule to CO2 and H2O is the final goal of the photocatalytic process of organic pollutants, where the TOC content at a given irradiation time is reduced. The organic molecule breaks down into intermediate products, which are finally mineralized through the oxidative attack of the hydroxyl radical or by the direct attack of the photogenerated holes. Figure 8D implies that the initial content of TOC (38.2 mg/L) in the phenol suspension decreased gradually with visible light irradiation time. However, the remaining amount in the suspension after photocatalytic treatment of BiOBr/ZnO/WO3 for 300 min of visible light irradiation decreased to 4.58 mg/L with 88% degradation in the TOC content. These results emphasize the degradation of phenol intermediates to CO2 and H2O.

Analysis of Variance Study

Analysis of variance (ANOVA) study for the analysis of the quadratic surface and the conditions of the model is presented in Table 3. The ANOVA study covers the degrees of freedom (DF), that is, the amount of freedom to vary values at the end of the computation of the statistics. Fischer’s F-value test is the ratio between the mean square of the model and the residual error where higher F-values with a P-value (probability) are justified as the lowest, as applicable by a highly significant regression model. Also, the probability results greater than 0.05 imply a nonsignificant impact, whereas the results below 0.05 imply a significant impact. (37,38) The correlation between the practical results and the expected results was quantitatively evaluated with the coefficient of regression R2. Adjusted R2 is also a monitor of a fit’s perfection, correcting the R2 value in the model for the sample by utilizing the DF in its calculations if the adjusted R2 is much lower than R2; as a result, the model is not fitted. (36) The R2 results implied that the high BiOBr/ZnO/WO3 phenol degradation coefficient (R2 = 0.999) was close to the adjusted R2 values (0.998), indicating a significant correlation among the actual and anticipated values and showed that the quadratic mods utilized highly adequate values to achieve the expected results. Model F-values (36.94) also demonstrated that the statistical analysis was appropriate by evaluating probability values (0.0005) lower than 0.05, implying that the model is essential. A nonsignificant number of designs lacking fit (0.200) also demonstrated that the designs created were realistic. The ideal conditions for phenol degradation from the model are the catalyst dose of 0.08 g/0.03 L, pH of 9, and initial phenol concentration of 10 mg L–1 with a predicted 94.40 percent efficiency of phenol degradation. Although the initial efficiency of phenol degradation was 95%, which exemplifies the precision of the models, the optimal phenol degradation capacity of 39.37 mg g–1 was achieved under conditions of 0.08 g/0.03 L catalyst dose, a pH of 9, and 200 mg L–1 initial phenol concentration.
Table 3. ANOVA Study of the Response Surface for the Degradation of Phenol by BiOBr/ZnO/WO3
catalystsourceDFSSMSF-valueprob.> F
BiOBr/ZnO/WO3model104068.3406.8036.940.0005
 error51.81400.3628  
 lack of fit41.81400.4536 0.2000
 pure error100  
 total (model + error)154070.20   
The plots of expected results versus actual BiOBr/ZnO/WO3 phenol degradation results are shown in Figure 9A; the results were found to be well dispersed near the straight line, expecting an incredible link between the practical and expected output results. The accuracy of the designs was also evaluated and is presented in Figure 9B with the residual plot against the run order; the residuals were non-uniformly dispersed about ±2.50 for the adsorbent. This implied an effective fitting of the model with the practical data. The normal residual probability plot is a graphical description, a diagnostic tool to assess the deviation from the hypothesis whether errors are uniformly distributed or not, where the points will follow a straight line. However, with normal data, some scattering is anticipated. (23)Figure 9C shows the plots of normal residual probability, wherein we can clearly observe that the results were uniformly scattered as the points in the plot form a fairly straight line. For more discussion of the data obtained, Pareto graphical analysis was applied, as depicted in Figure 9D. According to the Pareto diagram, the percentage of efficacy for each phenol degradation variable is in the following order: quadratic effect of initial phenol concentration (23.45 percent) > initial phenol concentration (12.92 percent) > solution pH (12 percent) > catalyst dose used (5.40 percent) > solution pH (12 percent) > catalyst dose used (5.40 percent).

Figure 9

Figure 9. A) Predicted values vs actual values of phenol degradation, (B) studentized residuals vs run order of phenol degradation, (C) normal probability plot of regular residuals for phenol degradation, and (D) phenol Pareto graphic analysis.

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T-Test

The T-test has been utilized for investigating the importance of the parameter for the correlation coefficient. A high t-value combined with a small probability value (p < 0.05) of the parameters implies that the corresponding model term is of high significance. (37) In Table 4, the t values, probability values in addition to coefficients are listed, providing all data achieved by Design-Expert software (V.11). The results indicate that the most important parameter is the pH, backed by the monophenol concentration. The coefficient of interaction between the pH and phenol concentration is also significant, followed by the correlation coefficient of the monophenol concentration with the dose of the catalyst.
Table 4. Estimated Effects and Coefficients
termcoefficientT ratioprob.
constant53.5933.3190.0009
A: pH12.006.72700.0214
B: catalyst dose6.7643.79100.0631
C: phenol concentration–11.525–6.67200.0217
AB0.2600.145710.8975
AC4.862–2.72500.0112
BC1.687–0.945410.0444
ABC2.572–1.4420.0286

Essential and Interaction Influences

Essential influences reflect the average variation for each variable between the maximum and small degrees. Unless a variable’s influence is positive, the efficiency of degradation increases and the factor shifts from low to high levels. (37)Figure 10A presents the main effects plot, where at a minimum degree of initial monophenol concentration (10 mg L–1), higher degrees of pH of 9, and a catalyst dose of 0.08 g, the maximum design was obtained. The negative value (C = −11.52) of the phenol initial concentration effect indicates that the quantity of deteriorated monophenol decreases in the case of the initial phenol concentration increasing from 10 to 200 mg L–1. The influences of pH and catalyst dose, fortunately, are positive, implying that the response increases with the increase of these two factors. Figure 10B shows an interaction plot; once the variation in the result from a low to a high level for a variable relies on the level of the second variable, the interaction is effective, that is, whenever the layers do not run parallel. (38,39) The interaction plot exhibits a significant interaction between various factors, where all the lines representing the impacts in the graph quadrants are not parallel. The interaction plot suggests a significant interaction between various factors, where all the lines representing the impacts in the graph quadrants are not parallel.

Figure 10

Figure 10. (A) Main effects of different parameters on phenol deterioration by BiOBr/ZnO/WO3 and (B) interaction effects of different parameters on phenol deterioration by BiOBr/ZnO/WO3.

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Suggested Photocatalytic Mechanism

For revealing the photodegradation mechanism of phenol by BiOBr/WO3/ZnO, the formation of oxidative radicals was investigated by adding trapping agents to the phenol solution, such as benzoquinone (BQ) for scavenging the superoxide radical •O2– and isopropanol for scavenging the hydroxyl radical •OH. The results shown in Figure 11A indicate that the addition of the BQ trapping agent significantly suppressed the degradation of phenol to 31.60%, while the addition of the isopropanol trapping agent reduced the degradation of phenol to 44.80%, proving that the superoxide radical •O2– and the hydroxyl radical •OH play a decisive role in the degradation of phenol by BiOBr/WO3/ZnO.

Figure 11

Figure 11. (A) Effect of scavengers on the photodegradation efficiency of phenol, (B) suggested photocatalytic degradation mechanism of phenol with BiOBr/WO3/ZnO, (C) photocatalytic stability of BiOBr/WO3/ZnO toward phenol degradation, (D) photocatalytic system efficiency for the degradation of phenol and malachite green at the initial concentration, 50 mg/L; BiOBr/WO3/ZnO and TiO2 P25 dose, 0.05 g/0.03 L; and pH, 6, and (E) realistic application of refinery petroleum wastewater.

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Based on the above findings, the proposed photocatalytic mechanism of phenol degradation using BiOBr/WO3/ZnO is illustrated in Figure 11B. ZnO, WO3, and BiOBr can be activated easily at simulated visible-light illumination which led to the generation of electrons and holes. When the CB electrons of BiOBr were transferred to the CBs of ZnO and WO3, these excited electrons showed a reduction behavior and react with oxygen O2 to produce the superoxide radical •O2– and then simultaneously caused the transfer of VB holes of ZnO and WO3 to the VB of BiOBr. Positive holes can oxidize phenol directly or react with H2O generating hydroxyl radicals •OH; generally, the degradation of phenol occurs by oxidation with •O2– and •OH radicals. The •OH radical is the most efficient oxidizing species, and it can degrade organic contaminants on the photocatalyst surface. In such a way, it is possible to effectively separate photogenerated electrons and holes and to effectively impede the recombination of electron–hole pairs, which is one of the main elements that can improve the photocatalytic activity. Photocatalytic reactions can result in a greater quantity of electrons on the BiOBr surface and holes on the ZnO and WO3 surfaces, leading to the superior visible-light photocatalytic activity of the ternary photocatalyst BiOBr/ZnO/WO3.

Catalytic Stability Study

The recyclability and stability of the BiOBr/ZnO/WO3 photocatalyst toward the degradation of aqueous solutions of phenol were investigated. Figure 11C illustrates the reuse of BiOBr/ZnO/WO3. For five cycles after desorption with ethanol, the photocatalytic degradation efficiency of phenol after the first cycle was 95%, which then decreased to 90% in the fifth cycle. This indicates that the decrease of BiOBr/ZnO/WO3 photocatalytic activity is negligible and emphasizes the long-term stability of the prepared BiOBr/ZnO/WO3 photocatalyst.
Based on the degradation efficiency (%) and degradation capacity, a comparative study of the current work and various photocatalysts for the degradation of phenol was done and is discussed in Table 5. The findings listed in the table demonstrate that BiOBr/ZnO/WO3 is a promising photocatalyst compared to other photocatalysts. Therefore, BiOBr/ZnO/WO3 is considered a promising catalyst for the simultaneous degradation of phenol in aqueous solutions.
Table 5. Comparative Study of Photocatalytic Degradation Efficiency (%) and Degradation Capacity of Phenol with Various Photocatalysts
adsorbentsdegradation %degradation capacity, q(mg/g)references
N-doped meso-titania69.228 (2)
TiO2/Gr/30PW91.045.5 (35)
TiO2/rGO90.022.7 (36)
Ag3PO4–Ag2CO373.924.6 (37)
BiOBr/WO3/ZnO95.039.37current work

Investigation of Photocatalytic System Efficiency

The photocatalytic efficiency of the BiOBr/ZnO/WO3 ternary nanocomposite was investigated toward the degradation of malachite green in addition to phenol, and the results were compared with the efficiency of commercial TiO2 P25 nano-powder toward the photodegradation of phenol and malachite green under the same experimental conditions. The results depicted in Figure 11D indicate that the efficiency of BiOBr/ZnO/WO3 toward the degradation of malachite green (93.6%) is greater than that for the degradation of phenol (90%), while the commercial TiO2 P25 nano-powder has a lower efficiency toward the degradation of both malachite green and phenol that reached 74 and 51.55%, respectively, which emphasize that BiOBr/ZnO/WO3 has a superior photocatalytic activity than the commercial TiO2 P25 nano-powder.

Realistic Application of Refinery Petroleum Wastewater

The efficiency of ternary photodegradable BiOBr/ZnO/WO3 was investigated for the treatment of real petroleum refinery wastewater samples. The analytical characterization results of the collected refinery wastewater sample before treatment were as follows: pH, 7.9 ± 0.2; total dissolved solids (TDS), 2.48 ± 0.4 g/L; phenol, 35 ± 0.5 mg/L; chemical oxygen demand (COD), 750 ± 0.8 mg/L; and biological oxygen demand (BOD), 210 ± 0.6 mg/L.
The results depicted in Figure 11E imply that the phenol content of petroleum wastewater decreased drastically with irradiation time rather than the COD and BOD contents, where the removal efficiency of phenol reached 89% after 300 min of irradiation, while that of COD and BOD reached 80.2 and 42.6%, respectively. These results imply the effectiveness of BiOBr/ZnO/WO3 for the treatment of organic pollutants. Generally, these findings revealed that BiOBr/ZnO/WO3 has the potency to be utilized in the eco-friendly treatment of refinery wastewater with high photocatalytic activity.

Conclusions

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Herein, single-nanophase ZnO, WO3, and BiOBr were synthesized, in addition to their binary- and ternary-phase BiOBr/ZnO, BiOBr/WO3, and BiOBr/ZnO/WO3 p–n heterojunctions, by the solvothermal technique. Their catalytic efficiency for phenol degradation was assessed under visible-light irradiation. The results indicate that the ternary BiOBr/ZnO/WO3 p–n heterojunction exhibits the highest photocatalytic activity that reached the degradation equilibrium after 60 min with an efficiency of 90%. RSM was used for optimizing the impact of degradation factors. Under the optimum conditions of 0.08 g/0.03 L catalyst dose, the pH of 9, and an initial monophenol concentration of 10 mg L–1, the degradation efficiency reached 95%. Also, the maximum phenol degradation capacity (39.37 mg g–1) was achieved under the conditions of 0.08 g/0.03 L catalyst dose, pH of 9, and 200 mg L–1 initial phenol concentration. The radical scavenging test proved that the superoxide radical •O2– and the hydroxyl radical •OH play a decisive role in the degradation of phenol by BiOBr/WO3/ZnO.

Experimental Section

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Materials and Methods

All the reagents utilized in this paper were obtained from Shanghai Chemical Company and were of analytical purity, and demineralized water was utilized for all preparations.

Synthesis of WO3 NPs

Sodium tungstate dihydrate powder (Na2WO4·2H2O, 0.003 mol) was first mixed in demineralized water (20 mL). (40) The final pH of the starting liquid was changed in two phases. First, by magnetic stirring, the pH limit for the liquid was acidified to 1.58 by hydrochloric acid (HCl, 37%) and then a white precipitate was formed. Finally, the liquid was diluted to 40 mL and then the mixture was mixed with oxalic acid (H2C2O4, 0.022 mol) to change the end pH to 2. Sodium chloride (NaCl, 0.068 mol) was added after stirring for 30 min and then heated at 90 °C for 3 h. The as-deposited substrate was then rinsed after the reaction was completed; the prepared salt was subsequently washed with demineralized water repeatedly, then calcined at 500 °C, and dried in air.

Preparation of Nano ZnO

Nano ZnO was prepared as follows: (41) 1.48 g of Zn(CH3COO)2·2H2O (Sigma-Aldrich, India) was dissolved in 63 mL of absolute ethanol in a 250 mL Schott bottle and heated with continuous stirring at 60° C. 0.74 g of NaOH was also dissolved separately in 33 mL of absolute ethanol in a 100 mL Schott bottle under the same Zn(CH3COO)2·2H2O condition. After both solutions had been fully dissolved, NaOH was added slowly to Zn(CH3COO)2·2H2O with vigorous stirring at 60 °C. The solution mixture was left to stand for 3 h before the reaction was finished. A white precipitate (ZnO) was produced and collected within 10 min by centrifugation at 4000 rpm and washed twice with acetone and once with ultrapure water to eliminate all the impurities. The product obtained was then dried at room temperature and then calcined at 500 °C and ground to form a powder.

Synthesis of Nano BiOBr and BiOBr/ZnO/WO3 Ternary Photocatalysts

The hydrolysis solvothermal process method was used for the preparation of BiOBr nanocrystals. Generally, to 0.035 L of 1,2-ethanediol (EG), 2.43 g of bismuth nitrate pentahydrate was added followed by 0.595 g of KBr with vigorous stirring until a transparent solution was obtained. Then, at room temperature, 0.3 L of demineralized water was gradually dropped into a transparent solution, and plenty of precipitate was immediately obtained. The obtained precipitate was purified, rinsed repeatedly with demineralized water, and then allowed to dry at 80 °C. (42) Typically, for BiOBr/ZnO/WO3 synthesis, 2.43 g of bismuth nitrate pentahydrate was added to 0.035 L of 1,2-ethanediol and stirred until the mixture became clear. Then, with vigorous stirring, 0.595 g of KBr was added and continuously stirred until the mixture became transparent. Subsequently, stoichiometric quantities of ZnO and WO3 with proportions of 4BiOBr/1ZnO/1WO3 (0.607 g equal to 25 wt% of bismuth nitrate pentahydrate) were dissipated by ultrasonication in 0.30 L of deionized water and stepwise added to the transparent solution at room temperature. The resultant mixture was collected, rinsed with demineralized water, and dried at 80 °C in air. (43,44)

Equipment

A Shimadzu XRD-600 diffractometer operating at a voltage of 40 KV and a current of 20 mA was utilized to record the patterns of XRD at both low angles (2θ range, 0.5–10) and wide angles (2θ range, 10–80) with Ni-filtered Cu Kα radiation (λ = 1.54° A). An FTIR spectrophotometer (Perkin-Elmer 720) was used to perform FTIR analysis. The KBr technique was applied nearly in a quantitative manner for all samples under investigation since the sample weight and that of KBr were fixed constant. XPS spectra were collected on K-ALPHA (Thermo Fisher Scientific, USA) with monochromatic X-ray Al K-α radiation of −10–1350 eV and a spot size of 400 μm at a pressure of 10–9 mbar with a full-spectrum pass energy of 200 eV and at a narrow-spectrum of 50 eV. Analysis by SEM coupled with EDS (SEM–EDX) was done using a scanning electron microscope JEOL GSM 6510LV. A transmission electron microscope (JEOL2100, 200 kV) was utilized to observe the particle size and structure morphologies of the synthesized photocatalysts. The photoelectrochemical measurements were conducted with an OrigaFlex-Pack OGF01A/potentiostat–galvanostat (Origalys, France) system. A UV–vis spectrophotometer (Jasco V-507) coupled with a Shimadzu IRS-2200 was utilized to perform UV–vis DRS and for the detection of malachite green dye concentration at λmax = 617 nm. The PL spectral analysis was done using a PL spectrometer (HITACHI F7000). For the quantitative analysis of the reaction intermediates, TOC analysis was employed using a high-sensitivity Shimadzu apparatus (4 μg C L–1 to 25,000 mg C L–1), model TOC-VCSH.

