Design of a Metal-Oxide Solid Solution for Sub-ppm H2 DetectionClick to copy article linkArticle link copied!
- Elena Spagnoli*Elena Spagnoli*Email: [email protected]Department of Physics and Earth Sciences, University of Ferrara, via Giuseppe Saragat 1, Ferrara 44122, ItalyMore by Elena Spagnoli
- Andrea Gaiardo*Andrea Gaiardo*Email: [email protected]MNF-Micro Nano Facility Sensors and Devices Center, Bruno Kessler Foundation, via Sommarive 18, Trento 38123, ItalyMore by Andrea Gaiardo
- Barbara FabbriBarbara FabbriDepartment of Physics and Earth Sciences, University of Ferrara, via Giuseppe Saragat 1, Ferrara 44122, ItalyMore by Barbara Fabbri
- Matteo ValtMatteo ValtMNF-Micro Nano Facility Sensors and Devices Center, Bruno Kessler Foundation, via Sommarive 18, Trento 38123, ItalyMore by Matteo Valt
- Soufiane KrikSoufiane KrikDepartment of Physics and Earth Sciences, University of Ferrara, via Giuseppe Saragat 1, Ferrara 44122, ItalySensing Technologies Lab, Faculty of Science and Technology, Free University of Bozen-Bolzano, piazza Università 1, Bolzano 39100, ItalyMore by Soufiane Krik
- Matteo ArditMatteo ArditDepartment of Physics and Earth Sciences, University of Ferrara, via Giuseppe Saragat 1, Ferrara 44122, ItalyMore by Matteo Ardit
- Giuseppe CrucianiGiuseppe CrucianiDepartment of Physics and Earth Sciences, University of Ferrara, via Giuseppe Saragat 1, Ferrara 44122, ItalyMore by Giuseppe Cruciani
- Michele Della CianaMichele Della CianaDepartment of Physics and Earth Sciences, University of Ferrara, via Giuseppe Saragat 1, Ferrara 44122, ItalyNational Research Council, Institute for Microelectronics and Microsystems, via Gobetti 101, Bologna 40129, ItalyMore by Michele Della Ciana
- Lia VanzettiLia VanzettiMNF-Micro Nano Facility Sensors and Devices Center, Bruno Kessler Foundation, via Sommarive 18, Trento 38123, ItalyMore by Lia Vanzetti
- Gabriele VolaGabriele VolaCimprogetti S.r.l. Lime Technologies, via Pasubio, Bergamo 24044, ItalyMore by Gabriele Vola
- Sandro GherardiSandro GherardiDepartment of Physics and Earth Sciences, University of Ferrara, via Giuseppe Saragat 1, Ferrara 44122, ItalyMore by Sandro Gherardi
- Pierluigi BelluttiPierluigi BelluttiMNF-Micro Nano Facility Sensors and Devices Center, Bruno Kessler Foundation, via Sommarive 18, Trento 38123, ItalyMore by Pierluigi Bellutti
- Cesare MalagùCesare MalagùDepartment of Physics and Earth Sciences, University of Ferrara, via Giuseppe Saragat 1, Ferrara 44122, ItalyMore by Cesare Malagù
- Vincenzo GuidiVincenzo GuidiDepartment of Physics and Earth Sciences, University of Ferrara, via Giuseppe Saragat 1, Ferrara 44122, ItalyMore by Vincenzo Guidi
Abstract
Hydrogen is largely adopted in industrial processes and is one of the leading options for storing renewable energy. Due to its high explosivity, detection of H2 has become essential for safety in industries, storage, and transportation. This work aims to design a sensing film for high-sensitivity H2 detection. Chemoresistive gas sensors have extensively been studied for H2 monitoring due to their good sensitivity and low cost. However, further research and development are still needed for a reliable H2 detection at sub-ppm concentrations. Metal-oxide solid solutions represent a valuable approach for tuning the sensing properties by modifying their composition, morphology, and structure. The work started from a solid solution of Sn and Ti oxides, which is known to exhibit high sensitivity toward H2. Such a solid solution was empowered by the addition of Nb, which─according to earlier studies on titania films─was expected to inhibit grain growth at high temperatures, to reduce the film resistance and to impact the sensor selectivity and sensitivity. Powders were synthesized through the sol–gel technique by keeping the Sn–Ti ratio constant at the optimal value for H2 detection with different Nb concentrations (1.5–5 atom %). Such solid solutions were thermally treated at 650 and 850 °C. The sensor based on the solid solution calcined at 650 °C and with the lowest content of Nb exhibited an extremely high sensitivity toward H2, paving the way for H2 ppb detection. For comparison, the response to 50 ppm of H2 was increased 6 times vs SnO2 and twice that of (Sn,Ti)xO2.
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License Summary*
You are free to share(copy and redistribute) this article in any medium or format and to adapt(remix, transform, and build upon) the material for any purpose, even commercially within the parameters below:
Creative Commons (CC): This is a Creative Commons license.
Attribution (BY): Credit must be given to the creator.
*Disclaimer
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License Summary*
You are free to share(copy and redistribute) this article in any medium or format and to adapt(remix, transform, and build upon) the material for any purpose, even commercially within the parameters below:
Creative Commons (CC): This is a Creative Commons license.
Attribution (BY): Credit must be given to the creator.
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Experimental Section
Synthesis of SnO2, (Sn,Ti)xO2, and (Sn,Ti,Nb)xO2 Powders
Sn/Ti/Nb molar ratio | calcination temperature (°C) | label |
---|---|---|
100 | 650 | SnO2 650 |
70:30:0 | 650 | ST30 650 |
66.5:28.5:5 | 650 | STN 5 650 |
66.5:28.5:5 | 850 | STN 5 850 |
69.0:29.5:1.5 | 650 | STN 1.5 650 |
69.0:29.5:1.5 | 850 | STN 1.5 850 |
Material Characterization
Gas Sensor Preparation and Characterization


Results
Morphological, Structural, and Chemical Characterization
Figure 1
Figure 1. Distribution of particle diameters (nm) in STN samples, revealing the influence of annealing temperature on grain coalescence. Black dotted lines indicate the mean value of the distributions.
sample | specific surface area by BET method (m2/g) | pore size: D-H desorption average pore diameter (4V/A) (nm) |
---|---|---|
ST30 650 | 50.42 | 12.66 |
STN 1.5 650 | 43.72 | 16.71 |
STN 5 650 | 48.36 | 12.52 |
STN 1.5 850 | 22.63 | 23.95 |
Figure 2
Figure 2. X-ray powder diffraction patterns collected at RT. Gray lines parallel to the y axis mark peak positions for ST30 650 to highlight the shift for STN peaks. The fractions of rutile-type (s.g. P42/mnm) and anatase-type (s.g. I41/amd) phases were ∼98 and 2 wt %, respectively.
EDX | STN 1.5 650 | STN 5 650 | STN 1.5 850 | STN 5 850 |
---|---|---|---|---|
Ti | 22.0 | 22.7 | 26.7 | 21.2 |
Nb | 1.7 | 5.3 | 1.4 | 5.0 |
Sn | 76.3 | 72.0 | 71.9 | 73.8 |
XPS | STN 1.5 650 | STN 5 650 | STN 1.5 850 | STN 5 850 |
---|---|---|---|---|
Ti | 29.3 | 30.2 | 29.4 | 25.2 |
Nb | 3.8 | 9.8 | 3.4 | 12.4 |
Sn | 66.9 | 60.0 | 67.2 | 62.4 |
Gas Sensing Properties
Figure 3
Figure 3. (a) STN film dynamical responses at 450 °C to 0.4, 1, 2 (inset) 10, 25, 50, and 100 ppm of H2 in dry air and (b) their calibration curves fitted with a power law function. A linear plot for concentrations lower than 2 ppm (inset) was used to estimate the theoretical LOD. (c) Response to four-cycle injection of 0.4 and 100 ppm of H2 as a function of time. (d) Comparison between the responses of STN, ST30 650, and SnO2 films to the same concentration of H2 (sensors performing at their optimal working temperature of 450 °C for STN and ST30 650 and 400 °C for SnO2 650). (25) The legend of graph (d) also applies to graphs (a), (b), and (c).
Figure 4
Figure 4. Influence of humidity on the conductance baseline and conductance after injection of 50 ppm of H2. The temperature inside the chamber was 29 °C in the whole range of RH %.
Figure 5
material | concentration | response | optimal operating temperature (°C) | LOD | reference |
---|---|---|---|---|---|
STN 1.5 650 | 100 ppm | 80a | 450 | 0.4 ppm/5 ppbf | this work |
STN 5 650 | 100 ppm | 34a | 450 | 0.4 ppm/13 ppbf | this work |
SnO2 | 100 ppm | 15c | 400 | (50) | |
Pd/SnO2 | 100 ppm | 28.5c | 160 | 0.25 ppm | (51) |
Co/SnO2 | 100 ppm | 23c | 330 | (52) | |
WO3 | 100 ppm | 4.8 | 250 | 0.25 ppmf | (53) |
WO3–CuO | 100 ppm | 39 | 250 | 0.31 ppmf | (53) |
CuO | 100 ppm | 1.7d | 200 | 2 ppm | (54) |
ZnO | 100 ppm | 0.95e | 250 | (55) | |
Ag/ZnO | 300 ppm | 4.79e | 250 | 5 ppm | (55) |
Gas response ,
Gas response,
Gas response ,
Gas response ,
Gas response , where G is the conductance, R is the resistance, and V is the voltage.
Indicates theoretical LOD.
Discussion

Conclusions
Supporting Information
The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acssensors.1c02481.
In-depth description of material characterization methods and gas sensor preparation; morphological, textural, and structural characterizations; response variation according to the temperature change; fit parameters for calibration curves; response and recovery times; and film conductance vs temperature and energy barrier measurement (PDF)
Terms & Conditions
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This article references 65 other publications.
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- 5Uslu, H.; Büyükpınar, Ç.; Unutkan, T.; Serbest, H.; SAN, N.; Turak, F.; Bakırdere, S. A Novel Analytical Method for Sensitive Determination of Lead: Hydrogen Assisted T-Shape Slotted Quartz Tube-Atom Trap-Flame Atomic Absorption Spectrometry. Microchem. J. 2018, 137, 155– 159, DOI: 10.1016/j.microc.2017.10.015Google Scholar5https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhslagtb3F&md5=75498cf3eec01364d7118991e25be383A novel analytical method for sensitive determination of lead: Hydrogen assisted T-shape slotted quartz tube-atom trap-flame atomic absorption spectrometryUslu, Humeysa; Buyukpinar, Cagdas; Unutkan, Tugce; Serbest, Hakan; San, Nevin; Turak, Fatma; Bakirdere, SezginMicrochemical Journal (2018), 137 (), 155-159CODEN: MICJAN; ISSN:0026-265X. (Elsevier B.V.)Lead is a toxic metal which affects human health badly due to its high toxicity. The wide application range of lead causes environmental contamination of air, water and soil. Flame at. absorption spectrometry is one of the simple and economical instrument used for the detn. of heavy metals, but it has low sensitivity due to low sample introduction efficiency. In this study, a sensitive anal. method was developed by using T-shaped slotted quartz tube as an atom trap unit to get lower detection limit for lead. The trapped atoms were released using hydrogen gas which supplies reducing environment in T-SQT-AT-FAAS system. Factors such as trapping period, sample and fuel flow rates were optimized to obtain high sensitivity. Under the optimum conditions, limits of detection and quantitation were found to be 0.6 and 2.1 μg L- 1, resp. Accuracy of the developed method was checked and results found under the optimum conditions agreed with the certified value of coal fly ash std. ref. material. The developed method was applied to water samples to figure out its suitability.
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- 7Farrah, D.; Bernard-Salas, J.; Spoon, H. W. W.; Soifer, B. T.; Armus, L.; Brandl, B.; Charmandaris, V.; Desai, V.; Higdon, S.; Devost, D.; Houck, J. High-Resolution Mid-Infrared Spectroscopy of Ultraluminous Infrared Galaxies. Astrophys. J. 2007, 667, 149– 169, DOI: 10.1086/520834Google Scholar7https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXhtFyju77I&md5=2f0629451a5069086106df053c51c7a0High-resolution mid-infrared spectroscopy of ultraluminous infrared galaxiesFarrah, D.; Bernard-Salas, J.; Spoon, H. W. W.; Soifer, B. T.; Armus, L.; Brandl, B.; Charmandaris, V.; Desai, V.; Higdon, S.; Devost, D.; Houck, J.Astrophysical Journal (2007), 667 (1, Pt. 1), 149-169CODEN: ASJOAB; ISSN:0004-637X. (University of Chicago Press)We present R ∼ 600, 10-37 μm spectra of 53 ultraluminous IR galaxies (ULIRGs), taken using the IR Spectrograph on board Spitzer. The spectra show fine-structure emission lines of neon, oxygen, sulfur, silicon, argon, chlorine, iron, and phosphorous; mol. hydrogen lines, and C2H2, HCN, and OH- absorption features. We employ diagnostics based on the fine-structure lines, the polycyclic arom. hydrocarbon (PAH) features and the 9.7 μm silicate absorption feature, to show that the IR emission from most ULIRGs is powered mostly by star formation, with only ∼20% of ULIRGs hosting an AGN with a greater IR luminosity than the starburst. The detection of [Ne V] λ14.32 in just under half the sample, however, implies that an AGN contributes significantly to the mid-IR flux in ∼42% of ULIRGs. The starbursts and AGNs in ULIRGs appear more extincted, and for the starbursts more compact than those in lower luminosity systems. The excitations and electron densities in the narrow-line regions of ULIRGs appear comparable to those of starbursts with L .ltorsim. 1011.5 L.sun., although the NLR gas in ULIRGs may be more dense. We show that the [Ne II] λ12.81 + [Ne III] λ15.56 luminosity correlates with both IR luminosity and the luminosity of the 6.2 and 11.2 μm PAH features, and derive a calibration between PAH luminosity and star formation rate. Finally, we show that ULIRGs with silicate absorption strengths Ssil of 0.8 .ltorsim. Ssil .ltorsim. 2.4 are likely to be powered mainly by star formation, but that ULIRGs with Ssil .ltorsim. 0.8, and possibly those with Ssil ⪆ 2.4, contain an IR-luminous AGN.
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- 10Valt, M.; Fabbri, B.; Gaiardo, A.; Gherardi, S.; Casotti, D.; Cruciani, G.; Pepponi, G.; Vanzetti, L.; Iacob, E.; Malagù, C.; Bellutti, P.; Guidi, V. Aza-Crown-Ether Functionalized Graphene Oxide for Gas Sensing and Cation Trapping Applications. Mater. Res. Express 2019, 6, 075603 DOI: 10.1088/2053-1591/ab11fbGoogle Scholar10https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXisVOgtL3J&md5=dcbdae87b000a2ec41c629d186cb716dAza-crown-ether functionalized graphene oxide for gas sensing and cation trapping applicationsValt, M.; Fabbri, B.; Gaiardo, A.; Gherardi, S.; Casotti, D.; Cruciani, G.; Pepponi, G.; Vanzetti, L.; Iacob, E.; Malagu, C.; Bellutti, P.; Guidi, V.Materials Research Express (2019), 6 (7), 075603CODEN: MREAC3; ISSN:2053-1591. (IOP Publishing Ltd.)Graphene oxide has been functionalized with 1-aza-15-crown-5 ether via chem. route synthesis. Modification of graphene oxide was achieved via nucleophilic attack where the amine groups of an aza-crown ether mol. can easily react with the epoxy sites of graphene oxide basal plane. Owing to the inherent two-dimensional character of graphene oxide, it resulted in large specific-surface material with strong affinity for charged chem. species. Such property was exploited for reversible and controlled interaction of adsorbed species, envisaging two possible applications of the functionalized graphene oxide. Thus, an easy-to-fabricate and high-sensitivity functionalized graphene oxide-based gas sensor was achieved. The sensing material proved to be highly stable and capable of selectively detecting humidity at room temp. over a wide range of concns. Moreover, the porous scaffold built by the functionalization, together with the well-known affinity of crown ethers to metal ions, allow the use of aza-crown ether functionalized graphene oxide for cation trapping application, e.g. pre-concn. of trace amt. of metals or filter for water. Remarkable results in this field have been obtained with respect to some heavy-metal cations of environmental interest. We also demonstrated significant enhancement in performance vs. pure graphene oxide in both tested applications. More generally, the functionalization approach we pursued appears to be quite flexible in the tested applications. In fact, with an appropriate selection of crown ethers with specific cage-like structure, functionalized graphene oxide allows the capture of any desired guest in order to prep. a wide range of other crown-ether-GO nanocomposites for different applications.
- 11Gaiardo, A.; Fabbri, B.; Guidi, V.; Bellutti, P.; Giberti, A.; Gherardi, S.; Vanzetti, L.; Malagù, C.; Zonta, G. Metal Sulfides as Sensing Materials for Chemoresistive Gas Sensors. Sensors 2016, 16, 296 DOI: 10.3390/s16030296Google Scholar11https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXnvFygsQ%253D%253D&md5=2239f5f5b7f6a8a9e4b04ab3e267ba45Metal sulfides as sensing materials for chemoresistive gas sensorsGaiardo, Andrea; Fabbri, Barbara; Guidi, Vincenzo; Bellutti, Pierluigi; Giberti, Alessio; Gherardi, Sandro; Vanzetti, Lia; Malagu, Cesare; Zonta, GiuliaSensors (2016), 16 (3), 296/1-296/19CODEN: SENSC9; ISSN:1424-8220. (MDPI AG)This work aims at a broad overview of the results obtained with metal-sulfide materials in the field of chemoresistive gas sensing. Indeed, despite the well-known elec., optical, structural and morphol. features previously described in the literature, metal sulfides present lack of investigation for gas sensing applications, a field in which the metal oxides still maintain a leading role owing to their high sensitivity, low cost, small dimensions and simple integration, in spite of the wide assortment of sensing materials. However, despite their great advantages, metal oxides have shown significant drawbacks, which have led to the search for new materials for gas sensing devices. In this work, Cadmium Sulfide and Tin (IV) Sulfide were investigated as functional materials for thick-film chemoresistive gas-sensors fabrication and they were tested both in thermo- and in photo-activation modes. Furthermore, elec. characterization was carried out in order to verify their gas sensing properties and material stability, by comparing the results obtained with metal sulfides to those obtained by using their metal-oxides counterparts. The results highlighted the possibility to use metal sulfides as a novel class of sensing materials, owing to their selectivity to specific compds., stability, and the possibility to operate at room temp.
- 12Tricoli, A.; Righettoni, M.; Pratsinis, S. E. Minimal Cross-Sensitivity to Humidity during Ethanol Detection by SnO2–TiO2 Solid Solutions. Nanotechnology 2009, 20, 315502 DOI: 10.1088/0957-4484/20/31/315502Google Scholar12https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXhtVynu7%252FL&md5=37168a3fe2a23bc1eb3672dbc12395a7Minimal cross-sensitivity to humidity during ethanol detection by SnO2-TiO2 solid solutionsTricoli, Antonio; Righettoni, Marco; Pratsinis, Sotiris E.Nanotechnology (2009), 20 (31), 315502/1-315502/10CODEN: NNOTER; ISSN:1361-6528. (Institute of Physics Publishing)A nanocomposite material is presented that optimally combines the excellent gas sensitivity of SnO2 and the selectivity of TiO2. Nanostructured, rutile titanium-tin oxide solid solns. ≤81.5% Ti, as detd. by x-ray diffraction, were made by scalable spray combustion (flame spray pyrolysis) of organometallic precursor solns., directly deposited and in situ annealed onto sensing electrodes in one step. Above that content, segregation of anatase TiO2 takes place. It was discovered that at low titanium contents (<5 Ti%), these materials exhibit higher sensitivity to ethanol vapor than pure SnO2 and, in particular, limited cross-sensitivity to relative humidity, a long standing challenge for metal oxide gas sensors. These solid solns. are aggregated nanoparticles with an enhanced presence of Ti on their surface as indicated by Raman and IR-spectroscopy. The presence of such low Ti-content in the SnO2 lattice drastically reduces the band gap of these solid solns., as detd. by UV-vis absorption, almost to that of pure TiO2. Furthermore, titania reduces the no. of rooted and terminal OH species (that are correlated to the cross-sensitivity of tin oxide to water) on the particle surface as detd. by IR-spectroscopy. The present material represents a new class of sensors where detection of gases and org. vapors can be accomplished without pre-treatment of the gas mixt., avoiding other semiconducting components that require more heating power and that add bulkiness to a sensing device. This is attractive in developing miniaturized sensors esp. for microelectronics and medical diagnostics.
- 13Pargoletti, E.; Verga, S.; Chiarello, G. L.; Longhi, M.; Cerrato, G.; Giordana, A.; Cappelletti, G. Exploring SnxTi1–xO2 Solid Solutions Grown onto Graphene Oxide (GO) as Selective Toluene Gas Sensors. Nanomaterials 2020, 10, 761 DOI: 10.3390/nano10040761Google Scholar13https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXhtVOgsL7F&md5=b0e5b32dfa35f8a8f55701817699c238Exploring SnxTi1-xO2 solid solutions grown onto graphene oxide (GO) as selective toluene gas sensorsPargoletti, Eleonora; Verga, Simone; Chiarello, Gian Luca; Longhi, Mariangela; Cerrato, Giuseppina; Giordana, Alessia; Cappelletti, GiuseppeNanomaterials (2020), 10 (4), 761CODEN: NANOKO; ISSN:2079-4991. (MDPI AG)The major drawback of oxide-based sensors is the lack of selectivity. In this context, SnxTi1-xO2/graphene oxide (GO)-based materials were synthesized via a simple hydrothermal route, varying the titanium content in the tin dioxide matrix. Then, toluene and acetone gas sensing performances of the as-prepd. sensors were systematically investigated. Specifically, by using 32:1 SnO2/GO and 32:1 TiO2/GO, a greater selectivity towards acetone analyte, also at room temp., was obtained even at ppb level. However, solid solns. possessing a higher content of tin relative to titanium (as 32:1 Sn0.55Ti0.45O2/GO) exhibited higher selectivity towards bigger and non-polar mols. (such as toluene) at 350 °C, rather than acetone. A deep exptl. investigation of structural (XRPD and Raman), morphol. (SEM, TEM, BET surface area and pores vol.) and surface (XPS analyses) properties allowed us to give a feasible explanation of the different selectivity. Moreover, by exploiting the UV light, the lowest operating temp. to obtain a significant and reliable signal was 250 °C, keeping the greater selectivity to the toluene analyte. Hence, the feasibility of tuning the chem. selectivity by engineering the relative amt. of SnO2 and TiO2 is a promising feature that may guide the future development of miniaturized chemoresistors.
- 14Radecka, M.; Zakrzewska, K.; Rękas, M. SnO2–TiO2 Solid Solutions for Gas Sensors. Sens. Actuators, B 1998, 47, 194– 204, DOI: 10.1016/S0925-4005(98)00023-9Google Scholar14https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1cXksV2gur8%253D&md5=ea175915d58aa89d2d4304d96e074408SnO2-TiO2 solid solutions for gas sensorsRadecka, Marta; Zakrzewska, Katarzyna; Rgkas, MieczystawSensors and Actuators, B: Chemical (1998), 47 (1-3), 194-204CODEN: SABCEB; ISSN:0925-4005. (Elsevier Science S.A.)Mixed oxide gas sensors of SnO2-TiO2 were prepd. as polycryst. ceramics and radiofrequency-sputtered thin films. The influence of the chem. and phase compn. on the crystallog. structure, microstructure and sensor performance is discussed. The measurements of the elec. resistance as a function of hydrogen partial pressure were performed with air or argon as a ref. gas. The results are analyzed in terms of the surface and bulk interaction models. Probably hydrogen detection in air involves the preadsorbed O- species. Hydrogen interaction with the SnO2-TiO2 system in Ar atm. is governed by bulk diffusion of oxygen vacancies.
- 15Carotta, M. C.; Gherardi, S.; Guidi, V.; Malagù, C.; Martinelli, G.; Vendemiati, B.; Sacerdoti, M.; Ghiotti, G.; Morandi, S. Electrical and Spectroscopic Properties of Ti0.2Sn0.8O2 Solid Solution for Gas Sensing. Thin Solid Films 2009, 517, 6176– 6183, DOI: 10.1016/j.tsf.2009.04.002Google Scholar15https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXoslajsrs%253D&md5=f0c9219917fe5b888a6bd7e0c57c9ba5Electrical and spectroscopic properties of Ti0.2Sn0.8O2 solid solution for gas sensingCarotta, M. C.; Gherardi, S.; Guidi, V.; Malagu, C.; Martinelli, G.; Vendemiati, B.; Sacerdoti, M.; Ghiotti, G.; Morandi, S.Thin Solid Films (2009), 517 (22), 6176-6183CODEN: THSFAP; ISSN:0040-6090. (Elsevier B.V.)In this work we report the synthesis, microstructure, elec. and spectroscopic properties, and sensing performances of TixSn1-xO2 (x = 0.1, 0.2, 0.3, 0.5, 0.7, 0.9) nano-powders and of SnO2 and TiO2 ref. samples, prepd. via sol-gel route starting from metal-org. precursors working in hydro-alc. media. Actually, the attention is particularly focused on properties of the sample with x = 0.2, in comparison with ones of the other solid solns. and of the single oxides. Indeed, this solid soln. showed a borderline behavior between that of the solid soln. with x = 0.1 and that of the other solid solns. with x ≥ 0.3. An abrupt change in the structural, elec. and spectroscopic properties has been obsd., passing from sample with x = 0.1, showing a behavior very similar to that of SnO2, to 1 x = 0.3 showing a behavior very similar to that of TiO2. The borderline properties of the mixed oxide with x = 0.2 represent the expected continuous transition among the 2 behaviors.
