Photo-electrochemical properties of amorphous WO3 supported on TiO2 hybrid catalysts

In this work, we have carried out ivestigations on photo-electrochemical energy conversion and storage on WO₃/TiO₂ hybrid materials. The band gap excitation of the hybrid WO₃/TiO₂ having an amorphous WO₃ phase led to an effective photo-charging to form a tungsten bronze structure by the intercalation of protons while a reversible discharging through de-intercalation could also be observed.     

The Effects of Al2O3 Addition and WO3 Modification on Catalytic Activities of NiO/TiO2 for Acid Catalysis

NiO/Al₂O₃–TiO₂/WO₃ catalysts for acid catalysis were prepared by the addition of Al₂O₃ and the modification with WO₃. The strong acid sites were formed through the bonding between dispersed WO₃ and TiO₂. The larger the dispersed WO₃ amount, the higher both the acidity and catalytic activity. The addition of Al₂O₃ up to 5 mol% enhanced acidity and catalytic activity of NiO/Al₂O₃–TiO₂/WO₃ gradually due to the interaction between Al₂O₃ and TiO₂ and consequent formation of Al–O–Ti bond. The presence of NiO may attract reactants and enhance the local concentration of reactants near acid sites and consequently increase catalytic activity.     

Photocatalytic WO3 and TiO2 Films on Brass

This paper reports on the structure, mechanical, and photocatalytic properties of titanium dioxide (TiO₂) and tungsten oxide (WO₃) films on a brass substrate. TiO₂ and WO₃ films have been successfully deposited on brass by a simple sol‐gel dip‐coating method and it has been shown that, while both films possess photocatalytic properties, WO₃ films were superior to TiO₂. Higher surface area and rod‐like morphology of WO₃ films might have contributed to their higher photocatalytic activity. Nanoindentation results have shown that both films attach well to the substrate and possess good mechanical properties.     

An HREM study of the WO3/TiO2 monolayer catalyst system. Proposals for the overlayer structure

High resolution electron microscopy (HREM) has been used to characterise the WO₃/TiO₂ (anatase) catalyst system. Comparisons between pure samples of TiO₂ in the uncalcined and calcined states with titania in the catalyst (loaded with 10 wt% WO₃) indicate that the tungsten oxide overlayer preserves the surface roughness of the support (as observed in the pure uncalcined material). The calcination of pure anatase results in significant grain growth and surface smoothing. In the electron microscope, the tungsten oxide overlayer is revealed as 2D pseudo-hexagonal shaped clusters which appear to be epitaxially related to the support. After noting that the anatase support predominantly exposes {112}, {011}, {110} and (001) type facets we have combined this information with structural data on the overlayer derived from a previous EXAFS and XANES study by Hilbrig et al. that reported the presence of WO₄ species and six-coordinate WO₅ groups. By considering the arrangement of terminating oxygen atoms on each of the aforementioned anatase surfaces, we suggest ways in which the WO _x species may be linked together to form the tungsten oxide overlayer. This approach has led us to conclude that, with the exception of the (001) surface, the overlayer may consist of WO₄ dimers rather than chains of linked WO₅ groups terminated by WO₄ species.     

基于WO3-MoO3和TiO2/CdS复合电极的光电致变色器件

电致变色广泛应用于智能窗领域,但电致变色材料仍需外部电源驱动,将太阳能电池与电致变色材料结合起来的光电致变色器件可实现无需外部供电的智能变色调控。性能优异的变色阴极和光阳极是当下光电致变色器件的研究热点。通过水热法制备WO₃-MoO₃薄膜,研究其电致变色性能;通过水热法结合连续离子层沉积法制备TiO₂/CdS复合薄膜,研究其光电转换性能。最后将WO₃-MoO₃薄膜和TiO₂/CdS复合薄膜分别作为光电致变色器件的变色阴极、光阳极构建WO₃/MoO₃-TiO₂/CdS光电致变色器件。WO₃/MoO₃-TiO₂/CdS光电致变色器件具有较大的光学调制范围(630nm处为41.99%)、更高的着色效率(35.787%),将其作为智能窗应用在现代建筑、通行工具等领域具有重要应用价值。     