High-Performance Liquid Chromatography Analytical Procedure

High-performance liquid chromatography (HPLC) was used to analyze the resulting solutions after the reaction time has ended. An Agilent 1200 series (Waldbronn, Germany) HPLC devise model outfitted with an auto-sampler and a photodiode array detector (wavelength set at 190–400 nm in the full UV scan range) was used to analyze the phenol limits. A constant flow level of 1.0 mL/min with a reversed column phase C8 (4.6 × 25 cm, 300 A°, and 5 μm) was used. For elution, the mobile phase consisting of a 40 percent acetonitrile and 60 percent water mixture was utilized. Samples of the solution were taken at different reaction times to evaluate the phenol concentration and then photocatalysts were filtered and collected at 5000 rpm in a centrifuge.

Photocatalytic Performance

The degradation of phenol was utilized to evaluate the photocatalytic efficiency of the synthesized photocatalysts. A batch system was used to perform all experimental runs, where 0.05 g of each prepared photocatalyst was put into 30 mL of phenol contaminants (50 mg/l) at ambient temperature (25 ± 2 °C); first, all experimental runs were shaken in the dark for 1 h to reach the adsorption–desorption equilibrium and then visible-light illumination (tungsten lamp 300 W, λ > 400 nm) was switched on for 300 min. Samples were collected at different times, and the residual phenol concentration was assessed using the HPLC instrument. The percentage of phenol removal (R %) and the capacity for adsorption (qt, mg g–1) were determined using eqs 4 and 5, respectively. (24,25)
(4)
(5)
where the sorption capacity of the sorbent at intervals t (mg/g) is represented as qt, the starting phenol concentration as Co (mg/L), the remaining phenol concentration at intervals t as Ct (mg/L), the catalyst mass as m (g), and the quantity of phenol solution as V (L).
Relying on the solution concentration, kinetic information was gained by studying the pseudo-first-order kinetic system (eq 6), while depending upon the sorption equilibrium capacity, the pseudo-second-order kinetic model (eq 7) was studied. (26,27)
(6)
(7)
where the first-order rate constant is given by K1 (min–1), the second-order rate constant by K2 (g mg–1 min–1), and the quantity of phenol uptake at equilibrium by qe.
The conversion of phenol intermediates is represented by TOC as the instant TOC and TOC0, the initial TOC.

Factorial Design and Optimization

Depending on the CCD, a simplified RSM has been included to optimize the effect of other variables such as the pH, catalyst dose, and starting phenol concentration on the degradation efficiency. The verity of parameters that indicate the optimum phenol degradation efficiency was analyzed using the CCD model. Each degradation factor has three elevated levels designated as +1, 0, and −1. In the model, the catalyst dose was within 0.02–0.08 g/30 mL, the pH ranged from 3 to 9, and the initial phenol concentration varied from 10 to 200 mg L–1. Design-Expert software (V.11) was used to analyze statistical data. All the optimized tests were shaken in the dark for 1 h until the sorption balance was achieved and then the tests were conducted under visible light for 300 min. The phenol degradation efficiency behavior was described by the following polynomial equation of second order
(8)
where Y is the response variable, βo, βi, βij, and βii are the regression coefficients for the intercept, linear effect, double interaction, and quadratic effects, respectively, and Xi and Xj are the independent variables. (45)

Realistic Application of Refinery Petroleum Wastewater

A real wastewater sample was collected from a refinery petroleum company in Egypt. The TDS, pH, and organic constituents of the sample were characterized using standard methods (e.g., American Society for Testing and Materials and American Public Health Association Guidelines, 20th edition) for the examination of water and wastewater. For the degradation treatment, 1 g/L of BiOBr/ZnO/WO3 nanocomposite was dispersed in 100 mL of collected wastewater sample and irradiated for 300 min under visible light. At the end of the degradation time, the treated wastewater samples were separated by filtration, and the treatment efficiency was determined based on the decrease of organic pollutants, including phenol, COD (mg/L), and BOD (mg/L) at different time intervals, where COD and BOD are representatives of organic pollutants in wastewater.

Author Information

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  • Corresponding Author
  • Author
    • Hager R. Ali - Spectroscopic Division, Analysis and Evaluation Department, Egyptian Petroleum Research Institute (EPRI), Nasr City 11727 Cairo, Egypt
  • Author Contributions

    H.R.A. contributed equally.

  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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All authors gratefully thank the Egyptian Petroleum Research Institute staff for their encouragement and for providing analysis.