- 16Carotta, M. C.; Fioravanti, A.; Gherardi, S.; Malagù, C.; Sacerdoti, M.; Ghiotti, G.; Morandi, S. (Ti,Sn) Solid Solutions as Functional Materials for Gas Sensing. Sens. Actuators, B 2014, 194, 195– 205, DOI: 10.1016/j.snb.2013.12.021Google Scholar16https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXitF2gtL0%253D&md5=7f27c4e064f7a9eea711d7f141151ddeStudy on (Ti,Sn) solid solutions as functional materials for gas sensingCarotta, M. C.; Fioravanti, A.; Gherardi, S.; Malagu, C.; Sacerdoti, M.; Ghiotti, G.; Morandi, S.Sensors and Actuators, B: Chemical (2014), 194 (), 195-205CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)Metal-oxide semiconductors are widely used as functional materials for gas sensing because of their chemoresistive effect when interacting with ambient gases. For this work, nanosized TixSn1-xO2 have been synthesized at increasing Ti molar ratio (x = 0, 0.1, 0.2, 0.25, 0.3, 0.5, 0.7, 0.8, 0.9, 0.95, 1) and extensively investigated through a wide variety of characterizations. It turned out that the merging process of the two single oxides formed new compds. with improved gas responses compared to pure TiO2 and also to pure SnO2. Moreover, all investigated physico-chem. characteristics resulted tuneable through the titanium content in the solid soln. Each characterization carried out onto TixSn1-xO2 solid solns. made it possible to identify two classes of materials with SnO2-like or TiO2-like behaviors, the best CO response being on the intersection of the two species of materials. Moreover, a very interesting anal. on the generally accepted elec. transport model through polycryst. semiconductors has been carried out. Indeed, the comparison with exptl. evidences has highlighted a conduction mechanism not previously considered.
- 17Carney, C. M.; Yoo, S.; Akbar, S. A. TiO2–SnO2 Nanostructures and Their H2 Sensing Behavior. Sens. Actuators, B 2005, 108, 29– 33, DOI: 10.1016/j.snb.2004.11.058Google Scholar17https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXltFWntbg%253D&md5=6aed24306c27027ff79dce4664b436fdTiO2-SnO2 nanostructures and their H2 sensing behaviorCarney, Carmen M.; Yoo, Sehoon; Akbar, Sheikh A.Sensors and Actuators, B: Chemical (2005), 108 (1-2), 29-33CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)Pure TiO2 and mixed oxide samples of TiO2 and SnO2 sintered samples having different surface areas were synthesized using a heat treatment in H2 bearing gas. Nanostructures of solid solns. and spinodally-decompd. samples of mixed oxides were compared to the oriented nanofibers formed in pure TiO2 created by the same heat treatment. Comparisons between the sensing characteristics of the samples were made to det. that the samples with higher surface areas were more sensitive to H2 in the presence of O2.
- 18Shi, Y.; Xu, H.; Liu, T.; Zeb, S.; Nie, Y.; Zhao, Y.; Qin, C.; Jiang, X. Advanced Development of Metal Oxide Nanomaterials for H2 Gas Sensing Applications. Mater. Adv. 2021, 2, 1530– 1569, DOI: 10.1039/D0MA00880JGoogle Scholar18https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXjtV2qu7c%253D&md5=fed6c113bb83a27640991436953085afAdvanced development of metal oxide nanomaterials for H2 gas sensing applicationsShi, Yushu; Xu, Huiyan; Liu, Tongyao; Zeb, Shah; Nie, Yong; Zhao, Yiming; Qin, Chengyuan; Jiang, XuchuanMaterials Advances (2021), 2 (5), 1530-1569CODEN: MAADC9; ISSN:2633-5409. (Royal Society of Chemistry)A review. Hydrogen (H2) has been considered as one of the cleanest renewable energy sources. However, it is still challenging to use H2 due to its hazardous flammable and explosive properties under mild conditions in the event of leakage, and the difficulty to detect or sense it through human sensory organs because of its colorless and odorless nature. Traditional detection methods are usually complicated and the testing instruments are expensive. Thus, it is of significant importance to develop sensors for H2 detection with facile operation conditions, low costs, and excellent performance (i.e., sensitivity, selectivity, and stability). To overcome the problems and for practically detecting H2 gas, metal oxide (MOx) nanomaterials have become more crucial in such a gas sensor because of the simple prepn. method, high surface area, high sensitivity, and low costs. This review will focus on the recent state-of-the-art advances in resistive H2 gas sensors based on MOx nanomaterials, starting from a brief introduction of resistive gas sensors. The following sections will focus on the synthesis of different structures and types of such MOx nanomaterials, including mono/binary/ternary/ternary or more complicated MOx nanomaterials. Meanwhile, we highlight some regulation methods such as surface or inner decoration by noble or non-noble metals to improve the performance as well as summarize and compare different structures (core-shell and heterojunction), and mechanisms in H2 sensing. Finally, the opportunities and challenges of MOx-based H2 gas sensors are proposed in detail.
- 19Zeng, W.; Liu, T.; Wang, Z.; Tsukimoto, S.; Saito, M.; Ikuhara, Y. Selective Detection of Formaldehyde Gas Using a Cd-Doped TiO2-SnO2 Sensor. Sensors 2009, 9, 9029– 9038, DOI: 10.3390/s91109029Google Scholar19https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXhsVylurrE&md5=1328dfdc32ea78a92004856a2d7bad25Selective detection of formaldehyde gas using a cd-doped TiO2-SnO2 sensorZeng, Wen; Liu, Tianmo; Wang, Zhongchang; Tsukimoto, Susumu; Saito, Mitsuhiro; Ikuhara, YuichiSensors (2009), 9 (11), 9029-9038CODEN: SENSC9; ISSN:1424-8220. (Molecular Diversity Preservation International)We report the microstructure and gas-sensing properties of a nonequil. TiO2-SnO2 solid soln. prepd. by the sol-gel method. In particular, we focus on the effect of Cd doping on the sensing behavior of the TiO2-SnO2 sensor. Of all volatile org. compd. gases examd., the sensor with Cd doping exhibits exclusive selectivity as well as high sensitivity to formaldehyde, a main harmful indoor gas. The key gas-sensing quantities, max. sensitivity, optimal working temp., and response and recovery time, are found to meet the basic industrial needs. This makes the Cd-doped TiO2-SnO2 composite a promising sensor material for detecting the formaldehyde gas.
- 20Carotta, M. C.; Cervi, A.; Giberti, A.; Guidi, V.; Malagù, C.; Martinelli, G.; Puzzovio, D. Metal-Oxide Solid Solutions for Light Alkane Sensing. Sens. Actuators, B 2008, 133, 516– 520, DOI: 10.1016/j.snb.2008.03.012Google Scholar20https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXptVClsL8%253D&md5=22cddad5d0f616f5d9a93ab35d868cdfMetal-oxide solid solutions for light alkane sensingCarotta, M. C.; Cervi, A.; Giberti, A.; Guidi, V.; Malagu, C.; Martinelli, G.; Puzzovio, D.Sensors and Actuators, B: Chemical (2008), 133 (2), 516-520CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)Sensing of light alkanes via chemoresistive gas sensors was addressed. Screen-printed films of a solid soln. of mixed Sn and Ti oxides were selected for the purpose. The films sensitively detect 100 ppm of such gases and 500 ppm of methane, the two levels being by far lower than the alarm limits for these gases. Information about the working mechanism of chem. reactions on the surface is discussed under either dry or wet condition.
- 21Carotta, M. C.; Guidi, V.; Malagù, C.; Vendemiati, B.; Zanni, A.; Martinelli, G.; Sacerdoti, M.; Licoccia, S.; Vona, M. L. Di.; Traversa, E. Vanadium and Tantalum-Doped Titanium Oxide (TiTaV): A Novel Material for Gas Sensing. Sens. Actuators, B 2005, 108, 89– 96, DOI: 10.1016/j.snb.2004.11.070Google Scholar21https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXltFWmurk%253D&md5=ff62526f70037c3e45dfec96df058d60Vanadium and tantalum-doped titanium oxide (TiTaV): a novel material for gas sensingCarotta, Maria Cristina; Guidi, Vincenzo; Malagu, Cesare; Vendemiati, Beatrice; Zanni, Alex; Martinelli, Giuliano; Sacerdoti, Michele; Licoccia, Silvia; Di Vona, Maria Luisa; Traversa, EnricoSensors and Actuators, B: Chemical (2005), 108 (1-2), 89-96CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)A new material based on titanium dioxide modified by tantalum and vanadium was synthesized. The prepd. powders were deposited to produce gas sensors as thick films through screen-printing technol. The cryst. phase and morphol. were examd. by XRD and SEM analyses. Ta addn. inhibited the anatase-to-rutile phase transformation and hindered grain growth during heating, while vanadium did the opposite. The sensors were tested with different gases showing good selectivity; in particular, the samples with greatest content of Ta showed good response to benzene, only slightly influenced by presence of carbon monoxide.
- 22Ferroni, M.; Carotta, M.; Guidi, V.; Martinelli, G.; Ronconi, F.; Richard, O.; Van Dyck, D.; Van Landuyt, J. Structural Characterization of Nb–TiO2 Nanosized Thick-Films for Gas Sensing Application. Sens. Actuators, B 2000, 68, 140– 145, DOI: 10.1016/S0925-4005(00)00474-3Google Scholar22https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXmtVKmsro%253D&md5=1c8bde660b8c0638f21a2ea5420f19d6Structural characterization of Nb-TiO2 nanosized thick-films for gas sensing applicationFerroni, M.; Carotta, M. C.; Guidi, V.; Martinelli, G.; Ronconi, F.; Richard, O.; Van Dyck, D.; Van Landuyt, J.Sensors and Actuators, B: Chemical (2000), 68 (1-3), 140-145CODEN: SABCEB; ISSN:0925-4005. (Elsevier Science S.A.)Pure and Nb-doped TiO2 thick-films were prepd. by screen-printing, starting from nanosized powders. Grain growth and cryst. phase modification occurred as consequence of firing at high temp. It has been shown that niobium addn. inhibits grain coarsening and hinders anatase-to-rutile phase transition. These semiconducting films exhibited n-type behavior, while Nb acted as donor-dopant. Gas measurements demonstrated that the films are suitable for CO or NO2 sensing. Microstructural characterization by electron microscopy and DTA highlights the dependence of gas-sensing behavior on film's properties.
- 23Guidi, V.; Carotta, M. C.; Ferroni, M.; Martinelli, G.; Sacerdoti, M. Effect of Dopants on Grain Coalescence and Oxygen Mobility in Nanostructured Titania Anatase and Rutile. J. Phys. Chem. B 2003, 107, 120– 124, DOI: 10.1021/jp013572uGoogle Scholar23https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38Xpt1ynsr0%253D&md5=8329c8b4f4a7f3dd485b479212baf5e8Effect of Dopants on Grain Coalescence and Oxygen Mobility in Nanostructured Titania Anatase and RutileGuidi, V.; Carotta, M. C.; Ferroni, M.; Martinelli, G.; Sacerdoti, M.Journal of Physical Chemistry B (2003), 107 (1), 120-124CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)Grain growth and the anatase-to-rutile phase transition in nanostructured titania have been investigated by electron microscopy, X-ray diffraction, and DTA. For pure TiO2, thermal treatment resulted in complete phase transition and considerable grain coarsening, because of the grain boundary nucleation mechanism for the rutile phase. The effect of doping of the TiO2 nanophase has also been addressed. Phase transition turned out to be strongly affected by the presence of Ta and Nb because nucleation of rutile was favored at the surface of anatase grains. Doping allowed the maintenance of the ultrafine anatase phase even at high annealing temp. Thermal anal. highlighted that oxygen mobility in the titania lattice is affected by doping and related to the inhibition of grain coalescence and phase transition.
- 24Gardecka, A. J.; Goh, G. K. L.; Sankar, G.; Parkin, I. P. On the Nature of Niobium Substitution in Niobium Doped Titania Thin Films by AACVD and Its Impact on Electrical and Optical Properties. J. Mater. Chem. A 2015, 3, 17755– 17762, DOI: 10.1039/c5ta03772gGoogle Scholar24https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXht1GmurfK&md5=4dccae6cc23f85f6ce037ebe7bd486a3On the nature of niobium substitution in niobium doped titania thin films by AACVD and its impact on electrical and optical propertiesGardecka, A. J.; Goh, G. K. L.; Sankar, G.; Parkin, I. P.Journal of Materials Chemistry A: Materials for Energy and Sustainability (2015), 3 (34), 17755-17762CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)Niobium doped TiO2 thin films were deposited on silica coated glass substrate using aerosol assisted CVD (AACVD) from hexane soln., at 500°. The as-deposited films appeared blue, were transparent in the visible, were reflective in the IR region at ∼30% and were elec. conductive (n = 1.23 × 1019 cm-3, μ = 18.9 cm2 V-1 s-1, sheet resistance = 120 Ω .box.-1). The structure of the films was studied using XRD, Raman spectroscopy, XPS and x-ray absorption spectroscopy (XAS). No visible phase segregation was found by XRD nor by Raman, though anal. of the Nb K-edge using XANES and EXAFS revealed niobium both incorporated into the titanium dioxide lattice as well as present as Nb2O5. The high resoln. TEM imaging showed sub 4 nm Nb2O5 crystals within the lattice. This work questions the soly. limit of niobium in the TiO2 lattice and suggests previous literature on Nb-doped TiO2 may have overestimated the degree of niobium substitution.
- 25Carotta, M. C.; Benetti, M.; Guidi, V.; Gherardi, S.; Malagu’, C.; Vendemiati, B.; Martinelli, G. Nanostructured (Sn,Ti,Nb)O2 Solid Solution for Hydrogen Sensing. MRS Proc. 2006, 915, 0915– R07-10, DOI: 10.1557/PROC-0915-R07-10Google ScholarThere is no corresponding record for this reference.
- 26Chiorino, A.; Ghiotti, G.; Prinetto, F.; Carotta, M.; Gnani, D.; Martinelli, G. Preparation and Characterization of SnO2 and MoOx–SnO2 Nanosized Powders for Thick Film Gas Sensors. Sens. Actuators, B 1999, 58, 338– 349, DOI: 10.1016/S0925-4005(99)00094-5Google Scholar26https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXnvFWlsrw%253D&md5=1a2e0b36a4548985d84dede039076a31Preparation and characterization of SnO2 and MoOx-SnO2 nanosized powders for thick film gas sensorsChiorino, A.; Ghiotti, G.; Prinetto, F.; Carotta, M. C.; Gnani, D.; Martinelli, G.Sensors and Actuators, B: Chemical (1999), 58 (1-3), 338-349CODEN: SABCEB; ISSN:0925-4005. (Elsevier Science S.A.)This work gives results about the characterization of SnO2 materials, prepd. via the sol-gel route, pure and Mo6+-added. The materials were characterized as powders or thick films using a variety of techniques. The morphol. of the powders was analyzed by XRD, SEM, TEM and HRTEM, their texture by volumetric measurements. The morphol. of the thick films was analyzed by SEM. The goal of obtaining powders and films made by regularly shaped and nanosized (30 50 nm) particles, even after thermal treatments at 850° is attained. FTIR spectroscopic and elec. measurements were employed on powders and films, resp., to obtain information on the electronic effect due to the molybdenum addn. FTIR results show that Mo lowers the intensity of the light scattered by free electrons and the intensity of a broad absorption, previously assigned to the photoionization of VO+[VO+ + hv → VO2+ + e- (c.b.)]. Accordingly, elec. data show that molybdenum markedly lowers (of ∼2 orders of magnitude) the conductance of the films in air. Elec. measurements show that Mo lowers the response of tin oxide towards CO, but leaves almost unaltered or enhances its ability to sense NO2, depending on the thermal pretreatments. Both pure and Mo-added materials treated at 650° show the same response to NO2. However, for the pure material treated at 850° the response to NO2 is halved, while it is almost unaffected by the thermal treatment on the Mo-added materials. The sensing temp. of max. response is in any case 150°. FTIR spectroscopy was also employed to obtain information on the Mo species present on the surface of the materials after treatments in oxygen and on how they are affected in the presence of the different testing gases. Also surface species formed by NO2 interaction were carefully studied.
- 27Gaiardo, A.; Fabbri, B.; Giberti, A.; Valt, M.; Gherardi, S.; Guidi, V.; Malagù, C.; Bellutti, P.; Pepponi, G.; Casotti, D.; Cruciani, G.; Zonta, G.; Landini, N.; Barozzi, M.; Morandi, S.; Vanzetti, L.; Canteri, R.; Della Ciana, M.; Migliori, A.; Demenev, E. Tunable Formation of Nanostructured SiC/SiOC Core-Shell for Selective Detection of SO2. Sens. Actuators, B 2020, 305, 127485 DOI: 10.1016/j.snb.2019.127485Google Scholar27https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXitlOgt7%252FJ&md5=0e49d93329904cb494fd7f24fa897f9bTunable formation of nanostructured SiC/SiOC core-shell for selective detection of SO2Gaiardo, A.; Fabbri, B.; Giberti, A.; Valt, M.; Gherardi, S.; Guidi, V.; Malagu, C.; Bellutti, P.; Pepponi, G.; Casotti, D.; Cruciani, G.; Zonta, G.; Landini, N.; Barozzi, M.; Morandi, S.; Vanzetti, L.; Canteri, R.; Della Ciana, M.; Migliori, A.; Demenev, E.Sensors and Actuators, B: Chemical (2020), 305 (), 127485CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)Silicon carbide is a well-known material with high thermal, mech. and chem. stability. These properties have allowed, over time, its wide use as an inert material to be employed as a substrate or support in different applications. In this work, we demonstrate that, under proper conditions, it is possible to activate the chem. reactivity of nanostructured SiC, which can be employed for chemoresistive purposes. With this aim, a com. powder of SiC has been characterized from a morphol., structural and thermal point of view. Then, screen-printed thick films were obtained from SiC powder and thus tested as a functional material for chemoresistive gas sensors, in thermo-activation mode. The samples were exposed to 13 gases with important chem. differences. Analyses showed that SiC is an extremely selective functional material for the detection of sulfur dioxide (SO2) in concns. within the ppm range. This interesting result was found at high working temps. (600-800°C), useful for harsh environments, and the measurements proved to be completely free from humidity neg. interference. Thermo-gravimetric and XPS characterizations highlighted that the high selectivity of the SiC layer is promoted by the thermal formation of a SiC/SiOC core-shell, tunable by controlling temp. and humidity parameters. An interpretation of the gas sensing mechanism occurring between SO2 mols. and SiC/SiOC core-shell has been proposed. The unexpected chem. activity, identified for nanostructured SiC, can be exploited for the specific detection of SO2, since this gaseous compd. plays an important role in air pollution, industrial processes and winemaking.
- 28Guidi, V.; Fabbri, B.; Gaiardo, A.; Gherardi, S.; Giberti, A.; Malagù, C.; Zonta, G.; Bellutti, P. Metal Sulfides as a New Class of Sensing Materials. Procedia Eng. 2015, 120, 138– 141, DOI: 10.1016/j.proeng.2015.08.586Google Scholar28https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhsFWntbzK&md5=e7acc05f6a12bf1fc888a0195e830f4fMetal Sulfides as a New Class of Sensing MaterialsGuidi, V.; Fabbri, B.; Gaiardo, A.; Gherardi, S.; Giberti, A.; Malagu, C.; Zonta, G.; Bellutti, P.Procedia Engineering (2015), 120 (), 138-141CODEN: PERNBE; ISSN:1877-7058. (Elsevier Ltd.)In the recent years, metal sulfide nanostructured materials have become established in different research fields thanks to their excellent properties. Among the potential applications, metal sulfides may have a high standing role for gas sensing, in which, despite the wide assortment of sensing materials, still metal-oxides maintain a leading role because of their high sensitivity, low cost, small dimensions and simple integration. Experimentation carried out in this work with CdS and SnS2 thick film sensors has showed an unexpected improvements of the chemoresistive properties with respect to their oxides counterparts, in particular toward selectivity to specific compds., stability and the possibility to operate at room temp. This opens towards the study of a novel class of sensing materials, which may solve the const. drift of the signal suffered by metal-oxides and ascribed to the in/out diffusion of oxygen vacancies, which alters the doping level.
- 29Gaiardo, A.; Fabbri, B.; Giberti, A.; Guidi, V.; Bellutti, P.; Malagù, C.; Valt, M.; Pepponi, G.; Gherardi, S.; Zonta, G.; Martucci, A.; Sturaro, M.; Landini, N. ZnO and Au/ZnO Thin Films: Room-Temperature Chemoresistive Properties for Gas Sensing Applications. Sens. Actuators, B 2016, 237, 1085– 1094, DOI: 10.1016/j.snb.2016.07.134Google Scholar29https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xht1ymtL7J&md5=17afd8eaac5508605b297ff68b855940ZnO and Au/ZnO thin films: Room-temperature chemoresistive properties for gas sensing applicationsGaiardo, A.; Fabbri, B.; Giberti, A.; Guidi, V.; Bellutti, P.; Malagu, C.; Valt, M.; Pepponi, G.; Gherardi, S.; Zonta, G.; Martucci, A.; Sturaro, M.; Landini, N.Sensors and Actuators, B: Chemical (2016), 237 (), 1085-1094CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)Zinc Oxide has been widely investigated for its photocatalytic properties, which enhance the bulk/surface charge transfer at room temp. At the same time, the doping of semiconductor materials with metals allows the modification of their phys. and chem. properties, and hence their performance as gas sensors. The aim of this work was to investigate the difference between thin-film sensors based on pure ZnO nanoparticles and on gold-cluster decorated ZnO in photo-activation mode. The nanopowders were synthesized through simple sol-gel methods and chem., morphol. and structurally characterized. Thin films were deposited by spin coating onto alumina substrates. The sensing layers were tested with several gases in photo-activation mode, illuminated with radiation wavelengths of 525, 468, 400 and 385 nm. Gold-decorated ZnO thin film showed some interesting features, such as better chemoresistive properties than pure ZnO under photo-activation mode, when illuminated with a wavelength of 385 nm. A selective response of the sensing film to NO2 under green light irradn. was obsd., in particular in dry air condition. Furthermore, the humidity effect on the sensing responses was investigated, highlighting a possible application of Au/ZnO for the detection of few ppm of SO2 with a high percentage of relative humidity.
- 30Zonta, G.; Astolfi, M.; Casotti, D.; Cruciani, G.; Fabbri, B.; Gaiardo, A.; Gherardi, S.; Guidi, V.; Landini, N.; Valt, M.; Malagù, C. Reproducibility Tests with Zinc Oxide Thick-Film Sensors. Ceram. Int. 2020, 46, 6847– 6855, DOI: 10.1016/j.ceramint.2019.11.178Google Scholar30https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXit1Wrt7zN&md5=dba0f188b916c678a4bd2975a29dd8f5Reproducibility tests with zinc oxide thick-film sensorsZonta, G.; Astolfi, M.; Casotti, D.; Cruciani, G.; Fabbri, B.; Gaiardo, A.; Gherardi, S.; Guidi, V.; Landini, N.; Valt, M.; Malagu, C.Ceramics International (2020), 46 (5), 6847-6855CODEN: CINNDH; ISSN:0272-8842. (Elsevier Ltd.)Reproducibility of the sensor response is one of the fundamental themes for obtaining marketable devices with a high degree of reliability. This parameter becomes decisive esp. if the sensor signals are used to identify compd. mixts. by means of recognition algorithms. In fact, to apply the same algorithm to different devices, sensors must be identical within a min. error margin. This point became crucial for medical diagnostic tools, e.g., for cancer screening and monitoring. A set of three thermo-activated thick-film Zinc Oxide (ZnO) sensors, obtained from the same screen-printing deposition, have been tested in lab. with diverse gases and two biol. fecal samples. Fecal samples have been employed in the clin. validation protocol of a device for non-invasive colorectal cancer pre-screening, as emitters of oncol. volatile biomarkers. Sensors showed a good reproducibility degree, with an error lower than 10% of response value for all compds., reaching 1%-2% for some gases.
- 31Agents, C. Commission Directive (EU) 2017/164. Off. J. Eur. Union 2017, 1989, 115– 120Google ScholarThere is no corresponding record for this reference.
- 32Zhang, H.; Sun, Z.; Hu, Y. H. Steam Reforming of Methane: Current States of Catalyst Design and Process Upgrading. Renewable Sustainable Energy Rev. 2021, 149, 111330 DOI: 10.1016/j.rser.2021.111330Google Scholar32https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXhsVClt7zL&md5=eb47016338478acbdff13520f64fc62cSteam reforming of methane: Current states of catalyst design and process upgradingZhang, Haotian; Sun, Zhuxing; Hu, Yun HangRenewable & Sustainable Energy Reviews (2021), 149 (), 111330CODEN: RSERFH; ISSN:1364-0321. (Elsevier Ltd.)A review. Methane (CH4) is the major component of currently abundant natural gas and a prominent green-house gas. Steam reforming of methane (SRM) is an important technol. for the conversion of CH4 into H2 and syngas. To improve the catalytic activity and coking resistance of SRM catalysts, great efforts (including the addn. of promoters, development of advanced supports, and structural modification, etc.) have been made with considerable progress in the past decade. Meanwhile, a series of novel processes have been explored for more efficient and energy-saving SRM. In this scenario, a comprehensive review on the recent advances in SRM is necessary to provide a constructive insight into the development of SRM technol., however, is still lacking. Herein, the improvements in catalyst construction for conventional SRM and the newly developed SRM processes in the past decade are presented and analyzed. First, the crit. issues of SRM catalysts are briefly introduced. Then, the recent research advances of the most popular Ni based catalysts and the catalysts based on the other non-noble metals (Co, Cu, Mo, etc.) and the efficient but costly noble metals (Au, Pt, Pd, Rh, Ru, etc.) are discussed. Furthermore, the development of the representative modified SRM processes, including thermo-photo hybrid SRM, sorbent enhanced SRM, oxidative SRM, chem. looping SRM, plasma and elec.-field enhanced SRM, is demonstrated, and their advantages and limits are compared. Finally, a crit. perspective is provided to enlighten future work on this significant area.