TiO2/WO3 hybrid structures produced through a sacrificial polymer layer technique for pollutant photo- and photoelectrooxidation under ultraviolet and visible light illumination

TiO₂/WO₃ hybrid structures were produced on graphite substrates following a three step procedure: (i) electrochemical deposition of WO₃ under potentiostatic conditions, (ii) electrochemical deposition of TiO₂–polyaniline (PANI) composite layers by potentiostatic polymerization of aniline in the presence of TiO₂ nanoparticles, (iii) high temperature (450 °C) treatment for decomposition of the PANI structure. Experiments on the photoelectrochemical response of the composite layers were carried out by cyclic voltammetry and chronoamperommetry in the dark and under illumination by using low power lamps emitting in the visible and UV spectrum ranges. The oxidation of three pollutants—oxalate ions, methanol and malachite green was used to evaluate the photoelectrocatalytic activity of the TiO₂/WO₃ structures. The photocurrents registered for the photooxidation of oxalate were higher than photocurrents measured at hybrid TiO₂/WO₃ electrodes obtained in conventional two-step electrodeposition of WO₃ and subsequently TiO₂ from corresponding salt solutions. The efficiency of the malachite green photodegradation in our experiments was also about two orders of magnitude higher than that obtained in TiO₂/WO₃ structures synthesized in a conventional way. These results are (very probably) due to the proposed synthetic approach involving PANI polymer layer as an immobilizing matrix and the opportunity to disperse homogeneously TiO₂ nanoparticles on the WO₃ surface provided.     

Catalytic hydrolysis of chlorofluorocarbon (CFC-12) over WO3/ZrO2

The catalytic decomposition of CFC-12 (CCl₂F₂) in the presence of water vapor was investigated over a series of solid acids WO₃/ZrO₂. Compared with tungstic acid, ammonium metatungstate is a better source of tungsten oxide for the preparation of WO₃/ZrO₂ catalysts. CFC-12 decomposition activities of WO₃/ZrO₂ catalysts are in good agreement with their acidities. Enhancing the acidities of catalysts is favorable to increase their CFC-12 decomposition activities. WO₃/ZrO₂ catalysts calcined at higher temperature exhibit good catalytic activity and stability for the hydrolysis of CFC-12, and show better structural stability during the reaction.     

Influence of the V2O5 Loading on the Structure and Activity of V2O5/TiO2 SCR Catalysts for Vehicle Application

In this paper the effect of the vanadium oxide loading on the surface vanadia structure and the activity as well as selectivity in the catalytic reduction of NO with NH₃ was studied for a V₂O₅/TiO₂ model system. A series of TiO₂ (WO _x stabilized anatase) supported vanadia catalysts with varying loadings were characterized by laser Raman spectroscopy, ⁵¹V MAS-NMR, V K XANES. To determine the acidic properties, DRIFTS measurements were done with pyridine adsorbed on the samples. The measurements indicate that with increasing active phase loading square pyramidal coordinated surface vanadia species are replaced by an amorphous highly dispersed vanadium oxide phase with a coordination like V₂O₅. In addition, the ratio of Brønsted to Lewis acid sites is shifted from a comparatively low to an equal level at high loadings. This structural change is accompanied by a clearly improved catalytic activity and selectivity.     