References

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    A review. In the past ten years we have witnessed a revival of, and subsequent rapid expansion in, the research on zinc oxide (ZnO) as a semiconductor. Being initially considered as a substrate for GaN and related alloys, the availability of high-quality large bulk single crystals, the strong luminescence demonstrated in optically pumped lasers and the prospects of gaining control over its elec. cond. have led a large no. of groups to turn their research for electronic and photonic devices to ZnO in its own right. The high electron mobility, high thermal cond., wide and direct band gap and large exciton binding energy make ZnO suitable for a wide range of devices, including transparent thin-film transistors, photodetectors, light-emitting diodes and laser diodes that operate in the blue and UV region of the spectrum. In spite of the recent rapid developments, controlling the elec. cond. of ZnO has remained a major challenge. While a no. of research groups have reported achieving p-type ZnO, there are still problems concerning the reproducibility of the results and the stability of the p-type cond. Even the cause of the commonly obsd. unintentional n-type cond. in as-grown ZnO is still under debate. One approach to address these issues consists of growing high-quality single cryst. bulk and thin films in which the concns. of impurities and intrinsic defects are controlled. In this review we discuss the status of ZnO as a semiconductor. We first discuss the growth of bulk and epitaxial films, growth conditions and their influence on the incorporation of native defects and impurities. We then present the theory of doping and native defects in ZnO based on d.-functional calcns., discussing the stability and electronic structure of native point defects and impurities and their influence on the elec. cond. and optical properties of ZnO. We pay special attention to the possible causes of the unintentional n-type cond., emphasize the role of impurities, critically review the current status of p-type doping and address possible routes to controlling the elec. cond. in ZnO. Finally, we discuss band-gap engineering using MgZnO and CdZnO alloys.
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  6. 6
    Wang, S. L.; Zhu, Y.; Luo, X. 2D WC/WO3Heterogeneous Hybrid for Photocatalytic Decomposition of Organic Compounds with Vis-NIR Light. Adv. Funct. Mater. 2018, 28, 1705357,  DOI: 10.1002/adfm.201705357
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  7. 7
    Xia, J.; Di, J.; Yin, S. Solvothermal synthesis and enhanced visible-light photocatalytic decontamination of bisphenol A (BPA) by g-C3N4/BiOBr heterojunctions. Mater. Sci. Semicond. Process. 2014, 24, 96– 103,  DOI: 10.1016/j.mssp.2014.02.036
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    7
    Solvothermal synthesis and enhanced visible-light photocatalytic decontamination of bisphenol A (BPA) by g-C3N4/BiOBr heterojunctions
    Xia, Jiexiang; Di, Jun; Yin, Sheng; Li, Huaming; Xu, Hui; Xu, Li; Shu, Huoming; He, Minqing
    Materials Science in Semiconductor Processing (2014), 24 (), 96-103CODEN: MSSPFQ; ISSN:1369-8001. (Elsevier Ltd.)
    Graphite-like C3N4 hybridized BiOBr photocatalysts have been synthesized through an EG-assisted solvothermal process in the presence of reactable ionic liq. 1-hexadecyl-3-methylimidazolium bromide ([C16mim]Br). The as-prepd. samples were characterized by X-ray diffraction (XRD), Fourier transform IR spectroscopy (FT-IR), SEM (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), diffuse reflectance spectroscopy (DRS), photoluminescence (PL) spectroscopy and photocurrent. The g-C3N4/BiOBr photocatalysts showed high efficiency for the degrdn. of bisphenol A (BPA) and rhodamine B (RhB) under visible light irradn. The results assumed that a loading amt. of g-C3N4 over BiOBr lead to an increase of the photocatalytic activity under visible light irradn. and showed much higher photocatalytic activity than that of pure BiOBr sample. The enhanced photocatalytic performance could be attributed to the high sepn. efficiency of the photogenerated electron-hole pairs. The trapping expts. of radicals showed that hole was the main reactive species for the photocatalytic degrdn. of RhB. A possible mechanism of g-C3N4/BiOBr on the enhancement of visible light performance was proposed.
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  8. 8
    Motawea, E. A.; Ali, H. R. Exploitation of Heterostructure Photocatalyst Impregnated Alginate Beads for Enhanced Removal of Methyl Orange under Solar Light. Petrol. Petrochem. Eng. J. 2018, 2, 1– 10,  DOI: 10.23880/ppej-16000180
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  9. 9
    Berger, S.; Tsuchiya, H.; Ghicov, A.; Schmuki, P. High photocurrent conversion efficiency in self-organized porous WO3. Appl. Phys. Lett. 2006, 88, 203119,  DOI: 10.1063/1.2206696
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    9
    High photocurrent conversion efficiency in self-organized porous WO3
    Berger, S.; Tsuchiya, H.; Ghicov, A.; Schmuki, P.
    Applied Physics Letters (2006), 88 (20), 203119/1-203119/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
    Self-organized porous structures of WO3 were grown on W by an anodic oxidn., and their photoelectrochem. properties were characterized. The porous WO3 layers show a regular morphol. with av. pore sizes of approx. 70 nm and a pore wall thickness of approx. 10 nm. As formed layers show an amorphous structure but the layers can be altered to a cryst. monoclinic structure by thermal annealing. The annealed porous WO3 layers show a very high specific photocurrent conversion efficiency.
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  10. 10
    Momeni, M. M.; Hakimian, M.; Kazempour, A. In-Situ Manganese Doping of TiO2 Nanostructures via Single-Step Electrochemical Anodizing of Titanium in an Electrolyte Containing Potassium Permanganate: A Good Visible-Light Photocatalyst. Ceram. Int. 2015, 41, 13692,  DOI: 10.1016/j.ceramint.2015.07.158
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    10
    In-situ manganese doping of TiO2 nanostructures via single-step electrochemical anodizing of titanium in an electrolyte containing potassium permanganate: A good visible-light photocatalyst
    Momeni, Mohamad Mohsen; Hakimian, Mohaddeseh; Kazempour, Ali
    Ceramics International (2015), 41 (10_Part_A), 13692-13701CODEN: CINNDH; ISSN:0272-8842. (Elsevier Ltd.)
    It is desirable to induce remarkable red-shift in the optical absorption edges of TiO2 so that this class of low-cost materials can be used as optimum photocatalysts beyond the UV range. This work reports on the room-temp. electrochem. fabrication of manganese-doped TiO2 nanotubes (MnTNT) and the investigation of their optical property and photocatalytic activity. TiO2 nanotubes (TNT) were doped with different concns. of manganese and prepd. nanostructures have been characterized using different techniques for analyzing their structure, morphol., compn., band gap and optical absorption property. Characterization of the as-prepd. samples indicated that dopant concn. in anodizing soln. significantly influenced the morphol., structure, photoabsorption and photocatalytic activity of fabricated films. The optical absorption range of TiO2 film gradually expands and shifts to the red with increasing dosages and band gap of the TiO2 films were reduced. Moreover, the photocatalytic activity of the TiO2 films for removal of methylene blue was enhanced by doping with an appropriate amt. of manganese. The sample MnTNT4 exhibited better photocatalytic activity than the undoped TNT and MnTNT fabricated using other manganese concns.
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  11. 11
    Momeni, M. M.; Nazari, Z. Preparation of TiO2 and WO3-TiO2 nanotubes decorated with PbO nanoparticles by chemical bath deposition process: A stable and efficient photo catalyst. Ceram. Int. 2016, 42, 8691– 8697,  DOI: 10.1016/j.ceramint.2016.02.103
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    11
    Preparation of TiO2 and WO3-TiO2 nanotubes decorated with PbO nanoparticles by chemical bath deposition process: A stable and efficient photo catalyst
    Momeni, Mohamad Mohsen; Nazari, Zohre
    Ceramics International (2016), 42 (7), 8691-8697CODEN: CINNDH; ISSN:0272-8842. (Elsevier Ltd.)
    We present a new method for synthesizing Pb/TNTs and Pb/WTNTs composite with good photo catalytic activity. TiO2 nanotube (TNTs) and WO3-TiO2 nanotubes (WTNTs) were prepd. by one-step electrochem. anodizing method and lead has been successfully deposited on these nanotubes by chem. bath deposition process. The morphol., crystal structure, elemental compn. and light absorption capability of the prepd. samples were evaluated using various characterization techniques. Results showed that the fabricated films have highly ordered nanotube morphol. Diffuse reflectance spectra showed an increase in the visible absorption relative to bare samples. The degrdn. of methylene blue was used as a model reaction to evaluate the photo catalytic activity of these novel visible-light-responsive photo catalysts. Results showed that the photo catalytic activity of bare WTNTs samples is higher than that with undoped TNTs sample. Compared with unmodified TNTs and WTNTs, the Pb/TNTs and Pb/WTNTs samples exhibited enhanced photo catalytic activity in the degrdn. of methylene blue. The sample Pb/WTNTs exhibited better photo catalytic activity than other samples. Also prepd. photo catalysts showed good stability and could be recycled several times without significant loss of their activity. This work provides an insight in designing and synthesizing new WTNTs-based hybrid materials for effective visible light-activated photo catalysis. Since Pb/TNTs and Pb/WTNTs electrodes can be easily removed and replaced after the photo catalytic reaction, avoiding the filtration step after photoreaction or the immobilizing process required for photo catalyst particles, the operation in the photo-reactor becomes much easier from an engineering point of view. The catalysts prepd. in this study exhibit industrially relevant interests due to the low cost and high photo catalytic activity.
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  12. 12
    Zeng, Q.; Li, J.; Bai, J.; Li, X.; Xia, L.; Zhou, B. Preparation of vertically aligned WO3 nanoplate array films based on peroxotungstate reduction reaction and their excellent photoelectrocatalytic performance. Appl. Catal., B 2017, 202, 388– 396,  DOI: 10.1016/j.apcatb.2016.09.045
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    12
    Preparation of vertically aligned WO3 nanoplate array films based on peroxotungstate reduction reaction and their excellent photoelectrocatalytic performance
    Zeng, Qingyi; Li, Jinhua; Bai, Jing; Li, Xuejin; Xia, Ligang; Zhou, Baoxue
    Applied Catalysis, B: Environmental (2017), 202 (), 388-396CODEN: ACBEE3; ISSN:0926-3373. (Elsevier B.V.)
    Here, the authors developed a novel, facile, controllable and scalable method based on peroxotungstate redn. reaction to prep. vertically aligned WO3 nanoplate array (NPA) films with preferentially exposed highly reactive (002) facets used in efficient photoelectrocatalytic (PEC) applications. In this method, a slow and controllable redn. of peroxotungstates by ethanol was used, which was the crit. step to ensure the uniform and ordered synthesis of orthorhombic WO3·H2O NPA films which assembled directly on F-doped tin oxide substrates under the capping effect of oxalate, and subsequently WO3·H2O NPA films were converted into monoclinic WO3 NPA films by calcination. The effects of synthetic temp. and time, and the concn. of oxalate on the cryst. phase and morphol. of the WO3·H2O films were studied systematically. The WO3 NPA film annealed at an optimized temp. of 500° exhibited the highest water splitting c.d. of ∼1.42 mA/cm2 at 1.23 V vs. RHE in 0.1M Na2SO4 under AM 1.5 G illumination. It was further improved by decorating with a Co-Pi co-catalyst, which achieved a more stable c.d. of ∼1.95 mA/cm2 with an incident photon-to-current conversion efficiency of ∼51% at 400 nm. The WO3 NPA film also showed excellent stability and efficiency (rate const. ∼0.8127 h-1) for PEC degrdn. of methylene blue.
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  13. 13
    Zeng, X.; Wang, Z.; Wang, G. Highly dispersed TiO2 nanocrystals and WO3 nanorods on reduced graphene oxide: Z-scheme photocatalysis system for accelerated photocatalytic water disinfection. Appl. Catal., B 2017, 218, 163– 173,  DOI: 10.1016/j.apcatb.2017.06.055
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    13
    Highly dispersed TiO2 nanocrystals and WO3 nanorods on reduced graphene oxide: Z-scheme photocatalysis system for accelerated photocatalytic water disinfection
    Zeng, Xiangkang; Wang, Zhouyou; Wang, Gen; Gengenbach, Thomas R.; McCarthy, David T.; Deletic, Ana; Yu, Jiaguo; Zhang, Xiwang
    Applied Catalysis, B: Environmental (2017), 218 (), 163-173CODEN: ACBEE3; ISSN:0926-3373. (Elsevier B.V.)
    Coupling TiO2 with WO3 to develop photocatalytic heterojunctions is one of the most widely used strategies to realize their superior photoactivity. However, the interfacial charge transfer in these heterojunctions is not efficient to achieve an optimized activity. For the first time, the present study reports a facile hydrolysis-hydrothermal approach, whereby ultradispersed TiO2 nanocrystals and WO3 nanorods are concurrently anchored onto reduced graphene oxide (rGO) and formed a novel Z-scheme heterojunction photocatalyst TiO2/rGO/WO3 (TRW). Transmission electron microscope (TEM), X-ray diffraction (XRD), XPS, UV-vis diffuse reflectance spectroscopy (UV-vis DRS) and photoluminescence spectra (PL) are employed to characterize TRW. Control expts. indicate that, in the synthesis process, glucose and the byproduct sodium chloride from the hydrolysis reactions are crit. for forming highly dispersed and uniform-sized TiO2 nanocrystals and WO3 nanorods. Compared with TiO2/WO3 nanocomposites, TRW shows enhanced activity for bacterial inactivation under simulated solar light. As confirmed by electrochem. characterizations and the reactive oxygen species, rGO in TRW suppresses the recombination of electron-hole pairs and boosts the O2 redn. reactions during photocatalytic process. Z-scheme electron transfer in TRW is proposed based on surface redox reactions and XPS anal. after light irradn. This study could provide a new clue for designing graphene-based heterojunction photocatalysts for environmental applications.
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  14. 14
    Momeni, M. M.; Ghayeb, Y.; Davarzadeh, M. Electrochemical construction of different titania-tungsten trioxide nanotubular composite and their photocatalytic activity for pollutant degradation: a recyclable photocatalysts. J. Mater. Sci.: Mater. Electron. 2015, 26, 1560– 1567,  DOI: 10.1007/s10854-014-2575-x
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    14
    Electrochemical construction of different titania-tungsten trioxide nanotubular composite and their photocatalytic activity for pollutant degradation: a recyclable photocatalysts
    Momeni, Mohamad Mohsen; Ghayeb, Yousef; Davarzadeh, Mahsa
    Journal of Materials Science: Materials in Electronics (2015), 26 (3), 1560-1567CODEN: JSMEEV; ISSN:0957-4522. (Springer)
    Different TiO2-WO3 nanotubular (TWNs) electrodes were fabricated by in situ anodization of titanium in a single-step process using sodium tungstate as the tungsten source. The morphol. and structure were characterized by field-emission SEM, X-ray diffraction and energy dispersive X-ray spectroscopy. Optical properties were investigated by ultra UV-Vis diffuse reflectance spectra. The resulting TWNs showed a tube diam. of 80-110 nm, wall thickness of 20-40 nm and tube lengths in the range of 7-8 μm. The visible light photocatalytic activity of the TWNs electrodes was evaluated by measuring the degrdn. of methylene blue dye under simulated sunlight conditions and compared with photo-catalytic activity of pure TiO2 nanotubes (TNs). The results showed that TWNs electrodes have excellent photo-catalytic performance. The sample C, that formed by anodic oxidn. in a DMSO electrolyte contg. 4 g/l sodium tungstate, exhibited better photo-catalytic activity than the TNs and TWNs fabricated using other W concns. under Xe illumination. The anodization process developed in this study is facile, reproducible, and inexpensive, and can be easily scaled up, thereby pioneering the fabrication of high performance photo-catalysts with promising environmental applications.
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  15. 15
    Momeni, M. M.; Ghayeb, Y.; Ghonchegi, Z. Fabrication and characterization of copper doped TiO2 nanotube arrays by in situ electrochemical method as efficient visible-light photocatalyst. Ceram. Int. 2015, 41, 8735– 8741,  DOI: 10.1016/j.ceramint.2015.03.094
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    15
    Fabrication and characterization of copper doped TiO2 nanotube arrays by in situ electrochemical method as efficient visible-light photocatalyst
    Momeni, Mohamad Mohsen; Ghayeb, Yousef; Ghonchegi, Zohre
    Ceramics International (2015), 41 (7), 8735-8741CODEN: CINNDH; ISSN:0272-8842. (Elsevier Ltd.)
    Highly ordered copper doped TiO2 nanotube arrays (CuTiO2NTs) thin-film were prepd. in an aq. soln. contg. NH4F and different concns. of copper nitrate via the electrochem. oxidn. of titanium substrates. The resulting nanotubes were characterized by FE-SEM, XRD, XPS and EDX. The CuTiO2NTs showed a tube diam. of 40-90 nm and wall thickness of 20-30 nm. Diffuse reflectance spectra showed a shift toward longer wavelengths relative to pure TiO2 nanotubes (TiO2NTs). The visible light photo-catalytic activity of the CuTiO2NTs electrodes was evaluated by the removal of methylene blue (MB) dye and the prodn. of hydrogen. The results showed that CuTiO2NTs samples exhibited better photo-catalytic activity than the TiO2NTs. This work demonstrated a feasible and simple anodization method to fabricate an effective, reproducible, and inexpensive visible-light-driven photo-catalyst for hydrogen evolution and environmental applications.
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  16. 16
    Lei, R.; Ni, H.; Chen, R.; Zhang, B.; Zhan, W.; Li, Y. Growth of Fe 2 O 3 /SnO 2 nanobelt arrays on iron foil for efficient photocatalytic degradation of methylene blue. Chem. Phys. Lett. 2017, 673, 1– 6,  DOI: 10.1016/j.cplett.2017.01.052
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    16
    Growth of Fe2O3/SnO2 nanobelt arrays on iron foil for efficient photocatalytic degradation of methylene blue
    Lei, Rui; Ni, Hongwei; Chen, Rongsheng; Zhang, Bowei; Zhan, Weiting; Li, Yang
    Chemical Physics Letters (2017), 673 (), 1-6CODEN: CHPLBC; ISSN:0009-2614. (Elsevier B.V.)
    Tin(IV) oxide has been intensively employed in optoelectronic devices due to its excellent elec. and optical properties. But the high recombination rates of the photogenerated electron-hole pairs of SnO2 nanomaterials often results in low photocatalytic efficiency. Herein, we proposed a facile route to prep. a novel Fe2O3/SnO2 heterojunction structure. The nanobelt arrays grown on iron foil naturally form a Schottky-type contact and provide a direct pathway for the photogenerated excitons. Hence, the Fe2O3/SnO2 nanobelt arrays exhibit much improved photocatalytic performance with the degrdn. rate const. on the Fe2O3/SnO2 film of approx. 12 times to that of α-Fe2O3 nanobelt arrays.
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  17. 17
    Tsay, C.-Y.; Fan, K.-S.; Chen, S.-H.; Tsai, C.-H. Preparation and characterization of ZnO transparent semiconductor thin films by sol-gel method. J. Alloys Compd. 2010, 495, 126– 130,  DOI: 10.1016/j.jallcom.2010.01.100
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    17
    Preparation and characterization of ZnO transparent semiconductor thin films by sol-gel method
    Tsay, Chien-Yie; Fan, Kai-Shiung; Chen, Sih-Han; Tsai, Chia-Hao
    Journal of Alloys and Compounds (2010), 495 (1), 126-130CODEN: JALCEU; ISSN:0925-8388. (Elsevier B.V.)
    Transparent semiconductor thin films of zinc oxide (ZnO) were deposited onto alkali-free glass substrates by the sol-gel method and spin-coating technique. In this study, authors investigate the influence of the heating rate of the preheating process (4 or 10 °C/min) on the crystn., surface morphol., and optical properties of sol-gel derived ZnO thin films. The ZnO sol was synthesized by dissolving zinc acetate dehydrate in ethanol, and then adding monoethanolamine. The as-coated films were preheated at 300 °C for 10 min and annealed at 500 °C for 1 h in air ambiance. Exptl. results indicate that the heating rate of the preheating process strongly affected the surface morphol. and transparency of ZnO thin film. Specifically, a heating rate of 10 °C/min for the preheating process produces a preferred orientation along the (0 0 2) plane and a high transmittance of 92% at a wavelength of 550 nm. Furthermore, this study reports the fabrication of thin-film transistors (TFTs) with a transparent ZnO active channel layer and evaluates their elec. performance.
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  18. 18
    Sakthivel, S.; Neppolian, B.; Shankar, M. V.; Arabindoo, B.; Palanichamy, M.; Murugesan, V. Solar photocatalytic degradation of azo dye: Comparison of photocatalytic efficiency of ZnO and TiO2. Sol. Energy Mater. Sol. Cells 2003, 77, 65– 82,  DOI: 10.1016/S0927-0248(02)00255-6
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    18
    Solar photocatalytic degradation of azo dye: comparison of photocatalytic efficiency of ZnO and TiO2
    Sakthivel, S.; Neppolian, B.; Shankar, M. V.; Arabindoo, B.; Palanichamy, M.; Murugesan, V.
    Solar Energy Materials and Solar Cells (2003), 77 (1), 65-82CODEN: SEMCEQ; ISSN:0927-0248. (Elsevier Science B.V.)
    The photocatalytic activity of com. ZnO powder was investigated and compared with that of Degussa P25 TiO2. Lab. expts. with Acid brown 14 as the model pollutant were carried out to evaluate the performance of both ZnO and TiO2 catalysts. Solar light was used as the energy source for the photocatalytic expts. These catalysts were examd. for surface area, particle size, and crystallinity. The effect of initial dye concn., catalyst loading, irradn. time, pH, adsorption of Acid brown 14 on ZnO and TiO2, intensity of light and comparison of photocatalytic activity with different com. catalysts were studied. The progress of photocatalytic degrdn. of the Acid brown 14 was obsd. by monitoring the change in substrate concn. of the model compd. employing HPLC and measuring the absorbance in UV-Visible spectrophotometer for decolorization. The photodegrdn. rate was detd. for each expt. and the highest values were obsd. for ZnO suggesting that it absorbs large fraction of the solar spectrum and absorption of more light quanta than TiO2. The complete mineralization was confirmed by TOC anal., COD measurement, and estn. of the formation of inorg. ions such as NH4+, NO3-, Cl-, and SO42-.
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  19. 19
    Li, D.; Haneda, H.; Ohashi, N.; Saito, N.; Hishita, S. Morphological reform of ZnO particles induced by coupling with MOx (M=V,W,Ce) and the effects on photocatalytic activity. Thin Solid Films 2005, 486, 20– 23,  DOI: 10.1016/j.tsf.2004.11.237
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    19
    Morphological reform of ZnO particles induced by coupling with MOx (M = V,W,Ce) and the effects on photocatalytic activity
    Li, Di; Haneda, Hajime; Ohashi, Naoki; Saito, Noriko; Hishita, Shunichi
    Thin Solid Films (2005), 486 (1-2), 20-23CODEN: THSFAP; ISSN:0040-6090. (Elsevier B.V.)
    Morphol. reform of originally prismatic ZnO particles was obsd. during the coupling process with MOx (M = V,W,Ce) precursor by impregnation. The prismatic morphol. of ZnO particles transferred to sheet shape morphol. during coupling with vanadium oxide, and to rod-like shape morphol. during coupling with cesium oxide, however, no change was obsd. when ZnO was coupled with tungsten oxide. Photocatalytic test indicated that the photocatalytic activity of ZnO was enhanced by coupling with vanadium or tungsten oxide, while suppressed by cesium oxide. VOx-ZnO composite sheets demonstrated the highest photocatalytic activity for acetaldehyde decompn., being higher than that of com. P 25.
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  20. 20
    El-saied, H. A.-a.; Motawea, E. A.-T. Optimization and Adsorption Behavior of Nanostructured NiFe2O4/Poly AMPS Grafted Biopolymer. J. Polym. Environ. 2020, 28, 2335– 2351,  DOI: 10.1007/s10924-020-01774-z
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    20
    Optimization and Adsorption Behavior of Nanostructured NiFe2O4/Poly AMPS Grafted Biopolymer
    El-saied, Hend Al-aidy; Motawea, Eman Al-Tohamy
    Journal of Polymers and the Environment (2020), 28 (9), 2335-2351CODEN: JPENFW; ISSN:1572-8919. (Springer)
    Abstr.: By grafting polysaccharides backbone of biopolymer (alginate) on synthetic polymer nanocomposite chains (PAMPS/NiFe2O4) to remove methylene blue and toxic heavy metal (Cu2+) from aq. solns., a superadsorbent was prepd. Using FTIR, TGA, X-ray diffraction, TEM, and SEM studied the structures of native and grafted alginate hydrogels. Adsorption expts. have been optimized using RSM/CCD response surface methodol. and analyzed as a pH soln. and adsorbent dose function. The initial concns. of metal and dye, temp., and contact time were also discussed and isothermal, thermodn. adsorption, and kinetic theor. consts. were calcd. as well. Results revealed that alginate grafted nanocomposite PAMPS/NiFe2O4 enhanced the proportion of methylene blue (MB) color removal up to (98.32%) and metal ion discharge (83%). The optimum cationic dye MB and Cu2+ ions adsorption capability were acquired at pH (5.75 and 4) and temp. (318.15 K) resp. For both MB dye and Cu2+ ions, the pseudo-2nd-order model has effectively defined the adsorption kinetics and the Freundlich model could precisely explain adsorption isotherms than the Cu2+ Langmuir adsorption model, while the adsorption of MB dye showed a greater presence for both Freundlich and Langmuir designs.
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  21. 21
    Lv, J.; Dai, K.; Zhang, J.; Liu, Q.; Liang, C.; Zhu, G. Facile constructing novel 2D porous g-C3N4/BiOBr hybrid with enhanced visible-light-driven photocatalytic activity. Sep. Purif. Technol. 2017, 178, 6– 17,  DOI: 10.1016/j.seppur.2017.01.019
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    21
    Facile constructing novel 2D porous g-C3N4/BiOBr hybrid with enhanced visible-light-driven photocatalytic activity
    Lv, Jiali; Dai, Kai; Zhang, Jinfeng; Liu, Qi; Liang, Changhao; Zhu, Guangping
    Separation and Purification Technology (2017), 178 (), 6-17CODEN: SPUTFP; ISSN:1383-5866. (Elsevier B.V.)
    Porous graphitic carbon nitride (Pg-C3N4) nanosheets have been prepd. via thermal decompn., and then novel 2D Pg-C3N4/BiOBr hybrid is designed by a facile hydrothermal process. The as-prepd. Pg-C3N4/BiOBr hybrids are characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM) and UV-visible diffuse reflectance spectroscopy (DRS). The results show that BiOBr tightly composited on the surface of Pg-C3N4. Enhanced electron and hole sepn. efficiency is confirmed by photoluminescence (PL) spectroscopy measurements and the photoelectrochem. evaluation. The photoactivity performance of Pg-C3N4/BiOBr is tested under visible-light irradn., the result shows that coupling semiconductor of Pg-C3N4/BiOBr apparently enhances the photocatalytic activity. An optimal Pg-C3N4 content has been detd. to be 20 wt.%, corresponding to apparent pseudo-first-order rate const. kapp of 0.088 min-1, which is 3.7 times, 4.2 times and 7.3 times as high as that of Pg-C3N4, BiOBr and common g-C3N4, resp. Furthermore, photocatalytic stability and mechanism of enhanced photocatalytic process are also investigated.
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  22. 22
    Huang, W.; Hua, X.; Zhao, Y. Enhancement of visible-light-driven photocatalytic performance of BiOBr nanosheets by Co2+ doping. J. Mater. Sci.: Mater. Electron. 2019, 30, 14967– 14976,  DOI: 10.1007/s10854-019-01869-x
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    22
    Enhancement of visible-light-driven photocatalytic performance of BiOBr nanosheets by Co2+ doping
    Huang, Wenmao; Hua, Xin; Zhao, Yaping; Li, Kai; Tang, Liping; Zhou, Man; Cai, Zaisheng
    Journal of Materials Science: Materials in Electronics (2019), 30 (16), 14967-14976CODEN: JSMEEV; ISSN:0957-4522. (Springer)