- 33Wilhelm, D.; Simbeck, D.; Karp, A.; Dickenson, R. Syngas Production for Gas-to-Liquids Applications: Technologies, Issues and Outlook. Fuel Process. Technol. 2001, 71, 139– 148, DOI: 10.1016/S0378-3820(01)00140-0Google Scholar33https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXjsFWmsr8%253D&md5=8a1a573841e975f57ee68d651e01e2b6Syngas production for gas-to-liquids applications: technologies, issues and outlookWilhelm, D. J.; Simbeck, D. R.; Karp, A. D.; Dickenson, R. L.Fuel Processing Technology (2001), 71 (1-3), 139-148CODEN: FPTEDY; ISSN:0378-3820. (Elsevier Science B.V.)The main gas-to-liqs. (GTL) interest now is in Fischer-Tropsch (F-T) synthesis of hydrocarbons. While synthesis gas (syngas) for GTL can be produced from any carbon-based feedstock (hydrocarbons, coal, petroleum coke, biomass), the lowest cost routes to syngas so far are based on natural gas. Thus, the focus for GTL has been largely on assocd. gas, so-called stranded or remotely located gas reserves, and larger gas reserves that are not currently being economically exploited. The principal technologies for producing syngas from natural gas are: catalytic steam methane reforming (SMR), two-step reforming, autothermal reforming (ATR), partial oxidn. (POX), and heat exchange reforming. The distinguishing characteristics of these technologies and their com. uses are discussed. Ongoing R&D efforts to develop lower-cost syngas generation technologies are also briefly discussed. Relevant com. experience with large-scale syngas generation for GTL is also discussed. As a frame of ref., in terms of syngas flow rates, a 20,000 b/day F-T plant would be comparable to three 2500 mt/day methanol plants. Single-train methanol plants are now producing more than 2500 t/day-and plants approaching 3000 mt/day have been announced. The projected relative economies of scale of the various syngas prodn. technologies indicate that two-step reforming and ultimately, ATR, should be the technologies of choice for large-scale GTL plants. Nevertheless, for a 20,000 b/day F-T liqs. plant, capital charges still dominate the manufg. costs. Syngas prodn. (oxygen plant and reforming) comprises half of the total capital cost of this size GTL plant. While air-blown reforming eliminates the expensive oxygen plant, air-blown reforming is unlikely to be competitive with, or offer the flexibility of, oxygen-blown reforming. The reasons for this conclusion are discussed. The proposed and future GTL facilities should be substantially less costly than their very expensive predecessors-as the result of improvements in FT catalyst and reactor design, the most significant of which have been pioneered by Sasol. In the absence of a breakthrough technol., economy of scale will be the only significant mechanism by which GTL can achieve greater economic viability. However, even with such further cost redns., the economic viability of GTL plants will remain confined to special situations until crude price levels rise substantially. In the long term, if a ceramic membrane reactor (combining air sepn. and partial oxidn.) can be developed that enables the 20% redn. in GTL investment costs that the R&D effort is targeting, GTL could become economically viable at crude prices below US20/b.
- 34Lantto, V.; Rompplainen, P.; Leppävuori, S. A Study of the Temperature Dependence of the Barrier Energy in Porous Tin Dioxide. Sens. Actuators 1988, 14, 149– 163, DOI: 10.1016/0250-6874(88)80062-3Google Scholar34https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL1cXltl2ruro%253D&md5=6d0f8ebad3769354c03c6502f0223796A study of the temperature dependence of the barrier energy in porous tin dioxideLantto, V.; Romppainen, P.; Leppavuori, S.Sensors and Actuators (1988), 14 (2), 149-63CODEN: SEACDX; ISSN:0250-6874.The dependence of the conductance on temp. of some com. and thick-film SnO2 semiconductor gas sensors was measured at 350 to 875 K at different partial pressures of O2 in N2. The measurements were carried out using different heating and cooling rates. The values of the barrier energy between particles in the ceramic material were calcd. from these results on the basis of the single-barrier model for the conductance. The value of the barrier energy in pure O2 at a fixed temp. was detd. using the temp.-stimulated change in the conductance. The results are discussed in the light of some other expts. and theor. models given to describe the barrier energy. A discussion on the effect of different barrier heights between different particles is given on the basis of a random-barrier network model. By using quick cooling from 875 to 350 K, it is possible to get high barrier values at this low temp. This may be the modus operandi of temp.-pulsed sensors.
- 35International Organization for Standardization. Determination of the Specific Surface Area of Solids by Gas Adsorption─BET Method (ISO 9277:2010(E)); ISO, 2010; Vol. 9277, p 30.Google ScholarThere is no corresponding record for this reference.
- 36Hirata, T. Oxygen Position, Octahedral Distortion, and Bond-Valence Parameter from Bond Lengths in Ti1–xSnxO2 (0≤ x≤1). J. Am. Ceram. Soc. 2000, 83, 3205– 3207, DOI: 10.1111/j.1151-2916.2000.tb01706.xGoogle Scholar36https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXps1ek&md5=0b91e6ea1340b857e2c198b0d6201592Oxygen position, octahedral distortion, and bond-valence parameter from bond lengths in Ti1-xSnxO2 (0 ≤ x ≤ 1)Hirata, ToshiyaJournal of the American Ceramic Society (2000), 83 (12), 3205-3207CODEN: JACTAW; ISSN:0002-7820. (American Ceramic Society)Based on the virtual crystal approxn. (or Vegard's law), the bond lengths of Ti1-xSnxO2 were deduced from those of TiO2 and SnO2, to allow the oxygen position and octahedral distortion to be detd. as a function of x. The oxygen positional parameter (u) increased linearly when the Sn4++ cation (which has a larger ionic radius) was substituted for the Ti4+ cation, whereas the octahedral distortion exhibited a nonlinear decay with increasing x in Ti1-xSnxO2. At the same time, the bond-valence parameter, which relates bond valence to bond length, so that the central atom in the octahedron can retain a const. valence of +4.0, exhibited a correlation with u for Ti1-xSnxO2. The present results indicate that the different phonon/phys. properties of TiO2 and SnO2 and/or their dependence on x in Ti1-xSnxO2 can be assocd. with different octahedral distortions.
- 37Howard, C. J.; Sabine, T. M.; Dickson, F. Structural and Thermal Parameters for Rutile and Anatase. Acta Crystallogr., Sect. B: Struct. Sci. 1991, 47, 462– 468, DOI: 10.1107/S010876819100335XGoogle ScholarThere is no corresponding record for this reference.
- 38Shannon, R. D. Revised Effective Ionic Radii and Systematic Studies of Interatomic Distances in Halides and Chalcogenides. Acta Crystallogr., Sect. A: Cryst. Phys., Diffr., Theor. Gen. Crystallogr. 1976, 32, 751– 767, DOI: 10.1107/S0567739476001551Google ScholarThere is no corresponding record for this reference.
- 39Jung, W.; Tuller, H. L. Investigation of Surface Sr Segregation in Model Thin Film Solid Oxidefuel Cell Perovskite Electrodes. Energy Environ. Sci. 2012, 5, 5370– 5378, DOI: 10.1039/C1EE02762JGoogle Scholar39https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhs1CgsbvO&md5=1c4c504db646da1c40a77876aada5088Investigation of surface Sr segregation in model thin film solid oxide fuel cell perovskite electrodesJung, Woo Chul; Tuller, Harry L.Energy & Environmental Science (2012), 5 (1), 5370-5378CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)While SOFC perovskite oxide cathodes have been the subject of numerous studies, the crit. factors governing their kinetic behavior have remained poorly understood. This has been due to a no. of factors including the morphol. complexity of the electrode and the electrode- electrolyte interface as well as the evolution of the surface chem. with varying operating conditions. In this work, the surface chem. compn. of dense thin film SrTi1-xFexO3-δ electrodes, with considerably simplified and well-defined electrode geometry, was investigated by means of XPS, focusing on surface cation segregation. An appreciable degree of Sr-excess was found at the surface of STF specimens over the wide compn. range studied. The detailed nature of the Sr-excess is discussed by means of depth and take-off angle dependent XPS spectra, in combination with chem. and thermal treatments. Furthermore, the degree of surface segregation was successfully controlled by etching the films, and/or prepg. intentionally Sr deficient films. Electrochem. Impedance Spectroscopy studies, under circumstances where surface chem. was controlled, were used to examine and characterize the blocking effect of Sr segregation on the surface oxygen exchange rate.
- 40Hamada, I.; Uozumi, A.; Morikawa, Y.; Yanase, A.; Katayama-Yoshida, H. A Density Functional Theory Study of Self-Regenerating Catalysts LaFe1– xMxO3–y (M = Pd, Rh, Pt). J. Am. Chem. Soc. 2011, 133, 18506– 18509, DOI: 10.1021/ja110302tGoogle Scholar40https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhtlKgsL7O&md5=f936ad0a9f6a65b895bb94d439154d5aA Density Functional Theory Study of Self-Regenerating Catalysts LaFe1-xMxO3 (M = Pd, Rh, Pt)Hamada, Ikutaro; Uozumi, Akifumi; Morikawa, Yoshitada; Yanase, Akira; Katayama-Yoshida, HiroshiJournal of the American Chemical Society (2011), 133 (46), 18506-18509CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Periodic d. functional theory was used to investigate the stability and electronic structures of precious-metal atoms in the vicinity of LaFe1-xMxO3 (M = Pd, Rh, Pt) perovskite catalyst surfaces. It was found that the surface segregation of Pd and Pt is significantly stabilized by the introduction of O vacancies, whereas the solid-soln. phase is favorable for Rh, suggesting an important role of O vacancies in the self-regeneration of Pd and Pt. On the basis of the results, we propose a possible scenario for the self-regeneration of the precious metal in the perovskite catalyst.
- 41Farva, U.; Kim, J. Growth Temperature-Dependent Morphological, Optical, and Electrical Study of SnO2 Thin Film by Atomic Layer Deposition. Mater. Chem. Phys. 2021, 267, 124584 DOI: 10.1016/j.matchemphys.2021.124584Google Scholar41https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXptVKrur8%253D&md5=990029d5669b7157065f3b0da803fdd6Growth temperature-dependent morphological, optical, and electrical study of SnO2 thin film by atomic layer depositionFarva, Umme; Kim, JehaMaterials Chemistry and Physics (2021), 267 (), 124584CODEN: MCHPDR; ISSN:0254-0584. (Elsevier B.V.)Low temp., high quality SnO2 thin film successfully deposited by the at. layer deposition (ALD) method using tetrakis (dimethylamino)Sn (TDMASn) and O3-plasma. The influence of various growth temps. having ranges between 115°C to 250°C on the film growth rate, morphol., compn., optical and elec. properties have been elucidated, and remarkable differences were noticed for possible electron transport layer (ETL). It was worth observing that the film growth rate steeply increased from 0.046 nm/cycle to 0.192 nm/cycle between the growth temp. range 115-250°C because of the rapid dissocn. of TDMASn precursor relative to temp. increase. The optical transmittances of films showed 81%-97% at the visible region for all growth temps.; however, the optical bandgap energy of the SnO2 film was decreased from 3.4 eV to 3.1 eV while increasing deposition temp. During lower deposition temp. of 115°C, the film obtained high resistivity (7.3 x 102 Ω cm), while at a high growth temp. of 200°C almost impurity-free low resistivity (8.9 x 10-4 Ω cm) film can be achieved apart from high carrier concn. (1.4 x 1021 cm-3) and 12.5 cm2 V-1s-1 mobility.
- 42Chen, Q. Nb2O5 Improved Photoluminescence, Magnetic and Faraday Rotation Properties of Magneto-Optical Glasses. J. Non-Cryst. Solids 2019, 519, 119451 DOI: 10.1016/j.jnoncrysol.2019.05.027Google Scholar42https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhtVCitrnO&md5=46aa1e127dda48126ac26a0ff7e34b40Nb2O5 improved photoluminescence, magnetic and Faraday rotation properties of magneto-optical glassesChen, QiulingJournal of Non-Crystalline Solids (2019), 519 (), 119451CODEN: JNCSBJ; ISSN:0022-3093. (Elsevier B.V.)The high polarizability, low photon energy, high non-linear character and dual functions in glass network make diamagnetic Nb2O5 attractive to magneto optical glass based photonics and sensing devices. In this paper, we report for the first time the influence of Nb2O5 on glass formation, structure, photoluminescence, magnetic and Faraday rotation properties of heavy metal oxide diamagnetic glass. Results suggested that Nb2O5 doping amt. greatly influenced its coordination nos. and roles in glass network. Ni2O5 amt. ≤ 5 mol% in glass presented in NiO4 which played glass former role and strengthened the PbO4, BiO6, BiO3 and BO3 units composed glass network connectivity, transparent and homogeneous glasses were obtained. DSC measurement showed that the 1%, 2% and 5%Nb2O5 doping increased the Tg and thermal stability of glass. Nb2O5 doping amt. higher than 5% presented as NiO6 units which played glass modifier role in glass which distorted glass structure and produced BiNbO4 and Nb2O5 cryst. A red-shift of absorption edge from 500 nm to 529 nm was obsd. for Nb2O5 doped glasses. Due to the high optical basicity of host, niobium existed in glass only as Ni5+, and the electron transfers between O2- and Nb5+ displayed two broad emission bands centered at 376 cm and 493 nm (excited at 267 nm) in photoluminescence spectra. 5Nb2O5-5B2O3-45PbO-45Bi2O3 glass exhibited significant thermal stability (100 °C), good photoluminescence, high magnetic susceptibility (57.32 × 10-6 emu/g), and Verdet const. (0.1713 min/G.cm at 633 nm). The novelty of this work is to combine the high polarizability, dual roles properties of Nb2O5 and the high optical basicity of diamagnetic host glass to achieve a diamagnetic valence of Nb and enhance Faraday rotation performance.
- 43Xu, Y.; Wu, S.; Wan, P.; Sun, J.; Hood, Z. D. Introducing Ti3+ Defects Based on Lattice Distortion for Enhanced Visible Light Photoreactivity in TiO2 Microspheres. RSC Adv. 2017, 7, 32461– 32467, DOI: 10.1039/C7RA04885HGoogle Scholar43https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtVKnsLzN&md5=cfad44bc84ecd73bcb82eddf1852689fIntroducing Ti3+ defects based on lattice distortion for enhanced visible light photoreactivity in TiO2 microspheresXu, Yunfan; Wu, Sujuan; Wan, Piaopiao; Sun, Jianguo; Hood, Zachary D.RSC Advances (2017), 7 (52), 32461-32467CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)Defective titanium dioxide (TiO2) is of much significance due to its improved visible light photoreactivity. Generally, the existence of defects leads to imperfections in the crystal lattice, which in turn affect the dynamics of the evolution of defects and the corresponding phys. properties of TiO2. Until now, how lattice distortion affects the formation of Ti3+ defects as well as the corresponding visible light photoreactivity in TiO2 has remained elusive. Herein, we have successfully introduced Ti3+ defects based on lattice distortion in TiO2 microspheres and found the photocurrent of anatase TiO2 has been significantly enhanced from 1.78 to 80μA cm-2 with an increase in photocatalytic activity of almost three times under visible light irradn. Furthermore, we show that lattice distortions have minimal contribution to enhancing the visible light photocatalytic activity because the band gap cannot be narrowed due to the absence of Ti3+ defects, yet the existence of lattice distortions could suppress the recombination of electron-hole pairs. Moreover, the formation of Ti3+ defects is energetically favored in lattice-distorted TiO2 compared to that of pristine TiO2. This work highlights the design and development of highly efficient TiO2 photocatalysts that operate under visible light irradn.
- 44Di Valentin, C.; Pacchioni, G.; Selloni, A. Reduced and N-Type Doped TiO2: Nature of Ti3+ Species. J. Phys. Chem. C 2009, 113, 20543– 20552, DOI: 10.1021/jp9061797Google Scholar44https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXhtFOksL7F&md5=192855a2886565ebfdf1f054af4c5e90Reduced and n-Type Doped TiO2: Nature of Ti3+ SpeciesDi Valentin, Cristiana; Pacchioni, Gianfranco; Selloni, AnnabellaJournal of Physical Chemistry C (2009), 113 (48), 20543-20552CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)Defect states in reduced and n-type doped titania are of fundamental importance in several technol. important applications. Still, the exact nature of these states, often referred to as "Ti3+ centers", is largely unclear and a matter of debate. The problem is complicated by the fact that electronic structure calcns. based on d. functional theory (DFT) in the local d. approxn. (LDA) or semilocal generalized gradient approxn. (GGA) provide results that do not account for many of the exptl. obsd. fingerprints of the formation of Ti3+ centers in reduced TiO2. Here, we investigate the properties of at least four different types of Ti3+ centers in bulk anatase, (1) 6-fold-coordinated Ti6c3+ ions introduced by F- or Nb-doping, (2) Ti6c3+-OH species assocd. with H-doping, (3) undercoordinated Ti5c3+ species assocd. with oxygen vacancies, and (4) interstitial Ti5c3+ species. The characterization of these different kinds of Ti3+ centers is based on DFT + U and/or hybrid functional calcns., which are known to (partially) correct the self-interaction error of local and semilocal DFT functionals. We found that strongly localized solns. where an excess electron is on a single Ti3+ ion are very close in energy and sometimes degenerate with partly or highly delocalized solns. where the extra charge is distributed over several Ti ions. The defect states corresponding to these different solns. lie at different energies in the band gap of the material. This has important implications for the cond. mechanism in reduced or n-type doped titania and suggests a significant role of temp. in detg. the degree of localization of the trapped charge.
- 45Huang, J.; Wan, Q. Gas Sensors Based on Semiconducting Metal Oxide One-Dimensional Nanostructures. Sensors 2009, 9, 9903– 9924, DOI: 10.3390/s91209903Google Scholar45https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC383gtVOltQ%253D%253D&md5=94242a950f23f3a87aaef5158e3a586cGas sensors based on semiconducting metal oxide one-dimensional nanostructuresHuang Jin; Wan QingSensors (Basel, Switzerland) (2009), 9 (12), 9903-24 ISSN:1424-8220.This article provides a comprehensive review of recent (2008 and 2009) progress in gas sensors based on semiconducting metal oxide one-dimensional (1D) nanostructures. During last few years, gas sensors based on semiconducting oxide 1D nanostructures have been widely investigated. Additionally, modified or doped oxide nanowires/nanobelts have also been synthesized and used for gas sensor applications. Moreover, novel device structures such as electronic noses and low power consumption self-heated gas sensors have been invented and their gas sensing performance has also been evaluated. Finally, we also point out some challenges for future investigation and practical application.
- 46Spagnoli, E.; Krik, S.; Fabbri, B.; Valt, M.; Ardit, M.; Gaiardo, A.; Vanzetti, L.; Della Ciana, M.; Cristino, V.; Vola, G.; Caramori, S.; Malagù, C.; Guidi, V. Development and Characterization of WO3 Nanoflakes for Selective Ethanol Sensing. Sens. Actuators, B 2021, 347, 130593 DOI: 10.1016/j.snb.2021.130593Google Scholar46https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXhvVagtr3F&md5=9ce2c2d5d9104bc57eaaa18b3d0673cdDevelopment and characterization of WO3 nanoflakes for selective ethanol sensingSpagnoli, E.; Krik, S.; Fabbri, B.; Valt, M.; Ardit, M.; Gaiardo, A.; Vanzetti, L.; Della Ciana, M.; Cristino, V.; Vola, G.; Caramori, S.; Malagu, C.; Guidi, V.Sensors and Actuators, B: Chemical (2021), 347 (), 130593CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)Despite an increasing demand for applications, the partial selectivity of metal oxide-based gas sensors limits their practical use in some cases, such as for ethanol detection. Consequently, the search for a performing ethanol sensor is still an open challenge. In this work, tungsten oxide nanoflake powders were synthesized by means of solvothermal technique in sight of ethanol sensing. The powders were characterized by X-ray diffraction, SEM, energy dispersion X-ray spectroscopy, textural and optical absorbance analyses and XPS and screen-printed as a paste on alumina substrates. Elec. characterization showed that these films responded well to ethanol and the conductance in the presence of this gas only decreased by about 20% in mild humidity conditions, remaining const. over a range of 20-70 RH%. The operational temp. of the film was 250°C, namely a lower level with respect to mostly used WO3 sensors in the literature. Marginal influence by typical interferents in some applications of an ethanol sensor was recorded. Among alcs., the response to ethanol prevailed because of an interplay between catalytic properties of the sensing film and gas diffusivity in a porous medium.
- 47Gaiardo, A.; Zonta, G.; Gherardi, S.; Malagù, C.; Fabbri, B.; Valt, M.; Vanzetti, L.; Landini, N.; Casotti, D.; Cruciani, G.; Della Ciana, M.; Guidi, V. Nanostructured SmFeO3 Gas Sensors: Investigation of the Gas Sensing Performance Reproducibility for Colorectal Cancer Screening. Sensors 2020, 20, 5910 DOI: 10.3390/s20205910Google Scholar47https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXisV2jtr3I&md5=f79246438b3c0a0090c05c23d675d5c4Nanostructured SmFeO3 gas sensors: investigation of the gas sensing performance reproducibility for colorectal cancer screeningGaiardo, Andrea; Zonta, Giulia; Gherardi, Sandro; Malagu, Cesare; Fabbri, Barbara; Valt, Matteo; Vanzetti, Lia; Landini, Nicolo; Casotti, Davide; Cruciani, Giuseppe; Della Ciana, Michele; Guidi, VincenzoSensors (2020), 20 (20), 5910CODEN: SENSC9; ISSN:1424-8220. (MDPI AG)Among the various chemoresistive gas sensing properties studied so far, the sensing response reproducibility, i.e., the capability to reproduce a device with the same sensing performance, has been poorly investigated. However, the reproducibility of the gas sensing performance is of fundamental importance for the employment of these devices in on-field applications, and to demonstrate the reliability of the process development. This sensor property became crucial for the prepn. of medical diagnostic tools, in which the use of specific chemoresistive gas sensors along with a dedicated algorithm can be used for screening diseases. In this work, the reproducibility of SmFeO3 perovskite-based gas sensors has been investigated. A set of four SmFeO3 devices, obtained from the same screen-printing deposition, have been tested in lab. with both controlled concns. of CO and biol. fecal samples. The fecal samples tested were employed in the clin. validation protocol of a prototype for non-invasive colorectal cancer prescreening. Sensors showed a high reproducibility degree, with an error lower than 2% of the response value for the test with CO and lower than 6% for fecal samples. Finally, the reproducibility of the SmFeO3 sensor response and recovery times for fecal samples was also evaluated.
- 48Valt, M.; Caporali, M.; Fabbri, B.; Gaiardo, A.; Krik, S.; Iacob, E.; Vanzetti, L.; Malagù, C.; Banchelli, M.; D’Andrea, C.; Serrano-Ruiz, M.; Vanni, M.; Peruzzini, M.; Guidi, V. Air Stable Nickel-Decorated Black Phosphorus and Its Room-Temperature Chemiresistive Gas Sensor Capabilities. ACS Appl. Mater. Interfaces 2021, 13, 44711– 44722, DOI: 10.1021/acsami.1c10763Google Scholar48https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXhvFymtLfO&md5=73fbe9fbb32e41a37540958b3fcb46a9Air Stable Nickel-Decorated Black Phosphorus and Its Room-Temperature Chemiresistive Gas Sensor CapabilitiesValt, Matteo; Caporali, Maria; Fabbri, Barbara; Gaiardo, Andrea; Krik, Soufiane; Iacob, Erica; Vanzetti, Lia; Malagu, Cesare; Banchelli, Martina; D'Andrea, Cristiano; Serrano-Ruiz, Manuel; Vanni, Matteo; Peruzzini, Maurizio; Guidi, VincenzoACS Applied Materials & Interfaces (2021), 13 (37), 44711-44722CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)In the rapidly emerging field of layered two-dimensional functional materials, black phosphorus, the P-counterpart of graphene, is a potential candidate for various applications, e.g., nanoscale optoelectronics, rechargeable ion batteries, electrocatalysts, thermoelecs., solar cells, and sensors. Black phosphorus has shown superior chem. sensing performance; in particular, it is selective for the detection of NO2, an environmental toxic gas, for which black phosphorus has highlighted high sensitivity at a ppb level. In this work, by applying a multiscale characterization approach, we demonstrated a stability and functionality improvement of nickel-decorated black phosphorus films for gas sensing prepd. by a simple, reproducible, and affordable deposition technique. Furthermore, we studied the elec. behavior of these films once implemented as functional layers in gas sensors by exposing them to different gaseous compds. and under different relative humidity conditions. Finally, the influence on sensing performance of nickel nanoparticle dimensions and concn. correlated to the decoration technique and film thickness was investigated.
