Au-TiO2/Chit modified sensor for electrochemical detection of trace organophosphates insecticides

In this paper, Au–TiO₂/Chit modified electrode was prepared with Au–TiO₂ nanocomposite (Au–TiO₂) and Chitosan (Chit) as a conjunct. The Au–TiO₂ nanocomposite and the films were characterized by electrochemical and spectroscopy methods. A set of experimental conditions was also optimized for the film's fabrication. The electrochemical and electrocatalytic behaviors of Au–TiO₂/Chit modified electrode to trace organophosphates (OPs) insecticides such as parathion were discussed in this work. By differential pulse voltammetry (DPV) measurement, the current responses of Au–TiO₂/Chit modified electrode were linear with parathion concentration ranging from 1.0 ng/ml to 7.0 × 10³ ng/ml with the detection limit of 0.5 ng/ml. In order to evaluate the performance of the detection system, we also examined the real samples successfully in this work. It exhibited a sensitive, rapid and easy-to-use method for the fast determination of trace OPs insecticides.     

Preparation and Characterisation of Nano-Structured WO<Subscript>3</Subscript>-TiO<Subscript>2</Subscript> Layers for Photoelectrochromic Devices

Nano-structured WO₃-TiO₂ layers were prepared by the sol-gel route. To obtain transparent, porous and crack free layers up to 0.8 μ m with a single dipping cycle a templating strategy was used. As a template three-dimensionally network based on organically modified silane was introduced to the WO₃ and TiO₂ sols. The WO₃ layers were dip-coated onto the conductive glass substrate (TCO) and the TiO₂ layers on the top of the WO₃ layer. The morphology and the structure of the layers were determined by Scanning Electron Microscopy (SEM), High Resolution Transmission Electron Microscopy (HR-TEM), Energy Dispersive X-Ray Spectroscopy (EDXS), Auger and Infrared spectroscopy. SEM image of the WO₃-TiO₂ layer confirmed the nano-porosity of the layers and give the size of the particles of about 10 nm for TiO₂ and 30 nm for WO₃ layer. Further analysis indicated that the titanium sol penetrates the WO₃ layer. Particles in the WO₃ layer consist of a crystalline monoclinic WO₃ core surrounded by a 5–10 nm amorphous phase consisting of WO₃, TiO₂ and SiO₂. The WO₃-TiO₂ layers were used to assemble all solid state photoelectrochromic (PE) devices. Under 1 sun irradiation (1000 W/m²) the visible transmittance of the PE device changes from 62% to 1.6%. The colouring and bleaching processes last about 10 minutes.     

Quantitative Raman and ESCA characterization of titania supported tungsten catalysts

Summary The distribution of supported species in a series of W/TiO₂ catalysts (1.8 – 28 wt% WO₃) has been determined by Raman and X-ray photoelectron spectroscopy (XPS, ESCA). The results show that three tungsten species are present on oxidic W/TiO₂ catalysts. A tungsten interaction species is formed almost exclusively for catalysts with W loadings lower or equal to 6.7 wt% WO₃. WO₃ is observed above 6.7 wt% WO₃. For W loadings higher than 10 wt%, a disordered W species W_DS is also present. The amounts of W_DS and WO₃ increase with increasing W content above 10 wt% WO₃.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday     

Selective photocatalytic oxidation of alcohols to aldehydes in water by TiO2 partially coated with WO3

Semiconductor TiO₂ particles loaded with WO₃ (WO₃/TiO₂), synthesized by impregnation of tungstic acid followed by calcination, were used for photocatalytic oxidation of alcohols in water with molecular oxygen under irradiation at λ>350 nm. The WO₃/TiO₂ catalysts promote selective oxidation of alcohols to aldehydes and show higher catalytic activity than pure TiO₂. In particular, a catalyst loading 7.6 wt % WO₃ led to higher aldehyde selectivity than previously reported photocatalytic systems. The high aldehyde selectivity arises because subsequent photocatalytic decomposition of the formed aldehyde is suppressed on the catalyst. The TiO₂ surface of the catalyst, which is active for oxidation, is partially coated by the WO₃ layer, which leads to a decrease in the amount of formed aldehyde adsorbed on the TiO₂ surface. This suppresses subsequent decomposition of the aldehyde on the TiO₂ surface and results in high aldehyde selectivity. The WO₃/TiO₂ catalyst can selectively oxidize various aromatic alcohols and is reusable without loss of catalytic activity or selectivity.     