    In this work, Co2+ modification influence on the visible-light-induced photocatalytic performance of BiOBr was investigated. BiOBr and Co2+-doped BiOBr (Co/BiOBr) nanosheets were fabricated through a facile solvothermal way. The morphol., structure, chem. compn. and optical properties of the photocatalysts were characterized by various techniques. The results confirmed the successful synthesis of Co/BiOBr nanosheets and indicated the doped Co2+ had little influence on the surface morphol. and crystal structure but expanded the light absorption region. Photoelectrochem. measurements were applied to evaluate the semiconducting properties of Co/BiOBr, and the results implied that compared with the undoped sample, Co/BiOBr had higher charge transfer efficiency and smaller charge transfer resistance which were beneficial to the improvement of visible-light-driven photocatalytic performance. The as-synthesized Co/BiOBr nanosheets exhibited excellent catalytic activity and stability in the photodecompn. of contaminants.
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  23. 23
    Khampuanbut, A.; Santalelat, S.; Pankiew, A. Visible-light-driven WO3/BiOBr heterojunction photocatalysts for oxidative coupling of amines to imines: Energy band alignment and mechanistic insight. J. Colloid Interface Sci. 2020, 560, 213– 224,  DOI: 10.1016/j.jcis.2019.10.057
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    Visible-light-driven WO3/BiOBr heterojunction photocatalysts for oxidative coupling of amines to imines: Energy band alignment and mechanistic insight
    Khampuanbut, Amornrat; Santalelat, Sarunya; Pankiew, Apirak; Channei, Duangdao; Pornsuwan, Soraya; Faungnawakij, Kajornsak; Phanichphant, Sukon; Inceesungvorn, Burapat
    Journal of Colloid and Interface Science (2020), 560 (), 213-224CODEN: JCISA5; ISSN:0021-9797. (Elsevier B.V.)
    The visible-light-driven WO3/BiOBr heterojunction was for the first time detd. for its photocatalytic activity toward oxidative coupling of amines at room temp. using mol. oxygen as a green oxidant. The WO3/BiOBr heterojunction exhibits superior photocatalytic activity and photostability compared with pure BiOBr and WO3 due to an increased oxygen vacancy concn., an effective sepn. of photogenerated electron-hole pairs and an efficient interfacial charge transfer. Addnl., the WO3/BiOBr also shows 2.3 and 41.1 times higher activity than that of TiO2 P25 and BiVO4 Alfa Aesar, resp. Detn. of energy band line-up indicates that the WO3/BiOBr is a type II-heterojunction where electron-hole pairs are efficiently sepd. Mechanistic studies based on radical quenching expt., EPR trapping study and Hammett plot reveal that the main reaction pathway is the electron transfer route mediated by superoxide radical. A possible surface reaction mechanism, the insightful information on the structure-activity relationship and the involvement of reactive oxygen species elucidated in this work lay an important background for the material design and encourage a further development of highly efficient photocatalysts toward org. fine chem. syntheses.
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  24. 24
    Yang, H.; Zhang, Q.; Chen, Y.; Huang, Y.; Yang, F.; Lu, Z. Ultrasonic-microwave synthesis of ZnO/BiOBr functionalized cotton fabrics with antibacterial and photocatalytic properties. Carbohydr. Polym. 2018, 201, 162– 171,  DOI: 10.1016/j.carbpol.2018.08.068
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    24
    Ultrasonic-microwave synthesis of ZnO/BiOBr functionalized cotton fabrics with antibacterial and photocatalytic properties
    Yang, Hao; Zhang, Qingxia; Chen, Ying; Huang, Yong; Yang, Fang; Lu, Zhong
    Carbohydrate Polymers (2018), 201 (), 162-171CODEN: CAPOD8; ISSN:0144-8617. (Elsevier Ltd.)
    ZnO coated fabrics have attracted wide attentions due to their antibacterial and photocatalytic self-cleaning properties. However, the photo-response of ZnO only in UV region limits its application. In this paper, ZnO/BiOBr functionalized cotton fabrics were synthesized by a facile and time-saving ultrasonic-microwave combined method. Compared with ZnO coated fabric, the photocatalytic activity of ZnO/BiOBr coated fabric under visible light irradn. was remarkably improved at no sacrifice of its antibacterial activity. Simultaneously, it also showed good resistance to bacterial adhesion and photocorrosion. The introduction of two-dimensional BiOBr nanoflakes not only enhanced the visible light absorption, but also reduced the recombination rate of electron-hole pairs, thus significantly improving the photocatalytic self-cleaning performance of the coated fabric under visible light irradn. The ZnO/BiOBr coated cotton fabric with both antibacterial and self-cleaning functionalities may have broad application prospects in the fields of textile, medicine and chem. industry.
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    Tae Kwon, Y.; Yong Song, K.; In Lee, W.; Jin Choi, G.; Rag Do, Y. Photocatalytic behavior of WO3-loaded TiO2 in an oxidation reaction. J. Catal. 2000, 191, 192– 199,  DOI: 10.1006/jcat.1999.2776
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    Keller, V.; Bernhardt, P.; Garin, F. Photocatalytic oxidation of butyl acetate in vapor phase on TiO2, Pt/TiO2 and WO3/TiO2 catalysts. J. Catal. 2003, 215, 129– 138,  DOI: 10.1016/S0021-9517(03)00002-2
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    Photocatalytic oxidation of butyl acetate in vapor phase on TiO2, Pt/TiO2 and WO3/TiO2 catalysts
    Keller, V.; Bernhardt, P.; Garin, F.
    Journal of Catalysis (2003), 215 (1), 129-138CODEN: JCTLA5; ISSN:0021-9517. (Elsevier Science)
    The photocatalytic degrdn. of Bu acetate in the gas phase was investigated in a fixed-bed continuous annular reactor using a titanium dioxide semiconductor, Pt/TiO2 and WO3/TiO2 catalysts. Platinum was deposited on the titanium by adsorption of PtCl62- anions, and WO3/TiO2 was prepd. by a conventional impregnation method using an aq. soln. of ammonium paratungstate. Different samples, with different nominal wt. loadings in Pt and WO3, were tested. For each catalyst sample studied, air contg. Bu acetate and water vapors in various molar ratios was fed at 200 cm3/min to the photoreactor. The roles of the reaction temp. and of H2O in the photocatalytic oxidn. of Bu acetate and the influence of the content of TiO2, Pt, and WO3 were investigated. Although an initial decay in photocatalytic activity was obsd., partly issued from an initial deactivation, total mineralization was achieved under all exptl. conditions. For relative water humidity between 50 and 75% and for adequate TiO2 covering ratios, the photocatalytic activity of TiO2 toward the photocatalytic degrdn. of Bu acetate can be greatly improved by the addn. of WO3, mainly due to a prevention of the initial deactivation and of photogenerated charge recombination. This optimized photocatalyst is very stable on stream and no regeneration treatments are needed. The influence of Pt and WO3 on photocatalytic activity are discussed with regard to chem. and electronic modifications of TiO2.
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    El-Salamony, R. A.; Amdeha, E.; Badawy, N. A.; Ghoneim, S. A.; Al-Sabagh, A. M. Visible light sensitive activated carbon-metal oxide (TiO2, WO3, NiO, and SnO) nano-catalysts for photo-degradation of methylene blue: a comparative study. Toxicol. Environ. Chem. 2018, 100, 143– 156,  DOI: 10.1080/02772248.2018.1497634
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    Visible light sensitive activated carbon-metal oxide (TiO2, WO3, NiO, and SnO) nano-catalysts for photo-degradation of methylene blue: a comparative study
    El-Salamony, Radwa A.; Amdeha, Enas; Badawy, Nagwa A.; Ghoneim, Salwa A.; Al-Sabagh, Ahmed M.
    Toxicological & Environmental Chemistry (2018), 100 (2), 143-156CODEN: TECSDY; ISSN:1029-0486. (Taylor & Francis Ltd.)
    Four composites of metal oxide doped with activated carbon with a metal oxide wt. of 20% were prepd. using mechano-mixing method. The nano-catalysts were characterized by N2-adsorption-desorption, X-ray diffraction anal., transmission electron microscopy, Fourier-transform IR spectroscopy, UV-diffuse reflectance, and photoluminescence spectroscopy. Photo-catalytic degrdn. of methylene blue dye under UV 254 nm and visible light was examd. In general, prepd. catalysts are more active for degrdn. of dye under visible light than UV, reaching 96% within 180 min irradn. using the SnO catalyst. Photo-degrdn. of methylene blue followed pseudo first order reaction mechanism with a rate const. of 14.8 × 10-3 min-1, and the time required for removal of 50% of dye was 47 min.
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    Amdeha, E.; Mohamed, R. S. A green synthesized recyclable ZnO/MIL-101(Fe) for Rhodamine B dye removal via adsorption and photo-degradation under UV and visible light irradiation. Environ. Technol. 2019, 42, 842– 859,  DOI: 10.1080/09593330.2019.1647290
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    Wang, H.; Zhang, L.; Chen, Z. Semiconductor heterojunction photocatalysts: Design, construction, and photocatalytic performances. Chem. Soc. Rev. 2014, 43, 5234– 5244,  DOI: 10.1039/c4cs00126e
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    Semiconductor heterojunction photocatalysts: design, construction, and photocatalytic performances
    Wang, Huanli; Zhang, Lisha; Chen, Zhigang; Hu, Junqing; Li, Shijie; Wang, Zhaohui; Liu, Jianshe; Wang, Xinchen
    Chemical Society Reviews (2014), 43 (15), 5234-5244CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
    A review. Semiconductor-mediated photocatalysis has received tremendous attention as it holds great promise to address the worldwide energy and environmental issues. To overcome the serious drawbacks of fast charge recombination and the limited visible-light absorption of semiconductor photocatalysts, many strategies have been developed in the past few decades and the most widely used one is to develop photocatalytic heterojunctions. This review attempts to summarize the recent progress in the rational design and fabrication of heterojunction photocatalysts, such as the semiconductor-semiconductor heterojunction, the semiconductor-metal heterojunction, the semiconductor-carbon heterojunction and the multicomponent heterojunction. The photocatalytic properties of the four junction systems are also discussed in relation to the environmental and energy applications, such as degrdn. of pollutants, hydrogen generation and photocatalytic disinfection. This tutorial review ends with a summary and some perspectives on the challenges and new directions in this exciting and still emerging area of research.
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    Zhang, J.; Zhang, L.; Shen, X.; Xu, P.; Liu, J. Synthesis of BiOBr/WO3p-n heterojunctions with enhanced visible light photocatalytic activity. CrystEngComm 2016, 18, 3856– 3865,  DOI: 10.1039/c6ce00824k
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    Synthesis of BiOBr/WO3 p-n heterojunctions with enhanced visible light photocatalytic activity
    Zhang, Junlei; Zhang, Lisha; Shen, Xiaofeng; Xu, Pengfei; Liu, Jianshe
    CrystEngComm (2016), 18 (21), 3856-3865CODEN: CRECF4; ISSN:1466-8033. (Royal Society of Chemistry)
    A prerequisite for the development of photocatalysis techniques is to obtain photocatalysts with remarkable activity. Herein, we have reported BiOBr/WO3 p-n heterojunctions as novel and efficient visible-light-driven photocatalysts. The BiOBr/WO3 p-n heterojunctions have been prepd. through an electrospinning-calcination-solvothermal method, and they all present a flower-like superstructure. The photocatalytic activities of these p-n heterojunctions are investigated by degrading rhodamine B (RhB), methyl orange (MO) and para-chlorophenol (4-CP) under visible light irradn. (λ > 400 nm), resp. When RhB serves as the target pollutant, all BiOBr/WO3 p-n heterojunctions with different theor. molar ratios of BiOBr and WO3 (1/0.5, 1/1, 1/2) exhibit higher photocatalytic activity than pure WO3 or BiOBr. Esp., the BiOBr/WO3 p-n heterojunction with a molar ratio of 1/1 displays the highest photocatalytic activity among all the as-synthesized catalysts, even higher than the activity from the mixt. of two individual photocatalysts with the same wt. of components (WO3 and BiOBr). In addn., when MO or 4-CP acts as the target pollutant, the BiOBr/WO3 p-n heterojunction with a molar ratio of 1/1 still exhibits excellent photocatalytic performance. Furthermore, the recycling expt. confirms that the BiOBr/WO3 p-n heterojunction is essentially stable during the photocatalytic process. The enhanced photocatalytic activity of the BiOBr/WO3 p-n heterojunction is predominantly attributed to the efficient sepn. of photogenerated electrons and holes. The photogenerated holes (h+) and superoxide radical anions ( .O2-) have been found to be the primary reactive species responsible for the nearly complete mineralization of RhB dye in water.
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    Rafiee, E.; Noori, E.; Zinatizadeh, A. A.; Zanganeh, H. Photocatalytic degradation of phenol using a new developed TiO2/graphene/heteropoly acid nanocomposite: Synthesis, characterization and process optimization. RSC Adv. 2016, 6, 96554– 96562,  DOI: 10.1039/c6ra09897e
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    Photocatalytic degradation of phenol using a new developed TiO2/graphene/heteropoly acid nanocomposite: synthesis, characterization and process optimization
    Rafiee, Ezzat; Noori, Elham; Zinatizadeh, Ali Akbar; Zanganeh, Hadis
    RSC Advances (2016), 6 (99), 96554-96562CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)
    A TiO2/graphene (TiO2/Gr) nanocomposite was synthesized using bottom-up assembly. The TiO2/Gr nanocomposite was modified with 12-tungstophosphoric acid (H3PW12O40, TiO2/Gr/xPW). The structural properties of the nanocomposite have been characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), SEM (SEM), zeta potential, Brunauer-Emmett-Teller (BET), Fourier transform IR (FTIR), and diffuse reflectance spectra (DRS). Results of DRS showed a visible shift when the TiO2/Gr nanocomposite was modified with PW. The photocatalytic activity of the synthesized nanocomposite was measured by the degrdn. of phenol under visible and UV light irradn. The effects of initial concn. of phenol, concn. of photocatalyst, reaction time, loading of PW and initial pH on phenol removal efficiency in batch expts. were investigated. The results showed that the degrdn. efficiency is decreased with an increase in initial concn. of phenol from 50 to 150 mg L-1 while pH did not show a significant impact. As a result, TiO2/Gr/xPW exhibited a higher visible-light photocatalytic activity in comparison with TiO2/Gr and pure TiO2 with the max. degrdn. efficiency of 91, 68, and 15%, resp. This clearly shows that among the modified composites, the catalyst with 20 wt% PW showed max. visible shift. COD measurements under optimum conditions showed 78% phenol mineralization. And also, the reusability of the catalyst was proved when 80% degrdn. could be achieved after three consecutive batches.
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    Ali, M. H. H.; Al-qahtani, K. M.; El-sayed, S. M. Enhancing photodegradation of 2,4,6 trichlorophenol and organic pollutants in industrial effluents using nanocomposite of TiO2 doped with reduced graphene oxide. Egypt. J. Aquat. Res. 2019, 45, 321– 328,  DOI: 10.1016/j.ejar.2019.08.003
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    Ali, H. R. Photocoupling of Ag3PO4-Ag2CO3 with molecularly imprinted polymer for enhanced removal of phenol under solar light: Application of taguchi method. Int. J. Appl. Eng. Res. 2017, 12, 3353– 3359
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    Abd El Salam, H. M.; Younis, S. A.; Ali, H. R.; Zaki, T. Statistical modeling and optimization of phenol adsorption from water by modified Cu3(BTC)2: Kinetic, isotherm, and thermodynamic analysis. Microporous Mesoporous Mater. 2017, 241, 210– 217,  DOI: 10.1016/j.micromeso.2016.12.010
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    Statistical modeling and optimization of phenol adsorption from water by modified Cu3(BTC)2: Kinetic, isotherm, and thermodynamic analysis
    Abd El Salam, H. M.; Younis, S. A.; Ali, H. R.; Zaki, T.
    Microporous and Mesoporous Materials (2017), 241 (), 210-217CODEN: MIMMFJ; ISSN:1387-1811. (Elsevier B.V.)
    Cu3(BTC)2 and Ni1.5Cu1.5(BTC)2 were synthesized in the presence of microwave irradn. The morphol. and the structure of the prepd. MOFs were characterized by XRD, TEM, TGA, FTIR, Raman, and nitrogen adsorption/desorption methods. The adsorption activities of the samples towards the phenols from aq. solns. were achieved including kinetic and equil. approaches with different nonlinear models for modeling. The exptl. data clarified that the adsorption of phenols on Cu3(BTC)2 and Ni1.5Cu1.5(BTC)2 had been processed via a pore-filling mechanism. Thermodn. parameters were also detd. Also, a three levels-four factor half-factorial design was successfully employed for exptl. design and anal. of the results through response surface methodol. (RSM). The significance of the independent variables was tested and optimized by the anal. of variance (ANOVA) and t-test statistics. The optimum pH, adsorbent dose, and temp. are 5.0, 1 g/l, and 30°, resp., for both samples. Under these conditions, the predicted removal efficiency of 50 mg/l phenols is 71.32% (35.65 mg/g) and 78.95% (39.47 mg/g), resp.
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    Rodriguez, A. F. R.; Coaquira, J. A. H.; Morales, M. A. Synthesis, characterization and magnetic properties of polymer-Fe3O4 nanocomposite. Spectrochim. Acta, Part A 2013, 100, 101– 103,  DOI: 10.1016/j.saa.2012.02.081
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    Synthesis, characterization and magnetic properties of polymer-Fe3O4 nanocomposite
    Rodriguez, A. F. R.; Coaquira, J. A. H.; Morales, M. A.; Faria, F. S. E. D. V.; Cunha, R. M.; Santos, J. G.; Silveira, L. B.; Candela, D. R. S.; Baggio-Saitovitch, E. M.; Rabelo, D.; Azevedo, R. B.; Morais, P. C.
    Spectrochimica Acta, Part A: Molecular and Biomolecular Spectroscopy (2013), 100 (), 101-103CODEN: SAMCAS; ISSN:1386-1425. (Elsevier B.V.)
    The chem. stability of magnetic particles is of great importance for their applications in medicine and biotechnol. The most challenging problem in physics of disordered systems of magnetic nanoparticles is the investigation of their dynamic properties. The chem. copptn. process was used to synthesize spherical magnetite nanoparticles of 14 nm. The as-prepd. magnetite nanoparticles were aged in the matrix. Magnetic properties and aging effect were studied by Moessbauer spectroscopy at temps. ranging from 77-300 K, and x-ray diffraction. At room temp., the Moessbauer spectrum showed superparamagnetic behavior of the particles, while well-defined sextets were obsd. at 77 K, indicating a blocked regime. The superparamagnetic magnetite nanoparticles can be used as microbead biosensors.
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    Mäkelä, M. Experimental design and response surface methodology in energy applications: A tutorial review. Energy Convers. Manage. 2017, 151, 630– 640,  DOI: 10.1016/j.enconman.2017.09.021
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    Tebbouche, L.; Hank, D.; Zeboudj, S.; Namane, A.; Hellal, A. Evaluation of the phenol biodegradation byAspergillus niger: application of full factorial design methodology. Desalin. Water Treat. 2016, 57, 6124– 6130,  DOI: 10.1080/19443994.2015.1053991
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    Evaluation of the phenol biodegradation by Aspergillus niger: application of full factorial design methodology
    Tebbouche, Latifa; Hank, Dalila; Zeboudj, Saliha; Namane, Abdelkader; Hellal, Amina
    Desalination and Water Treatment (2016), 57 (13), 6124-6130CODEN: DWTSAW; ISSN:1944-3986. (Taylor & Francis Ltd.)
    The ability of Aspergillus niger to degrade phenol in an aerobic batch culture was investigated under different parameters such as initial concn. of phenol, pH, and temp. The results showed that A. niger can grow using phenol as the sole source of carbon. A high concn. of phenol (1,000 mg/L) was completely degraded after 140 h at T = 30°C and pH 5.5. The main and the interactive effects of initial phenol concn. (200-1,000 mg/L), pH (2.5-8.5), and temp. (25-35°C) on the biodegrdn. of phenol were studied in this work. A full factorial design 23 was used to det. the optimum conditions for the phenol biodegrdn. process. The max. amt. of degraded phenol was 1.32 mg/h, achieved at 200 mg/L of initial phenol concn., pH 8.5, and T = 35°C.
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    Choquette-Labbé, M.; Shewa, W.; Lalman, J.; Shanmugam, S. Photocatalytic degradation of phenol and phenol derivatives using a Nano-TiO2 catalyst: Integrating quantitative and qualitative factors using response surface methodology. Water (Switzerland) 2014, 6, 1785– 1806,  DOI: 10.3390/w6061785
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    38
    Photocatalytic degradation of phenol and phenol derivatives using a nano-TiO2 catalyst: integrating quantitative and qualitative factors using response surface methodology
    Choquette-Labbe, Marissa; Shewa, Wudneh A.; Lalman, Jerald A.; Shanmugam, Saravanan R.
    Water (Basel, Switzerland) (2014), 6 (6), 1785-1806, 22 pp.CODEN: WATEGH; ISSN:2073-4441. (MDPI AG)
    Due to the toxicity effects and endocrine disrupting properties of phenolic compds., their removal from water and wastewater has gained widespread global attention. In this study, the photocatalytic degrdn. of phenolic compds. in the presence of titanium dioxide (TiO2) nano-particles and UV light was investigated. A full factorial design consisting of three factors at three levels was used to examine the effect of particle size, temp. and reactant type on the apparent degrdn. rate const. The individual effect of TiO2 particle size (5, 10 and 32 nm), temp. (23, 30 and 37 °C) and reactant type (phenol, o-cresol and m-cresol) on the apparent degrdn. rate const. was detd. A regression model was developed to relate the apparent degrdn. const. to the various factors. The largest photocatalytic activity was obsd. at an optimum TiO2 particle size of 10 nm for all reactants. The apparent degrdn. rate const. trend was as follows: o-cresol > m-cresol > phenol. The ANOVA data indicated no significant interaction between the exptl. factors. The lowest activation energy was obsd. for o-cresol degrdn. using 5-nm TiO2 particles. A max. degrdn. rate const. of 0.0138 min-1 was recorded for o-cresol at 37 °C and a TiO2 particle size of 13 nm at a D-optimality value of approx. 0.98. The response model adequately related the apparent degrdn. rate const. to the factors within the range of factors under consideration.
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    Hydrothermal synthesis and characterization of WO3 nanostructures: Effect of reaction time
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    Materials Research Express (2020), 7 (1), 015911CODEN: MREAC3; ISSN:2053-1591. (IOP Publishing Ltd.)
    1-D and 2-D WO3 nanostructures were successfully prepd. by hydrothermal technique as a low temp., low cost, compatible with the environment, and powerful method with controllability of particle size, shape, and stoichiometry. The effect of hydrothermal duration time was studied to investigate morphol., structural and optical properties and to propose the possible growth mechanisms of WO3 nanostructures. X-ray diffraction (XRD), Field emission SEM(FESEM), Fourier transform IR spectroscopy(FTIR), and Diffuse reflectance spectroscopy(DRS) analyses were done on the samples synthesized at different hydrothermal duration times of 6, 12, 24, and 36 h. The results indicated that the morphol. evolutions of nanostructures strongly depend on hydrothermal duration time and concn. of capping agents. Two crystal phase transitions in accordance with the morphol. evolution were also obsd. The absorption edge of the samples exhibited a blue- and then red-shift by increasing the reaction time. The bandgaps of the samples were almost independent of the reaction time and the samples were transparent in a wide range of the visible light region. So, they can be regarded as excellent candidates for optoelectronic devices.
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    Younis, S. A.; Motawea, E. A.; Moustafa, Y. M.; Lee, J.; Kim, K.-H. A strategy for the efficient removal of chlorophenols in petrochemical wastewater by organophilic and aminated silica@alginate microbeads: Taguchi optimization and isotherm modeling based on partition coefficient. J. Hazard. Mater. 2020, 397, 122792,  DOI: 10.1016/j.jhazmat.2020.122792
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    A strategy for the efficient removal of chlorophenols in petrochemical wastewater by organophilic and aminated silica@alginate microbeads: Taguchi optimization and isotherm modeling based on partition coefficient
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    Journal of Hazardous Materials (2020), 397 (), 122792CODEN: JHMAD9; ISSN:0304-3894. (Elsevier B.V.)
    Through in situ encapsulation of cetyltrimethylammonium bromide (CTAB) and urea-functionalized SiO2 nanoparticles in alginate hydrogel, two types of new functionalized microbeads, CTAB-SiO2@alginate (organophilic) and urea-SiO2@alginate (aminated), were produced. Their adsorption behavior toward multiple chlorophenols (CPs: e.g., 4-chlorophenol (MCP), 2,4-dichlorophenol (DCP), and 2,4,6-trichlorophenol (TCP)) in petrochem. wastewater was assessed with the aid of Taguchi's L9 orthogonal array at three levels. In terms of the partition coeff. (PC: μmol/g·μM (or L/g)), the use of three-parameter models (hybrid Langmuir-Freundlich and Redlich-Peterson) yielded the best fit (R2 ≈ 1). Furthermore, the performance evaluation in terms of PC metric indicated that CTAB-SiO2@alginate (7.85 L/g) was better to treat total CPs than urea-modified SiO2@alginate microbeads (3.83 L/g). The enhanced performance of the former reflects the significant contribution of CTAB functionality (sp2 carbon tail and quaternary amine (N+) cationic head sites) for accelerating uptake of mol. (or suspended) and ionizable CPs mols. (e.g., with the aid of salting-out effect at a high initial CPs concn. and salinity) via hydrophobic/electrostatic interactions. The high performance of the CTAB-SiO2@alginate was demonstrated against petroleum hydrocarbons, CPs, and phenol contaminants using real petrochem. wastewater (up to three reusable cycles).
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    Bakr, A.-S. A.; Moustafa, Y. M.; Motawea, E. A.; Yehia, M. M.; Khalil, M. M. H. Removal of ferrous ions from their aqueous solutions onto NiFe2O4-alginate composite beads. J. Environ. Chem. Eng. 2015, 3, 1486– 1496,  DOI: 10.1016/j.jece.2015.05.020
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    Removal of ferrous ions from their aqueous solutions onto NiFe2O4-alginate composite beads
    Bakr, Al-Sayed A.; Moustafa, Yasser M.; Motawea, Eman A.; Yehia, Mohamed M.; Khalil, Mostafa M. H.
    Journal of Environmental Chemical Engineering (2015), 3 (3), 1486-1496CODEN: JECEBG; ISSN:2213-3437. (Elsevier Ltd.)
    This paper deals with the exptl. investigation related to the removal of Fe(II) from aq. solns. by synthesized NiFe2O4-alginate composite beads and nano-NiFe2O4 at different temps. and const. stirring rate of 150 rpm. The adsorption process was optimized by response surface methodol. RSM/CCD and studied as a function of contact time, pH and adsorbent mass. The results revealed that the max. adsorption capacities were 158.4 and 69.8 mg/g for NiFe2O4-alginate composite beads and nano-NiFe2O4 when the initial Fe(II) concns. were 350 and 250 mg/L at 318 K, resp. The kinetics of Fe(II) removal by synthesized materials were best described by the pseudo-second-order model and the adsorption isotherms were seen to be consistent with Langmuir's adsorption isotherm. Also, the thermodn. parameters of the adsorption (Gibbs free energy, entropy, and enthalpy) were discussed. Therefore, the results demonstrated that the adsorption process was spontaneous and endothermic and the synthesized NiFe2O4-alginate composite beads material could act as a highly-effective nano-adsorbent of Fe(II) removal more than nano-NiFe2O4 from the aq. solns.
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  1. Iftekhar Ahmad, Mohammad Muneer, Abdelrahman S. Khder, Saleh A. Ahmed. Novel Type-II Heterojunction Binary Composite (CdS/AgI) with Outstanding Visible Light-Driven Photocatalytic Performances toward Methyl Orange and Tetracycline Hydrochloride. ACS Omega 2023, 8 (25) , 22708-22720. https://doi.org/10.1021/acsomega.3c01517
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  3. Xiaolong Wu, Jing Xu, Pengfei Zhu, Mei Liu, Ming Duan, Shasha Zhang. High performance visible light response of a Z-type Bi 2 WO 6 /BiOBr/RGO heterojunction photocatalyst for the degradation of norfloxacin. Dalton Transactions 2022, 51 (47) , 17994-18009. https://doi.org/10.1039/D2DT03038A
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  • Abstract