- 49Madou, M. J.; Morrison, S. R. Gas Sensors Based on Semiconductor Powders. In Chemical Sensing with Solid State Devices; Elsevier, 1989; Vol. 8, pp 479– 516. https://doi.org/10.1016/B978-0-12-464965-1.50017-X.Google ScholarThere is no corresponding record for this reference.
- 50Umar, A.; Ammar, H. Y.; Kumar, R.; Almas, T.; Ibrahim, A. A.; AlAssiri, M. S.; Abaker, M.; Baskoutas, S. Efficient H2 Gas Sensor Based on 2D SnO2 Disks: Experimental and Theoretical Studies. Int. J. Hydrogen Energy 2020, 45, 26388– 26401, DOI: 10.1016/j.ijhydene.2019.04.269Google Scholar50https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXpvFOhsr4%253D&md5=e2de7dc2e7b6be5a334e4ac76a13e2f8Efficient H2 gas sensor based on 2D SnO2 disks: Experimental and theoretical studiesUmar, Ahmad; Ammar, H. Y.; Kumar, Rajesh; Almas, Tubia; Ibrahim, Ahmed A.; AlAssiri, M. S.; Abaker, M.; Baskoutas, S.International Journal of Hydrogen Energy (2020), 45 (50), 26388-26401CODEN: IJHEDX; ISSN:0360-3199. (Elsevier Ltd.)2D SnO2 disks with excellent purity and crystallinity were synthesized through a low cost, facile hydrothermal process and were characterized in terms of their morphol., structural, optical and electrochem. properties. The 2D disk-like morphol. of synthesized SnO2 presented the av. thickness of ∼1μm and possessed the typical rutile tetragonal phase for the SnO2 with preferred growth along (100) plane. As-synthesized SnO2 disks were used for the fabrication of gas sensors for reducing gases like H2, CO, and C3H8. With the optimized temp. at 400°C, the as-synthesized SnO2 electrode expressed the gas responses of 14.7, 9.3 and 8.1 for H2, CO, and C3H8, resp. Contrary, the reasonable response times of 4 s, 3 s, and 8 s and the recovery times of 331 s, 201 s, and 252 s were recorded for H2, CO, and C3H8 gases, resp. The DFT studies conducted herein suggest that the adsorbed oxygenated species act as a primary redox mediator for gas sensing reaction between reductive gases like H2, CO and C3H8, and SnO2 sensor. From DFT anal., a very low heat of adsorption (≤0.2 eV) estd. which suggested the physisorption of the H2 mols. on the surface of the sensing material (i.e. SnO2). In contrast, the deposited oxygen atom forms strong chem. bonds with O2c and O3c sites. The oxygen atom bonded to O2c site control the cond. of the sensor better than the O3c sites.
- 51Wang, F.; Hu, K.; Liu, H.; Zhao, Q.; Wang, K.; Zhang, Y. Low Temperature and Fast Response Hydrogen Gas Sensor with Pd Coated SnO2 Nanofiber Rods. Int. J. Hydrogen Energy 2020, 45, 7234– 7242, DOI: 10.1016/j.ijhydene.2019.12.152Google Scholar51https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXnvVOmsw%253D%253D&md5=721696caaff24ad933c75221e5a8665fLow temperature and fast response hydrogen gas sensor with Pd coated SnO2 nanofiber rodsWang, Feipeng; Hu, Kelin; Liu, Hongcheng; Zhao, Qi; Wang, Kaizheng; Zhang, YuxinInternational Journal of Hydrogen Energy (2020), 45 (11), 7234-7242CODEN: IJHEDX; ISSN:0360-3199. (Elsevier Ltd.)In this work, we introduced a structure of Pd coated SnO2 nanofiber rods (NFRs) prepd. by electrospinning and magnet sputtering. Pd was first deposited on the obtained nanofibers as a catalyst and then fully dispersed during the resulting of SnO2 to improve the hydrogen response. The gas sensing tests showed the palladium enhanced the hydrogen response at low temp. (160°C). When the hydrogen gas concn. was 100 ppm, the limit of detection (LOD) of sensor was as low as 0.25 ppm and the response time was as short as 4 s. Moreover, Pd coated SnO2 also had excellent hydrogen selectivity and repeatability. The gas sensor was suitable for the detection of hydrogen in low-temp. environment. This work provided a new method for the low temp. hydrogen gas sensor with a fast response and low LOD.
- 52Liu, L.; Guo, C.; Li, S.; Wang, L.; Dong, Q.; Li, W. Improved H2 Sensing Properties of Co-Doped SnO2 Nanofibers. Sens. Actuators, B 2010, 150, 806– 810, DOI: 10.1016/j.snb.2010.07.022Google Scholar52https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXhtlehtL%252FF&md5=91d63c28809941e12ba099f0a263be52Improved H2 sensing properties of Co-doped SnO2 nanofibersLiu, Li; Guo, Chuangchang; Li, Shouchun; Wang, Lianyuan; Dong, Qiongye; Li, WeiSensors and Actuators, B: Chemical (2010), 150 (2), 806-810CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)Pure and Co-doped SnO2 nanofibers are synthesized via an electrospinning method and characterized by XRD, SEM, and transmission electron microscope (TEM). Comparing with pure SnO2 nanofibers, Co-doped SnO2 nanofibers exhibit improved H2 sensing properties. Among all the samples (pure, 0.5%, 1%, and 3% Co-doped SnO2 nanofibers), 1% Co-doped SnO2 nanofibers show the highest response with very short response/recovery times. The response is up to 24 when the corresponding sensor is exposed to 100 ppm H2 at 330°, and the response and recovery times are 2 and 3 s, resp. Good selectivity is also obsd. These results make Co-doped SnO2 nanofibers good candidates for fabricating high performance H2 sensors in practical.
- 53Ding, W.; Ansari, N.; Yang, Y.; Bachagha, K. Superiorly Sensitive and Selective H2 Sensor Based on P-n Heterojunction of WO3–CoO Nanohybrids and Its Sensing Mechanism. Int. J. Hydrogen Energy 2021, 46, 28823– 28837, DOI: 10.1016/j.ijhydene.2021.06.070Google Scholar53https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXhsVOktr%252FJ&md5=c2a069ee78de72aebd9d4c83acaaa6e9Superiorly sensitive and selective H2 sensor based on p-n heterojunction of WO3-CoO nanohybrids and its sensing mechanismDing, Wei; Ansari, Nadeem; Yang, Yanhui; Bachagha, KareemInternational Journal of Hydrogen Energy (2021), 46 (56), 28823-28837CODEN: IJHEDX; ISSN:0360-3199. (Elsevier Ltd.)In this study, an excellent hydrogen gas sensor based on the WO3-CoO nanohybrids (WCNHs) heterojunction structure has been successfully fabricated. The WCNHs device showed superior sensitivity, admirable selectivity as well as excellent long-term stability for target gas. In particular, the considerable gas sensing response of WCNHs (5:4) towards 100 ppm hydrogen gas (H2) concn. was reached 39, which is superior to that of the outstanding candidates. Esp., the detection limit capability was as low as 311 ppb. The remarkable response of WCNHs (5:4) can mainly be ascribed to appropriate morphol. characteristics and the promising p-n heterojunction architecture, resulting in efficient absorbing behavior and beneficial charge carrier transportation. As a Result, the aims of improving Ra (intrinsic resistance) and decreasing Rg (test resistance) have been simultaneously achieved ultimately leading to an impressive response value of WCNHs sensing materials. The present results verified that WCNHs heterojunction structure was an outstanding design to enhance the H2 sensing performance for WO3-based gas sensors.
- 54Nakate, U. T.; Lee, G. H.; Ahmad, R.; Patil, P.; Hahn, Y.-B.; Yu, Y. T.; Suh, E. Nano-Bitter Gourd like Structured CuO for Enhanced Hydrogen Gas Sensor Application. Int. J. Hydrogen Energy 2018, 43, 22705– 22714, DOI: 10.1016/j.ijhydene.2018.09.162Google Scholar54https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXitVSjt7zO&md5=ffd9eca3e0b7896d6172ebc56dc630ceNano-bitter gourd like structured CuO for enhanced hydrogen gas sensor applicationNakate, Umesh T.; Lee, Gun Hee; Ahmad, Rafiq; Patil, Pramila; Hahn, Yoon-Bong; Yu, Y. T.; Suh, Eun-kyungInternational Journal of Hydrogen Energy (2018), 43 (50), 22705-22714CODEN: IJHEDX; ISSN:0360-3199. (Elsevier Ltd.)Hydrogen gas sensing were studied using nano-bitter gourd like structured CuO material synthesized via a chem. route. Morphol. of CuO was revealed using FE-SEM and TEM image anal. CuO phase confirmation and mol. structural fingerprint were verified by XRD and Raman anal., resp. Elemental compn. and at. states of elements were studied by EDS and XPS techniques, resp. A remarkable high gas response of 175% was recorded by CuO sensor towards 100 ppm hydrogen (H2) at the operating temp. 200° with response time 150 s. The lowest detection of H2 was obsd. at 2 ppm concn. with the gas response of 5%. The gas response was studied as functions of different operating temps. and concns. Transient gas response and stability were also confirmed for CuO sensor. Hydrogen sensing mechanism of CuO sensor was elucidated.
- 55Agarwal, S.; Kumar, S.; Agrawal, H.; Moinuddin, M. G.; Kumar, M.; Sharma, S. K.; Awasthi, K. An Efficient Hydrogen Gas Sensor Based on Hierarchical Ag/ZnO Hollow Microstructures. Sens. Actuators, B 2021, 346, 130510 DOI: 10.1016/j.snb.2021.130510Google Scholar55https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXhslSqur%252FO&md5=e9bed29b0b34363df0479fb6ed1a0cddAn efficient hydrogen gas sensor based on hierarchical Ag/ZnO hollow microstructuresAgarwal, Sonalika; Kumar, Sanjay; Agrawal, Himanshu; Moinuddin, Mohamad G.; Kumar, Manoj; Sharma, Satinder K.; Awasthi, KamlendraSensors and Actuators, B: Chemical (2021), 346 (), 130510CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)The design of hierarchical zinc oxide (ZnO) microstructures modified with silver (Ag) nanoparticles have emerged as an effective approach for improving the hydrogen gas sensing performance. Here, we report a simple, low-cost chem. co-pptn. method to obtain the Ag/ZnO hollow microstructures and morphol. characterized them by field emission SEM. FESEM images revealed the clear hollow hexagonal tube-like morphol. The existence of Ag in ZnO was confirmed by X-ray diffraction and energy-dispersive X-ray spectroscopy. UV visible absorption and photoluminescence (PL) spectra were also recorded to observe the effect of Ag nanofiller on the optical properties of ZnO. Furthermore, the gas sensing properties of the as-prepd. bare ZnO and Ag/ZnO sensor were investigated. The thoroughly sensing expts. demonstrated that after modification with Ag nanoparticles the ZnO sensor shows superior sensitivity 479% toward 300 ppm hydrogen gas concn., whereas 101% response was noted for the pure ZnO sensor at 250°C working temp. Meanwhile, Ag/ZnO hybrids exhibited excellent selectivity, fast response, and recovery time and also obtained a good and stable response signal at 5 ppm H2 exposure, which indicated that the lower concn. measurement is also attainable. This enhancement in the sensing performance of Ag/ZnO structures toward hydrogen is due to the chem. and electronic sensitization effect of Ag nanoparticles. As a result, such microstructure is attributed to more oxygen species and active sites, and it enhances the sensitivity of a sensor. Moreover, this type of hybrid opens a new path and supports the next generation of innovative materials to fabricate highly selective and sensitive H2 gas sensing devices.
- 56Barsan, N.; Rebholz, J.; Weimar, U. Conduction Mechanism Switch for SnO2 Based Sensors during Operation in Application Relevant Conditions; Implications for Modeling of Sensing. Sens. Actuators, B 2015, 207, 455– 459, DOI: 10.1016/j.snb.2014.10.016Google Scholar56https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhslOru7jJ&md5=6ced05e3f38bc5ab5a765b7930c8e804Conduction mechanism switch for SnO2 based sensors during operation in application relevant conditions; implications for modeling of sensingBarsan, Nicolae; Rebholz, Julia; Weimar, UdoSensors and Actuators, B: Chemical (2015), 207 (Part_A), 455-459CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)In this paper we present exptl. evidence for a conduction mechanism switch for gas sensors based on SnO2 porous, thick film sensing layers under exposure to CO in the presence of humidity. In dry air and CO concn. below 250 ppm the conduction is controlled by the surface depletion layers formed by the trapping of electrons from conduction band on adsorbed oxygen species. In the presence of humidity and at CO concn. exceeding 3 ppm the surface depletion layers are replaced by surface accumulation layers and the conduction mechanism changes accordingly. We also present a model that takes into account the influence of humidity at low CO concns.
- 57Barsan, N.; Weimar, U. Conduction Model of Metal Oxide Gas Sensors. J. Electroceram. 2001, 7, 143– 167, DOI: 10.1023/a:1014405811371Google Scholar57https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38XjsFWjtbw%253D&md5=63535a1a4b0561d1226e873cb862bd77Conduction model of metal oxide gas sensorsBarsan, Nicolae; Weimar, UdoJournal of Electroceramics (2002), 7 (3), 143-167CODEN: JOELFJ; ISSN:1385-3449. (Kluwer Academic Publishers)Tin dioxide is a widely used sensitive material for gas sensors. Many research and development groups in academia and industry are contributing to the increase of (basic) knowledge/(applied) know-how. However, from a systematic point of view the knowledge gaining process seems not to be coherent. One reason is the lack of a general applicable model which combines the basic principles with measurable sensor parameters. The approach in the presented work is to provide a frame model that deals with all contributions involved in conduction within a real world sensor. For doing so, one starts with identifying the different building blocks of a sensor. Afterwards, their main inputs are analyzed in combination with the gas reaction involved in sensing. At the end, the contributions are summarized together with their interactions. The work presented here is one step towards a general applicable model for real world gas sensors.
- 58Arbiol, J.; Cerdà, J.; Dezanneau, G.; Cirera, A.; Peiró, F.; Cornet, A.; Morante, J. R. Effects of Nb Doping on the TiO2 Anatase-to-Rutile Phase Transition. J. Appl. Phys. 2002, 92, 853– 861, DOI: 10.1063/1.1487915Google Scholar58https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38XkvFyjsro%253D&md5=374ceeacd074f18e37cfff48a4422d46Effects of Nb doping on the TiO2 anatase-to-rutile phase transitionArbiol, J.; Cerda, J.; Dezanneau, G.; Cirera, A.; Peiro, F.; Cornet, A.; Morante, J. R.Journal of Applied Physics (2002), 92 (2), 853-861CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)The authors study the influence of Nb doping on the TiO2 anatase-to-rutile phase transition, using combined TEM, Raman spectroscopy, x-ray diffraction and selected area electron diffraction anal. This approach enabled anatase-to-rutile phase transition hindering to be clearly obsd. for low Nb-doped TiO2 samples. Also, there was clear grain growth inhibition in the samples contg. Nb. The use of high resoln. TEM with the authors' samples provides an innovative perspective compared with previous research on this issue. The authors' anal. shows that Nb is segregated from the anatase structure before and during the phase transformation, giving NbO nanoclusters on the surface of the TiO2 rutile nanoparticles.
- 59Uyanga, E.; Gibaud, A.; Daniel, P.; Sangaa, D.; Sevjidsuren, G.; Altantsog, P.; Beuvier, T.; Lee, C. H.; Balagurov, A. M. Structural and Vibrational Investigations of Nb-Doped TiO2 Thin Films. Mater. Res. Bull. 2014, 60, 222– 231, DOI: 10.1016/j.materresbull.2014.08.035Google Scholar59https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhsVGjt7zO&md5=f43ed6d451e3bf9aef1c52feaaad1db4Structural and vibrational investigations of Nb-doped TiO2 thin filmsUyanga, E.; Gibaud, A.; Daniel, P.; Sangaa, D.; Sevjidsuren, G.; Altantsog, P.; Beuvier, T.; Lee, Chih Hao; Balagurov, A. M.Materials Research Bulletin (2014), 60 (), 222-231CODEN: MRBUAC; ISSN:0025-5408. (Elsevier Ltd.)Acid-catalyzed sol-gel and spin-coating methods were used to prep. Nb-doped TiO2 thin film. In this work, we studied the effect of niobium doping on the structure, surface, and absorption properties of TiO2 by energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), X-ray reflectometry (XRR), XPS, Raman, and UV-vis absorption spectroscopy at various annealing temps. EDX spectra show that the Nb:Ti at. ratios of the niobium-doped titania films are in good agreement with the nominal values (5 and 10%). XPS results suggest that charge compensation is achieved by the formation of Ti vacancies. Specific niobium phases are not obsd., thus confirming that niobium is well incorporated into the titania crystal lattice. Thin films are amorphous at room temp. and the formation of anatase phase appeared at an annealing temp. close to 400°C. The rutile phase was not obsd. even at 900 °C (XRD and Raman spectroscopy). Grain sizes and electron densities increased when the temp. was raised. Nb-doped films have higher electron densities and lower grain sizes due to niobium doping. Grain size inhibition can be explained by lattice stress induced by the incorporation of larger Nb5+ ions into the lattice. The band gap energy of indirect transition of the TiO2 thin films was calcd. to be about 3.03 eV. After niobium doping, it decreased to 2.40 eV.
- 60Ruiz, A. M.; Dezanneau, G.; Arbiol, J.; Cornet, A.; Morante, J. R. Insights into the Structural and Chemical Modifications of Nb Additive on TiO2 Nanoparticles. Chem. Mater. 2004, 16, 862– 871, DOI: 10.1021/cm0351238Google Scholar60https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXps1ensw%253D%253D&md5=90faa7ee88ca2a31b37bcff9f1924028Insights into the Structural and Chemical Modifications of Nb Additive on TiO2 NanoparticlesRuiz, Ana M.; Dezanneau, G.; Arbiol, J.; Cornet, A.; Morante, Joan R.Chemistry of Materials (2004), 16 (5), 862-871CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)Solid soln. NbxTi1-xO2+δ nanoparticles were synthesized by a sol-gel method with 0.0 ≤ x ≤ 0.1. Structural and microstructural properties have been studied by XPS, XRD, Raman spectroscopy, and TEM as a function of the Nb/Ti at. ratio and thermal treatment temp. (600-900°C). XRD analyses showed that a percentage of the nominal added Nb was assimilated in substitutional Ti sites in the bulk of TiO2 adopting a pentavalent state. On the other hand, XPS detected a high concn. of Nb at the surface. On the basis of the careful anal. of the XRD and XPS spectra it is reasonable to assume that the concn. of Nb at the surface of the nanoparticles is higher than that in the bulk, esp. for rutile, giving a U-shaped Nb concn. profile. The niobium incorporation stabilizes the titania obstructing the diffusion of anatase-type surface atoms, which prevents grain coarsening and phase transformation. The soly. limit of niobium into titania is greater for the anatase phase (x >0.1) than for the rutile phase (x = 0.06). Once the soly. limit of Nb atoms is surpassed, a ternary phase ascribed to TiNb2O7 has been detected. In addn., the crystallite sizes and the percentage of rutile phase were quite similar for Nb contents above the soly. limit. XRD and XPS measurements suggest that niobium mainly enters into titania phase with valence +5, while Ti maintains its higher oxidn. state (4+), the extra charge being thus partially compensated by titanium vacancies. As derived from XPS analyses in the core levels and the valence band regions, the addn. of Nb resulted in a displacement of the Fermi level toward the conduction band. In consequence, the Nb-altered samples presented a more marked n-type feature, as compared with that of the undoped TiO2.
- 61Zeng, W.; Liu, T.; Wang, Z. Impact of Nb Doping on Gas-Sensing Performance of TiO2 Thick-Film Sensors. Sens. Actuators, B 2012, 166–167, 141– 149, DOI: 10.1016/j.snb.2012.02.016Google Scholar61https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38Xlt1ylsLk%253D&md5=2185bb673d6c708cfeac7616724c70fcImpact of Nb doping on gas-sensing performance of TiO2 thick-film sensorsZeng, Wen; Liu, Tianmo; Wang, ZhongchangSensors and Actuators, B: Chemical (2012), 166-167 (), 141-149CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)Using a simple hydrothermal method, the pristine and Nb doped TiO2 is prepd., and their microstructures and gas-sensing responses to the harmful volatile org. compds. are investigated with a special focus on the impact of Nb additive. We find that the gas response of TiO2 is enhanced significantly by doping Nb, which is understood in theory upon proposed adsorption models. Combining exptl. measurements with first-principles calcns., the working mechanism underlying such improvement in gas-sensing functions by the Nb additive is discussed.
- 62Pan, X.; Yang, M.-Q.; Fu, X.; Zhang, N.; Xu, Y.-J. Defective TiO2 with Oxygen Vacancies: Synthesis, Properties and Photocatalytic Applications. Nanoscale 2013, 5, 3601– 3614, DOI: 10.1039/c3nr00476gGoogle Scholar62https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXmt1Sgtrg%253D&md5=6b2177641fd78fa1b49132130d9c28b3Defective TiO2 with oxygen vacancies: synthesis, properties and photocatalytic applicationsPan, Xiaoyang; Yang, Min-Quan; Fu, Xianzhi; Zhang, Nan; Xu, Yi-JunNanoscale (2013), 5 (9), 3601-3614CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)A review. Titanium dioxide (TiO2), as an important semiconductor metal oxide, has been widely investigated in the field of photocatalysis. The properties of TiO2, including its light absorption, charge transport and surface adsorption, are closely related to its defect disorder, which in turn plays a significant role in the photocatalytic performance of TiO2. Among all the defects identified in TiO2, oxygen vacancy is one of the most important and is supposed to be the prevalent defect in many metal oxides, which has been widely investigated both by theor. calcns. and exptl. characterizations. Here, we give a short review on the existing strategies for the synthesis of defective TiO2 with oxygen vacancies, and the defect related properties of TiO2 including structural, electronic, optical, dissociative adsorption and reductive properties, which are intimately related to the photocatalytic performance of TiO2. In particular, photocatalytic applications with regard to defective TiO2 are outlined. In addn., we offer some perspectives on the challenge and new direction for future research in this field. We hope that this tutorial mini-review would provide some useful contribution to the future design and fabrication of defective semiconductor-based nanomaterials for diverse photocatalytic applications.
- 63Koo, W.-T.; Cho, H.-J.; Kim, D.-H.; Kim, Y. H.; Shin, H.; Penner, R. M.; Kim, I.-D. Chemiresistive Hydrogen Sensors: Fundamentals, Recent Advances, and Challenges. ACS Nano 2020, 14, 14284– 14322, DOI: 10.1021/acsnano.0c05307Google Scholar63https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXitFygs73F&md5=c18a45ec8d320b0818c80c56a2ee76dfChemiresistive Hydrogen Sensors: Fundamentals, Recent Advances, and ChallengesKoo, Won-Tae; Cho, Hee-Jin; Kim, Dong-Ha; Kim, Yoon Hwa; Shin, Hamin; Penner, Reginald M.; Kim, Il-DooACS Nano (2020), 14 (11), 14284-14322CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)A review. Hydrogen (H2) is one of the next-generation energy sources because it is abundant in nature and has a high combustion efficiency that produces environmentally benign products (H2O). However, H2/air mixts. are explosive at H2 concns. above 4%, thus any leakage of H2 must be rapidly and reliably detected at much lower concns. to ensure safety. Among the various types of H2 sensors, chemiresistive sensors are one of the most promising sensing systems due to their simplicity and low cost. This review highlights the advances in H2 chemiresistors, including metal-, semiconducting metal oxide-, carbon-based materials, and other materials. The underlying sensing mechanisms for different types of materials are discussed, and the correlation of sensing performances with nanostructures, surface chem., and electronic properties is presented. In addn., the discussion of each material emphasizes key advances and strategies to develop superior H2 sensors. Furthermore, recent key advances in other types of H2 sensors are briefly discussed. Finally, the review concludes with a brief outlook, perspective, and future directions.
- 64Mokrushin, A. S.; Simonenko, T. L.; Simonenko, N. P.; Gorobtsov, P. Y.; Kadyrov, N. C.; Simonenko, E. P.; Sevastyanov, V. G.; Kuznetsov, N. T. Chemoresistive Gas-Sensing Properties of Highly Dispersed Nb2O5 Obtained by Programmable Precipitation. J. Alloys Compd. 2021, 868, 159090 DOI: 10.1016/j.jallcom.2021.159090Google Scholar64https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXkvVShu7Y%253D&md5=a1dbd5a5884aebfb7aac1bb9ce73d763Chemoresistive gas-sensing properties of highly dispersed Nb2O5 obtained by programmable precipitationMokrushin, Artem S.; Simonenko, Tatiana L.; Simonenko, Nikolay P.; Gorobtsov, Philipp Yu.; Kadyrov, Nail C.; Simonenko, Elizaveta P.; Sevastyanov, Vladimir G.; Kuznetsov, Nikolay T.Journal of Alloys and Compounds (2021), 868 (), 159090CODEN: JALCEU; ISSN:0925-8388. (Elsevier B.V.)Nb2O5 powder obtained by programmable pptn. was used to form a thick gas-sensing film as part of a chemoresistive gas sensor, by screen-printing. The coating of orthorhombic Nb2O5 consisted of nanoparticles with a size of 41.0 ± 2.5 nm. XPS revealed Nb5+, Nb4+ and Nb2+ as well as oxygen vacancies in the crystal structure of niobium oxide. As a result of studying the chemoresistive gas-sensing properties of Nb2O5, it has been shown that among the analyzed gases (H2, CO, NH3, H2S and O2), the greatest sensitivity was obsd. for oxygen and hydrogen sulfide. Nanocryst. niobium oxide showed a high and reproducible response to 0.02-20% O2 (S1 = 1.1-19.0) at a very low detection temp. of 200°C for oxygen sensors. At an operating detection temp. of 250°C, a high and reproducible response to low concns. of hydrogen sulfide of 4-100 ppm (S2 = 1.2-6.6) was detected for Nb2O5. The influence of humidity on the received signals when detecting oxygen and hydrogen sulfide was studied in detail: there was a decrease in the resistance and the response value at 95% humidity in the medium of both gases. However, unlike the process of detecting H2S (when the response of S2 was almost lost), when detg. oxygen, the response of S1 was reduced by a factor of two only, which suggests the possibility of detg. the content of O2 in high humidity conditions.