Selectivity in the Ligand Functionalization of Photocatalytic Metal Oxide Nanoparticles for Phase Transfer and Self-Assembly Applications

The functionalization of photocatalytic metal oxide nanoparticles of TiO₂, ZnO, WO₃ and CuO with amine-terminated (oleylamine) and thiol-terminated (dodecane-1-thiol) alkyl-chain ligands was studied under ambient conditions. A high selectivity was observed in the binding specificity of a ligand towards nanoparticles of these different oxides. It was observed that oleylamine binds stably to only TiO₂ and WO₃, whereas dodecane-1-thiol binds stably only to ZnO and CuO. Similarly, polar-to-nonpolar solvent phase transfer of TiO₂ and WO₃ nanoparticles could be achieved by using oleylamine, but not dodecane-1-thiol, whereas the opposite holds for ZnO and CuO. The surface chemistry of ligand-functionalized nanoparticles was probed by attenuated total reflectance (ATR)-FTIR spectroscopy, which enabled the occupation of the ligands at the active sites to be elucidated. The photostability of the ligands on the nanoparticle surface was determined by the photocatalytic self-cleaning properties of the material. Although TiO₂ and WO₃ degrade the ligands within 24 h under both UV and visible light, ligands on ZnO and CuO remain unaffected. The gathered insights are also highly relevant from an application point of view. As an example, because the ligand-functionalized nanoparticles are hydrophobic in nature, they can be self-assembled at the air-water interface to give nanoparticle films with demonstrated photocatalytic as well as anti-fogging properties.     

Enhanced photocatalytic activity of electrosynthesised tungsten trioxide–titanium dioxide bi-layer coatings under ultraviolet and visible light illumination

Bi-layer WO₃–TiO₂ coatings have been synthesised on stainless steel (SS) substrates by consecutive cathodic electrodeposition of WO₃ (from peroxytungstate solutions) and TiO₂ electrosynthesis (from titanium oxosulfate solutions). The resulting TiO₂–WO₃/SS photoelectrodes have been screened for their photoresponse under ultraviolet (UV) and visible (vis) light illumination by photovoltammetry in supporting electrolyte (sodium sulfate) and malachite green (a typical dye) solutions. They were also evaluated for malachite green photooxidation during constant potential bulk photoelectrolysis. It was found that both photocurrent values and dye removal rates were higher at TiO₂–WO₃/SS than at plain WO₃/SS photoelectrodes, under both UV and vis illumination (up to 85% and 67% malachite green degradation has been achieved respectively from its 10 ppm solutions after 2 h). The enhancement of the UV and, as reported here for the first time, vis photocatalytic activity of WO₃ by the inclusion of TiO₂ is interpreted by reduced electron-hole recombination rates due to electron transfer from TiO₂ to WO₃ (during UV activation) and hole transfer from WO₃ to TiO₂ (during UV and vis light activation).     