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    Figure 1

    Figure 1. XRD spectra of the synthesized WO3, ZnO, BiOBr, BiOBr/WO3, BiOBr/ZnO, and BiOBr/WO3/ZnO.

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    Figure 2

    Figure 2. FTIR patterns of WO3, ZnO, BiOBr, BiOBr/WO3, BiOBr/ZnO, and BiOBr/WO3/ZnO.

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    Figure 3

    Figure 3. XPS spectrum of BiOBr/ZnO/WO3: (a) survey spectrum, (b) Bi 4f spectrum, (c) Br 3d spectrum, (d) W 4f spectrum, (e) Zn 2p spectrum, and (f) O 1s spectrum.

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    Figure 4

    Figure 4. Optical properties of the prepared photocatalysts: (A) UV–vis DRS spectra, (B) Taucʼs plots [(αhv)2 vs Hv] for WO3 and ZnO photocatalysts, (C) Taucʼs plots [(αhv)1/2vs Hv] for BiOBr, BiOBr/ZnO, BiOBr/WO3, and BiOBr/ZnO/WO3, and (D) PL spectra.

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    Figure 5

    Figure 5. Photoelectrochemical measurements: (a) Nyquist plots of EIS, (b) EIS Bode plots, and (c) LSV curves for BiOBr and BiOBr/ZnO/WO3.

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    Figure 6

    Figure 6. SEM images of the synthesized (A) ZnO NPs, (B) WO3NPs, (C) BiOBr NPs, and (D) BiOBr/ZnO/WO3 nanocomposites, TEM images of (E) ZnO NPs, (F) WO3NPs, (G) BiOBr NPs, and (H) BiOBr/ZnO/WO3, and (I) EDX spectra of BiOBr/ZnO/WO3.

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    Figure 7

    Figure 7. (A) Degradation capacity of phenol vs time with different catalysts, (B) degradation percentage at an equilibrium time of 300 min, and (C) kinetics of the photodegradation of phenol using different photocatalysts at the initial concentration of 50 mg/L, dose of 0.05 g/0.03 L, and a pH of 6.

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    Figure 8

    Figure 8. (A) 3D diagram of the combined effect of pH and the initial concentration of phenol for the degradation efficiency of phenol at a BiOBr/ZnO/WO3 dose of 0.08 g/0.03 L, (B) 3D diagram of the combined effect of pH and dose of BiOBr/ZnO/WO3 for the degradation efficiency of phenol at an initial phenol concentration of 10 mg L–1 and a contact time of 300 min, (C) proposed photocatalytic degradation pathway of phenol under visible light irradiation, and (D) total organic carbon (TOC) content in phenol suspension vs visible light irradiation time after degradation with BiOBr/ZnO/WO3 at the initial phenol concentration of 50 mg/L, catalyst dose of 0.08 g/0.03 L, and a pH of 9.

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    Figure 9

    Figure 9. A) Predicted values vs actual values of phenol degradation, (B) studentized residuals vs run order of phenol degradation, (C) normal probability plot of regular residuals for phenol degradation, and (D) phenol Pareto graphic analysis.

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    Figure 10

    Figure 10. (A) Main effects of different parameters on phenol deterioration by BiOBr/ZnO/WO3 and (B) interaction effects of different parameters on phenol deterioration by BiOBr/ZnO/WO3.

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    Figure 11

    Figure 11. (A) Effect of scavengers on the photodegradation efficiency of phenol, (B) suggested photocatalytic degradation mechanism of phenol with BiOBr/WO3/ZnO, (C) photocatalytic stability of BiOBr/WO3/ZnO toward phenol degradation, (D) photocatalytic system efficiency for the degradation of phenol and malachite green at the initial concentration, 50 mg/L; BiOBr/WO3/ZnO and TiO2 P25 dose, 0.05 g/0.03 L; and pH, 6, and (E) realistic application of refinery petroleum wastewater.