- 65Guo, Y.; He, X.; Huang, W.; Wang, M. Microstructure Effects on Effective Gas Diffusion Coefficient of Nanoporous Materials. Transp. Porous Media 2019, 126, 431– 453, DOI: 10.1007/s11242-018-1165-4Google ScholarThere is no corresponding record for this reference.
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Abstract
Figure 1
Figure 1. Distribution of particle diameters (nm) in STN samples, revealing the influence of annealing temperature on grain coalescence. Black dotted lines indicate the mean value of the distributions.
Figure 2
Figure 2. X-ray powder diffraction patterns collected at RT. Gray lines parallel to the y axis mark peak positions for ST30 650 to highlight the shift for STN peaks. The fractions of rutile-type (s.g. P42/mnm) and anatase-type (s.g. I41/amd) phases were ∼98 and 2 wt %, respectively.
Figure 3
Figure 3. (a) STN film dynamical responses at 450 °C to 0.4, 1, 2 (inset) 10, 25, 50, and 100 ppm of H2 in dry air and (b) their calibration curves fitted with a power law function. A linear plot for concentrations lower than 2 ppm (inset) was used to estimate the theoretical LOD. (c) Response to four-cycle injection of 0.4 and 100 ppm of H2 as a function of time. (d) Comparison between the responses of STN, ST30 650, and SnO2 films to the same concentration of H2 (sensors performing at their optimal working temperature of 450 °C for STN and ST30 650 and 400 °C for SnO2 650). (25) The legend of graph (d) also applies to graphs (a), (b), and (c).
Figure 4
Figure 4. Influence of humidity on the conductance baseline and conductance after injection of 50 ppm of H2. The temperature inside the chamber was 29 °C in the whole range of RH %.
Figure 5
References
This article references 65 other publications.
- 1Basu, A. K.; Tatiya, S.; Bhatt, G.; Bhattacharya, S. Fabrication Processes for Sensors for Automotive Applications: A Review. In Sensors for Automotive and Aerospace Applications; Springer, 2019; 123– 142.There is no corresponding record for this reference.
- 2Chauhan, P. S.; Bhattacharya, S. Hydrogen Gas Sensing Methods, Materials, and Approach to Achieve Parts per Billion Level Detection: A Review. Int. J. Hydrogen Energy 2019, 44, 26076– 26099, DOI: 10.1016/j.ijhydene.2019.08.0522https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhs1ylsL7P&md5=3b305e968673202509dd7b0eda05e3e0Hydrogen gas sensing methods, materials, and approach to achieve parts per billion level detection: A reviewChauhan, Pankaj Singh; Bhattacharya, ShantanuInternational Journal of Hydrogen Energy (2019), 44 (47), 26076-26099CODEN: IJHEDX; ISSN:0360-3199. (Elsevier Ltd.)A review. Being a clean source of energy, hydrogen gas is in high demand in various industrial and com. applications. However, the explosive nature of H2 gas >4% concn. makes it highly dangerous to store, transport and use. Further, the small size gas mols. of H2 are prone to leak through the smallest possible holes and cracks. Hence, the detection of H2 gas becomes essential even at trace levels. This article reviews various gas sensing strategies including methods, materials, and integrated systems available for the sensitive detection of H2 gas for a bunch of different applications. The article also reviews some approaches which are available in the literature to detect ppb level of H2 gas concns. This review article aims at explaining the different aspects of H2 gas sensing technol. in a simple yet exhaustive manner.
- 3Zappi, A.; Hernandez, R.; Holmes, W. E. A Review of Hydrogen Production from Anaerobic Digestion. Int. J. Environ. Sci. Technol. 2021, 18, 4075– 4090, DOI: 10.1007/s13762-020-03117-w3https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXhtFKjsb3P&md5=b837dcadd4bca6e20b721e952cda74d5A review of hydrogen production from anaerobic digestionZappi, A.; Hernandez, R.; Holmes, W. E.International Journal of Environmental Science and Technology (2021), 18 (12), 4075-4090CODEN: IJESHU; ISSN:1735-1472. (Springer)A review. Recent advances in the utilization of hydrogen as an alternative fuel source to conventional fossil fuels have led to a search for a renewable process of producing hydrogen. Most hydrogen today is produced from hydrocarbons in a process that also releases high levels of carbon dioxide and carbon monoxide, two established greenhouse gasses; because of this harmful means of prodn., research has been directed toward using anaerobic digestion to produce useful levels of hydrogen gas. Anaerobic systems have been shown to produce a biogas that is easily used in producing energy, but certain processes can be performed to further enhance the concns. of hydrogen. These processes include the inhibition of microorganisms that lower hydrogen concns. and the const. removal of hydrogen to promote hydrogen-producing bacteria. Exptl. designs and large-scale applications have shown this process to be environmentally viable with limited, but promising, economic potential. With a const. increase for the need of hydrogen gas, the sustainable prodn. of hydrogen is becoming more important. This explores some of the recent research on this topic and explores the processes behind using anaerobic digestion for hydrogen prodn.
- 4Richter, D.; Fried, A.; Wert, B. P.; Walega, J. G.; Tittel, F. K. Development of a Tunable Mid-IR Difference Frequency Laser Source for Highly Sensitive Airborne Trace Gas Detection. Appl. Phys. B: Lasers Opt. 2002, 75, 281– 288, DOI: 10.1007/s00340-002-0948-y4https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38XnslajsLg%253D&md5=acdff8b05724405496f4213f07fa5f95Development of a tunable mid-IR difference frequency laser source for highly sensitive airborne trace gas detectionRichter, D.; Fried, A.; Wert, B. P.; Walega, J. G.; Tittel, F. K.Applied Physics B: Lasers and Optics (2002), 75 (2-3), 281-288CODEN: APBOEM; ISSN:0946-2171. (Springer-Verlag)The development of a compact tunable mid-IR laser system at 3.5 μm for quant. airborne spectroscopic trace gas absorption measurements is reported. The mid-IR laser system is based on difference frequency generation (DFG) in periodically poled LiNbO3 and uses optical fiber amplified near-IR diode and fiber lasers as pump sources operating at 1083 nm and 1562 nm, resp. This paper describes the optical sensor architecture, performance characteristics of individual pump lasers and DFG, as well as its application to wavelength modulation spectroscopy employing an astigmatic Herriott multi-pass gas absorption cell. This compact system permits detection of formaldehyde with a minimal detectable concn. (1σ replicate precision) of 74 parts-per-trillion by vol. (pptv) for 1 min of averaging time and was achieved using calibrated gas stds., zero air background and rapid dual-beam subtraction. This corresponds to a path length-normalized replicate fractional absorption sensitivity of 2.5 × 10-10 cm-1.
- 5Uslu, H.; Büyükpınar, Ç.; Unutkan, T.; Serbest, H.; SAN, N.; Turak, F.; Bakırdere, S. A Novel Analytical Method for Sensitive Determination of Lead: Hydrogen Assisted T-Shape Slotted Quartz Tube-Atom Trap-Flame Atomic Absorption Spectrometry. Microchem. J. 2018, 137, 155– 159, DOI: 10.1016/j.microc.2017.10.0155https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhslagtb3F&md5=75498cf3eec01364d7118991e25be383A novel analytical method for sensitive determination of lead: Hydrogen assisted T-shape slotted quartz tube-atom trap-flame atomic absorption spectrometryUslu, Humeysa; Buyukpinar, Cagdas; Unutkan, Tugce; Serbest, Hakan; San, Nevin; Turak, Fatma; Bakirdere, SezginMicrochemical Journal (2018), 137 (), 155-159CODEN: MICJAN; ISSN:0026-265X. (Elsevier B.V.)Lead is a toxic metal which affects human health badly due to its high toxicity. The wide application range of lead causes environmental contamination of air, water and soil. Flame at. absorption spectrometry is one of the simple and economical instrument used for the detn. of heavy metals, but it has low sensitivity due to low sample introduction efficiency. In this study, a sensitive anal. method was developed by using T-shaped slotted quartz tube as an atom trap unit to get lower detection limit for lead. The trapped atoms were released using hydrogen gas which supplies reducing environment in T-SQT-AT-FAAS system. Factors such as trapping period, sample and fuel flow rates were optimized to obtain high sensitivity. Under the optimum conditions, limits of detection and quantitation were found to be 0.6 and 2.1 μg L- 1, resp. Accuracy of the developed method was checked and results found under the optimum conditions agreed with the certified value of coal fly ash std. ref. material. The developed method was applied to water samples to figure out its suitability.
- 6Kamiński, M.; Kartanowicz, R.; Jastrzębski, D.; Kamiński, M. M. Determination of Carbon Monoxide, Methane and Carbon Dioxide in Refinery Hydrogen Gases and Air by Gas Chromatography. J. Chromatogr. A 2003, 989, 277– 283, DOI: 10.1016/S0021-9673(03)00032-36https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXhs1Kms7o%253D&md5=ace70bfac6045fedf2abcabcb5f4182dDetermination of carbon monoxide, methane and carbon dioxide in refinery hydrogen gases and air by gas chromatographyKaminski, Marian; Kartanowicz, Rafal; Jastrzebski, Daniel; Kaminski, Marcin M.Journal of Chromatography, A (2003), 989 (2), 277-283CODEN: JCRAEY; ISSN:0021-9673. (Elsevier Science B.V.)This paper illustrates a method for detg. trace amts. of CO, CH4 and CO2 with the detection limit of 0.15, 0.15 and 0.20 μg/l, resp., in refinery H gases or in air. A simple modification of a gas chromatograph equipped with a flame-ionization detector is presented. A Porapak Q column, addnl. connected with a short mol. sieve 5A packed column and a catalytic hydrogenation reactor on the Ni catalyst were applied. The principle of the anal. method proposed is the sepn. of CO from O2 before the introduction of CO to the methanizer. The anal. procedure and examples of the results obtained were presented. The modification applied makes it possible to use the GC instrument for other detns., requiring use of the Porapak Q column and the flame-ionization detector. In such cases, the short mol. sieve 5A column and the methanizer can be by-passed.
- 7Farrah, D.; Bernard-Salas, J.; Spoon, H. W. W.; Soifer, B. T.; Armus, L.; Brandl, B.; Charmandaris, V.; Desai, V.; Higdon, S.; Devost, D.; Houck, J. High-Resolution Mid-Infrared Spectroscopy of Ultraluminous Infrared Galaxies. Astrophys. J. 2007, 667, 149– 169, DOI: 10.1086/5208347https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXhtFyju77I&md5=2f0629451a5069086106df053c51c7a0High-resolution mid-infrared spectroscopy of ultraluminous infrared galaxiesFarrah, D.; Bernard-Salas, J.; Spoon, H. W. W.; Soifer, B. T.; Armus, L.; Brandl, B.; Charmandaris, V.; Desai, V.; Higdon, S.; Devost, D.; Houck, J.Astrophysical Journal (2007), 667 (1, Pt. 1), 149-169CODEN: ASJOAB; ISSN:0004-637X. (University of Chicago Press)We present R ∼ 600, 10-37 μm spectra of 53 ultraluminous IR galaxies (ULIRGs), taken using the IR Spectrograph on board Spitzer. The spectra show fine-structure emission lines of neon, oxygen, sulfur, silicon, argon, chlorine, iron, and phosphorous; mol. hydrogen lines, and C2H2, HCN, and OH- absorption features. We employ diagnostics based on the fine-structure lines, the polycyclic arom. hydrocarbon (PAH) features and the 9.7 μm silicate absorption feature, to show that the IR emission from most ULIRGs is powered mostly by star formation, with only ∼20% of ULIRGs hosting an AGN with a greater IR luminosity than the starburst. The detection of [Ne V] λ14.32 in just under half the sample, however, implies that an AGN contributes significantly to the mid-IR flux in ∼42% of ULIRGs. The starbursts and AGNs in ULIRGs appear more extincted, and for the starbursts more compact than those in lower luminosity systems. The excitations and electron densities in the narrow-line regions of ULIRGs appear comparable to those of starbursts with L .ltorsim. 1011.5 L.sun., although the NLR gas in ULIRGs may be more dense. We show that the [Ne II] λ12.81 + [Ne III] λ15.56 luminosity correlates with both IR luminosity and the luminosity of the 6.2 and 11.2 μm PAH features, and derive a calibration between PAH luminosity and star formation rate. Finally, we show that ULIRGs with silicate absorption strengths Ssil of 0.8 .ltorsim. Ssil .ltorsim. 2.4 are likely to be powered mainly by star formation, but that ULIRGs with Ssil .ltorsim. 0.8, and possibly those with Ssil ⪆ 2.4, contain an IR-luminous AGN.
- 8Sears, J.; Rogers, T.; McCoskey, J.; Lockrem, L.; Watts, H.; Pingel, L.; Conca, J. Proton Transfer Reaction Mass Spectrometry as a Real-Time Method for Continuous Soil Organic Vapor Detection. In Continuous Soil Gas Measurements: Worst Case Risk Parameters; ASTM International: 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, 2013; pp 32– 44. https://doi.org/10.1520/STP157020130026.There is no corresponding record for this reference.
- 9G, N. First Fifty Years of Chemoresistive Gas Sensors. Chemosensors 2015, 3, 1– 20, DOI: 10.3390/chemosensors3010001There is no corresponding record for this reference.
- 10Valt, M.; Fabbri, B.; Gaiardo, A.; Gherardi, S.; Casotti, D.; Cruciani, G.; Pepponi, G.; Vanzetti, L.; Iacob, E.; Malagù, C.; Bellutti, P.; Guidi, V. Aza-Crown-Ether Functionalized Graphene Oxide for Gas Sensing and Cation Trapping Applications. Mater. Res. Express 2019, 6, 075603 DOI: 10.1088/2053-1591/ab11fb10https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXisVOgtL3J&md5=dcbdae87b000a2ec41c629d186cb716dAza-crown-ether functionalized graphene oxide for gas sensing and cation trapping applicationsValt, M.; Fabbri, B.; Gaiardo, A.; Gherardi, S.; Casotti, D.; Cruciani, G.; Pepponi, G.; Vanzetti, L.; Iacob, E.; Malagu, C.; Bellutti, P.; Guidi, V.Materials Research Express (2019), 6 (7), 075603CODEN: MREAC3; ISSN:2053-1591. (IOP Publishing Ltd.)Graphene oxide has been functionalized with 1-aza-15-crown-5 ether via chem. route synthesis. Modification of graphene oxide was achieved via nucleophilic attack where the amine groups of an aza-crown ether mol. can easily react with the epoxy sites of graphene oxide basal plane. Owing to the inherent two-dimensional character of graphene oxide, it resulted in large specific-surface material with strong affinity for charged chem. species. Such property was exploited for reversible and controlled interaction of adsorbed species, envisaging two possible applications of the functionalized graphene oxide. Thus, an easy-to-fabricate and high-sensitivity functionalized graphene oxide-based gas sensor was achieved. The sensing material proved to be highly stable and capable of selectively detecting humidity at room temp. over a wide range of concns. Moreover, the porous scaffold built by the functionalization, together with the well-known affinity of crown ethers to metal ions, allow the use of aza-crown ether functionalized graphene oxide for cation trapping application, e.g. pre-concn. of trace amt. of metals or filter for water. Remarkable results in this field have been obtained with respect to some heavy-metal cations of environmental interest. We also demonstrated significant enhancement in performance vs. pure graphene oxide in both tested applications. More generally, the functionalization approach we pursued appears to be quite flexible in the tested applications. In fact, with an appropriate selection of crown ethers with specific cage-like structure, functionalized graphene oxide allows the capture of any desired guest in order to prep. a wide range of other crown-ether-GO nanocomposites for different applications.
- 11Gaiardo, A.; Fabbri, B.; Guidi, V.; Bellutti, P.; Giberti, A.; Gherardi, S.; Vanzetti, L.; Malagù, C.; Zonta, G. Metal Sulfides as Sensing Materials for Chemoresistive Gas Sensors. Sensors 2016, 16, 296 DOI: 10.3390/s1603029611https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXnvFygsQ%253D%253D&md5=2239f5f5b7f6a8a9e4b04ab3e267ba45Metal sulfides as sensing materials for chemoresistive gas sensorsGaiardo, Andrea; Fabbri, Barbara; Guidi, Vincenzo; Bellutti, Pierluigi; Giberti, Alessio; Gherardi, Sandro; Vanzetti, Lia; Malagu, Cesare; Zonta, GiuliaSensors (2016), 16 (3), 296/1-296/19CODEN: SENSC9; ISSN:1424-8220. (MDPI AG)This work aims at a broad overview of the results obtained with metal-sulfide materials in the field of chemoresistive gas sensing. Indeed, despite the well-known elec., optical, structural and morphol. features previously described in the literature, metal sulfides present lack of investigation for gas sensing applications, a field in which the metal oxides still maintain a leading role owing to their high sensitivity, low cost, small dimensions and simple integration, in spite of the wide assortment of sensing materials. However, despite their great advantages, metal oxides have shown significant drawbacks, which have led to the search for new materials for gas sensing devices. In this work, Cadmium Sulfide and Tin (IV) Sulfide were investigated as functional materials for thick-film chemoresistive gas-sensors fabrication and they were tested both in thermo- and in photo-activation modes. Furthermore, elec. characterization was carried out in order to verify their gas sensing properties and material stability, by comparing the results obtained with metal sulfides to those obtained by using their metal-oxides counterparts. The results highlighted the possibility to use metal sulfides as a novel class of sensing materials, owing to their selectivity to specific compds., stability, and the possibility to operate at room temp.
- 12Tricoli, A.; Righettoni, M.; Pratsinis, S. E. Minimal Cross-Sensitivity to Humidity during Ethanol Detection by SnO2–TiO2 Solid Solutions. Nanotechnology 2009, 20, 315502 DOI: 10.1088/0957-4484/20/31/31550212https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXhtVynu7%252FL&md5=37168a3fe2a23bc1eb3672dbc12395a7Minimal cross-sensitivity to humidity during ethanol detection by SnO2-TiO2 solid solutionsTricoli, Antonio; Righettoni, Marco; Pratsinis, Sotiris E.Nanotechnology (2009), 20 (31), 315502/1-315502/10CODEN: NNOTER; ISSN:1361-6528. (Institute of Physics Publishing)A nanocomposite material is presented that optimally combines the excellent gas sensitivity of SnO2 and the selectivity of TiO2. Nanostructured, rutile titanium-tin oxide solid solns. ≤81.5% Ti, as detd. by x-ray diffraction, were made by scalable spray combustion (flame spray pyrolysis) of organometallic precursor solns., directly deposited and in situ annealed onto sensing electrodes in one step. Above that content, segregation of anatase TiO2 takes place. It was discovered that at low titanium contents (<5 Ti%), these materials exhibit higher sensitivity to ethanol vapor than pure SnO2 and, in particular, limited cross-sensitivity to relative humidity, a long standing challenge for metal oxide gas sensors. These solid solns. are aggregated nanoparticles with an enhanced presence of Ti on their surface as indicated by Raman and IR-spectroscopy. The presence of such low Ti-content in the SnO2 lattice drastically reduces the band gap of these solid solns., as detd. by UV-vis absorption, almost to that of pure TiO2. Furthermore, titania reduces the no. of rooted and terminal OH species (that are correlated to the cross-sensitivity of tin oxide to water) on the particle surface as detd. by IR-spectroscopy. The present material represents a new class of sensors where detection of gases and org. vapors can be accomplished without pre-treatment of the gas mixt., avoiding other semiconducting components that require more heating power and that add bulkiness to a sensing device. This is attractive in developing miniaturized sensors esp. for microelectronics and medical diagnostics.
- 13Pargoletti, E.; Verga, S.; Chiarello, G. L.; Longhi, M.; Cerrato, G.; Giordana, A.; Cappelletti, G. Exploring SnxTi1–xO2 Solid Solutions Grown onto Graphene Oxide (GO) as Selective Toluene Gas Sensors. Nanomaterials 2020, 10, 761 DOI: 10.3390/nano1004076113https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXhtVOgsL7F&md5=b0e5b32dfa35f8a8f55701817699c238Exploring SnxTi1-xO2 solid solutions grown onto graphene oxide (GO) as selective toluene gas sensorsPargoletti, Eleonora; Verga, Simone; Chiarello, Gian Luca; Longhi, Mariangela; Cerrato, Giuseppina; Giordana, Alessia; Cappelletti, GiuseppeNanomaterials (2020), 10 (4), 761CODEN: NANOKO; ISSN:2079-4991. (MDPI AG)The major drawback of oxide-based sensors is the lack of selectivity. In this context, SnxTi1-xO2/graphene oxide (GO)-based materials were synthesized via a simple hydrothermal route, varying the titanium content in the tin dioxide matrix. Then, toluene and acetone gas sensing performances of the as-prepd. sensors were systematically investigated. Specifically, by using 32:1 SnO2/GO and 32:1 TiO2/GO, a greater selectivity towards acetone analyte, also at room temp., was obtained even at ppb level. However, solid solns. possessing a higher content of tin relative to titanium (as 32:1 Sn0.55Ti0.45O2/GO) exhibited higher selectivity towards bigger and non-polar mols. (such as toluene) at 350 °C, rather than acetone. A deep exptl. investigation of structural (XRPD and Raman), morphol. (SEM, TEM, BET surface area and pores vol.) and surface (XPS analyses) properties allowed us to give a feasible explanation of the different selectivity. Moreover, by exploiting the UV light, the lowest operating temp. to obtain a significant and reliable signal was 250 °C, keeping the greater selectivity to the toluene analyte. Hence, the feasibility of tuning the chem. selectivity by engineering the relative amt. of SnO2 and TiO2 is a promising feature that may guide the future development of miniaturized chemoresistors.
- 14Radecka, M.; Zakrzewska, K.; Rękas, M. SnO2–TiO2 Solid Solutions for Gas Sensors. Sens. Actuators, B 1998, 47, 194– 204, DOI: 10.1016/S0925-4005(98)00023-914https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1cXksV2gur8%253D&md5=ea175915d58aa89d2d4304d96e074408SnO2-TiO2 solid solutions for gas sensorsRadecka, Marta; Zakrzewska, Katarzyna; Rgkas, MieczystawSensors and Actuators, B: Chemical (1998), 47 (1-3), 194-204CODEN: SABCEB; ISSN:0925-4005. (Elsevier Science S.A.)Mixed oxide gas sensors of SnO2-TiO2 were prepd. as polycryst. ceramics and radiofrequency-sputtered thin films. The influence of the chem. and phase compn. on the crystallog. structure, microstructure and sensor performance is discussed. The measurements of the elec. resistance as a function of hydrogen partial pressure were performed with air or argon as a ref. gas. The results are analyzed in terms of the surface and bulk interaction models. Probably hydrogen detection in air involves the preadsorbed O- species. Hydrogen interaction with the SnO2-TiO2 system in Ar atm. is governed by bulk diffusion of oxygen vacancies.
- 15Carotta, M. C.; Gherardi, S.; Guidi, V.; Malagù, C.; Martinelli, G.; Vendemiati, B.; Sacerdoti, M.; Ghiotti, G.; Morandi, S. Electrical and Spectroscopic Properties of Ti0.2Sn0.8O2 Solid Solution for Gas Sensing. Thin Solid Films 2009, 517, 6176– 6183, DOI: 10.1016/j.tsf.2009.04.00215https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXoslajsrs%253D&md5=f0c9219917fe5b888a6bd7e0c57c9ba5Electrical and spectroscopic properties of Ti0.2Sn0.8O2 solid solution for gas sensingCarotta, M. C.; Gherardi, S.; Guidi, V.; Malagu, C.; Martinelli, G.; Vendemiati, B.; Sacerdoti, M.; Ghiotti, G.; Morandi, S.Thin Solid Films (2009), 517 (22), 6176-6183CODEN: THSFAP; ISSN:0040-6090. (Elsevier B.V.)In this work we report the synthesis, microstructure, elec. and spectroscopic properties, and sensing performances of TixSn1-xO2 (x = 0.1, 0.2, 0.3, 0.5, 0.7, 0.9) nano-powders and of SnO2 and TiO2 ref. samples, prepd. via sol-gel route starting from metal-org. precursors working in hydro-alc. media. Actually, the attention is particularly focused on properties of the sample with x = 0.2, in comparison with ones of the other solid solns. and of the single oxides. Indeed, this solid soln. showed a borderline behavior between that of the solid soln. with x = 0.1 and that of the other solid solns. with x ≥ 0.3. An abrupt change in the structural, elec. and spectroscopic properties has been obsd., passing from sample with x = 0.1, showing a behavior very similar to that of SnO2, to 1 x = 0.3 showing a behavior very similar to that of TiO2. The borderline properties of the mixed oxide with x = 0.2 represent the expected continuous transition among the 2 behaviors.
