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Varistores à base de WO3 - revis?o
摘要： Varistors are elements that are part of electric power transmission and distribution systems or of special electrical installations. Varistors are manufactured in a wide variety of types, depending on their application, such as low-voltage devices with a layer of a few grains of thickness and low breakdown voltage, to varistors with a breakdown voltage of several kilovolts, such as those used in the lightning arresters of electric power distribution networks. Varistors, whose physical operation has been extensively studied, share common elements such as metal-semiconductor Schottky barrier junctions. Several studies have focused on the development of varistor ceramics for high and low voltage applications, including ZnO, SnO2, TiO2, and more recently, WO3-based ceramics. Unlike the first three compositions, WO3-based ceramics present an intrinsic varistor behavior because they contain monoclinic and triclinic phases. The addition of electron donor and acceptor dopants and heat treatments in different atmospheres also alter the non-linear properties of these systems, since they affect the formation of the Schottky barrier. This paper offers a review of the literature on the new varistor ceramic composition based on tungsten oxide (WO3).
关键词： electrical properties,WO3,varistors
更新于2025-09-11 14:15:04
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Boosting the Photocatalytic Oxidative Desulfurization of Dibenzothiophene by Decoration of MWO4 (M=Cu, Zn, Ni) on WO3
摘要： The surface of WO3 was partially decorated with transition metal tungstate MWO4 (M=Cu, Zn, Ni) using impregnation method followed by solid-state reaction. It is found that MWO4/WO3 photocatalysts showed a higher activity for photocatalytic oxidative desulfurization (PODS) of dibenzothiophene (DBT) than pure WO3 or MWO4 under visible light irradiation. Moreover, the activity for PODS of DBT on MWO4/WO3 depends on the content of MWO4 decoration on WO3 surfaces. 0.2% CuWO4/WO3, 1% ZnWO4/WO3, and 0.5% NiWO4/WO3 exhibited the highest activity among CuWO4/WO3, ZnWO4/WO3 and NiWO4/WO3 samples. However, as compared with 1% ZnWO4/WO3 and 0.5% NiWO4/WO3, the 0.2 % CuWO4/WO3 sample exhibited superior visible light photocatalytic activity for DBT conversion. Brunauer-Emmett-Teller method (BET), SEM, and ultraviolet-visible diffuse reflectance spectra (UV-vis DRS), high resolution transmission electron microscope (HRTEM), photoluminescence spectroscopy (PL), and a series of titration experiments were used to seek the reason for the positive impact of MWO4 on the photocatalytic activity of WO3. As compared with pure WO3, no notable changes of specific surface areas, morphologies, and light absorption are observed after MWO4 (M=Cu, Zn, Ni) decoration. The formation of heterojunction structure between MWO4 and WO3, which promotes charge separation efficiency, was the main reason for the high photocatalytic activity of MWO4/WO3 photocatalyst. Moreover, difference in PODS activity between MWO4/WO3 heterojunctions is proved to be affected by their charge separation and transfer efficiency and amount of active species.
关键词： MWO4/WO3 heterojunction,photocatalytic oxidative desulfurization,dibenzothiophene,WO3
更新于2025-09-10 09:29:36
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Ultrathin WO3 nanosheets modified by g-C3N4 for highly efficient acetone vapor detection
摘要： In this work, ultrathin WO3 nanosheets were prepared by self-assembly approach and their phase and morphology were regulated by changing the heat treatment temperature. Then, g-C3N4 modified WO3 nanosheets sensitive material was fabricated via a facile liquid ultrasonic mixing method. The microstructure, morphology, chemical composition, oxidation state and surface area of WO3 nanosheets and g-C3N4/WO3 nanocomposite were comparatively studied by X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM), Transmission Electron Microscope (TEM), X-ray Photoelectron Spectroscopy (XPS), and Brunauer-Emmett-Teller (BET). Sensing performances of WO3 nanosheets and g-C3N4/WO3 composite with different g-C3N4 loading amount were investigated with acetone as a target gas. Compared to WO3 nanosheets, the g-C3N4/WO3 gas sensor exhibits good response, excellent selectivity, transient response and trace detection ability to acetone vapor. Effects of g-C3N4 content on gas sensitivity were also investigated. The response (Ra/Rg) of the gas sensor based on 1 wt% g-C3N4/WO3 was 35 toward 100 ppm acetone at 340 °C, which was about 300% higher than the response value of pure WO3 sensor. The sensor also showed a fast response/recovery speed (9 s/3.8 s) and a wide linear detection range (from 0.5 ppm to 500 ppm). These unique sensing properties were attributed to the synergistic effects including the contribution of WO3 ultrathin nanosheets, suitable crystal phase and porous surface, and the sensitization of g-C3N4, which increases the specific surface area and regulates the electrical properties. This work will contribute to the development of new acetone sensors and expand the application of g-C3N4 composite materials.