TiO<Subscript>2</Subscript>/WO<Subscript>3</Subscript> photoanodes with enhanced photocatalytic activity for air treatment in a polymer electrolyte cell

The application of electrochemically enhanced photocatalysis in air treatment using a Nafion-based photoelectrochemical cell and TiO₂/WO₃ photoanodes for organic vapor photooxidation under both UV and visible light irradiation is briefly presented. In that direction, the obtained results regarding the preparation and characterization of the TiO₂/WO₃ photoanodes with enhanced photocatalytic activity are reviewed. Particular emphasis is given in the comparison of the photocatalytic behavior of bilayer TiO₂/WO₃ coatings, electrosynthesized on stainless steel mesh and powder C + mixed (WO₃ + TiO₂) photoanodes. The advantages of using a high surface area C + mixed (WO₃ + TiO₂) powder catalysts as photoanodes against their plain TiO₂ + C and WO₃ + C analogues are discussed.     

Solvothermal synthesis of WO3/TiO2/carbon fiber composite photocatalysts for enhanced performance under sunlight illumination

Carbon fiber (CF)‐based WO₃/TiO₂ composite catalysts (WO₃/TiO₂/CF) were successfully synthesized by solvothermal method. The catalysts were characterized by XPS, SEM, BET, XRD, FTIR, Raman and UV–Vis. The analyses confirmed the WO₃/TiO₂ nanoparticles with high crystallinity deposited on the carbon structure. The photocatalytic degradation of Orange II azo dye under UV and sunlight illumination with the synthesized catalyst was explored. The composite catalyst displayed high performance (85%) for Orange II degradation while that of for WO₃/TiO₂ was found as 76%. The effects of CF amount, solution pH, initial dye concentration and catalyst dose on photocatalytic performance were studied. It was found that the degradation efficiency increased from 68% to 90% with the increasing CF amount from 3 wt% to 5 wt%, while the further increase in CF amount (7–10 wt%) decreased the photodegradation due to the blocking the active sites of WO₃/TiO₂. The enhanced photocatalytic efficiency was mainly attributed to the electrical properties of the CF and reduced bandgap.     

Enhanced ethanol sensing properties of WO3 modified TiO2 nanorods

Pristine and WO₃ decorated TiO₂ nanorods (NRs) were synthesised to investigate n-n-type heterojunction gas sensing properties. TiO₂ NRs were fabricated via hydrothermal method on fluorine-doped tin oxide coated glass (FTO) substrates. Then, tungsten was sputtered on the TiO₂ NRs and thermally oxidised to obtain WO₃ nanoparticles. The heterostructure was characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX) spectroscopy. Fabricated sensor devices were exposed to VOCs such as toluene, xylene, acetone and ethanol, and humidity at different operation temperatures. Experimental results demonstrated that the heterostructure has better sensor response toward ethanol at 200 °C. Enhanced sensing properties are attributed to the heterojunction formation by decorating TiO₂ NRs with WO₃.     

An improved Re/W separation protocol for preparation of carrier-free186Re

An Al₂(WO₄)₃ target bombarded with a proton beam (28.5 MeV, 20 A) for 1 hour was completely dissolved in about 5 ml of hot 2N NaOH and the clear solution was neutralized with 2N HCl. The resulted white precipitate of Al₂(WO₄)₃ can be separated from the solution by centrifugation and decantation. The supematant containing radioactive Re as ReO ₄ ^– was loaded onto a column (1 cm×10 cm) of activated alumina (100–200 mesh). Eluted with 10 ml of saline, the carrier-free ReO ₄ ^– was collected, while the small amount of Al₂(WO₄)₃ in the supematant was adsorbed on the column. The total yield of ReO ₄ ^– was 94.7% and the breakthrough of WO ₄ ^2– , only 1.0·10^–6 M. The whole separation process can be accomplished within 30 minutes. This rapid and efficient Re/W separation protocol is applicable to the preparation of carrier-free¹⁸⁶Re, when an enrichel Al₂(¹⁸⁶WO₄)₃ target is used.     