- 16Carotta, M. C.; Fioravanti, A.; Gherardi, S.; Malagù, C.; Sacerdoti, M.; Ghiotti, G.; Morandi, S. (Ti,Sn) Solid Solutions as Functional Materials for Gas Sensing. Sens. Actuators, B 2014, 194, 195– 205, DOI: 10.1016/j.snb.2013.12.02116https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXitF2gtL0%253D&md5=7f27c4e064f7a9eea711d7f141151ddeStudy on (Ti,Sn) solid solutions as functional materials for gas sensingCarotta, M. C.; Fioravanti, A.; Gherardi, S.; Malagu, C.; Sacerdoti, M.; Ghiotti, G.; Morandi, S.Sensors and Actuators, B: Chemical (2014), 194 (), 195-205CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)Metal-oxide semiconductors are widely used as functional materials for gas sensing because of their chemoresistive effect when interacting with ambient gases. For this work, nanosized TixSn1-xO2 have been synthesized at increasing Ti molar ratio (x = 0, 0.1, 0.2, 0.25, 0.3, 0.5, 0.7, 0.8, 0.9, 0.95, 1) and extensively investigated through a wide variety of characterizations. It turned out that the merging process of the two single oxides formed new compds. with improved gas responses compared to pure TiO2 and also to pure SnO2. Moreover, all investigated physico-chem. characteristics resulted tuneable through the titanium content in the solid soln. Each characterization carried out onto TixSn1-xO2 solid solns. made it possible to identify two classes of materials with SnO2-like or TiO2-like behaviors, the best CO response being on the intersection of the two species of materials. Moreover, a very interesting anal. on the generally accepted elec. transport model through polycryst. semiconductors has been carried out. Indeed, the comparison with exptl. evidences has highlighted a conduction mechanism not previously considered.
- 17Carney, C. M.; Yoo, S.; Akbar, S. A. TiO2–SnO2 Nanostructures and Their H2 Sensing Behavior. Sens. Actuators, B 2005, 108, 29– 33, DOI: 10.1016/j.snb.2004.11.05817https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXltFWntbg%253D&md5=6aed24306c27027ff79dce4664b436fdTiO2-SnO2 nanostructures and their H2 sensing behaviorCarney, Carmen M.; Yoo, Sehoon; Akbar, Sheikh A.Sensors and Actuators, B: Chemical (2005), 108 (1-2), 29-33CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)Pure TiO2 and mixed oxide samples of TiO2 and SnO2 sintered samples having different surface areas were synthesized using a heat treatment in H2 bearing gas. Nanostructures of solid solns. and spinodally-decompd. samples of mixed oxides were compared to the oriented nanofibers formed in pure TiO2 created by the same heat treatment. Comparisons between the sensing characteristics of the samples were made to det. that the samples with higher surface areas were more sensitive to H2 in the presence of O2.
- 18Shi, Y.; Xu, H.; Liu, T.; Zeb, S.; Nie, Y.; Zhao, Y.; Qin, C.; Jiang, X. Advanced Development of Metal Oxide Nanomaterials for H2 Gas Sensing Applications. Mater. Adv. 2021, 2, 1530– 1569, DOI: 10.1039/D0MA00880J18https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXjtV2qu7c%253D&md5=fed6c113bb83a27640991436953085afAdvanced development of metal oxide nanomaterials for H2 gas sensing applicationsShi, Yushu; Xu, Huiyan; Liu, Tongyao; Zeb, Shah; Nie, Yong; Zhao, Yiming; Qin, Chengyuan; Jiang, XuchuanMaterials Advances (2021), 2 (5), 1530-1569CODEN: MAADC9; ISSN:2633-5409. (Royal Society of Chemistry)A review. Hydrogen (H2) has been considered as one of the cleanest renewable energy sources. However, it is still challenging to use H2 due to its hazardous flammable and explosive properties under mild conditions in the event of leakage, and the difficulty to detect or sense it through human sensory organs because of its colorless and odorless nature. Traditional detection methods are usually complicated and the testing instruments are expensive. Thus, it is of significant importance to develop sensors for H2 detection with facile operation conditions, low costs, and excellent performance (i.e., sensitivity, selectivity, and stability). To overcome the problems and for practically detecting H2 gas, metal oxide (MOx) nanomaterials have become more crucial in such a gas sensor because of the simple prepn. method, high surface area, high sensitivity, and low costs. This review will focus on the recent state-of-the-art advances in resistive H2 gas sensors based on MOx nanomaterials, starting from a brief introduction of resistive gas sensors. The following sections will focus on the synthesis of different structures and types of such MOx nanomaterials, including mono/binary/ternary/ternary or more complicated MOx nanomaterials. Meanwhile, we highlight some regulation methods such as surface or inner decoration by noble or non-noble metals to improve the performance as well as summarize and compare different structures (core-shell and heterojunction), and mechanisms in H2 sensing. Finally, the opportunities and challenges of MOx-based H2 gas sensors are proposed in detail.
- 19Zeng, W.; Liu, T.; Wang, Z.; Tsukimoto, S.; Saito, M.; Ikuhara, Y. Selective Detection of Formaldehyde Gas Using a Cd-Doped TiO2-SnO2 Sensor. Sensors 2009, 9, 9029– 9038, DOI: 10.3390/s9110902919https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXhsVylurrE&md5=1328dfdc32ea78a92004856a2d7bad25Selective detection of formaldehyde gas using a cd-doped TiO2-SnO2 sensorZeng, Wen; Liu, Tianmo; Wang, Zhongchang; Tsukimoto, Susumu; Saito, Mitsuhiro; Ikuhara, YuichiSensors (2009), 9 (11), 9029-9038CODEN: SENSC9; ISSN:1424-8220. (Molecular Diversity Preservation International)We report the microstructure and gas-sensing properties of a nonequil. TiO2-SnO2 solid soln. prepd. by the sol-gel method. In particular, we focus on the effect of Cd doping on the sensing behavior of the TiO2-SnO2 sensor. Of all volatile org. compd. gases examd., the sensor with Cd doping exhibits exclusive selectivity as well as high sensitivity to formaldehyde, a main harmful indoor gas. The key gas-sensing quantities, max. sensitivity, optimal working temp., and response and recovery time, are found to meet the basic industrial needs. This makes the Cd-doped TiO2-SnO2 composite a promising sensor material for detecting the formaldehyde gas.
- 20Carotta, M. C.; Cervi, A.; Giberti, A.; Guidi, V.; Malagù, C.; Martinelli, G.; Puzzovio, D. Metal-Oxide Solid Solutions for Light Alkane Sensing. Sens. Actuators, B 2008, 133, 516– 520, DOI: 10.1016/j.snb.2008.03.01220https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXptVClsL8%253D&md5=22cddad5d0f616f5d9a93ab35d868cdfMetal-oxide solid solutions for light alkane sensingCarotta, M. C.; Cervi, A.; Giberti, A.; Guidi, V.; Malagu, C.; Martinelli, G.; Puzzovio, D.Sensors and Actuators, B: Chemical (2008), 133 (2), 516-520CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)Sensing of light alkanes via chemoresistive gas sensors was addressed. Screen-printed films of a solid soln. of mixed Sn and Ti oxides were selected for the purpose. The films sensitively detect 100 ppm of such gases and 500 ppm of methane, the two levels being by far lower than the alarm limits for these gases. Information about the working mechanism of chem. reactions on the surface is discussed under either dry or wet condition.
- 21Carotta, M. C.; Guidi, V.; Malagù, C.; Vendemiati, B.; Zanni, A.; Martinelli, G.; Sacerdoti, M.; Licoccia, S.; Vona, M. L. Di.; Traversa, E. Vanadium and Tantalum-Doped Titanium Oxide (TiTaV): A Novel Material for Gas Sensing. Sens. Actuators, B 2005, 108, 89– 96, DOI: 10.1016/j.snb.2004.11.07021https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXltFWmurk%253D&md5=ff62526f70037c3e45dfec96df058d60Vanadium and tantalum-doped titanium oxide (TiTaV): a novel material for gas sensingCarotta, Maria Cristina; Guidi, Vincenzo; Malagu, Cesare; Vendemiati, Beatrice; Zanni, Alex; Martinelli, Giuliano; Sacerdoti, Michele; Licoccia, Silvia; Di Vona, Maria Luisa; Traversa, EnricoSensors and Actuators, B: Chemical (2005), 108 (1-2), 89-96CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)A new material based on titanium dioxide modified by tantalum and vanadium was synthesized. The prepd. powders were deposited to produce gas sensors as thick films through screen-printing technol. The cryst. phase and morphol. were examd. by XRD and SEM analyses. Ta addn. inhibited the anatase-to-rutile phase transformation and hindered grain growth during heating, while vanadium did the opposite. The sensors were tested with different gases showing good selectivity; in particular, the samples with greatest content of Ta showed good response to benzene, only slightly influenced by presence of carbon monoxide.
- 22Ferroni, M.; Carotta, M.; Guidi, V.; Martinelli, G.; Ronconi, F.; Richard, O.; Van Dyck, D.; Van Landuyt, J. Structural Characterization of Nb–TiO2 Nanosized Thick-Films for Gas Sensing Application. Sens. Actuators, B 2000, 68, 140– 145, DOI: 10.1016/S0925-4005(00)00474-322https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXmtVKmsro%253D&md5=1c8bde660b8c0638f21a2ea5420f19d6Structural characterization of Nb-TiO2 nanosized thick-films for gas sensing applicationFerroni, M.; Carotta, M. C.; Guidi, V.; Martinelli, G.; Ronconi, F.; Richard, O.; Van Dyck, D.; Van Landuyt, J.Sensors and Actuators, B: Chemical (2000), 68 (1-3), 140-145CODEN: SABCEB; ISSN:0925-4005. (Elsevier Science S.A.)Pure and Nb-doped TiO2 thick-films were prepd. by screen-printing, starting from nanosized powders. Grain growth and cryst. phase modification occurred as consequence of firing at high temp. It has been shown that niobium addn. inhibits grain coarsening and hinders anatase-to-rutile phase transition. These semiconducting films exhibited n-type behavior, while Nb acted as donor-dopant. Gas measurements demonstrated that the films are suitable for CO or NO2 sensing. Microstructural characterization by electron microscopy and DTA highlights the dependence of gas-sensing behavior on film's properties.
- 23Guidi, V.; Carotta, M. C.; Ferroni, M.; Martinelli, G.; Sacerdoti, M. Effect of Dopants on Grain Coalescence and Oxygen Mobility in Nanostructured Titania Anatase and Rutile. J. Phys. Chem. B 2003, 107, 120– 124, DOI: 10.1021/jp013572u23https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38Xpt1ynsr0%253D&md5=8329c8b4f4a7f3dd485b479212baf5e8Effect of Dopants on Grain Coalescence and Oxygen Mobility in Nanostructured Titania Anatase and RutileGuidi, V.; Carotta, M. C.; Ferroni, M.; Martinelli, G.; Sacerdoti, M.Journal of Physical Chemistry B (2003), 107 (1), 120-124CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)Grain growth and the anatase-to-rutile phase transition in nanostructured titania have been investigated by electron microscopy, X-ray diffraction, and DTA. For pure TiO2, thermal treatment resulted in complete phase transition and considerable grain coarsening, because of the grain boundary nucleation mechanism for the rutile phase. The effect of doping of the TiO2 nanophase has also been addressed. Phase transition turned out to be strongly affected by the presence of Ta and Nb because nucleation of rutile was favored at the surface of anatase grains. Doping allowed the maintenance of the ultrafine anatase phase even at high annealing temp. Thermal anal. highlighted that oxygen mobility in the titania lattice is affected by doping and related to the inhibition of grain coalescence and phase transition.
- 24Gardecka, A. J.; Goh, G. K. L.; Sankar, G.; Parkin, I. P. On the Nature of Niobium Substitution in Niobium Doped Titania Thin Films by AACVD and Its Impact on Electrical and Optical Properties. J. Mater. Chem. A 2015, 3, 17755– 17762, DOI: 10.1039/c5ta03772g24https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXht1GmurfK&md5=4dccae6cc23f85f6ce037ebe7bd486a3On the nature of niobium substitution in niobium doped titania thin films by AACVD and its impact on electrical and optical propertiesGardecka, A. J.; Goh, G. K. L.; Sankar, G.; Parkin, I. P.Journal of Materials Chemistry A: Materials for Energy and Sustainability (2015), 3 (34), 17755-17762CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)Niobium doped TiO2 thin films were deposited on silica coated glass substrate using aerosol assisted CVD (AACVD) from hexane soln., at 500°. The as-deposited films appeared blue, were transparent in the visible, were reflective in the IR region at ∼30% and were elec. conductive (n = 1.23 × 1019 cm-3, μ = 18.9 cm2 V-1 s-1, sheet resistance = 120 Ω .box.-1). The structure of the films was studied using XRD, Raman spectroscopy, XPS and x-ray absorption spectroscopy (XAS). No visible phase segregation was found by XRD nor by Raman, though anal. of the Nb K-edge using XANES and EXAFS revealed niobium both incorporated into the titanium dioxide lattice as well as present as Nb2O5. The high resoln. TEM imaging showed sub 4 nm Nb2O5 crystals within the lattice. This work questions the soly. limit of niobium in the TiO2 lattice and suggests previous literature on Nb-doped TiO2 may have overestimated the degree of niobium substitution.
- 25Carotta, M. C.; Benetti, M.; Guidi, V.; Gherardi, S.; Malagu’, C.; Vendemiati, B.; Martinelli, G. Nanostructured (Sn,Ti,Nb)O2 Solid Solution for Hydrogen Sensing. MRS Proc. 2006, 915, 0915– R07-10, DOI: 10.1557/PROC-0915-R07-10There is no corresponding record for this reference.
- 26Chiorino, A.; Ghiotti, G.; Prinetto, F.; Carotta, M.; Gnani, D.; Martinelli, G. Preparation and Characterization of SnO2 and MoOx–SnO2 Nanosized Powders for Thick Film Gas Sensors. Sens. Actuators, B 1999, 58, 338– 349, DOI: 10.1016/S0925-4005(99)00094-526https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXnvFWlsrw%253D&md5=1a2e0b36a4548985d84dede039076a31Preparation and characterization of SnO2 and MoOx-SnO2 nanosized powders for thick film gas sensorsChiorino, A.; Ghiotti, G.; Prinetto, F.; Carotta, M. C.; Gnani, D.; Martinelli, G.Sensors and Actuators, B: Chemical (1999), 58 (1-3), 338-349CODEN: SABCEB; ISSN:0925-4005. (Elsevier Science S.A.)This work gives results about the characterization of SnO2 materials, prepd. via the sol-gel route, pure and Mo6+-added. The materials were characterized as powders or thick films using a variety of techniques. The morphol. of the powders was analyzed by XRD, SEM, TEM and HRTEM, their texture by volumetric measurements. The morphol. of the thick films was analyzed by SEM. The goal of obtaining powders and films made by regularly shaped and nanosized (30 50 nm) particles, even after thermal treatments at 850° is attained. FTIR spectroscopic and elec. measurements were employed on powders and films, resp., to obtain information on the electronic effect due to the molybdenum addn. FTIR results show that Mo lowers the intensity of the light scattered by free electrons and the intensity of a broad absorption, previously assigned to the photoionization of VO+[VO+ + hv → VO2+ + e- (c.b.)]. Accordingly, elec. data show that molybdenum markedly lowers (of ∼2 orders of magnitude) the conductance of the films in air. Elec. measurements show that Mo lowers the response of tin oxide towards CO, but leaves almost unaltered or enhances its ability to sense NO2, depending on the thermal pretreatments. Both pure and Mo-added materials treated at 650° show the same response to NO2. However, for the pure material treated at 850° the response to NO2 is halved, while it is almost unaffected by the thermal treatment on the Mo-added materials. The sensing temp. of max. response is in any case 150°. FTIR spectroscopy was also employed to obtain information on the Mo species present on the surface of the materials after treatments in oxygen and on how they are affected in the presence of the different testing gases. Also surface species formed by NO2 interaction were carefully studied.
- 27Gaiardo, A.; Fabbri, B.; Giberti, A.; Valt, M.; Gherardi, S.; Guidi, V.; Malagù, C.; Bellutti, P.; Pepponi, G.; Casotti, D.; Cruciani, G.; Zonta, G.; Landini, N.; Barozzi, M.; Morandi, S.; Vanzetti, L.; Canteri, R.; Della Ciana, M.; Migliori, A.; Demenev, E. Tunable Formation of Nanostructured SiC/SiOC Core-Shell for Selective Detection of SO2. Sens. Actuators, B 2020, 305, 127485 DOI: 10.1016/j.snb.2019.12748527https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXitlOgt7%252FJ&md5=0e49d93329904cb494fd7f24fa897f9bTunable formation of nanostructured SiC/SiOC core-shell for selective detection of SO2Gaiardo, A.; Fabbri, B.; Giberti, A.; Valt, M.; Gherardi, S.; Guidi, V.; Malagu, C.; Bellutti, P.; Pepponi, G.; Casotti, D.; Cruciani, G.; Zonta, G.; Landini, N.; Barozzi, M.; Morandi, S.; Vanzetti, L.; Canteri, R.; Della Ciana, M.; Migliori, A.; Demenev, E.Sensors and Actuators, B: Chemical (2020), 305 (), 127485CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)Silicon carbide is a well-known material with high thermal, mech. and chem. stability. These properties have allowed, over time, its wide use as an inert material to be employed as a substrate or support in different applications. In this work, we demonstrate that, under proper conditions, it is possible to activate the chem. reactivity of nanostructured SiC, which can be employed for chemoresistive purposes. With this aim, a com. powder of SiC has been characterized from a morphol., structural and thermal point of view. Then, screen-printed thick films were obtained from SiC powder and thus tested as a functional material for chemoresistive gas sensors, in thermo-activation mode. The samples were exposed to 13 gases with important chem. differences. Analyses showed that SiC is an extremely selective functional material for the detection of sulfur dioxide (SO2) in concns. within the ppm range. This interesting result was found at high working temps. (600-800°C), useful for harsh environments, and the measurements proved to be completely free from humidity neg. interference. Thermo-gravimetric and XPS characterizations highlighted that the high selectivity of the SiC layer is promoted by the thermal formation of a SiC/SiOC core-shell, tunable by controlling temp. and humidity parameters. An interpretation of the gas sensing mechanism occurring between SO2 mols. and SiC/SiOC core-shell has been proposed. The unexpected chem. activity, identified for nanostructured SiC, can be exploited for the specific detection of SO2, since this gaseous compd. plays an important role in air pollution, industrial processes and winemaking.
- 28Guidi, V.; Fabbri, B.; Gaiardo, A.; Gherardi, S.; Giberti, A.; Malagù, C.; Zonta, G.; Bellutti, P. Metal Sulfides as a New Class of Sensing Materials. Procedia Eng. 2015, 120, 138– 141, DOI: 10.1016/j.proeng.2015.08.58628https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhsFWntbzK&md5=e7acc05f6a12bf1fc888a0195e830f4fMetal Sulfides as a New Class of Sensing MaterialsGuidi, V.; Fabbri, B.; Gaiardo, A.; Gherardi, S.; Giberti, A.; Malagu, C.; Zonta, G.; Bellutti, P.Procedia Engineering (2015), 120 (), 138-141CODEN: PERNBE; ISSN:1877-7058. (Elsevier Ltd.)In the recent years, metal sulfide nanostructured materials have become established in different research fields thanks to their excellent properties. Among the potential applications, metal sulfides may have a high standing role for gas sensing, in which, despite the wide assortment of sensing materials, still metal-oxides maintain a leading role because of their high sensitivity, low cost, small dimensions and simple integration. Experimentation carried out in this work with CdS and SnS2 thick film sensors has showed an unexpected improvements of the chemoresistive properties with respect to their oxides counterparts, in particular toward selectivity to specific compds., stability and the possibility to operate at room temp. This opens towards the study of a novel class of sensing materials, which may solve the const. drift of the signal suffered by metal-oxides and ascribed to the in/out diffusion of oxygen vacancies, which alters the doping level.
- 29Gaiardo, A.; Fabbri, B.; Giberti, A.; Guidi, V.; Bellutti, P.; Malagù, C.; Valt, M.; Pepponi, G.; Gherardi, S.; Zonta, G.; Martucci, A.; Sturaro, M.; Landini, N. ZnO and Au/ZnO Thin Films: Room-Temperature Chemoresistive Properties for Gas Sensing Applications. Sens. Actuators, B 2016, 237, 1085– 1094, DOI: 10.1016/j.snb.2016.07.13429https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xht1ymtL7J&md5=17afd8eaac5508605b297ff68b855940ZnO and Au/ZnO thin films: Room-temperature chemoresistive properties for gas sensing applicationsGaiardo, A.; Fabbri, B.; Giberti, A.; Guidi, V.; Bellutti, P.; Malagu, C.; Valt, M.; Pepponi, G.; Gherardi, S.; Zonta, G.; Martucci, A.; Sturaro, M.; Landini, N.Sensors and Actuators, B: Chemical (2016), 237 (), 1085-1094CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)Zinc Oxide has been widely investigated for its photocatalytic properties, which enhance the bulk/surface charge transfer at room temp. At the same time, the doping of semiconductor materials with metals allows the modification of their phys. and chem. properties, and hence their performance as gas sensors. The aim of this work was to investigate the difference between thin-film sensors based on pure ZnO nanoparticles and on gold-cluster decorated ZnO in photo-activation mode. The nanopowders were synthesized through simple sol-gel methods and chem., morphol. and structurally characterized. Thin films were deposited by spin coating onto alumina substrates. The sensing layers were tested with several gases in photo-activation mode, illuminated with radiation wavelengths of 525, 468, 400 and 385 nm. Gold-decorated ZnO thin film showed some interesting features, such as better chemoresistive properties than pure ZnO under photo-activation mode, when illuminated with a wavelength of 385 nm. A selective response of the sensing film to NO2 under green light irradn. was obsd., in particular in dry air condition. Furthermore, the humidity effect on the sensing responses was investigated, highlighting a possible application of Au/ZnO for the detection of few ppm of SO2 with a high percentage of relative humidity.
- 30Zonta, G.; Astolfi, M.; Casotti, D.; Cruciani, G.; Fabbri, B.; Gaiardo, A.; Gherardi, S.; Guidi, V.; Landini, N.; Valt, M.; Malagù, C. Reproducibility Tests with Zinc Oxide Thick-Film Sensors. Ceram. Int. 2020, 46, 6847– 6855, DOI: 10.1016/j.ceramint.2019.11.17830https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXit1Wrt7zN&md5=dba0f188b916c678a4bd2975a29dd8f5Reproducibility tests with zinc oxide thick-film sensorsZonta, G.; Astolfi, M.; Casotti, D.; Cruciani, G.; Fabbri, B.; Gaiardo, A.; Gherardi, S.; Guidi, V.; Landini, N.; Valt, M.; Malagu, C.Ceramics International (2020), 46 (5), 6847-6855CODEN: CINNDH; ISSN:0272-8842. (Elsevier Ltd.)Reproducibility of the sensor response is one of the fundamental themes for obtaining marketable devices with a high degree of reliability. This parameter becomes decisive esp. if the sensor signals are used to identify compd. mixts. by means of recognition algorithms. In fact, to apply the same algorithm to different devices, sensors must be identical within a min. error margin. This point became crucial for medical diagnostic tools, e.g., for cancer screening and monitoring. A set of three thermo-activated thick-film Zinc Oxide (ZnO) sensors, obtained from the same screen-printing deposition, have been tested in lab. with diverse gases and two biol. fecal samples. Fecal samples have been employed in the clin. validation protocol of a device for non-invasive colorectal cancer pre-screening, as emitters of oncol. volatile biomarkers. Sensors showed a good reproducibility degree, with an error lower than 10% of response value for all compds., reaching 1%-2% for some gases.
- 31Agents, C. Commission Directive (EU) 2017/164. Off. J. Eur. Union 2017, 1989, 115– 120There is no corresponding record for this reference.
- 32Zhang, H.; Sun, Z.; Hu, Y. H. Steam Reforming of Methane: Current States of Catalyst Design and Process Upgrading. Renewable Sustainable Energy Rev. 2021, 149, 111330 DOI: 10.1016/j.rser.2021.11133032https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXhsVClt7zL&md5=eb47016338478acbdff13520f64fc62cSteam reforming of methane: Current states of catalyst design and process upgradingZhang, Haotian; Sun, Zhuxing; Hu, Yun HangRenewable & Sustainable Energy Reviews (2021), 149 (), 111330CODEN: RSERFH; ISSN:1364-0321. (Elsevier Ltd.)A review. Methane (CH4) is the major component of currently abundant natural gas and a prominent green-house gas. Steam reforming of methane (SRM) is an important technol. for the conversion of CH4 into H2 and syngas. To improve the catalytic activity and coking resistance of SRM catalysts, great efforts (including the addn. of promoters, development of advanced supports, and structural modification, etc.) have been made with considerable progress in the past decade. Meanwhile, a series of novel processes have been explored for more efficient and energy-saving SRM. In this scenario, a comprehensive review on the recent advances in SRM is necessary to provide a constructive insight into the development of SRM technol., however, is still lacking. Herein, the improvements in catalyst construction for conventional SRM and the newly developed SRM processes in the past decade are presented and analyzed. First, the crit. issues of SRM catalysts are briefly introduced. Then, the recent research advances of the most popular Ni based catalysts and the catalysts based on the other non-noble metals (Co, Cu, Mo, etc.) and the efficient but costly noble metals (Au, Pt, Pd, Rh, Ru, etc.) are discussed. Furthermore, the development of the representative modified SRM processes, including thermo-photo hybrid SRM, sorbent enhanced SRM, oxidative SRM, chem. looping SRM, plasma and elec.-field enhanced SRM, is demonstrated, and their advantages and limits are compared. Finally, a crit. perspective is provided to enlighten future work on this significant area.