关键词： g-C3N4 nanosheets,acetone detection,nanocomposites,WO3 nanosheets
更新于2025-09-10 09:29:36
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Convenient Fabrication of Carbon Doped WO3-x Ultrathin Nanosheets for Photocatalytic Aerobic Oxidation of Amines
摘要： It is an important chemical transformation for oxidation of amines to imines, on account of very important versatile applications of imines in organic synthesis. Here, we develop a convenient way to synthesize carbon doped WO3-x ultrathin nanosheets via an acid-assisted one-pot process. The carbon doped WO3-x ultrathin nanosheets exhibit excellent photocatalytic activity in the aerobic oxidation of amines to corresponding imines under visible light irradiation at room temperature. The high catalytic performance is attributed to remarkable visible light absorption ability and effective absorption of molecular oxygen and substrates. Rich oxygen-vacancies existing in the carbon doped WO3-x ultrathin nanosheets may play an important role, because oxygen-vacancies not only change the band structure but also act as catalytic sites to activate molecular oxygen by photoproduct electrons to generate superoxide radicals. Both photoproduct holes and superoxide radicals play important role for the oxidation of amines.
关键词： Aerobic oxidation,Carbon dropping,WO3-x,Nanosheets,Photocatalytic
更新于2025-09-10 09:29:36
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N Doped Carbon Dot Modified WO <sub/>3</sub> Nanoflakes for Efficient Photoelectrochemical Water Oxidation
摘要： It is a serious challenge to develop photoanodes with fast charge separation efficiency and surface reaction kinetics. Herein, the N doped carbon dot modified WO3 nanoflake (NCDs/WO3) is constructed by impregnation method. The resulting NCDs/WO3 exhibits an excellent photocurrent density of 1.42 mA cm?2 (1.0 V vs saturated calomel electrode, SCE) in 1 m H2SO4 solution under AM 1.5 G irradiation, which is 2.25 times higher than that of the pristine WO3. In addition, the onset potential of NCDs/WO3 photoanode represents a cathodic shift of 70 mV, indicating the charge separation and transfer process are both promoted. These results demonstrate N doped CD modified WO3 can further enhance the conductivity and electrochemical activity surface area, which contributes to the higher photoelectrochemical (PEC) performance. This work provides an efficient strategy for the development of doping carbon material with heteroatoms to increase the charge transfer and charge separation efficiency in PEC water oxidation.
关键词： WO3 nanoflakes,photoelectrochemical,N doped carbon dots,water oxidation
更新于2025-09-10 09:29:36
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Metal insulator transition driven by hydrated water of tungsten trioxide
摘要： Metallic nature to insulating nature transition (MIT) is found to occur in transition metal oxides and the study is of immense interest in materials research and condensed matter physics. Thermally stable layered orthorhombic WO30.33H2O having weak Van der Waals bonds between adjacent layers is synthesized by hydrothermal method. MIT is observed for the sample at a temperature of 343 K, by the method of dielectric relaxation spectroscopy (DRS). Multiple oxidation states of tungsten obtained from XPS in hydrated tungsten trioxide, caused by variation of oxygen vacancy is found to contribute to the transition. At the transition temperature there is breakage of hydrogen bond, simultaneously trapping the conduction electrons and liberating hydrogen ions for proton conduction. Intercalated water causes proton hoping by Grotthuss mechanism which scaffolds Mott transition and explain MIT in hydrated WO3.