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  • References

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      Janotti, Anderson; Van de Walle, Chris G.
      Reports on Progress in Physics (2009), 72 (12), 126501/1-126501/29CODEN: RPPHAG; ISSN:0034-4885. (Institute of Physics Publishing)
      A review. In the past ten years we have witnessed a revival of, and subsequent rapid expansion in, the research on zinc oxide (ZnO) as a semiconductor. Being initially considered as a substrate for GaN and related alloys, the availability of high-quality large bulk single crystals, the strong luminescence demonstrated in optically pumped lasers and the prospects of gaining control over its elec. cond. have led a large no. of groups to turn their research for electronic and photonic devices to ZnO in its own right. The high electron mobility, high thermal cond., wide and direct band gap and large exciton binding energy make ZnO suitable for a wide range of devices, including transparent thin-film transistors, photodetectors, light-emitting diodes and laser diodes that operate in the blue and UV region of the spectrum. In spite of the recent rapid developments, controlling the elec. cond. of ZnO has remained a major challenge. While a no. of research groups have reported achieving p-type ZnO, there are still problems concerning the reproducibility of the results and the stability of the p-type cond. Even the cause of the commonly obsd. unintentional n-type cond. in as-grown ZnO is still under debate. One approach to address these issues consists of growing high-quality single cryst. bulk and thin films in which the concns. of impurities and intrinsic defects are controlled. In this review we discuss the status of ZnO as a semiconductor. We first discuss the growth of bulk and epitaxial films, growth conditions and their influence on the incorporation of native defects and impurities. We then present the theory of doping and native defects in ZnO based on d.-functional calcns., discussing the stability and electronic structure of native point defects and impurities and their influence on the elec. cond. and optical properties of ZnO. We pay special attention to the possible causes of the unintentional n-type cond., emphasize the role of impurities, critically review the current status of p-type doping and address possible routes to controlling the elec. cond. in ZnO. Finally, we discuss band-gap engineering using MgZnO and CdZnO alloys.
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    6. 6
      Wang, S. L.; Zhu, Y.; Luo, X. 2D WC/WO3Heterogeneous Hybrid for Photocatalytic Decomposition of Organic Compounds with Vis-NIR Light. Adv. Funct. Mater. 2018, 28, 1705357,  DOI: 10.1002/adfm.201705357
      There is no corresponding record for this reference.
    7. 7
      Xia, J.; Di, J.; Yin, S. Solvothermal synthesis and enhanced visible-light photocatalytic decontamination of bisphenol A (BPA) by g-C3N4/BiOBr heterojunctions. Mater. Sci. Semicond. Process. 2014, 24, 96– 103,  DOI: 10.1016/j.mssp.2014.02.036
      7
      Solvothermal synthesis and enhanced visible-light photocatalytic decontamination of bisphenol A (BPA) by g-C3N4/BiOBr heterojunctions
      Xia, Jiexiang; Di, Jun; Yin, Sheng; Li, Huaming; Xu, Hui; Xu, Li; Shu, Huoming; He, Minqing
      Materials Science in Semiconductor Processing (2014), 24 (), 96-103CODEN: MSSPFQ; ISSN:1369-8001. (Elsevier Ltd.)
      Graphite-like C3N4 hybridized BiOBr photocatalysts have been synthesized through an EG-assisted solvothermal process in the presence of reactable ionic liq. 1-hexadecyl-3-methylimidazolium bromide ([C16mim]Br). The as-prepd. samples were characterized by X-ray diffraction (XRD), Fourier transform IR spectroscopy (FT-IR), SEM (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), diffuse reflectance spectroscopy (DRS), photoluminescence (PL) spectroscopy and photocurrent. The g-C3N4/BiOBr photocatalysts showed high efficiency for the degrdn. of bisphenol A (BPA) and rhodamine B (RhB) under visible light irradn. The results assumed that a loading amt. of g-C3N4 over BiOBr lead to an increase of the photocatalytic activity under visible light irradn. and showed much higher photocatalytic activity than that of pure BiOBr sample. The enhanced photocatalytic performance could be attributed to the high sepn. efficiency of the photogenerated electron-hole pairs. The trapping expts. of radicals showed that hole was the main reactive species for the photocatalytic degrdn. of RhB. A possible mechanism of g-C3N4/BiOBr on the enhancement of visible light performance was proposed.
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    8. 8
      Motawea, E. A.; Ali, H. R. Exploitation of Heterostructure Photocatalyst Impregnated Alginate Beads for Enhanced Removal of Methyl Orange under Solar Light. Petrol. Petrochem. Eng. J. 2018, 2, 1– 10,  DOI: 10.23880/ppej-16000180
      There is no corresponding record for this reference.
    9. 9
      Berger, S.; Tsuchiya, H.; Ghicov, A.; Schmuki, P. High photocurrent conversion efficiency in self-organized porous WO3. Appl. Phys. Lett. 2006, 88, 203119,  DOI: 10.1063/1.2206696
      9
      High photocurrent conversion efficiency in self-organized porous WO3
      Berger, S.; Tsuchiya, H.; Ghicov, A.; Schmuki, P.
      Applied Physics Letters (2006), 88 (20), 203119/1-203119/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
      Self-organized porous structures of WO3 were grown on W by an anodic oxidn., and their photoelectrochem. properties were characterized. The porous WO3 layers show a regular morphol. with av. pore sizes of approx. 70 nm and a pore wall thickness of approx. 10 nm. As formed layers show an amorphous structure but the layers can be altered to a cryst. monoclinic structure by thermal annealing. The annealed porous WO3 layers show a very high specific photocurrent conversion efficiency.
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    10. 10
      Momeni, M. M.; Hakimian, M.; Kazempour, A. In-Situ Manganese Doping of TiO2 Nanostructures via Single-Step Electrochemical Anodizing of Titanium in an Electrolyte Containing Potassium Permanganate: A Good Visible-Light Photocatalyst. Ceram. Int. 2015, 41, 13692,  DOI: 10.1016/j.ceramint.2015.07.158
      10
      In-situ manganese doping of TiO2 nanostructures via single-step electrochemical anodizing of titanium in an electrolyte containing potassium permanganate: A good visible-light photocatalyst
      Momeni, Mohamad Mohsen; Hakimian, Mohaddeseh; Kazempour, Ali
      Ceramics International (2015), 41 (10_Part_A), 13692-13701CODEN: CINNDH; ISSN:0272-8842. (Elsevier Ltd.)
      It is desirable to induce remarkable red-shift in the optical absorption edges of TiO2 so that this class of low-cost materials can be used as optimum photocatalysts beyond the UV range. This work reports on the room-temp. electrochem. fabrication of manganese-doped TiO2 nanotubes (MnTNT) and the investigation of their optical property and photocatalytic activity. TiO2 nanotubes (TNT) were doped with different concns. of manganese and prepd. nanostructures have been characterized using different techniques for analyzing their structure, morphol., compn., band gap and optical absorption property. Characterization of the as-prepd. samples indicated that dopant concn. in anodizing soln. significantly influenced the morphol., structure, photoabsorption and photocatalytic activity of fabricated films. The optical absorption range of TiO2 film gradually expands and shifts to the red with increasing dosages and band gap of the TiO2 films were reduced. Moreover, the photocatalytic activity of the TiO2 films for removal of methylene blue was enhanced by doping with an appropriate amt. of manganese. The sample MnTNT4 exhibited better photocatalytic activity than the undoped TNT and MnTNT fabricated using other manganese concns.
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    11. 11
      Momeni, M. M.; Nazari, Z. Preparation of TiO2 and WO3-TiO2 nanotubes decorated with PbO nanoparticles by chemical bath deposition process: A stable and efficient photo catalyst. Ceram. Int. 2016, 42, 8691– 8697,  DOI: 10.1016/j.ceramint.2016.02.103
      11
      Preparation of TiO2 and WO3-TiO2 nanotubes decorated with PbO nanoparticles by chemical bath deposition process: A stable and efficient photo catalyst
      Momeni, Mohamad Mohsen; Nazari, Zohre
      Ceramics International (2016), 42 (7), 8691-8697CODEN: CINNDH; ISSN:0272-8842. (Elsevier Ltd.)
      We present a new method for synthesizing Pb/TNTs and Pb/WTNTs composite with good photo catalytic activity. TiO2 nanotube (TNTs) and WO3-TiO2 nanotubes (WTNTs) were prepd. by one-step electrochem. anodizing method and lead has been successfully deposited on these nanotubes by chem. bath deposition process. The morphol., crystal structure, elemental compn. and light absorption capability of the prepd. samples were evaluated using various characterization techniques. Results showed that the fabricated films have highly ordered nanotube morphol. Diffuse reflectance spectra showed an increase in the visible absorption relative to bare samples. The degrdn. of methylene blue was used as a model reaction to evaluate the photo catalytic activity of these novel visible-light-responsive photo catalysts. Results showed that the photo catalytic activity of bare WTNTs samples is higher than that with undoped TNTs sample. Compared with unmodified TNTs and WTNTs, the Pb/TNTs and Pb/WTNTs samples exhibited enhanced photo catalytic activity in the degrdn. of methylene blue. The sample Pb/WTNTs exhibited better photo catalytic activity than other samples. Also prepd. photo catalysts showed good stability and could be recycled several times without significant loss of their activity. This work provides an insight in designing and synthesizing new WTNTs-based hybrid materials for effective visible light-activated photo catalysis. Since Pb/TNTs and Pb/WTNTs electrodes can be easily removed and replaced after the photo catalytic reaction, avoiding the filtration step after photoreaction or the immobilizing process required for photo catalyst particles, the operation in the photo-reactor becomes much easier from an engineering point of view. The catalysts prepd. in this study exhibit industrially relevant interests due to the low cost and high photo catalytic activity.
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    12. 12
      Zeng, Q.; Li, J.; Bai, J.; Li, X.; Xia, L.; Zhou, B. Preparation of vertically aligned WO3 nanoplate array films based on peroxotungstate reduction reaction and their excellent photoelectrocatalytic performance. Appl. Catal., B 2017, 202, 388– 396,  DOI: 10.1016/j.apcatb.2016.09.045
      12
      Preparation of vertically aligned WO3 nanoplate array films based on peroxotungstate reduction reaction and their excellent photoelectrocatalytic performance
      Zeng, Qingyi; Li, Jinhua; Bai, Jing; Li, Xuejin; Xia, Ligang; Zhou, Baoxue
      Applied Catalysis, B: Environmental (2017), 202 (), 388-396CODEN: ACBEE3; ISSN:0926-3373. (Elsevier B.V.)
      Here, the authors developed a novel, facile, controllable and scalable method based on peroxotungstate redn. reaction to prep. vertically aligned WO3 nanoplate array (NPA) films with preferentially exposed highly reactive (002) facets used in efficient photoelectrocatalytic (PEC) applications. In this method, a slow and controllable redn. of peroxotungstates by ethanol was used, which was the crit. step to ensure the uniform and ordered synthesis of orthorhombic WO3·H2O NPA films which assembled directly on F-doped tin oxide substrates under the capping effect of oxalate, and subsequently WO3·H2O NPA films were converted into monoclinic WO3 NPA films by calcination. The effects of synthetic temp. and time, and the concn. of oxalate on the cryst. phase and morphol. of the WO3·H2O films were studied systematically. The WO3 NPA film annealed at an optimized temp. of 500° exhibited the highest water splitting c.d. of ∼1.42 mA/cm2 at 1.23 V vs. RHE in 0.1M Na2SO4 under AM 1.5 G illumination. It was further improved by decorating with a Co-Pi co-catalyst, which achieved a more stable c.d. of ∼1.95 mA/cm2 with an incident photon-to-current conversion efficiency of ∼51% at 400 nm. The WO3 NPA film also showed excellent stability and efficiency (rate const. ∼0.8127 h-1) for PEC degrdn. of methylene blue.
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    13. 13
      Zeng, X.; Wang, Z.; Wang, G. Highly dispersed TiO2 nanocrystals and WO3 nanorods on reduced graphene oxide: Z-scheme photocatalysis system for accelerated photocatalytic water disinfection. Appl. Catal., B 2017, 218, 163– 173,  DOI: 10.1016/j.apcatb.2017.06.055
      13
      Highly dispersed TiO2 nanocrystals and WO3 nanorods on reduced graphene oxide: Z-scheme photocatalysis system for accelerated photocatalytic water disinfection
      Zeng, Xiangkang; Wang, Zhouyou; Wang, Gen; Gengenbach, Thomas R.; McCarthy, David T.; Deletic, Ana; Yu, Jiaguo; Zhang, Xiwang
      Applied Catalysis, B: Environmental (2017), 218 (), 163-173CODEN: ACBEE3; ISSN:0926-3373. (Elsevier B.V.)
      Coupling TiO2 with WO3 to develop photocatalytic heterojunctions is one of the most widely used strategies to realize their superior photoactivity. However, the interfacial charge transfer in these heterojunctions is not efficient to achieve an optimized activity. For the first time, the present study reports a facile hydrolysis-hydrothermal approach, whereby ultradispersed TiO2 nanocrystals and WO3 nanorods are concurrently anchored onto reduced graphene oxide (rGO) and formed a novel Z-scheme heterojunction photocatalyst TiO2/rGO/WO3 (TRW). Transmission electron microscope (TEM), X-ray diffraction (XRD), XPS, UV-vis diffuse reflectance spectroscopy (UV-vis DRS) and photoluminescence spectra (PL) are employed to characterize TRW. Control expts. indicate that, in the synthesis process, glucose and the byproduct sodium chloride from the hydrolysis reactions are crit. for forming highly dispersed and uniform-sized TiO2 nanocrystals and WO3 nanorods. Compared with TiO2/WO3 nanocomposites, TRW shows enhanced activity for bacterial inactivation under simulated solar light. As confirmed by electrochem. characterizations and the reactive oxygen species, rGO in TRW suppresses the recombination of electron-hole pairs and boosts the O2 redn. reactions during photocatalytic process. Z-scheme electron transfer in TRW is proposed based on surface redox reactions and XPS anal. after light irradn. This study could provide a new clue for designing graphene-based heterojunction photocatalysts for environmental applications.
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    14. 14
      Momeni, M. M.; Ghayeb, Y.; Davarzadeh, M. Electrochemical construction of different titania-tungsten trioxide nanotubular composite and their photocatalytic activity for pollutant degradation: a recyclable photocatalysts. J. Mater. Sci.: Mater. Electron. 2015, 26, 1560– 1567,  DOI: 10.1007/s10854-014-2575-x
      14
      Electrochemical construction of different titania-tungsten trioxide nanotubular composite and their photocatalytic activity for pollutant degradation: a recyclable photocatalysts
      Momeni, Mohamad Mohsen; Ghayeb, Yousef; Davarzadeh, Mahsa
      Journal of Materials Science: Materials in Electronics (2015), 26 (3), 1560-1567CODEN: JSMEEV; ISSN:0957-4522. (Springer)
      Different TiO2-WO3 nanotubular (TWNs) electrodes were fabricated by in situ anodization of titanium in a single-step process using sodium tungstate as the tungsten source. The morphol. and structure were characterized by field-emission SEM, X-ray diffraction and energy dispersive X-ray spectroscopy. Optical properties were investigated by ultra UV-Vis diffuse reflectance spectra. The resulting TWNs showed a tube diam. of 80-110 nm, wall thickness of 20-40 nm and tube lengths in the range of 7-8 μm. The visible light photocatalytic activity of the TWNs electrodes was evaluated by measuring the degrdn. of methylene blue dye under simulated sunlight conditions and compared with photo-catalytic activity of pure TiO2 nanotubes (TNs). The results showed that TWNs electrodes have excellent photo-catalytic performance. The sample C, that formed by anodic oxidn. in a DMSO electrolyte contg. 4 g/l sodium tungstate, exhibited better photo-catalytic activity than the TNs and TWNs fabricated using other W concns. under Xe illumination. The anodization process developed in this study is facile, reproducible, and inexpensive, and can be easily scaled up, thereby pioneering the fabrication of high performance photo-catalysts with promising environmental applications.
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    15. 15
      Momeni, M. M.; Ghayeb, Y.; Ghonchegi, Z. Fabrication and characterization of copper doped TiO2 nanotube arrays by in situ electrochemical method as efficient visible-light photocatalyst. Ceram. Int. 2015, 41, 8735– 8741,  DOI: 10.1016/j.ceramint.2015.03.094
      15
      Fabrication and characterization of copper doped TiO2 nanotube arrays by in situ electrochemical method as efficient visible-light photocatalyst
      Momeni, Mohamad Mohsen; Ghayeb, Yousef; Ghonchegi, Zohre
      Ceramics International (2015), 41 (7), 8735-8741CODEN: CINNDH; ISSN:0272-8842. (Elsevier Ltd.)
      Highly ordered copper doped TiO2 nanotube arrays (CuTiO2NTs) thin-film were prepd. in an aq. soln. contg. NH4F and different concns. of copper nitrate via the electrochem. oxidn. of titanium substrates. The resulting nanotubes were characterized by FE-SEM, XRD, XPS and EDX. The CuTiO2NTs showed a tube diam. of 40-90 nm and wall thickness of 20-30 nm. Diffuse reflectance spectra showed a shift toward longer wavelengths relative to pure TiO2 nanotubes (TiO2NTs). The visible light photo-catalytic activity of the CuTiO2NTs electrodes was evaluated by the removal of methylene blue (MB) dye and the prodn. of hydrogen. The results showed that CuTiO2NTs samples exhibited better photo-catalytic activity than the TiO2NTs. This work demonstrated a feasible and simple anodization method to fabricate an effective, reproducible, and inexpensive visible-light-driven photo-catalyst for hydrogen evolution and environmental applications.
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    16. 16
      Lei, R.; Ni, H.; Chen, R.; Zhang, B.; Zhan, W.; Li, Y. Growth of Fe 2 O 3 /SnO 2 nanobelt arrays on iron foil for efficient photocatalytic degradation of methylene blue. Chem. Phys. Lett. 2017, 673, 1– 6,  DOI: 10.1016/j.cplett.2017.01.052
      16
      Growth of Fe2O3/SnO2 nanobelt arrays on iron foil for efficient photocatalytic degradation of methylene blue
      Lei, Rui; Ni, Hongwei; Chen, Rongsheng; Zhang, Bowei; Zhan, Weiting; Li, Yang
      Chemical Physics Letters (2017), 673 (), 1-6CODEN: CHPLBC; ISSN:0009-2614. (Elsevier B.V.)
      Tin(IV) oxide has been intensively employed in optoelectronic devices due to its excellent elec. and optical properties. But the high recombination rates of the photogenerated electron-hole pairs of SnO2 nanomaterials often results in low photocatalytic efficiency. Herein, we proposed a facile route to prep. a novel Fe2O3/SnO2 heterojunction structure. The nanobelt arrays grown on iron foil naturally form a Schottky-type contact and provide a direct pathway for the photogenerated excitons. Hence, the Fe2O3/SnO2 nanobelt arrays exhibit much improved photocatalytic performance with the degrdn. rate const. on the Fe2O3/SnO2 film of approx. 12 times to that of α-Fe2O3 nanobelt arrays.
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    17. 17
      Tsay, C.-Y.; Fan, K.-S.; Chen, S.-H.; Tsai, C.-H. Preparation and characterization of ZnO transparent semiconductor thin films by sol-gel method. J. Alloys Compd. 2010, 495, 126– 130,  DOI: 10.1016/j.jallcom.2010.01.100
      17
      Preparation and characterization of ZnO transparent semiconductor thin films by sol-gel method
      Tsay, Chien-Yie; Fan, Kai-Shiung; Chen, Sih-Han; Tsai, Chia-Hao
      Journal of Alloys and Compounds (2010), 495 (1), 126-130CODEN: JALCEU; ISSN:0925-8388. (Elsevier B.V.)
      Transparent semiconductor thin films of zinc oxide (ZnO) were deposited onto alkali-free glass substrates by the sol-gel method and spin-coating technique. In this study, authors investigate the influence of the heating rate of the preheating process (4 or 10 °C/min) on the crystn., surface morphol., and optical properties of sol-gel derived ZnO thin films. The ZnO sol was synthesized by dissolving zinc acetate dehydrate in ethanol, and then adding monoethanolamine. The as-coated films were preheated at 300 °C for 10 min and annealed at 500 °C for 1 h in air ambiance. Exptl. results indicate that the heating rate of the preheating process strongly affected the surface morphol. and transparency of ZnO thin film. Specifically, a heating rate of 10 °C/min for the preheating process produces a preferred orientation along the (0 0 2) plane and a high transmittance of 92% at a wavelength of 550 nm. Furthermore, this study reports the fabrication of thin-film transistors (TFTs) with a transparent ZnO active channel layer and evaluates their elec. performance.