Determination of the surface coverage of WO3/TiO2 catalysts by CO2 chemisorption

The surface coverage of a series of WO₃/TiO₂ catalysts prepared by incipient wetness impregnation was monitored by CO₂ chemisorption. The coverage of the TiO₂ support increases from 31±2% for the 3.3 wt% WO₃/TiO₂ catalyst to ca. 86±2% for catalysts with W loadings ≥10.3 wt% WO₃. The leveling off of the surface coverage for the high-loading catalysts has been attributed to the formation of W multilayers or bulk WO₃. The surface coverage values obtained by CO₂ chemisorption were consistent with those measured previously using ion scattering spectroscopy. The apparent suitability of CO₂ chemisorption for monitoring the surface coverage of TiO₂-supported catalyst systems, in contrast to previous results for Al₂O₃-supported systems, will be discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ozonation of Reactive Orange 122 Using La3+-Doped WO3/TiO2/Sep Photocatalyst

La³⁺/WO₃/TiO₂/sep composites have been prepared by the sol–gel method. The degradation of dye was studied under the influence of various operational parameters such as initial pH, amounts of catalyst, concentrations of the dye, and ozone flow rate. The mineralization of Reactive Orange 122 has been confirmed by chemical oxygen demand measurements. The color removal of dye was found to follow a pseudo–first-order kinetics. Maximum color and chemical oxygen demand removal were 99.9% and 90% respectively, at a dye concentration of 200 mg/L, ozone flow rate of 2.0 L/min., 0.05 g/L weight of catalyst, and pH of 6.9 in 4 h. In addition, the catalyst was characterized by X-ray diffraction spectra, Fourier-Transform Infrared Spectroscopy, scanning electron microscopy, and a transmission electron microscope. This work could be a good candidate as a practical application for photocatalytic dye degradation.     

Sunlight assisted photoelectrocatalytic degradation of benzoic acid using stratified WO3/TiO2 thin films

The stratified WO₃/TiO₂ thin films have been deposited onto glass and FTO coated glass substrates using simple chemical a spray pyrolysis method. The structural, morphological, compositional and photoelectrocatalytic properties of the stratified WO₃/TiO₂ thin films are studied. The photoelectrochemical (PEC) study shows that, both short circuit current (I_sc) and open circuit voltage (V_oc) are (I_sc =1.192 mA and V_oc =0.925 V) relatively high at 50 ml spraying quantity of TiO₂ solution on pre-deposited WO₃. XRD analysis confirms that films are polycrystalline with monoclinic and tetragonal crystal structures for WO₃ and TiO₂ respectively. Specific surface area of 72.14 m² g⁻¹ is measured by Brunauer-Emmett-Teller (BET) technique. Photoelectrocatalytic degradation of benzoic acid (BA) dye in aqueous solutions is studied. The end result shows that the degradation percentage of benzoic acid (BA) using stratified WO₃/TiO₂ photoelectrode has reached 66% under sunlight illumination after 320 min. The amount of degradation is confirmed by COD analysis.     

An effective heterogeneous WO3/TiO2–SiO2 catalyst for selective oxidation of cyclopentene to glutaraldehyde by H2O2

TiO₂–SiO₂ mixed oxide with large pore size was synthesized by the xerogel method and it was then used to prepare the WO₃/TiO₂–SiO₂ catalyst by an incipient wetness method. The as‐prepared WO₃/TiO₂–SiO₂ sample was employed as the first heterogeneous catalyst in the liquid‐phase cyclopentene oxidation by aqueous H₂O₂, which exhibited higher selectivity (about 75%) to glutaraldehyde (GA) and, in turn, higher GA yield than the WO₃/SiO₂ heterogeneous catalyst and even the tungstic acid homogeneous catalyst under the same reaction conditions. The amorphous WO₃ phase was identified as the active sites and the loss of the active sites was proved to be not important. The lifetime of the catalyst was determined and its regeneration method was proposed. The effects of various factors on the catalytic behaviors, such as the WO₃ loading, the calcination temperature, the surface acidity and the reaction media, were investigated and discussed based on various characterizations including BET, XRD, XPS, FTIR, EXAFS and Raman spectra etc. This revised version was published online in July 2006 with corrections to the Cover Date.     