关键词： Grotthuss mechanism,Mott theory,Arrhenious plot,Temperature dependent dielectric study,Hydrated WO3,Metallic to insulating nature transition
更新于2025-09-10 09:29:36
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Decorating (001) Dominant Anatase TiO2 Nanoflakes Array with Uniform WO3 Clusters for Enhanced Photoelectrochemical Water Decontamination
摘要： A facile two-step chemical bath deposition (CBD) method has been developed for the preparation of uniformly crystalline anatase WO3/TiO2 array on FTO substrate. The synthesis starts from the hydrothermal growth of TiO2 array in a homogenous HCl aqueous solution containing stabilized titanium isopropoxide, NH4F and acetylacetone (AcAc). Electron microscopy and the XRD analysis suggest the addition of AcAc chelating agent can facilitate the preferential growth of anatase (001) facets that are interconnected and vertically aligned. While (101) dominant TiO2 bipyramid array may form without AcAc. The subsequent decoration of WO3 clusters on TiO2 array is achieved by post-depositing TiO2 array in (NH4)2WO4 aqueous solution followed with a calcination at 450 oC, the resultant WO3/TiO2 array shows a significantly elevated photocurrent performances owing to the high separation efficiency of charge carriers. The enhanced photoelectrocatalytic properties are explained by the efficient charge carrier separation at the heterojunction between WO3 and TiO2. A faster photoelectrochemical degradation of methylene under simulated sunlight further demonstrates the potential usefulness of WO3/TiO2 arrayed photoelectrocatalyst in solar-driven environmental purification and solar fuel synthesis.
关键词： hydrothermal process,WO3,water treatment,TiO2,semiconductor photoelectrocatalysis
更新于2025-09-10 09:29:36
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Photoelectrochemical removal of chlorfenvinphos by using WO3 nanorods: influence of annealing temperature and operation pH
摘要： A visible-light driven photoelectrochemical degradation process has been applied to a solution polluted with the organophosphate insecticide chlorfenvinphos. Different WO3 nanosheets/nanorods have been used as photoanodes. These nanostructured electrodes have been fabricated by anodization of tungsten and, subsequently, they have been subjected to a thermal treatment (annealing). The combined influence of annealing temperature (400o C and 600o C) and operation pH (1 and 3) on the photoelectrocatalytic behavior of these nanorods has been examined through a statistical analysis. Morphological, structural and photoelectrochemical characterizations have also been carried out. The chlorfenvinphos degradation efficiency depended both on annealing temperature and, specially, operation pH. At pH 1 and using an annealing temperature of 600o C, chlorfenvinphos has been effectively degraded following pseudo-first order kinetics with a coefficient of 7.8×10-3 min-1, and notably mineralized (more than 65% of Total Organic Carbon decrease).
关键词： anodization,WO3 nanorods,chlorfenvinphos,regression model,Photoelectrochemical degradation
更新于2025-09-10 09:29:36
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Visible-light photocatalytic fuel cell with Z-scheme g-C3N4/Fe0/TiO2 anode and WO3 cathode efficiently degrades berberine chloride and stably generates electricity
摘要： A visible-light Z-scheme g-C3N4/Fe0/TiO2 anodic catalyst was tested with cathodic WO3 in photocatalytic Fuel Cell (PFC) that efficiently degrades berberine chloride and simultaneously generate electricity at pH 2,5,7 and 13. The Stainless-steel mesh electrodes loaded with prepared catalyst were irradiated by visible-light in single chamber PFC. The highest removal of berberine Chloride, cell voltage, and power density were 91%, 0.8 V, and 16.4 W/m2 at a current density of 2.02 mA/cm2, respectively after 90 min irradiation in 0.05 M Na2SO4 electrolyte, with 10 ? external resistance. The impacts of pH and initial concentration of BEC on photocatalytic degradation and cell voltage were evaluated. The cell current density is enhanced while the photocatalyst activity increased. The constructed PFC maintained high-performance after 5 uses. Its use in degrading wide spectrum refractory pollutants and generate electricity is expected for the proved catalyst design, paired electrodes and high PFC performance for practical wastewater treatment.
关键词： Electricity generation,WO3,Visible-light,g-C3N4/Fe0/TiO2,Photocatalytic Fuel Cell,Berberine Chloride,Z-scheme
更新于2025-09-10 09:29:36
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Se—assisted synthesis of WO <sub/>3?x</sub> nanowires and its intrinsic metallicity
摘要： One dimensional WO3?x nanowires were successfully synthesized by a chemical vapor deposition method under a catalysis effect of non-metal selenium at an atmosphere pressure. The morphology ad structural characteristics were investigated by scanning electron microscopy (SEM), atom force microscopy (AFM), and transmission electron microscopy (TEM). Furthermore, X-ray photoelectron spectrum analysis con?rms existence of the oxygen vacancies in WO3?x nanowires. Based on the above results, a possible growth mechanism was proposed. The oxygen vacancy induced metallic nature of WO3?x nanowires was also con?rmed by the single-nanowire electrical measurements.
关键词： oxygen vacancy,metallic,WO3?x nanowires,chemical vapor deposition
更新于2025-09-09 09:28:46