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    18. 18
      Sakthivel, S.; Neppolian, B.; Shankar, M. V.; Arabindoo, B.; Palanichamy, M.; Murugesan, V. Solar photocatalytic degradation of azo dye: Comparison of photocatalytic efficiency of ZnO and TiO2. Sol. Energy Mater. Sol. Cells 2003, 77, 65– 82,  DOI: 10.1016/S0927-0248(02)00255-6
      18
      Solar photocatalytic degradation of azo dye: comparison of photocatalytic efficiency of ZnO and TiO2
      Sakthivel, S.; Neppolian, B.; Shankar, M. V.; Arabindoo, B.; Palanichamy, M.; Murugesan, V.
      Solar Energy Materials and Solar Cells (2003), 77 (1), 65-82CODEN: SEMCEQ; ISSN:0927-0248. (Elsevier Science B.V.)
      The photocatalytic activity of com. ZnO powder was investigated and compared with that of Degussa P25 TiO2. Lab. expts. with Acid brown 14 as the model pollutant were carried out to evaluate the performance of both ZnO and TiO2 catalysts. Solar light was used as the energy source for the photocatalytic expts. These catalysts were examd. for surface area, particle size, and crystallinity. The effect of initial dye concn., catalyst loading, irradn. time, pH, adsorption of Acid brown 14 on ZnO and TiO2, intensity of light and comparison of photocatalytic activity with different com. catalysts were studied. The progress of photocatalytic degrdn. of the Acid brown 14 was obsd. by monitoring the change in substrate concn. of the model compd. employing HPLC and measuring the absorbance in UV-Visible spectrophotometer for decolorization. The photodegrdn. rate was detd. for each expt. and the highest values were obsd. for ZnO suggesting that it absorbs large fraction of the solar spectrum and absorption of more light quanta than TiO2. The complete mineralization was confirmed by TOC anal., COD measurement, and estn. of the formation of inorg. ions such as NH4+, NO3-, Cl-, and SO42-.
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    19. 19
      Li, D.; Haneda, H.; Ohashi, N.; Saito, N.; Hishita, S. Morphological reform of ZnO particles induced by coupling with MOx (M=V,W,Ce) and the effects on photocatalytic activity. Thin Solid Films 2005, 486, 20– 23,  DOI: 10.1016/j.tsf.2004.11.237
      19
      Morphological reform of ZnO particles induced by coupling with MOx (M = V,W,Ce) and the effects on photocatalytic activity
      Li, Di; Haneda, Hajime; Ohashi, Naoki; Saito, Noriko; Hishita, Shunichi
      Thin Solid Films (2005), 486 (1-2), 20-23CODEN: THSFAP; ISSN:0040-6090. (Elsevier B.V.)
      Morphol. reform of originally prismatic ZnO particles was obsd. during the coupling process with MOx (M = V,W,Ce) precursor by impregnation. The prismatic morphol. of ZnO particles transferred to sheet shape morphol. during coupling with vanadium oxide, and to rod-like shape morphol. during coupling with cesium oxide, however, no change was obsd. when ZnO was coupled with tungsten oxide. Photocatalytic test indicated that the photocatalytic activity of ZnO was enhanced by coupling with vanadium or tungsten oxide, while suppressed by cesium oxide. VOx-ZnO composite sheets demonstrated the highest photocatalytic activity for acetaldehyde decompn., being higher than that of com. P 25.
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    20. 20
      El-saied, H. A.-a.; Motawea, E. A.-T. Optimization and Adsorption Behavior of Nanostructured NiFe2O4/Poly AMPS Grafted Biopolymer. J. Polym. Environ. 2020, 28, 2335– 2351,  DOI: 10.1007/s10924-020-01774-z
      20
      Optimization and Adsorption Behavior of Nanostructured NiFe2O4/Poly AMPS Grafted Biopolymer
      El-saied, Hend Al-aidy; Motawea, Eman Al-Tohamy
      Journal of Polymers and the Environment (2020), 28 (9), 2335-2351CODEN: JPENFW; ISSN:1572-8919. (Springer)
      Abstr.: By grafting polysaccharides backbone of biopolymer (alginate) on synthetic polymer nanocomposite chains (PAMPS/NiFe2O4) to remove methylene blue and toxic heavy metal (Cu2+) from aq. solns., a superadsorbent was prepd. Using FTIR, TGA, X-ray diffraction, TEM, and SEM studied the structures of native and grafted alginate hydrogels. Adsorption expts. have been optimized using RSM/CCD response surface methodol. and analyzed as a pH soln. and adsorbent dose function. The initial concns. of metal and dye, temp., and contact time were also discussed and isothermal, thermodn. adsorption, and kinetic theor. consts. were calcd. as well. Results revealed that alginate grafted nanocomposite PAMPS/NiFe2O4 enhanced the proportion of methylene blue (MB) color removal up to (98.32%) and metal ion discharge (83%). The optimum cationic dye MB and Cu2+ ions adsorption capability were acquired at pH (5.75 and 4) and temp. (318.15 K) resp. For both MB dye and Cu2+ ions, the pseudo-2nd-order model has effectively defined the adsorption kinetics and the Freundlich model could precisely explain adsorption isotherms than the Cu2+ Langmuir adsorption model, while the adsorption of MB dye showed a greater presence for both Freundlich and Langmuir designs.
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    21. 21
      Lv, J.; Dai, K.; Zhang, J.; Liu, Q.; Liang, C.; Zhu, G. Facile constructing novel 2D porous g-C3N4/BiOBr hybrid with enhanced visible-light-driven photocatalytic activity. Sep. Purif. Technol. 2017, 178, 6– 17,  DOI: 10.1016/j.seppur.2017.01.019
      21
      Facile constructing novel 2D porous g-C3N4/BiOBr hybrid with enhanced visible-light-driven photocatalytic activity
      Lv, Jiali; Dai, Kai; Zhang, Jinfeng; Liu, Qi; Liang, Changhao; Zhu, Guangping
      Separation and Purification Technology (2017), 178 (), 6-17CODEN: SPUTFP; ISSN:1383-5866. (Elsevier B.V.)
      Porous graphitic carbon nitride (Pg-C3N4) nanosheets have been prepd. via thermal decompn., and then novel 2D Pg-C3N4/BiOBr hybrid is designed by a facile hydrothermal process. The as-prepd. Pg-C3N4/BiOBr hybrids are characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM) and UV-visible diffuse reflectance spectroscopy (DRS). The results show that BiOBr tightly composited on the surface of Pg-C3N4. Enhanced electron and hole sepn. efficiency is confirmed by photoluminescence (PL) spectroscopy measurements and the photoelectrochem. evaluation. The photoactivity performance of Pg-C3N4/BiOBr is tested under visible-light irradn., the result shows that coupling semiconductor of Pg-C3N4/BiOBr apparently enhances the photocatalytic activity. An optimal Pg-C3N4 content has been detd. to be 20 wt.%, corresponding to apparent pseudo-first-order rate const. kapp of 0.088 min-1, which is 3.7 times, 4.2 times and 7.3 times as high as that of Pg-C3N4, BiOBr and common g-C3N4, resp. Furthermore, photocatalytic stability and mechanism of enhanced photocatalytic process are also investigated.
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    22. 22
      Huang, W.; Hua, X.; Zhao, Y. Enhancement of visible-light-driven photocatalytic performance of BiOBr nanosheets by Co2+ doping. J. Mater. Sci.: Mater. Electron. 2019, 30, 14967– 14976,  DOI: 10.1007/s10854-019-01869-x
      22
      Enhancement of visible-light-driven photocatalytic performance of BiOBr nanosheets by Co2+ doping
      Huang, Wenmao; Hua, Xin; Zhao, Yaping; Li, Kai; Tang, Liping; Zhou, Man; Cai, Zaisheng
      Journal of Materials Science: Materials in Electronics (2019), 30 (16), 14967-14976CODEN: JSMEEV; ISSN:0957-4522. (Springer)
      In this work, Co2+ modification influence on the visible-light-induced photocatalytic performance of BiOBr was investigated. BiOBr and Co2+-doped BiOBr (Co/BiOBr) nanosheets were fabricated through a facile solvothermal way. The morphol., structure, chem. compn. and optical properties of the photocatalysts were characterized by various techniques. The results confirmed the successful synthesis of Co/BiOBr nanosheets and indicated the doped Co2+ had little influence on the surface morphol. and crystal structure but expanded the light absorption region. Photoelectrochem. measurements were applied to evaluate the semiconducting properties of Co/BiOBr, and the results implied that compared with the undoped sample, Co/BiOBr had higher charge transfer efficiency and smaller charge transfer resistance which were beneficial to the improvement of visible-light-driven photocatalytic performance. The as-synthesized Co/BiOBr nanosheets exhibited excellent catalytic activity and stability in the photodecompn. of contaminants.
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    23. 23
      Khampuanbut, A.; Santalelat, S.; Pankiew, A. Visible-light-driven WO3/BiOBr heterojunction photocatalysts for oxidative coupling of amines to imines: Energy band alignment and mechanistic insight. J. Colloid Interface Sci. 2020, 560, 213– 224,  DOI: 10.1016/j.jcis.2019.10.057
      23
      Visible-light-driven WO3/BiOBr heterojunction photocatalysts for oxidative coupling of amines to imines: Energy band alignment and mechanistic insight
      Khampuanbut, Amornrat; Santalelat, Sarunya; Pankiew, Apirak; Channei, Duangdao; Pornsuwan, Soraya; Faungnawakij, Kajornsak; Phanichphant, Sukon; Inceesungvorn, Burapat
      Journal of Colloid and Interface Science (2020), 560 (), 213-224CODEN: JCISA5; ISSN:0021-9797. (Elsevier B.V.)
      The visible-light-driven WO3/BiOBr heterojunction was for the first time detd. for its photocatalytic activity toward oxidative coupling of amines at room temp. using mol. oxygen as a green oxidant. The WO3/BiOBr heterojunction exhibits superior photocatalytic activity and photostability compared with pure BiOBr and WO3 due to an increased oxygen vacancy concn., an effective sepn. of photogenerated electron-hole pairs and an efficient interfacial charge transfer. Addnl., the WO3/BiOBr also shows 2.3 and 41.1 times higher activity than that of TiO2 P25 and BiVO4 Alfa Aesar, resp. Detn. of energy band line-up indicates that the WO3/BiOBr is a type II-heterojunction where electron-hole pairs are efficiently sepd. Mechanistic studies based on radical quenching expt., EPR trapping study and Hammett plot reveal that the main reaction pathway is the electron transfer route mediated by superoxide radical. A possible surface reaction mechanism, the insightful information on the structure-activity relationship and the involvement of reactive oxygen species elucidated in this work lay an important background for the material design and encourage a further development of highly efficient photocatalysts toward org. fine chem. syntheses.
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    24. 24
      Yang, H.; Zhang, Q.; Chen, Y.; Huang, Y.; Yang, F.; Lu, Z. Ultrasonic-microwave synthesis of ZnO/BiOBr functionalized cotton fabrics with antibacterial and photocatalytic properties. Carbohydr. Polym. 2018, 201, 162– 171,  DOI: 10.1016/j.carbpol.2018.08.068
      24
      Ultrasonic-microwave synthesis of ZnO/BiOBr functionalized cotton fabrics with antibacterial and photocatalytic properties
      Yang, Hao; Zhang, Qingxia; Chen, Ying; Huang, Yong; Yang, Fang; Lu, Zhong
      Carbohydrate Polymers (2018), 201 (), 162-171CODEN: CAPOD8; ISSN:0144-8617. (Elsevier Ltd.)
      ZnO coated fabrics have attracted wide attentions due to their antibacterial and photocatalytic self-cleaning properties. However, the photo-response of ZnO only in UV region limits its application. In this paper, ZnO/BiOBr functionalized cotton fabrics were synthesized by a facile and time-saving ultrasonic-microwave combined method. Compared with ZnO coated fabric, the photocatalytic activity of ZnO/BiOBr coated fabric under visible light irradn. was remarkably improved at no sacrifice of its antibacterial activity. Simultaneously, it also showed good resistance to bacterial adhesion and photocorrosion. The introduction of two-dimensional BiOBr nanoflakes not only enhanced the visible light absorption, but also reduced the recombination rate of electron-hole pairs, thus significantly improving the photocatalytic self-cleaning performance of the coated fabric under visible light irradn. The ZnO/BiOBr coated cotton fabric with both antibacterial and self-cleaning functionalities may have broad application prospects in the fields of textile, medicine and chem. industry.
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    25. 25
      Tae Kwon, Y.; Yong Song, K.; In Lee, W.; Jin Choi, G.; Rag Do, Y. Photocatalytic behavior of WO3-loaded TiO2 in an oxidation reaction. J. Catal. 2000, 191, 192– 199,  DOI: 10.1006/jcat.1999.2776
      There is no corresponding record for this reference.
    26. 26
      Keller, V.; Bernhardt, P.; Garin, F. Photocatalytic oxidation of butyl acetate in vapor phase on TiO2, Pt/TiO2 and WO3/TiO2 catalysts. J. Catal. 2003, 215, 129– 138,  DOI: 10.1016/S0021-9517(03)00002-2
      26
      Photocatalytic oxidation of butyl acetate in vapor phase on TiO2, Pt/TiO2 and WO3/TiO2 catalysts
      Keller, V.; Bernhardt, P.; Garin, F.
      Journal of Catalysis (2003), 215 (1), 129-138CODEN: JCTLA5; ISSN:0021-9517. (Elsevier Science)
      The photocatalytic degrdn. of Bu acetate in the gas phase was investigated in a fixed-bed continuous annular reactor using a titanium dioxide semiconductor, Pt/TiO2 and WO3/TiO2 catalysts. Platinum was deposited on the titanium by adsorption of PtCl62- anions, and WO3/TiO2 was prepd. by a conventional impregnation method using an aq. soln. of ammonium paratungstate. Different samples, with different nominal wt. loadings in Pt and WO3, were tested. For each catalyst sample studied, air contg. Bu acetate and water vapors in various molar ratios was fed at 200 cm3/min to the photoreactor. The roles of the reaction temp. and of H2O in the photocatalytic oxidn. of Bu acetate and the influence of the content of TiO2, Pt, and WO3 were investigated. Although an initial decay in photocatalytic activity was obsd., partly issued from an initial deactivation, total mineralization was achieved under all exptl. conditions. For relative water humidity between 50 and 75% and for adequate TiO2 covering ratios, the photocatalytic activity of TiO2 toward the photocatalytic degrdn. of Bu acetate can be greatly improved by the addn. of WO3, mainly due to a prevention of the initial deactivation and of photogenerated charge recombination. This optimized photocatalyst is very stable on stream and no regeneration treatments are needed. The influence of Pt and WO3 on photocatalytic activity are discussed with regard to chem. and electronic modifications of TiO2.
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    27. 27
      El-Salamony, R. A.; Amdeha, E.; Badawy, N. A.; Ghoneim, S. A.; Al-Sabagh, A. M. Visible light sensitive activated carbon-metal oxide (TiO2, WO3, NiO, and SnO) nano-catalysts for photo-degradation of methylene blue: a comparative study. Toxicol. Environ. Chem. 2018, 100, 143– 156,  DOI: 10.1080/02772248.2018.1497634
      27
      Visible light sensitive activated carbon-metal oxide (TiO2, WO3, NiO, and SnO) nano-catalysts for photo-degradation of methylene blue: a comparative study
      El-Salamony, Radwa A.; Amdeha, Enas; Badawy, Nagwa A.; Ghoneim, Salwa A.; Al-Sabagh, Ahmed M.
      Toxicological & Environmental Chemistry (2018), 100 (2), 143-156CODEN: TECSDY; ISSN:1029-0486. (Taylor & Francis Ltd.)
      Four composites of metal oxide doped with activated carbon with a metal oxide wt. of 20% were prepd. using mechano-mixing method. The nano-catalysts were characterized by N2-adsorption-desorption, X-ray diffraction anal., transmission electron microscopy, Fourier-transform IR spectroscopy, UV-diffuse reflectance, and photoluminescence spectroscopy. Photo-catalytic degrdn. of methylene blue dye under UV 254 nm and visible light was examd. In general, prepd. catalysts are more active for degrdn. of dye under visible light than UV, reaching 96% within 180 min irradn. using the SnO catalyst. Photo-degrdn. of methylene blue followed pseudo first order reaction mechanism with a rate const. of 14.8 × 10-3 min-1, and the time required for removal of 50% of dye was 47 min.
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    28. 28
      Amdeha, E.; Mohamed, R. S. A green synthesized recyclable ZnO/MIL-101(Fe) for Rhodamine B dye removal via adsorption and photo-degradation under UV and visible light irradiation. Environ. Technol. 2019, 42, 842– 859,  DOI: 10.1080/09593330.2019.1647290
      There is no corresponding record for this reference.
    29. 29
      Wang, H.; Zhang, L.; Chen, Z. Semiconductor heterojunction photocatalysts: Design, construction, and photocatalytic performances. Chem. Soc. Rev. 2014, 43, 5234– 5244,  DOI: 10.1039/c4cs00126e
      29
      Semiconductor heterojunction photocatalysts: design, construction, and photocatalytic performances
      Wang, Huanli; Zhang, Lisha; Chen, Zhigang; Hu, Junqing; Li, Shijie; Wang, Zhaohui; Liu, Jianshe; Wang, Xinchen
      Chemical Society Reviews (2014), 43 (15), 5234-5244CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
      A review. Semiconductor-mediated photocatalysis has received tremendous attention as it holds great promise to address the worldwide energy and environmental issues. To overcome the serious drawbacks of fast charge recombination and the limited visible-light absorption of semiconductor photocatalysts, many strategies have been developed in the past few decades and the most widely used one is to develop photocatalytic heterojunctions. This review attempts to summarize the recent progress in the rational design and fabrication of heterojunction photocatalysts, such as the semiconductor-semiconductor heterojunction, the semiconductor-metal heterojunction, the semiconductor-carbon heterojunction and the multicomponent heterojunction. The photocatalytic properties of the four junction systems are also discussed in relation to the environmental and energy applications, such as degrdn. of pollutants, hydrogen generation and photocatalytic disinfection. This tutorial review ends with a summary and some perspectives on the challenges and new directions in this exciting and still emerging area of research.
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    30. 30
      Zhang, J.; Zhang, L.; Shen, X.; Xu, P.; Liu, J. Synthesis of BiOBr/WO3p-n heterojunctions with enhanced visible light photocatalytic activity. CrystEngComm 2016, 18, 3856– 3865,  DOI: 10.1039/c6ce00824k
      30
      Synthesis of BiOBr/WO3 p-n heterojunctions with enhanced visible light photocatalytic activity
      Zhang, Junlei; Zhang, Lisha; Shen, Xiaofeng; Xu, Pengfei; Liu, Jianshe
      CrystEngComm (2016), 18 (21), 3856-3865CODEN: CRECF4; ISSN:1466-8033. (Royal Society of Chemistry)
      A prerequisite for the development of photocatalysis techniques is to obtain photocatalysts with remarkable activity. Herein, we have reported BiOBr/WO3 p-n heterojunctions as novel and efficient visible-light-driven photocatalysts. The BiOBr/WO3 p-n heterojunctions have been prepd. through an electrospinning-calcination-solvothermal method, and they all present a flower-like superstructure. The photocatalytic activities of these p-n heterojunctions are investigated by degrading rhodamine B (RhB), methyl orange (MO) and para-chlorophenol (4-CP) under visible light irradn. (λ > 400 nm), resp. When RhB serves as the target pollutant, all BiOBr/WO3 p-n heterojunctions with different theor. molar ratios of BiOBr and WO3 (1/0.5, 1/1, 1/2) exhibit higher photocatalytic activity than pure WO3 or BiOBr. Esp., the BiOBr/WO3 p-n heterojunction with a molar ratio of 1/1 displays the highest photocatalytic activity among all the as-synthesized catalysts, even higher than the activity from the mixt. of two individual photocatalysts with the same wt. of components (WO3 and BiOBr). In addn., when MO or 4-CP acts as the target pollutant, the BiOBr/WO3 p-n heterojunction with a molar ratio of 1/1 still exhibits excellent photocatalytic performance. Furthermore, the recycling expt. confirms that the BiOBr/WO3 p-n heterojunction is essentially stable during the photocatalytic process. The enhanced photocatalytic activity of the BiOBr/WO3 p-n heterojunction is predominantly attributed to the efficient sepn. of photogenerated electrons and holes. The photogenerated holes (h+) and superoxide radical anions ( .O2-) have been found to be the primary reactive species responsible for the nearly complete mineralization of RhB dye in water.
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    31. 31
      Rafiee, E.; Noori, E.; Zinatizadeh, A. A.; Zanganeh, H. Photocatalytic degradation of phenol using a new developed TiO2/graphene/heteropoly acid nanocomposite: Synthesis, characterization and process optimization. RSC Adv. 2016, 6, 96554– 96562,  DOI: 10.1039/c6ra09897e
      31
      Photocatalytic degradation of phenol using a new developed TiO2/graphene/heteropoly acid nanocomposite: synthesis, characterization and process optimization
      Rafiee, Ezzat; Noori, Elham; Zinatizadeh, Ali Akbar; Zanganeh, Hadis