- 33Wilhelm, D.; Simbeck, D.; Karp, A.; Dickenson, R. Syngas Production for Gas-to-Liquids Applications: Technologies, Issues and Outlook. Fuel Process. Technol. 2001, 71, 139– 148, DOI: 10.1016/S0378-3820(01)00140-033https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXjsFWmsr8%253D&md5=8a1a573841e975f57ee68d651e01e2b6Syngas production for gas-to-liquids applications: technologies, issues and outlookWilhelm, D. J.; Simbeck, D. R.; Karp, A. D.; Dickenson, R. L.Fuel Processing Technology (2001), 71 (1-3), 139-148CODEN: FPTEDY; ISSN:0378-3820. (Elsevier Science B.V.)The main gas-to-liqs. (GTL) interest now is in Fischer-Tropsch (F-T) synthesis of hydrocarbons. While synthesis gas (syngas) for GTL can be produced from any carbon-based feedstock (hydrocarbons, coal, petroleum coke, biomass), the lowest cost routes to syngas so far are based on natural gas. Thus, the focus for GTL has been largely on assocd. gas, so-called stranded or remotely located gas reserves, and larger gas reserves that are not currently being economically exploited. The principal technologies for producing syngas from natural gas are: catalytic steam methane reforming (SMR), two-step reforming, autothermal reforming (ATR), partial oxidn. (POX), and heat exchange reforming. The distinguishing characteristics of these technologies and their com. uses are discussed. Ongoing R&D efforts to develop lower-cost syngas generation technologies are also briefly discussed. Relevant com. experience with large-scale syngas generation for GTL is also discussed. As a frame of ref., in terms of syngas flow rates, a 20,000 b/day F-T plant would be comparable to three 2500 mt/day methanol plants. Single-train methanol plants are now producing more than 2500 t/day-and plants approaching 3000 mt/day have been announced. The projected relative economies of scale of the various syngas prodn. technologies indicate that two-step reforming and ultimately, ATR, should be the technologies of choice for large-scale GTL plants. Nevertheless, for a 20,000 b/day F-T liqs. plant, capital charges still dominate the manufg. costs. Syngas prodn. (oxygen plant and reforming) comprises half of the total capital cost of this size GTL plant. While air-blown reforming eliminates the expensive oxygen plant, air-blown reforming is unlikely to be competitive with, or offer the flexibility of, oxygen-blown reforming. The reasons for this conclusion are discussed. The proposed and future GTL facilities should be substantially less costly than their very expensive predecessors-as the result of improvements in FT catalyst and reactor design, the most significant of which have been pioneered by Sasol. In the absence of a breakthrough technol., economy of scale will be the only significant mechanism by which GTL can achieve greater economic viability. However, even with such further cost redns., the economic viability of GTL plants will remain confined to special situations until crude price levels rise substantially. In the long term, if a ceramic membrane reactor (combining air sepn. and partial oxidn.) can be developed that enables the 20% redn. in GTL investment costs that the R&D effort is targeting, GTL could become economically viable at crude prices below US20/b.
- 34Lantto, V.; Rompplainen, P.; Leppävuori, S. A Study of the Temperature Dependence of the Barrier Energy in Porous Tin Dioxide. Sens. Actuators 1988, 14, 149– 163, DOI: 10.1016/0250-6874(88)80062-334https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL1cXltl2ruro%253D&md5=6d0f8ebad3769354c03c6502f0223796A study of the temperature dependence of the barrier energy in porous tin dioxideLantto, V.; Romppainen, P.; Leppavuori, S.Sensors and Actuators (1988), 14 (2), 149-63CODEN: SEACDX; ISSN:0250-6874.The dependence of the conductance on temp. of some com. and thick-film SnO2 semiconductor gas sensors was measured at 350 to 875 K at different partial pressures of O2 in N2. The measurements were carried out using different heating and cooling rates. The values of the barrier energy between particles in the ceramic material were calcd. from these results on the basis of the single-barrier model for the conductance. The value of the barrier energy in pure O2 at a fixed temp. was detd. using the temp.-stimulated change in the conductance. The results are discussed in the light of some other expts. and theor. models given to describe the barrier energy. A discussion on the effect of different barrier heights between different particles is given on the basis of a random-barrier network model. By using quick cooling from 875 to 350 K, it is possible to get high barrier values at this low temp. This may be the modus operandi of temp.-pulsed sensors.
- 35International Organization for Standardization. Determination of the Specific Surface Area of Solids by Gas Adsorption─BET Method (ISO 9277:2010(E)); ISO, 2010; Vol. 9277, p 30.There is no corresponding record for this reference.
- 36Hirata, T. Oxygen Position, Octahedral Distortion, and Bond-Valence Parameter from Bond Lengths in Ti1–xSnxO2 (0≤ x≤1). J. Am. Ceram. Soc. 2000, 83, 3205– 3207, DOI: 10.1111/j.1151-2916.2000.tb01706.x36https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXps1ek&md5=0b91e6ea1340b857e2c198b0d6201592Oxygen position, octahedral distortion, and bond-valence parameter from bond lengths in Ti1-xSnxO2 (0 ≤ x ≤ 1)Hirata, ToshiyaJournal of the American Ceramic Society (2000), 83 (12), 3205-3207CODEN: JACTAW; ISSN:0002-7820. (American Ceramic Society)Based on the virtual crystal approxn. (or Vegard's law), the bond lengths of Ti1-xSnxO2 were deduced from those of TiO2 and SnO2, to allow the oxygen position and octahedral distortion to be detd. as a function of x. The oxygen positional parameter (u) increased linearly when the Sn4++ cation (which has a larger ionic radius) was substituted for the Ti4+ cation, whereas the octahedral distortion exhibited a nonlinear decay with increasing x in Ti1-xSnxO2. At the same time, the bond-valence parameter, which relates bond valence to bond length, so that the central atom in the octahedron can retain a const. valence of +4.0, exhibited a correlation with u for Ti1-xSnxO2. The present results indicate that the different phonon/phys. properties of TiO2 and SnO2 and/or their dependence on x in Ti1-xSnxO2 can be assocd. with different octahedral distortions.
- 37Howard, C. J.; Sabine, T. M.; Dickson, F. Structural and Thermal Parameters for Rutile and Anatase. Acta Crystallogr., Sect. B: Struct. Sci. 1991, 47, 462– 468, DOI: 10.1107/S010876819100335XThere is no corresponding record for this reference.
- 38Shannon, R. D. Revised Effective Ionic Radii and Systematic Studies of Interatomic Distances in Halides and Chalcogenides. Acta Crystallogr., Sect. A: Cryst. Phys., Diffr., Theor. Gen. Crystallogr. 1976, 32, 751– 767, DOI: 10.1107/S0567739476001551There is no corresponding record for this reference.
- 39Jung, W.; Tuller, H. L. Investigation of Surface Sr Segregation in Model Thin Film Solid Oxidefuel Cell Perovskite Electrodes. Energy Environ. Sci. 2012, 5, 5370– 5378, DOI: 10.1039/C1EE02762J39https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhs1CgsbvO&md5=1c4c504db646da1c40a77876aada5088Investigation of surface Sr segregation in model thin film solid oxide fuel cell perovskite electrodesJung, Woo Chul; Tuller, Harry L.Energy & Environmental Science (2012), 5 (1), 5370-5378CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)While SOFC perovskite oxide cathodes have been the subject of numerous studies, the crit. factors governing their kinetic behavior have remained poorly understood. This has been due to a no. of factors including the morphol. complexity of the electrode and the electrode- electrolyte interface as well as the evolution of the surface chem. with varying operating conditions. In this work, the surface chem. compn. of dense thin film SrTi1-xFexO3-δ electrodes, with considerably simplified and well-defined electrode geometry, was investigated by means of XPS, focusing on surface cation segregation. An appreciable degree of Sr-excess was found at the surface of STF specimens over the wide compn. range studied. The detailed nature of the Sr-excess is discussed by means of depth and take-off angle dependent XPS spectra, in combination with chem. and thermal treatments. Furthermore, the degree of surface segregation was successfully controlled by etching the films, and/or prepg. intentionally Sr deficient films. Electrochem. Impedance Spectroscopy studies, under circumstances where surface chem. was controlled, were used to examine and characterize the blocking effect of Sr segregation on the surface oxygen exchange rate.
- 40Hamada, I.; Uozumi, A.; Morikawa, Y.; Yanase, A.; Katayama-Yoshida, H. A Density Functional Theory Study of Self-Regenerating Catalysts LaFe1– xMxO3–y (M = Pd, Rh, Pt). J. Am. Chem. Soc. 2011, 133, 18506– 18509, DOI: 10.1021/ja110302t40https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhtlKgsL7O&md5=f936ad0a9f6a65b895bb94d439154d5aA Density Functional Theory Study of Self-Regenerating Catalysts LaFe1-xMxO3 (M = Pd, Rh, Pt)Hamada, Ikutaro; Uozumi, Akifumi; Morikawa, Yoshitada; Yanase, Akira; Katayama-Yoshida, HiroshiJournal of the American Chemical Society (2011), 133 (46), 18506-18509CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Periodic d. functional theory was used to investigate the stability and electronic structures of precious-metal atoms in the vicinity of LaFe1-xMxO3 (M = Pd, Rh, Pt) perovskite catalyst surfaces. It was found that the surface segregation of Pd and Pt is significantly stabilized by the introduction of O vacancies, whereas the solid-soln. phase is favorable for Rh, suggesting an important role of O vacancies in the self-regeneration of Pd and Pt. On the basis of the results, we propose a possible scenario for the self-regeneration of the precious metal in the perovskite catalyst.
- 41Farva, U.; Kim, J. Growth Temperature-Dependent Morphological, Optical, and Electrical Study of SnO2 Thin Film by Atomic Layer Deposition. Mater. Chem. Phys. 2021, 267, 124584 DOI: 10.1016/j.matchemphys.2021.12458441https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXptVKrur8%253D&md5=990029d5669b7157065f3b0da803fdd6Growth temperature-dependent morphological, optical, and electrical study of SnO2 thin film by atomic layer depositionFarva, Umme; Kim, JehaMaterials Chemistry and Physics (2021), 267 (), 124584CODEN: MCHPDR; ISSN:0254-0584. (Elsevier B.V.)Low temp., high quality SnO2 thin film successfully deposited by the at. layer deposition (ALD) method using tetrakis (dimethylamino)Sn (TDMASn) and O3-plasma. The influence of various growth temps. having ranges between 115°C to 250°C on the film growth rate, morphol., compn., optical and elec. properties have been elucidated, and remarkable differences were noticed for possible electron transport layer (ETL). It was worth observing that the film growth rate steeply increased from 0.046 nm/cycle to 0.192 nm/cycle between the growth temp. range 115-250°C because of the rapid dissocn. of TDMASn precursor relative to temp. increase. The optical transmittances of films showed 81%-97% at the visible region for all growth temps.; however, the optical bandgap energy of the SnO2 film was decreased from 3.4 eV to 3.1 eV while increasing deposition temp. During lower deposition temp. of 115°C, the film obtained high resistivity (7.3 x 102 Ω cm), while at a high growth temp. of 200°C almost impurity-free low resistivity (8.9 x 10-4 Ω cm) film can be achieved apart from high carrier concn. (1.4 x 1021 cm-3) and 12.5 cm2 V-1s-1 mobility.
- 42Chen, Q. Nb2O5 Improved Photoluminescence, Magnetic and Faraday Rotation Properties of Magneto-Optical Glasses. J. Non-Cryst. Solids 2019, 519, 119451 DOI: 10.1016/j.jnoncrysol.2019.05.02742https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhtVCitrnO&md5=46aa1e127dda48126ac26a0ff7e34b40Nb2O5 improved photoluminescence, magnetic and Faraday rotation properties of magneto-optical glassesChen, QiulingJournal of Non-Crystalline Solids (2019), 519 (), 119451CODEN: JNCSBJ; ISSN:0022-3093. (Elsevier B.V.)The high polarizability, low photon energy, high non-linear character and dual functions in glass network make diamagnetic Nb2O5 attractive to magneto optical glass based photonics and sensing devices. In this paper, we report for the first time the influence of Nb2O5 on glass formation, structure, photoluminescence, magnetic and Faraday rotation properties of heavy metal oxide diamagnetic glass. Results suggested that Nb2O5 doping amt. greatly influenced its coordination nos. and roles in glass network. Ni2O5 amt. ≤ 5 mol% in glass presented in NiO4 which played glass former role and strengthened the PbO4, BiO6, BiO3 and BO3 units composed glass network connectivity, transparent and homogeneous glasses were obtained. DSC measurement showed that the 1%, 2% and 5%Nb2O5 doping increased the Tg and thermal stability of glass. Nb2O5 doping amt. higher than 5% presented as NiO6 units which played glass modifier role in glass which distorted glass structure and produced BiNbO4 and Nb2O5 cryst. A red-shift of absorption edge from 500 nm to 529 nm was obsd. for Nb2O5 doped glasses. Due to the high optical basicity of host, niobium existed in glass only as Ni5+, and the electron transfers between O2- and Nb5+ displayed two broad emission bands centered at 376 cm and 493 nm (excited at 267 nm) in photoluminescence spectra. 5Nb2O5-5B2O3-45PbO-45Bi2O3 glass exhibited significant thermal stability (100 °C), good photoluminescence, high magnetic susceptibility (57.32 × 10-6 emu/g), and Verdet const. (0.1713 min/G.cm at 633 nm). The novelty of this work is to combine the high polarizability, dual roles properties of Nb2O5 and the high optical basicity of diamagnetic host glass to achieve a diamagnetic valence of Nb and enhance Faraday rotation performance.
- 43Xu, Y.; Wu, S.; Wan, P.; Sun, J.; Hood, Z. D. Introducing Ti3+ Defects Based on Lattice Distortion for Enhanced Visible Light Photoreactivity in TiO2 Microspheres. RSC Adv. 2017, 7, 32461– 32467, DOI: 10.1039/C7RA04885H43https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtVKnsLzN&md5=cfad44bc84ecd73bcb82eddf1852689fIntroducing Ti3+ defects based on lattice distortion for enhanced visible light photoreactivity in TiO2 microspheresXu, Yunfan; Wu, Sujuan; Wan, Piaopiao; Sun, Jianguo; Hood, Zachary D.RSC Advances (2017), 7 (52), 32461-32467CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)Defective titanium dioxide (TiO2) is of much significance due to its improved visible light photoreactivity. Generally, the existence of defects leads to imperfections in the crystal lattice, which in turn affect the dynamics of the evolution of defects and the corresponding phys. properties of TiO2. Until now, how lattice distortion affects the formation of Ti3+ defects as well as the corresponding visible light photoreactivity in TiO2 has remained elusive. Herein, we have successfully introduced Ti3+ defects based on lattice distortion in TiO2 microspheres and found the photocurrent of anatase TiO2 has been significantly enhanced from 1.78 to 80μA cm-2 with an increase in photocatalytic activity of almost three times under visible light irradn. Furthermore, we show that lattice distortions have minimal contribution to enhancing the visible light photocatalytic activity because the band gap cannot be narrowed due to the absence of Ti3+ defects, yet the existence of lattice distortions could suppress the recombination of electron-hole pairs. Moreover, the formation of Ti3+ defects is energetically favored in lattice-distorted TiO2 compared to that of pristine TiO2. This work highlights the design and development of highly efficient TiO2 photocatalysts that operate under visible light irradn.
- 44Di Valentin, C.; Pacchioni, G.; Selloni, A. Reduced and N-Type Doped TiO2: Nature of Ti3+ Species. J. Phys. Chem. C 2009, 113, 20543– 20552, DOI: 10.1021/jp906179744https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXhtFOksL7F&md5=192855a2886565ebfdf1f054af4c5e90Reduced and n-Type Doped TiO2: Nature of Ti3+ SpeciesDi Valentin, Cristiana; Pacchioni, Gianfranco; Selloni, AnnabellaJournal of Physical Chemistry C (2009), 113 (48), 20543-20552CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)Defect states in reduced and n-type doped titania are of fundamental importance in several technol. important applications. Still, the exact nature of these states, often referred to as "Ti3+ centers", is largely unclear and a matter of debate. The problem is complicated by the fact that electronic structure calcns. based on d. functional theory (DFT) in the local d. approxn. (LDA) or semilocal generalized gradient approxn. (GGA) provide results that do not account for many of the exptl. obsd. fingerprints of the formation of Ti3+ centers in reduced TiO2. Here, we investigate the properties of at least four different types of Ti3+ centers in bulk anatase, (1) 6-fold-coordinated Ti6c3+ ions introduced by F- or Nb-doping, (2) Ti6c3+-OH species assocd. with H-doping, (3) undercoordinated Ti5c3+ species assocd. with oxygen vacancies, and (4) interstitial Ti5c3+ species. The characterization of these different kinds of Ti3+ centers is based on DFT + U and/or hybrid functional calcns., which are known to (partially) correct the self-interaction error of local and semilocal DFT functionals. We found that strongly localized solns. where an excess electron is on a single Ti3+ ion are very close in energy and sometimes degenerate with partly or highly delocalized solns. where the extra charge is distributed over several Ti ions. The defect states corresponding to these different solns. lie at different energies in the band gap of the material. This has important implications for the cond. mechanism in reduced or n-type doped titania and suggests a significant role of temp. in detg. the degree of localization of the trapped charge.
- 45Huang, J.; Wan, Q. Gas Sensors Based on Semiconducting Metal Oxide One-Dimensional Nanostructures. Sensors 2009, 9, 9903– 9924, DOI: 10.3390/s9120990345https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC383gtVOltQ%253D%253D&md5=94242a950f23f3a87aaef5158e3a586cGas sensors based on semiconducting metal oxide one-dimensional nanostructuresHuang Jin; Wan QingSensors (Basel, Switzerland) (2009), 9 (12), 9903-24 ISSN:1424-8220.This article provides a comprehensive review of recent (2008 and 2009) progress in gas sensors based on semiconducting metal oxide one-dimensional (1D) nanostructures. During last few years, gas sensors based on semiconducting oxide 1D nanostructures have been widely investigated. Additionally, modified or doped oxide nanowires/nanobelts have also been synthesized and used for gas sensor applications. Moreover, novel device structures such as electronic noses and low power consumption self-heated gas sensors have been invented and their gas sensing performance has also been evaluated. Finally, we also point out some challenges for future investigation and practical application.
- 46Spagnoli, E.; Krik, S.; Fabbri, B.; Valt, M.; Ardit, M.; Gaiardo, A.; Vanzetti, L.; Della Ciana, M.; Cristino, V.; Vola, G.; Caramori, S.; Malagù, C.; Guidi, V. Development and Characterization of WO3 Nanoflakes for Selective Ethanol Sensing. Sens. Actuators, B 2021, 347, 130593 DOI: 10.1016/j.snb.2021.13059346https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXhvVagtr3F&md5=9ce2c2d5d9104bc57eaaa18b3d0673cdDevelopment and characterization of WO3 nanoflakes for selective ethanol sensingSpagnoli, E.; Krik, S.; Fabbri, B.; Valt, M.; Ardit, M.; Gaiardo, A.; Vanzetti, L.; Della Ciana, M.; Cristino, V.; Vola, G.; Caramori, S.; Malagu, C.; Guidi, V.Sensors and Actuators, B: Chemical (2021), 347 (), 130593CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)Despite an increasing demand for applications, the partial selectivity of metal oxide-based gas sensors limits their practical use in some cases, such as for ethanol detection. Consequently, the search for a performing ethanol sensor is still an open challenge. In this work, tungsten oxide nanoflake powders were synthesized by means of solvothermal technique in sight of ethanol sensing. The powders were characterized by X-ray diffraction, SEM, energy dispersion X-ray spectroscopy, textural and optical absorbance analyses and XPS and screen-printed as a paste on alumina substrates. Elec. characterization showed that these films responded well to ethanol and the conductance in the presence of this gas only decreased by about 20% in mild humidity conditions, remaining const. over a range of 20-70 RH%. The operational temp. of the film was 250°C, namely a lower level with respect to mostly used WO3 sensors in the literature. Marginal influence by typical interferents in some applications of an ethanol sensor was recorded. Among alcs., the response to ethanol prevailed because of an interplay between catalytic properties of the sensing film and gas diffusivity in a porous medium.
- 47Gaiardo, A.; Zonta, G.; Gherardi, S.; Malagù, C.; Fabbri, B.; Valt, M.; Vanzetti, L.; Landini, N.; Casotti, D.; Cruciani, G.; Della Ciana, M.; Guidi, V. Nanostructured SmFeO3 Gas Sensors: Investigation of the Gas Sensing Performance Reproducibility for Colorectal Cancer Screening. Sensors 2020, 20, 5910 DOI: 10.3390/s2020591047https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXisV2jtr3I&md5=f79246438b3c0a0090c05c23d675d5c4Nanostructured SmFeO3 gas sensors: investigation of the gas sensing performance reproducibility for colorectal cancer screeningGaiardo, Andrea; Zonta, Giulia; Gherardi, Sandro; Malagu, Cesare; Fabbri, Barbara; Valt, Matteo; Vanzetti, Lia; Landini, Nicolo; Casotti, Davide; Cruciani, Giuseppe; Della Ciana, Michele; Guidi, VincenzoSensors (2020), 20 (20), 5910CODEN: SENSC9; ISSN:1424-8220. (MDPI AG)Among the various chemoresistive gas sensing properties studied so far, the sensing response reproducibility, i.e., the capability to reproduce a device with the same sensing performance, has been poorly investigated. However, the reproducibility of the gas sensing performance is of fundamental importance for the employment of these devices in on-field applications, and to demonstrate the reliability of the process development. This sensor property became crucial for the prepn. of medical diagnostic tools, in which the use of specific chemoresistive gas sensors along with a dedicated algorithm can be used for screening diseases. In this work, the reproducibility of SmFeO3 perovskite-based gas sensors has been investigated. A set of four SmFeO3 devices, obtained from the same screen-printing deposition, have been tested in lab. with both controlled concns. of CO and biol. fecal samples. The fecal samples tested were employed in the clin. validation protocol of a prototype for non-invasive colorectal cancer prescreening. Sensors showed a high reproducibility degree, with an error lower than 2% of the response value for the test with CO and lower than 6% for fecal samples. Finally, the reproducibility of the SmFeO3 sensor response and recovery times for fecal samples was also evaluated.
- 48Valt, M.; Caporali, M.; Fabbri, B.; Gaiardo, A.; Krik, S.; Iacob, E.; Vanzetti, L.; Malagù, C.; Banchelli, M.; D’Andrea, C.; Serrano-Ruiz, M.; Vanni, M.; Peruzzini, M.; Guidi, V. Air Stable Nickel-Decorated Black Phosphorus and Its Room-Temperature Chemiresistive Gas Sensor Capabilities. ACS Appl. Mater. Interfaces 2021, 13, 44711– 44722, DOI: 10.1021/acsami.1c1076348https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXhvFymtLfO&md5=73fbe9fbb32e41a37540958b3fcb46a9Air Stable Nickel-Decorated Black Phosphorus and Its Room-Temperature Chemiresistive Gas Sensor CapabilitiesValt, Matteo; Caporali, Maria; Fabbri, Barbara; Gaiardo, Andrea; Krik, Soufiane; Iacob, Erica; Vanzetti, Lia; Malagu, Cesare; Banchelli, Martina; D'Andrea, Cristiano; Serrano-Ruiz, Manuel; Vanni, Matteo; Peruzzini, Maurizio; Guidi, VincenzoACS Applied Materials & Interfaces (2021), 13 (37), 44711-44722CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)In the rapidly emerging field of layered two-dimensional functional materials, black phosphorus, the P-counterpart of graphene, is a potential candidate for various applications, e.g., nanoscale optoelectronics, rechargeable ion batteries, electrocatalysts, thermoelecs., solar cells, and sensors. Black phosphorus has shown superior chem. sensing performance; in particular, it is selective for the detection of NO2, an environmental toxic gas, for which black phosphorus has highlighted high sensitivity at a ppb level. In this work, by applying a multiscale characterization approach, we demonstrated a stability and functionality improvement of nickel-decorated black phosphorus films for gas sensing prepd. by a simple, reproducible, and affordable deposition technique. Furthermore, we studied the elec. behavior of these films once implemented as functional layers in gas sensors by exposing them to different gaseous compds. and under different relative humidity conditions. Finally, the influence on sensing performance of nickel nanoparticle dimensions and concn. correlated to the decoration technique and film thickness was investigated.
- 49Madou, M. J.; Morrison, S. R. Gas Sensors Based on Semiconductor Powders. In Chemical Sensing with Solid State Devices; Elsevier, 1989; Vol. 8, pp 479– 516. https://doi.org/10.1016/B978-0-12-464965-1.50017-X.There is no corresponding record for this reference.