Two-step alcohothermal synthesis and characterization of enhanced visible-light-active WO3-coated TiO2 heterostructure

A new kind of WO₃-coated TiO₂ heterostructure with higher photocatalytic activity was prepared via a novel two-step alcohothermal synthesis process. The effects of the WO₃ addition on the TiO₂/WO₃ products were systematically studied, including analysis of the phases, observation of the morphologies and calculation of the band gaps. Under illumination, the conduction band electrons of TiO₂ are excited and accompanied by the generation of positive holes. In this heterostructure, the conduction band electrons of WO₃ occupy the nearest valence band of TiO₂ and then combine with the internal holes, inhibiting the flow of the electrons transferred from the conduction band of TiO₂. Compared with anatase TiO₂, the WO₃-coated TiO₂ heterostructure (weight ratio of WO₃:TiO₂ = 1:2) with a finer grain size exhibits excellent photocatalytic performance.     

TiO2‐Modified Flower‐Like Bi2WO6 Nanostructures with Enhanced UV‐Vis Photocatalytic Activity

Anatase TiO₂‐modified flower‐like Bi₂WO₆ nanostructures were prepared by a simple hydrothermal reaction followed by layer‐by‐layer deposition and calcination. The photocatalytic activity was evaluated using Brilliant Red X3B, an anionic azo dye, as the target organic pollutant under UV‐Vis light irradiation. The experiment results showed that the photocatalytic activity of the hybrid increases first and then decreases with increasing loading amount of TiO₂. The hybrid coated with four layers of TiO₂ (containing 20 wt‐% TiO₂) showed the highest photocatalytic activity, which is 10.45 and 3.20 times higher than that of pure Bi₂WO₆ and TiO₂, respectively. The improved photocatalytic performance of TiO₂‐modified Bi₂WO₆ nanostructures could be ascribed to the improved light‐harvesting ability, efficient photo‐generated electron‐hole separation, and enhanced adsorption of the dye. This work may shed light on the design of complex architectures and the exploitation of their potential applications.     

The reactivity of V2O5-WO3-TiO2 catalyst supported on a ceramic filter candle for selective reduction of NO

For realizing the environmental issues and constituting an economical treatment system, a catalytic filter based on V₂O₅/TiO₂ supported on tubular filter elements has many advantages by removing NO_x and particulate simultaneously from flue gas. In order to improve the activity of a catalytic filter based on V₂O₅/TiO₂ supported on a commercial high temperature filter element (PRD-66), the promoting effects of WO₃ were investigated in an experimental unit. PRD-66 presented very good properties for SCR catalyst carrier since it contains much active material such as A1₂O₃ SiO{om2}, and MgO whose contributions were remarkable. For additional catalyst carrier, TiO₂ particles were coated in the pores of PRD-66 with relatively good distribution of the particle size less than 1 μm, by a coating process applying centrifugal force. WO₃, in the V₂O₅-WO₃-TiO₂/PRD-66 catalytic filter system, increased the SCR activity significantly and broadened the optimum temperature window. The catalytic filter shows the maximum NO conversion of more than 95% for NO concentration of 700 ppmv at face velocity of 0.02 m/sec, which is comparable to the current commercial catalytic filters of plate form.     

Photoelectrocatalytic activity of bi-layer TiO<Subscript>2</Subscript>/WO<Subscript>3</Subscript> coatings for the degradation of 4-chlorophenol: effect of morphology and catalyst loading

WO₃ and bi-layer WO₃/TiO₂ coatings of different catalyst loadings were electrosynthesized on stainless steel 304 (SS) substrates from acidic aqueous solutions by single-step and consecutive steps potentiostatic cathodic deposition. The resulting WO₃/SS and TiO₂/WO₃/SS photoelectrodes were screened for their photoresponse under ultraviolet (UV) and visible light illumination by photovoltammetry and photoamperometry in sulphate solutions, in the absence and presence of 4-chlorophenol (4-CP). They were also evaluated for bulk photo-oxidation of 4-CP under constant potential, in the voltage range determined on the basis of the photovoltammetric tests. The optimal weight ratio between TiO₂ and WO₃ was also established, ensuring the best performance of these photoelectrodes for the photooxidation of 4-CP under UV and visible light irradiation.     