      RSC Advances (2016), 6 (99), 96554-96562CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)
      A TiO2/graphene (TiO2/Gr) nanocomposite was synthesized using bottom-up assembly. The TiO2/Gr nanocomposite was modified with 12-tungstophosphoric acid (H3PW12O40, TiO2/Gr/xPW). The structural properties of the nanocomposite have been characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), SEM (SEM), zeta potential, Brunauer-Emmett-Teller (BET), Fourier transform IR (FTIR), and diffuse reflectance spectra (DRS). Results of DRS showed a visible shift when the TiO2/Gr nanocomposite was modified with PW. The photocatalytic activity of the synthesized nanocomposite was measured by the degrdn. of phenol under visible and UV light irradn. The effects of initial concn. of phenol, concn. of photocatalyst, reaction time, loading of PW and initial pH on phenol removal efficiency in batch expts. were investigated. The results showed that the degrdn. efficiency is decreased with an increase in initial concn. of phenol from 50 to 150 mg L-1 while pH did not show a significant impact. As a result, TiO2/Gr/xPW exhibited a higher visible-light photocatalytic activity in comparison with TiO2/Gr and pure TiO2 with the max. degrdn. efficiency of 91, 68, and 15%, resp. This clearly shows that among the modified composites, the catalyst with 20 wt% PW showed max. visible shift. COD measurements under optimum conditions showed 78% phenol mineralization. And also, the reusability of the catalyst was proved when 80% degrdn. could be achieved after three consecutive batches.
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    32. 32
      Ali, M. H. H.; Al-qahtani, K. M.; El-sayed, S. M. Enhancing photodegradation of 2,4,6 trichlorophenol and organic pollutants in industrial effluents using nanocomposite of TiO2 doped with reduced graphene oxide. Egypt. J. Aquat. Res. 2019, 45, 321– 328,  DOI: 10.1016/j.ejar.2019.08.003
      There is no corresponding record for this reference.
    33. 33
      Ali, H. R. Photocoupling of Ag3PO4-Ag2CO3 with molecularly imprinted polymer for enhanced removal of phenol under solar light: Application of taguchi method. Int. J. Appl. Eng. Res. 2017, 12, 3353– 3359
      There is no corresponding record for this reference.
    34. 34
      Abd El Salam, H. M.; Younis, S. A.; Ali, H. R.; Zaki, T. Statistical modeling and optimization of phenol adsorption from water by modified Cu3(BTC)2: Kinetic, isotherm, and thermodynamic analysis. Microporous Mesoporous Mater. 2017, 241, 210– 217,  DOI: 10.1016/j.micromeso.2016.12.010
      34
      Statistical modeling and optimization of phenol adsorption from water by modified Cu3(BTC)2: Kinetic, isotherm, and thermodynamic analysis
      Abd El Salam, H. M.; Younis, S. A.; Ali, H. R.; Zaki, T.
      Microporous and Mesoporous Materials (2017), 241 (), 210-217CODEN: MIMMFJ; ISSN:1387-1811. (Elsevier B.V.)
      Cu3(BTC)2 and Ni1.5Cu1.5(BTC)2 were synthesized in the presence of microwave irradn. The morphol. and the structure of the prepd. MOFs were characterized by XRD, TEM, TGA, FTIR, Raman, and nitrogen adsorption/desorption methods. The adsorption activities of the samples towards the phenols from aq. solns. were achieved including kinetic and equil. approaches with different nonlinear models for modeling. The exptl. data clarified that the adsorption of phenols on Cu3(BTC)2 and Ni1.5Cu1.5(BTC)2 had been processed via a pore-filling mechanism. Thermodn. parameters were also detd. Also, a three levels-four factor half-factorial design was successfully employed for exptl. design and anal. of the results through response surface methodol. (RSM). The significance of the independent variables was tested and optimized by the anal. of variance (ANOVA) and t-test statistics. The optimum pH, adsorbent dose, and temp. are 5.0, 1 g/l, and 30°, resp., for both samples. Under these conditions, the predicted removal efficiency of 50 mg/l phenols is 71.32% (35.65 mg/g) and 78.95% (39.47 mg/g), resp.
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    35. 35
      Rodriguez, A. F. R.; Coaquira, J. A. H.; Morales, M. A. Synthesis, characterization and magnetic properties of polymer-Fe3O4 nanocomposite. Spectrochim. Acta, Part A 2013, 100, 101– 103,  DOI: 10.1016/j.saa.2012.02.081
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      Synthesis, characterization and magnetic properties of polymer-Fe3O4 nanocomposite
      Rodriguez, A. F. R.; Coaquira, J. A. H.; Morales, M. A.; Faria, F. S. E. D. V.; Cunha, R. M.; Santos, J. G.; Silveira, L. B.; Candela, D. R. S.; Baggio-Saitovitch, E. M.; Rabelo, D.; Azevedo, R. B.; Morais, P. C.
      Spectrochimica Acta, Part A: Molecular and Biomolecular Spectroscopy (2013), 100 (), 101-103CODEN: SAMCAS; ISSN:1386-1425. (Elsevier B.V.)
      The chem. stability of magnetic particles is of great importance for their applications in medicine and biotechnol. The most challenging problem in physics of disordered systems of magnetic nanoparticles is the investigation of their dynamic properties. The chem. copptn. process was used to synthesize spherical magnetite nanoparticles of 14 nm. The as-prepd. magnetite nanoparticles were aged in the matrix. Magnetic properties and aging effect were studied by Moessbauer spectroscopy at temps. ranging from 77-300 K, and x-ray diffraction. At room temp., the Moessbauer spectrum showed superparamagnetic behavior of the particles, while well-defined sextets were obsd. at 77 K, indicating a blocked regime. The superparamagnetic magnetite nanoparticles can be used as microbead biosensors.
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    36. 36
      Mäkelä, M. Experimental design and response surface methodology in energy applications: A tutorial review. Energy Convers. Manage. 2017, 151, 630– 640,  DOI: 10.1016/j.enconman.2017.09.021
      There is no corresponding record for this reference.
    37. 37
      Tebbouche, L.; Hank, D.; Zeboudj, S.; Namane, A.; Hellal, A. Evaluation of the phenol biodegradation byAspergillus niger: application of full factorial design methodology. Desalin. Water Treat. 2016, 57, 6124– 6130,  DOI: 10.1080/19443994.2015.1053991
      37
      Evaluation of the phenol biodegradation by Aspergillus niger: application of full factorial design methodology
      Tebbouche, Latifa; Hank, Dalila; Zeboudj, Saliha; Namane, Abdelkader; Hellal, Amina
      Desalination and Water Treatment (2016), 57 (13), 6124-6130CODEN: DWTSAW; ISSN:1944-3986. (Taylor & Francis Ltd.)
      The ability of Aspergillus niger to degrade phenol in an aerobic batch culture was investigated under different parameters such as initial concn. of phenol, pH, and temp. The results showed that A. niger can grow using phenol as the sole source of carbon. A high concn. of phenol (1,000 mg/L) was completely degraded after 140 h at T = 30°C and pH 5.5. The main and the interactive effects of initial phenol concn. (200-1,000 mg/L), pH (2.5-8.5), and temp. (25-35°C) on the biodegrdn. of phenol were studied in this work. A full factorial design 23 was used to det. the optimum conditions for the phenol biodegrdn. process. The max. amt. of degraded phenol was 1.32 mg/h, achieved at 200 mg/L of initial phenol concn., pH 8.5, and T = 35°C.
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    38. 38
      Choquette-Labbé, M.; Shewa, W.; Lalman, J.; Shanmugam, S. Photocatalytic degradation of phenol and phenol derivatives using a Nano-TiO2 catalyst: Integrating quantitative and qualitative factors using response surface methodology. Water (Switzerland) 2014, 6, 1785– 1806,  DOI: 10.3390/w6061785
      38
      Photocatalytic degradation of phenol and phenol derivatives using a nano-TiO2 catalyst: integrating quantitative and qualitative factors using response surface methodology
      Choquette-Labbe, Marissa; Shewa, Wudneh A.; Lalman, Jerald A.; Shanmugam, Saravanan R.
      Water (Basel, Switzerland) (2014), 6 (6), 1785-1806, 22 pp.CODEN: WATEGH; ISSN:2073-4441. (MDPI AG)
      Due to the toxicity effects and endocrine disrupting properties of phenolic compds., their removal from water and wastewater has gained widespread global attention. In this study, the photocatalytic degrdn. of phenolic compds. in the presence of titanium dioxide (TiO2) nano-particles and UV light was investigated. A full factorial design consisting of three factors at three levels was used to examine the effect of particle size, temp. and reactant type on the apparent degrdn. rate const. The individual effect of TiO2 particle size (5, 10 and 32 nm), temp. (23, 30 and 37 °C) and reactant type (phenol, o-cresol and m-cresol) on the apparent degrdn. rate const. was detd. A regression model was developed to relate the apparent degrdn. const. to the various factors. The largest photocatalytic activity was obsd. at an optimum TiO2 particle size of 10 nm for all reactants. The apparent degrdn. rate const. trend was as follows: o-cresol > m-cresol > phenol. The ANOVA data indicated no significant interaction between the exptl. factors. The lowest activation energy was obsd. for o-cresol degrdn. using 5-nm TiO2 particles. A max. degrdn. rate const. of 0.0138 min-1 was recorded for o-cresol at 37 °C and a TiO2 particle size of 13 nm at a D-optimality value of approx. 0.98. The response model adequately related the apparent degrdn. rate const. to the factors within the range of factors under consideration.
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    39. 39
      Ocholi, O.; Menkiti, M.; Auta, M.; Ezemagu, I. Optimization of the operating parameters for the extractive synthesis of biolubricant from sesame seed oil via response surface methodology. Egypt. J. Pet. 2018, 27, 265– 275,  DOI: 10.1016/j.ejpe.2017.04.001
      There is no corresponding record for this reference.
    40. 40
      Tehrani, F. S.; Ahmadian, H.; Aliannezhadi, M. Hydrothermal synthesis and characterization of WO3 nanostructures: Effect of reaction time. Mater. Res. Express 2020, 7, 015911,  DOI: 10.1088/2053-1591/ab66fc
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      Hydrothermal synthesis and characterization of WO3 nanostructures: Effect of reaction time
      Tehrani, Fatemeh Shariatmadar; Ahmadian, Hamidreza; Aliannezhadi, Maryam
      Materials Research Express (2020), 7 (1), 015911CODEN: MREAC3; ISSN:2053-1591. (IOP Publishing Ltd.)
      1-D and 2-D WO3 nanostructures were successfully prepd. by hydrothermal technique as a low temp., low cost, compatible with the environment, and powerful method with controllability of particle size, shape, and stoichiometry. The effect of hydrothermal duration time was studied to investigate morphol., structural and optical properties and to propose the possible growth mechanisms of WO3 nanostructures. X-ray diffraction (XRD), Field emission SEM(FESEM), Fourier transform IR spectroscopy(FTIR), and Diffuse reflectance spectroscopy(DRS) analyses were done on the samples synthesized at different hydrothermal duration times of 6, 12, 24, and 36 h. The results indicated that the morphol. evolutions of nanostructures strongly depend on hydrothermal duration time and concn. of capping agents. Two crystal phase transitions in accordance with the morphol. evolution were also obsd. The absorption edge of the samples exhibited a blue- and then red-shift by increasing the reaction time. The bandgaps of the samples were almost independent of the reaction time and the samples were transparent in a wide range of the visible light region. So, they can be regarded as excellent candidates for optoelectronic devices.
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    41. 41
      Shamhari, N. M.; Wee, B. S.; Chin, S. F.; Kok, K. Y. Synthesis and characterization of zinc oxide nanoparticles with small particle size distribution. Acta Chim. Slov. 2018, 65, 578– 585,  DOI: 10.17344/acsi.2018.4213
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      Synthesis and characterization of zinc oxide nanoparticles with small particle size distribution
      Shamhari, Nuraqeelah Mohammad; Wee, Boon Siong; Chin, Suk Fun; Kok, Kuan Ying
      Acta Chimica Slovenica (2018), 65 (3), 578-585CODEN: ACSLE7; ISSN:1318-0207. (Slovenian Chemical Society)
      Solvothermal synthesis has shown to have a great potential to synthesize Zinc Oxide nanoparticles (ZnO NPs) with less than 10 nm size. In this study, we present a rapid synthesis of ZnO NPs in which ZnO NPs with more uniform shape and highly dispersed were synthesized using zinc acetate dihydrate (Zn(CH3COO)2 2H2O) and potassium hydroxide (KOH) as a precursor and abs. ethanol as solvent via solvothermal method. Few techniques were exploited to characterize synthesized ZnO NPs including X-ray diffraction (XRD), transmission electron microscope (TEM), Brunauer-Emmett- Teller (BET), energy-dispersive X-ray spectroscopy (EDX), fourier transform IR (FT-IR) spectroscopy, and UV visible (UV-Vis) spectroscopy. Synthesized ZnO NPs that were prepd. via solvothermal synthesis method at 60°C for 3 h exhibited a wurtzite structure with a cryst. size of 10.08 nm and particle size of 7.4 ± 1.2 nm. The UV-vis absorption spectrum has shown peak at 357 nm indicate the presence of ZnO NPs. Hence, better quality with uniform size ZnO NPs can be easily synthesized with reduced amt. of time via solvothermal synthesis method rather than using other complicated and lengthy synthesis methods.
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    42. 42
      Yuan, Q. L.; Zhang, Y.; Yin, H. Y.; Nie, Q. L.; Wu, W. W. Rapid, simple and low-cost fabrication of BiOBr ultrathin nanocrystals with enhanced visible light photocatalytic activity. J. Exp. Nanosci. 2016, 11, 359– 369,  DOI: 10.1080/17458080.2015.1065014
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      Rapid, simple and low-cost fabrication of BiOBr ultrathin nanocrystals with enhanced visible light photocatalytic activity
      Yuan, Qiu Li; Zhang, Yang; Yin, Hao Yong; Nie, Qiu Lin; Wu, Wei Wei
      Journal of Experimental Nanoscience (2016), 11 (5), 359-369CODEN: JENOBX; ISSN:1745-8080. (Taylor & Francis Ltd.)
      BiOBr ultrathin nanocrystals were prepd. by a rapid, simple and low-cost route, and characterized by X-ray diffraction, scanning electron microscope, transmission electron microscopy, energy dispersive X-ray, UV-vis diffuse reflectance spectroscopy and electrochem. impedance spectroscopy analyses. The size of the resulting BiOBr ultrathin nanocrystals is about 60-100 nm in width and 15-20 nm in thickness. The photocatalytic activity of the samples was evaluated in terms of the degrdn. of RhB. Compared with BiOBr three-dimensional microspheres and P25-TiO2, the BiOBr ultrathin nanocrystals exhibited the best visible-light-induced photocatalytic activity.
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    43. 43
      Liu, X.; Luo, J.; Zhu, Y.; Yang, Y.; Yang, S. Removal of methylene blue from aqueous solutions by an adsorbent based on metal-organic framework and polyoxometalate. J. Alloys Compd. 2015, 648, 986– 993,  DOI: 10.1016/j.jallcom.2015.07.065
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      Removal of Methylene Blue from aqueous solutions by an adsorbent based on metal-organic framework and polyoxometalate
      Liu, Xiaoxia; Luo, Jing; Zhu, Yating; Yang, Yun; Yang, Shuijin
      Journal of Alloys and Compounds (2015), 648 (), 986-993CODEN: JALCEU; ISSN:0925-8388. (Elsevier B.V.)
      A metal-org. framework (Cu3(BTC)2, BTC =1,3,5-benzenetricarboxylate) composite based on polyoxometalate (H6P2W18O62) was synthesized by a simple one-pot solvent-thermal method and applied as an adsorbent to remove Methylene Blue (MB) from wastewater. The chem. structure, morphol. and thermostability of the composite were characterized by FTIR Spectroscopy (FTIR), x-ray diffraction (XRD), Scanning Electron Microscope (SEM), Thermogravimetric Anal. (TG) and N adsorption-desorption isotherms. The removal rate of the composite H6P2W18O62@Cu3(BTC)2 was greater than that of the pure Cu3(BTC)2, esp. at higher initial concns., showing that the adsorption performance of porous Cu3(BTC)2 can be improved through the modification of H6P2W18O62. The effect factors contg. the initial concn., contact time, initial soln. pH and temp. of MB adsorption onto the composite were systematically explored. The exptl. isotherm data was found to fit the Freundlich model well and the process of MB adsorption onto H6P2W18O62@Cu3(BTC)2 was controlled by the pseudo-2nd-order kinetic model. The thermodn. parameters illustrated that the adsorption was spontaneous and exothermic process. These results show that designing a metal-org. framework composite is a quite promising strategy to achieve extreme application for metal-org. framework.
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    44. 44
      Younis, S. A.; Motawea, E. A.; Moustafa, Y. M.; Lee, J.; Kim, K.-H. A strategy for the efficient removal of chlorophenols in petrochemical wastewater by organophilic and aminated silica@alginate microbeads: Taguchi optimization and isotherm modeling based on partition coefficient. J. Hazard. Mater. 2020, 397, 122792,  DOI: 10.1016/j.jhazmat.2020.122792
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      A strategy for the efficient removal of chlorophenols in petrochemical wastewater by organophilic and aminated silica@alginate microbeads: Taguchi optimization and isotherm modeling based on partition coefficient
      Younis, Sherif A.; Motawea, Eman A.; Moustafa, Yasser M.; Lee, Jechan; Kim, Ki-Hyun
      Journal of Hazardous Materials (2020), 397 (), 122792CODEN: JHMAD9; ISSN:0304-3894. (Elsevier B.V.)
      Through in situ encapsulation of cetyltrimethylammonium bromide (CTAB) and urea-functionalized SiO2 nanoparticles in alginate hydrogel, two types of new functionalized microbeads, CTAB-SiO2@alginate (organophilic) and urea-SiO2@alginate (aminated), were produced. Their adsorption behavior toward multiple chlorophenols (CPs: e.g., 4-chlorophenol (MCP), 2,4-dichlorophenol (DCP), and 2,4,6-trichlorophenol (TCP)) in petrochem. wastewater was assessed with the aid of Taguchi's L9 orthogonal array at three levels. In terms of the partition coeff. (PC: μmol/g·μM (or L/g)), the use of three-parameter models (hybrid Langmuir-Freundlich and Redlich-Peterson) yielded the best fit (R2 ≈ 1). Furthermore, the performance evaluation in terms of PC metric indicated that CTAB-SiO2@alginate (7.85 L/g) was better to treat total CPs than urea-modified SiO2@alginate microbeads (3.83 L/g). The enhanced performance of the former reflects the significant contribution of CTAB functionality (sp2 carbon tail and quaternary amine (N+) cationic head sites) for accelerating uptake of mol. (or suspended) and ionizable CPs mols. (e.g., with the aid of salting-out effect at a high initial CPs concn. and salinity) via hydrophobic/electrostatic interactions. The high performance of the CTAB-SiO2@alginate was demonstrated against petroleum hydrocarbons, CPs, and phenol contaminants using real petrochem. wastewater (up to three reusable cycles).
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    45. 45
      Bakr, A.-S. A.; Moustafa, Y. M.; Motawea, E. A.; Yehia, M. M.; Khalil, M. M. H. Removal of ferrous ions from their aqueous solutions onto NiFe2O4-alginate composite beads. J. Environ. Chem. Eng. 2015, 3, 1486– 1496,  DOI: 10.1016/j.jece.2015.05.020
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      Removal of ferrous ions from their aqueous solutions onto NiFe2O4-alginate composite beads
      Bakr, Al-Sayed A.; Moustafa, Yasser M.; Motawea, Eman A.; Yehia, Mohamed M.; Khalil, Mostafa M. H.
      Journal of Environmental Chemical Engineering (2015), 3 (3), 1486-1496CODEN: JECEBG; ISSN:2213-3437. (Elsevier Ltd.)
      This paper deals with the exptl. investigation related to the removal of Fe(II) from aq. solns. by synthesized NiFe2O4-alginate composite beads and nano-NiFe2O4 at different temps. and const. stirring rate of 150 rpm. The adsorption process was optimized by response surface methodol. RSM/CCD and studied as a function of contact time, pH and adsorbent mass. The results revealed that the max. adsorption capacities were 158.4 and 69.8 mg/g for NiFe2O4-alginate composite beads and nano-NiFe2O4 when the initial Fe(II) concns. were 350 and 250 mg/L at 318 K, resp. The kinetics of Fe(II) removal by synthesized materials were best described by the pseudo-second-order model and the adsorption isotherms were seen to be consistent with Langmuir's adsorption isotherm. Also, the thermodn. parameters of the adsorption (Gibbs free energy, entropy, and enthalpy) were discussed. Therefore, the results demonstrated that the adsorption process was spontaneous and endothermic and the synthesized NiFe2O4-alginate composite beads material could act as a highly-effective nano-adsorbent of Fe(II) removal more than nano-NiFe2O4 from the aq. solns.
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      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXpt1yqs7s%253D&md5=e50ee44eadf1255bc6a7c631c6bcca94