- 50Umar, A.; Ammar, H. Y.; Kumar, R.; Almas, T.; Ibrahim, A. A.; AlAssiri, M. S.; Abaker, M.; Baskoutas, S. Efficient H2 Gas Sensor Based on 2D SnO2 Disks: Experimental and Theoretical Studies. Int. J. Hydrogen Energy 2020, 45, 26388– 26401, DOI: 10.1016/j.ijhydene.2019.04.26950https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXpvFOhsr4%253D&md5=e2de7dc2e7b6be5a334e4ac76a13e2f8Efficient H2 gas sensor based on 2D SnO2 disks: Experimental and theoretical studiesUmar, Ahmad; Ammar, H. Y.; Kumar, Rajesh; Almas, Tubia; Ibrahim, Ahmed A.; AlAssiri, M. S.; Abaker, M.; Baskoutas, S.International Journal of Hydrogen Energy (2020), 45 (50), 26388-26401CODEN: IJHEDX; ISSN:0360-3199. (Elsevier Ltd.)2D SnO2 disks with excellent purity and crystallinity were synthesized through a low cost, facile hydrothermal process and were characterized in terms of their morphol., structural, optical and electrochem. properties. The 2D disk-like morphol. of synthesized SnO2 presented the av. thickness of ∼1μm and possessed the typical rutile tetragonal phase for the SnO2 with preferred growth along (100) plane. As-synthesized SnO2 disks were used for the fabrication of gas sensors for reducing gases like H2, CO, and C3H8. With the optimized temp. at 400°C, the as-synthesized SnO2 electrode expressed the gas responses of 14.7, 9.3 and 8.1 for H2, CO, and C3H8, resp. Contrary, the reasonable response times of 4 s, 3 s, and 8 s and the recovery times of 331 s, 201 s, and 252 s were recorded for H2, CO, and C3H8 gases, resp. The DFT studies conducted herein suggest that the adsorbed oxygenated species act as a primary redox mediator for gas sensing reaction between reductive gases like H2, CO and C3H8, and SnO2 sensor. From DFT anal., a very low heat of adsorption (≤0.2 eV) estd. which suggested the physisorption of the H2 mols. on the surface of the sensing material (i.e. SnO2). In contrast, the deposited oxygen atom forms strong chem. bonds with O2c and O3c sites. The oxygen atom bonded to O2c site control the cond. of the sensor better than the O3c sites.
- 51Wang, F.; Hu, K.; Liu, H.; Zhao, Q.; Wang, K.; Zhang, Y. Low Temperature and Fast Response Hydrogen Gas Sensor with Pd Coated SnO2 Nanofiber Rods. Int. J. Hydrogen Energy 2020, 45, 7234– 7242, DOI: 10.1016/j.ijhydene.2019.12.15251https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXnvVOmsw%253D%253D&md5=721696caaff24ad933c75221e5a8665fLow temperature and fast response hydrogen gas sensor with Pd coated SnO2 nanofiber rodsWang, Feipeng; Hu, Kelin; Liu, Hongcheng; Zhao, Qi; Wang, Kaizheng; Zhang, YuxinInternational Journal of Hydrogen Energy (2020), 45 (11), 7234-7242CODEN: IJHEDX; ISSN:0360-3199. (Elsevier Ltd.)In this work, we introduced a structure of Pd coated SnO2 nanofiber rods (NFRs) prepd. by electrospinning and magnet sputtering. Pd was first deposited on the obtained nanofibers as a catalyst and then fully dispersed during the resulting of SnO2 to improve the hydrogen response. The gas sensing tests showed the palladium enhanced the hydrogen response at low temp. (160°C). When the hydrogen gas concn. was 100 ppm, the limit of detection (LOD) of sensor was as low as 0.25 ppm and the response time was as short as 4 s. Moreover, Pd coated SnO2 also had excellent hydrogen selectivity and repeatability. The gas sensor was suitable for the detection of hydrogen in low-temp. environment. This work provided a new method for the low temp. hydrogen gas sensor with a fast response and low LOD.
- 52Liu, L.; Guo, C.; Li, S.; Wang, L.; Dong, Q.; Li, W. Improved H2 Sensing Properties of Co-Doped SnO2 Nanofibers. Sens. Actuators, B 2010, 150, 806– 810, DOI: 10.1016/j.snb.2010.07.02252https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXhtlehtL%252FF&md5=91d63c28809941e12ba099f0a263be52Improved H2 sensing properties of Co-doped SnO2 nanofibersLiu, Li; Guo, Chuangchang; Li, Shouchun; Wang, Lianyuan; Dong, Qiongye; Li, WeiSensors and Actuators, B: Chemical (2010), 150 (2), 806-810CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)Pure and Co-doped SnO2 nanofibers are synthesized via an electrospinning method and characterized by XRD, SEM, and transmission electron microscope (TEM). Comparing with pure SnO2 nanofibers, Co-doped SnO2 nanofibers exhibit improved H2 sensing properties. Among all the samples (pure, 0.5%, 1%, and 3% Co-doped SnO2 nanofibers), 1% Co-doped SnO2 nanofibers show the highest response with very short response/recovery times. The response is up to 24 when the corresponding sensor is exposed to 100 ppm H2 at 330°, and the response and recovery times are 2 and 3 s, resp. Good selectivity is also obsd. These results make Co-doped SnO2 nanofibers good candidates for fabricating high performance H2 sensors in practical.
- 53Ding, W.; Ansari, N.; Yang, Y.; Bachagha, K. Superiorly Sensitive and Selective H2 Sensor Based on P-n Heterojunction of WO3–CoO Nanohybrids and Its Sensing Mechanism. Int. J. Hydrogen Energy 2021, 46, 28823– 28837, DOI: 10.1016/j.ijhydene.2021.06.07053https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXhsVOktr%252FJ&md5=c2a069ee78de72aebd9d4c83acaaa6e9Superiorly sensitive and selective H2 sensor based on p-n heterojunction of WO3-CoO nanohybrids and its sensing mechanismDing, Wei; Ansari, Nadeem; Yang, Yanhui; Bachagha, KareemInternational Journal of Hydrogen Energy (2021), 46 (56), 28823-28837CODEN: IJHEDX; ISSN:0360-3199. (Elsevier Ltd.)In this study, an excellent hydrogen gas sensor based on the WO3-CoO nanohybrids (WCNHs) heterojunction structure has been successfully fabricated. The WCNHs device showed superior sensitivity, admirable selectivity as well as excellent long-term stability for target gas. In particular, the considerable gas sensing response of WCNHs (5:4) towards 100 ppm hydrogen gas (H2) concn. was reached 39, which is superior to that of the outstanding candidates. Esp., the detection limit capability was as low as 311 ppb. The remarkable response of WCNHs (5:4) can mainly be ascribed to appropriate morphol. characteristics and the promising p-n heterojunction architecture, resulting in efficient absorbing behavior and beneficial charge carrier transportation. As a Result, the aims of improving Ra (intrinsic resistance) and decreasing Rg (test resistance) have been simultaneously achieved ultimately leading to an impressive response value of WCNHs sensing materials. The present results verified that WCNHs heterojunction structure was an outstanding design to enhance the H2 sensing performance for WO3-based gas sensors.
- 54Nakate, U. T.; Lee, G. H.; Ahmad, R.; Patil, P.; Hahn, Y.-B.; Yu, Y. T.; Suh, E. Nano-Bitter Gourd like Structured CuO for Enhanced Hydrogen Gas Sensor Application. Int. J. Hydrogen Energy 2018, 43, 22705– 22714, DOI: 10.1016/j.ijhydene.2018.09.16254https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXitVSjt7zO&md5=ffd9eca3e0b7896d6172ebc56dc630ceNano-bitter gourd like structured CuO for enhanced hydrogen gas sensor applicationNakate, Umesh T.; Lee, Gun Hee; Ahmad, Rafiq; Patil, Pramila; Hahn, Yoon-Bong; Yu, Y. T.; Suh, Eun-kyungInternational Journal of Hydrogen Energy (2018), 43 (50), 22705-22714CODEN: IJHEDX; ISSN:0360-3199. (Elsevier Ltd.)Hydrogen gas sensing were studied using nano-bitter gourd like structured CuO material synthesized via a chem. route. Morphol. of CuO was revealed using FE-SEM and TEM image anal. CuO phase confirmation and mol. structural fingerprint were verified by XRD and Raman anal., resp. Elemental compn. and at. states of elements were studied by EDS and XPS techniques, resp. A remarkable high gas response of 175% was recorded by CuO sensor towards 100 ppm hydrogen (H2) at the operating temp. 200° with response time 150 s. The lowest detection of H2 was obsd. at 2 ppm concn. with the gas response of 5%. The gas response was studied as functions of different operating temps. and concns. Transient gas response and stability were also confirmed for CuO sensor. Hydrogen sensing mechanism of CuO sensor was elucidated.
- 55Agarwal, S.; Kumar, S.; Agrawal, H.; Moinuddin, M. G.; Kumar, M.; Sharma, S. K.; Awasthi, K. An Efficient Hydrogen Gas Sensor Based on Hierarchical Ag/ZnO Hollow Microstructures. Sens. Actuators, B 2021, 346, 130510 DOI: 10.1016/j.snb.2021.13051055https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXhslSqur%252FO&md5=e9bed29b0b34363df0479fb6ed1a0cddAn efficient hydrogen gas sensor based on hierarchical Ag/ZnO hollow microstructuresAgarwal, Sonalika; Kumar, Sanjay; Agrawal, Himanshu; Moinuddin, Mohamad G.; Kumar, Manoj; Sharma, Satinder K.; Awasthi, KamlendraSensors and Actuators, B: Chemical (2021), 346 (), 130510CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)The design of hierarchical zinc oxide (ZnO) microstructures modified with silver (Ag) nanoparticles have emerged as an effective approach for improving the hydrogen gas sensing performance. Here, we report a simple, low-cost chem. co-pptn. method to obtain the Ag/ZnO hollow microstructures and morphol. characterized them by field emission SEM. FESEM images revealed the clear hollow hexagonal tube-like morphol. The existence of Ag in ZnO was confirmed by X-ray diffraction and energy-dispersive X-ray spectroscopy. UV visible absorption and photoluminescence (PL) spectra were also recorded to observe the effect of Ag nanofiller on the optical properties of ZnO. Furthermore, the gas sensing properties of the as-prepd. bare ZnO and Ag/ZnO sensor were investigated. The thoroughly sensing expts. demonstrated that after modification with Ag nanoparticles the ZnO sensor shows superior sensitivity 479% toward 300 ppm hydrogen gas concn., whereas 101% response was noted for the pure ZnO sensor at 250°C working temp. Meanwhile, Ag/ZnO hybrids exhibited excellent selectivity, fast response, and recovery time and also obtained a good and stable response signal at 5 ppm H2 exposure, which indicated that the lower concn. measurement is also attainable. This enhancement in the sensing performance of Ag/ZnO structures toward hydrogen is due to the chem. and electronic sensitization effect of Ag nanoparticles. As a result, such microstructure is attributed to more oxygen species and active sites, and it enhances the sensitivity of a sensor. Moreover, this type of hybrid opens a new path and supports the next generation of innovative materials to fabricate highly selective and sensitive H2 gas sensing devices.
- 56Barsan, N.; Rebholz, J.; Weimar, U. Conduction Mechanism Switch for SnO2 Based Sensors during Operation in Application Relevant Conditions; Implications for Modeling of Sensing. Sens. Actuators, B 2015, 207, 455– 459, DOI: 10.1016/j.snb.2014.10.01656https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhslOru7jJ&md5=6ced05e3f38bc5ab5a765b7930c8e804Conduction mechanism switch for SnO2 based sensors during operation in application relevant conditions; implications for modeling of sensingBarsan, Nicolae; Rebholz, Julia; Weimar, UdoSensors and Actuators, B: Chemical (2015), 207 (Part_A), 455-459CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)In this paper we present exptl. evidence for a conduction mechanism switch for gas sensors based on SnO2 porous, thick film sensing layers under exposure to CO in the presence of humidity. In dry air and CO concn. below 250 ppm the conduction is controlled by the surface depletion layers formed by the trapping of electrons from conduction band on adsorbed oxygen species. In the presence of humidity and at CO concn. exceeding 3 ppm the surface depletion layers are replaced by surface accumulation layers and the conduction mechanism changes accordingly. We also present a model that takes into account the influence of humidity at low CO concns.
- 57Barsan, N.; Weimar, U. Conduction Model of Metal Oxide Gas Sensors. J. Electroceram. 2001, 7, 143– 167, DOI: 10.1023/a:101440581137157https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38XjsFWjtbw%253D&md5=63535a1a4b0561d1226e873cb862bd77Conduction model of metal oxide gas sensorsBarsan, Nicolae; Weimar, UdoJournal of Electroceramics (2002), 7 (3), 143-167CODEN: JOELFJ; ISSN:1385-3449. (Kluwer Academic Publishers)Tin dioxide is a widely used sensitive material for gas sensors. Many research and development groups in academia and industry are contributing to the increase of (basic) knowledge/(applied) know-how. However, from a systematic point of view the knowledge gaining process seems not to be coherent. One reason is the lack of a general applicable model which combines the basic principles with measurable sensor parameters. The approach in the presented work is to provide a frame model that deals with all contributions involved in conduction within a real world sensor. For doing so, one starts with identifying the different building blocks of a sensor. Afterwards, their main inputs are analyzed in combination with the gas reaction involved in sensing. At the end, the contributions are summarized together with their interactions. The work presented here is one step towards a general applicable model for real world gas sensors.
- 58Arbiol, J.; Cerdà, J.; Dezanneau, G.; Cirera, A.; Peiró, F.; Cornet, A.; Morante, J. R. Effects of Nb Doping on the TiO2 Anatase-to-Rutile Phase Transition. J. Appl. Phys. 2002, 92, 853– 861, DOI: 10.1063/1.148791558https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38XkvFyjsro%253D&md5=374ceeacd074f18e37cfff48a4422d46Effects of Nb doping on the TiO2 anatase-to-rutile phase transitionArbiol, J.; Cerda, J.; Dezanneau, G.; Cirera, A.; Peiro, F.; Cornet, A.; Morante, J. R.Journal of Applied Physics (2002), 92 (2), 853-861CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)The authors study the influence of Nb doping on the TiO2 anatase-to-rutile phase transition, using combined TEM, Raman spectroscopy, x-ray diffraction and selected area electron diffraction anal. This approach enabled anatase-to-rutile phase transition hindering to be clearly obsd. for low Nb-doped TiO2 samples. Also, there was clear grain growth inhibition in the samples contg. Nb. The use of high resoln. TEM with the authors' samples provides an innovative perspective compared with previous research on this issue. The authors' anal. shows that Nb is segregated from the anatase structure before and during the phase transformation, giving NbO nanoclusters on the surface of the TiO2 rutile nanoparticles.
- 59Uyanga, E.; Gibaud, A.; Daniel, P.; Sangaa, D.; Sevjidsuren, G.; Altantsog, P.; Beuvier, T.; Lee, C. H.; Balagurov, A. M. Structural and Vibrational Investigations of Nb-Doped TiO2 Thin Films. Mater. Res. Bull. 2014, 60, 222– 231, DOI: 10.1016/j.materresbull.2014.08.03559https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhsVGjt7zO&md5=f43ed6d451e3bf9aef1c52feaaad1db4Structural and vibrational investigations of Nb-doped TiO2 thin filmsUyanga, E.; Gibaud, A.; Daniel, P.; Sangaa, D.; Sevjidsuren, G.; Altantsog, P.; Beuvier, T.; Lee, Chih Hao; Balagurov, A. M.Materials Research Bulletin (2014), 60 (), 222-231CODEN: MRBUAC; ISSN:0025-5408. (Elsevier Ltd.)Acid-catalyzed sol-gel and spin-coating methods were used to prep. Nb-doped TiO2 thin film. In this work, we studied the effect of niobium doping on the structure, surface, and absorption properties of TiO2 by energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), X-ray reflectometry (XRR), XPS, Raman, and UV-vis absorption spectroscopy at various annealing temps. EDX spectra show that the Nb:Ti at. ratios of the niobium-doped titania films are in good agreement with the nominal values (5 and 10%). XPS results suggest that charge compensation is achieved by the formation of Ti vacancies. Specific niobium phases are not obsd., thus confirming that niobium is well incorporated into the titania crystal lattice. Thin films are amorphous at room temp. and the formation of anatase phase appeared at an annealing temp. close to 400°C. The rutile phase was not obsd. even at 900 °C (XRD and Raman spectroscopy). Grain sizes and electron densities increased when the temp. was raised. Nb-doped films have higher electron densities and lower grain sizes due to niobium doping. Grain size inhibition can be explained by lattice stress induced by the incorporation of larger Nb5+ ions into the lattice. The band gap energy of indirect transition of the TiO2 thin films was calcd. to be about 3.03 eV. After niobium doping, it decreased to 2.40 eV.
- 60Ruiz, A. M.; Dezanneau, G.; Arbiol, J.; Cornet, A.; Morante, J. R. Insights into the Structural and Chemical Modifications of Nb Additive on TiO2 Nanoparticles. Chem. Mater. 2004, 16, 862– 871, DOI: 10.1021/cm035123860https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXps1ensw%253D%253D&md5=90faa7ee88ca2a31b37bcff9f1924028Insights into the Structural and Chemical Modifications of Nb Additive on TiO2 NanoparticlesRuiz, Ana M.; Dezanneau, G.; Arbiol, J.; Cornet, A.; Morante, Joan R.Chemistry of Materials (2004), 16 (5), 862-871CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)Solid soln. NbxTi1-xO2+δ nanoparticles were synthesized by a sol-gel method with 0.0 ≤ x ≤ 0.1. Structural and microstructural properties have been studied by XPS, XRD, Raman spectroscopy, and TEM as a function of the Nb/Ti at. ratio and thermal treatment temp. (600-900°C). XRD analyses showed that a percentage of the nominal added Nb was assimilated in substitutional Ti sites in the bulk of TiO2 adopting a pentavalent state. On the other hand, XPS detected a high concn. of Nb at the surface. On the basis of the careful anal. of the XRD and XPS spectra it is reasonable to assume that the concn. of Nb at the surface of the nanoparticles is higher than that in the bulk, esp. for rutile, giving a U-shaped Nb concn. profile. The niobium incorporation stabilizes the titania obstructing the diffusion of anatase-type surface atoms, which prevents grain coarsening and phase transformation. The soly. limit of niobium into titania is greater for the anatase phase (x >0.1) than for the rutile phase (x = 0.06). Once the soly. limit of Nb atoms is surpassed, a ternary phase ascribed to TiNb2O7 has been detected. In addn., the crystallite sizes and the percentage of rutile phase were quite similar for Nb contents above the soly. limit. XRD and XPS measurements suggest that niobium mainly enters into titania phase with valence +5, while Ti maintains its higher oxidn. state (4+), the extra charge being thus partially compensated by titanium vacancies. As derived from XPS analyses in the core levels and the valence band regions, the addn. of Nb resulted in a displacement of the Fermi level toward the conduction band. In consequence, the Nb-altered samples presented a more marked n-type feature, as compared with that of the undoped TiO2.
- 61Zeng, W.; Liu, T.; Wang, Z. Impact of Nb Doping on Gas-Sensing Performance of TiO2 Thick-Film Sensors. Sens. Actuators, B 2012, 166–167, 141– 149, DOI: 10.1016/j.snb.2012.02.01661https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38Xlt1ylsLk%253D&md5=2185bb673d6c708cfeac7616724c70fcImpact of Nb doping on gas-sensing performance of TiO2 thick-film sensorsZeng, Wen; Liu, Tianmo; Wang, ZhongchangSensors and Actuators, B: Chemical (2012), 166-167 (), 141-149CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)Using a simple hydrothermal method, the pristine and Nb doped TiO2 is prepd., and their microstructures and gas-sensing responses to the harmful volatile org. compds. are investigated with a special focus on the impact of Nb additive. We find that the gas response of TiO2 is enhanced significantly by doping Nb, which is understood in theory upon proposed adsorption models. Combining exptl. measurements with first-principles calcns., the working mechanism underlying such improvement in gas-sensing functions by the Nb additive is discussed.
- 62Pan, X.; Yang, M.-Q.; Fu, X.; Zhang, N.; Xu, Y.-J. Defective TiO2 with Oxygen Vacancies: Synthesis, Properties and Photocatalytic Applications. Nanoscale 2013, 5, 3601– 3614, DOI: 10.1039/c3nr00476g62https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXmt1Sgtrg%253D&md5=6b2177641fd78fa1b49132130d9c28b3Defective TiO2 with oxygen vacancies: synthesis, properties and photocatalytic applicationsPan, Xiaoyang; Yang, Min-Quan; Fu, Xianzhi; Zhang, Nan; Xu, Yi-JunNanoscale (2013), 5 (9), 3601-3614CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)A review. Titanium dioxide (TiO2), as an important semiconductor metal oxide, has been widely investigated in the field of photocatalysis. The properties of TiO2, including its light absorption, charge transport and surface adsorption, are closely related to its defect disorder, which in turn plays a significant role in the photocatalytic performance of TiO2. Among all the defects identified in TiO2, oxygen vacancy is one of the most important and is supposed to be the prevalent defect in many metal oxides, which has been widely investigated both by theor. calcns. and exptl. characterizations. Here, we give a short review on the existing strategies for the synthesis of defective TiO2 with oxygen vacancies, and the defect related properties of TiO2 including structural, electronic, optical, dissociative adsorption and reductive properties, which are intimately related to the photocatalytic performance of TiO2. In particular, photocatalytic applications with regard to defective TiO2 are outlined. In addn., we offer some perspectives on the challenge and new direction for future research in this field. We hope that this tutorial mini-review would provide some useful contribution to the future design and fabrication of defective semiconductor-based nanomaterials for diverse photocatalytic applications.
- 63Koo, W.-T.; Cho, H.-J.; Kim, D.-H.; Kim, Y. H.; Shin, H.; Penner, R. M.; Kim, I.-D. Chemiresistive Hydrogen Sensors: Fundamentals, Recent Advances, and Challenges. ACS Nano 2020, 14, 14284– 14322, DOI: 10.1021/acsnano.0c0530763https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXitFygs73F&md5=c18a45ec8d320b0818c80c56a2ee76dfChemiresistive Hydrogen Sensors: Fundamentals, Recent Advances, and ChallengesKoo, Won-Tae; Cho, Hee-Jin; Kim, Dong-Ha; Kim, Yoon Hwa; Shin, Hamin; Penner, Reginald M.; Kim, Il-DooACS Nano (2020), 14 (11), 14284-14322CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)A review. Hydrogen (H2) is one of the next-generation energy sources because it is abundant in nature and has a high combustion efficiency that produces environmentally benign products (H2O). However, H2/air mixts. are explosive at H2 concns. above 4%, thus any leakage of H2 must be rapidly and reliably detected at much lower concns. to ensure safety. Among the various types of H2 sensors, chemiresistive sensors are one of the most promising sensing systems due to their simplicity and low cost. This review highlights the advances in H2 chemiresistors, including metal-, semiconducting metal oxide-, carbon-based materials, and other materials. The underlying sensing mechanisms for different types of materials are discussed, and the correlation of sensing performances with nanostructures, surface chem., and electronic properties is presented. In addn., the discussion of each material emphasizes key advances and strategies to develop superior H2 sensors. Furthermore, recent key advances in other types of H2 sensors are briefly discussed. Finally, the review concludes with a brief outlook, perspective, and future directions.
- 64Mokrushin, A. S.; Simonenko, T. L.; Simonenko, N. P.; Gorobtsov, P. Y.; Kadyrov, N. C.; Simonenko, E. P.; Sevastyanov, V. G.; Kuznetsov, N. T. Chemoresistive Gas-Sensing Properties of Highly Dispersed Nb2O5 Obtained by Programmable Precipitation. J. Alloys Compd. 2021, 868, 159090 DOI: 10.1016/j.jallcom.2021.15909064https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXkvVShu7Y%253D&md5=a1dbd5a5884aebfb7aac1bb9ce73d763Chemoresistive gas-sensing properties of highly dispersed Nb2O5 obtained by programmable precipitationMokrushin, Artem S.; Simonenko, Tatiana L.; Simonenko, Nikolay P.; Gorobtsov, Philipp Yu.; Kadyrov, Nail C.; Simonenko, Elizaveta P.; Sevastyanov, Vladimir G.; Kuznetsov, Nikolay T.Journal of Alloys and Compounds (2021), 868 (), 159090CODEN: JALCEU; ISSN:0925-8388. (Elsevier B.V.)Nb2O5 powder obtained by programmable pptn. was used to form a thick gas-sensing film as part of a chemoresistive gas sensor, by screen-printing. The coating of orthorhombic Nb2O5 consisted of nanoparticles with a size of 41.0 ± 2.5 nm. XPS revealed Nb5+, Nb4+ and Nb2+ as well as oxygen vacancies in the crystal structure of niobium oxide. As a result of studying the chemoresistive gas-sensing properties of Nb2O5, it has been shown that among the analyzed gases (H2, CO, NH3, H2S and O2), the greatest sensitivity was obsd. for oxygen and hydrogen sulfide. Nanocryst. niobium oxide showed a high and reproducible response to 0.02-20% O2 (S1 = 1.1-19.0) at a very low detection temp. of 200°C for oxygen sensors. At an operating detection temp. of 250°C, a high and reproducible response to low concns. of hydrogen sulfide of 4-100 ppm (S2 = 1.2-6.6) was detected for Nb2O5. The influence of humidity on the received signals when detecting oxygen and hydrogen sulfide was studied in detail: there was a decrease in the resistance and the response value at 95% humidity in the medium of both gases. However, unlike the process of detecting H2S (when the response of S2 was almost lost), when detg. oxygen, the response of S1 was reduced by a factor of two only, which suggests the possibility of detg. the content of O2 in high humidity conditions.
- 65Guo, Y.; He, X.; Huang, W.; Wang, M. Microstructure Effects on Effective Gas Diffusion Coefficient of Nanoporous Materials. Transp. Porous Media 2019, 126, 431– 453, DOI: 10.1007/s11242-018-1165-4There is no corresponding record for this reference.
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In-depth description of material characterization methods and gas sensor preparation; morphological, textural, and structural characterizations; response variation according to the temperature change; fit parameters for calibration curves; response and recovery times; and film conductance vs temperature and energy barrier measurement (PDF)
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