Pd/Pt on Ti-containing Mixed Oxides as Dearomatization Catalysts: Physico-chemical Characterization and Activity

Pd/Pt supported on pure and doped TiO₂ (TiO₂–WO₃ and TiO₂–WO₃–SiO₂) were prepared and characterized by different techniques (XPS, TEM, XRD, H₂-TPR and TPD of ammonia). These catalysts were investigated in the hydrogenation of tetralin at 6.0 MPa, checking also their thio-tolerance by feeding increasing amounts of dibenzothiophene (DBT, 300 and 1000 wt ppm). The catalytic activity followed the order: Pd/Pt–TiO₂ > Pd/Pt–TiO₂–WO₃–SiO₂ > Pd/Pt–TiO₂–WO₃, evidencing a negative role of a second oxide inside TiO₂. The Pd/Pt–TiO₂ catalyst showed high activity regardless of reaction conditions (temperature, contact time, H₂/tetralin ratio) together with a good thio-tolerance up to 300 wt ppm of DBT.     

Selective catalytic reduction (SCR) of NO by NH3 over TiO2-supported V2O5–WO3 and V2O5–MoO3 catalysts

A comparison between commercial and model WO₃–V₂O₅/TiO₂ and MoO₃–V₂O₅/TiO₂ SCR catalysts is considered in this study. The data indicate that WO₃ and MoO₃ behave as “structural” and “chemical” promoters for the catalysts. MoO₃-based catalysts are more active but less selective than WO₃–V₂O₅/TiO₂ catalysts in the SCR reaction, although in the presence of water the catalytic performances of the investigated samples are comparable. This revised version was published online in August 2006 with corrections to the Cover Date.     

Excellent antimicrobial properties of mesoporous anatase TiO2 and Ag/TiO2 composite films

Optically transparent, crack-free, mesoporous anatase TiO₂ thin films were fabricated. The Ag/TiO₂ composite films were prepared by incorporating Ag in the pores of TiO₂ films with an impregnation method via photoreduction. The as-prepared composite films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectronic spectra (XPS) and N₂ adsorption. The release behavior of silver ions in the mesoporous composite film was also studied. Moreover, the antimicrobial behaviors of the mesoporous film were also investigated by confocal laser scanning microscopy. The antibacterial activities of the composite films were studied by a fluorescence label method using Escherichia coli (E. coli) as a model. The as-prepared mesoporous TiO₂ films showed much higher antimicrobial efficiency than that of glass and commercial P25 TiO₂ spinning film. The facts would result from the high surface area, small crystal size and more active sites for the mesoporous catalysis. After the doping of Ag, a significant improvement for the antimicrobial ability was obtained. To elucidate the roles of the membrane photocatalyst and the doped silver in the antimicrobial activity, cells from a silver-resistant E. coli were used. These results indicated that Ag nanoparticles in the mesoporous were not only an antimicrobial but also an intensifier for photocatalysis. The as-prepared mesoporous composite film is promising in application of photocatalysis, antimicrobial and self-clean technologies.     

Enhanced inactivation of E. coli bacteria using immobilized porous TiO2 photoelectrocatalysis

Immobilized TiO₂ nanotube electrodes with high surface areas were grown via electrochemical anodization in aqueous solution containing fluoride ions for photocatalysis applications. The photoelectrochemical properties of the grown immobilized TiO₂ film were studied by potentiodynamic measurements (linear sweep voltammetry), in addition to the calculation of the photocurrent response. The nanotube electrode properties were compared to mesoporous TiO₂ electrodes grown by anodization in sulfuric acid at high potentials (above the microsparking potential) and to 1 g/l P-25 TiO₂ powder. Photocatalyst films were evaluated by high resolution SEM and XRD for surface and crystallographic characterization. Finally, photoelectrocatalytic application of TiO₂ was studied via inactivation of E. coli. The use of the high surface area TiO₂ nanotubes resulted in a high photocurrent and an extremely rapid E. coli inactivation rate of ∼10⁶ CFU/ml bacteria within 10 min. The immobilized nanotube system is proven to be the most potent electrode for water purification.