Preparation of Bioactive PDMS-Modified CaO–SiO2–TiO2 Hybrids by the Sol-Gel Method

Much attention has been focused on the development of a new type of bioactive material with mechanical properties analogous to those of natural bone. The present authors previously showed that some polydimethylsiloxane (PDMS)-modified CaO–SiO₂–TiO₂ hybrids prepared by sol-gel method show apatite-forming ability in a simulated body fluid (SBF), which is indicative of bioactivity. In the present study, effects of composition of PDMS-modified CaO–SiO₂–TiO₂ hybrids on their bioactivity and mechanical properties were investigated. The bioactivity of the hybrids increased with decreasing PDMS content and increasing TiO₂ content. Their strain at failure increased with increasing PDMS content and decreasing TiO₂ content. Some samples showed high bioactivity, as well as analogous mechanical properties to those of human cancellous bones. This type of hybrids might be useful as a bone-repairing material.     

Selective aerobic photocatalytic oxidation of benzyl alcohol over spherical structured WO<Subscript>3</Subscript>/TiO<Subscript>2</Subscript> nanocomposite under visible light irradiation

TiO₂/WO₃ nanocomposite with nanodisk morphology was prepared and successfully used as a photocatalyst. The nanocomposite was obtained via sonochemical and hydrothermal methods, using pomegranate juice as a capping agent. The products were characterized by FE-SEM imaging, BET, EDAX spectroscopy, X-ray diffraction, DRS, and FT-IR spectroscopy. TiO₂/WO₃ nanocomposite showed high sensitivity to absorb visible light in compared to TiO₂. In an optimized condition, the yield of the aerobic photocatalytic oxidation of benzyl alcohol derivatives reached to 65% for the TiO₂/WO₃ nanocomposite, while the conversion percent of the derivatives was less than 8% and 50% on the TiO₂ and WO₃ nanoparticles, respectively. Experimental results were supported by density functional theory (DFT) calculations. The DFT results in several solvents of different dielectric constants, confirmed the strong dependence of light absorption and photocatalytic activity to adsorption energy of the substrates on the surface of the nanoparticles (E_ad). In addition, the theoretical results showed an inverse correlation between the adsorption energy of benzyl alcohol and its conversion percent, accordance to the experimental trend.

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Comparative Study of the Oxygen Storage Capacity of Pt/M<Subscript>x</Subscript>O<Subscript>y</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Systems

The oxygen storage capacity of 1% Pt/15% M_xO_y/Al₂O₃ systems containing a rare-earth or an alkaline-earth metal oxide or TiO₂ as the oxygen-storing component was studied. Oxygen storage capacity was evaluated as the amount of C₃H₈ reacting at 400°C with oxygen that was taken up by the catalyst during oxidative treatment. The systems containing a rare-earth metal oxide or TiO₂ possess the highest oxygen storage capacity among the catalysts examined (80 and 75 µmol C₃H₈/g Cat, respectively). Of the BaO and SrO systems, the latter is of interest, although its oxygen storage capacity (∼27 µmol C₃H₈/g Cat) is somewhat lower than the oxygen storage capacity of any rare-earth metal oxide or the TiO₂ system.__________Translated from Kinetika i Kataliz, Vol. 46, No. 4, 2005, pp. 585–589.Original Russian Text Copyright © 2005 by Sinel’nikov, Tolkachev, Stakheev.     

WO3/C hybrid material as a highly active catalyst support for formic acid electrooxidation

The hybrid material based on WO₃ and Vulcan XC-72R carbon has been used as the support of Pd nanocatalysts. The resultant Pd–WO₃/C catalysts in a large range of WO₃ content exhibit excellent catalytic activity and stability for formic acid electrooxidation. The great improvement in the catalytic performance is attributed to the uniform dispersion of Pd with less particle sizes on the WO₃/C support and the hydrogen spillover effect which greatly accelerates the dehydrogenation of HCOOH on Pd.     

Bactericidal effect of an energy storage TiO2–WO3 photocatalyst in dark

TiO₂–WO₃ composite photocatalyst films can be charged with reductive energy by irradiation with ultraviolet (UV) light. The photo-charged film exhibited a moderate bactericidal effect on Escherichia coli during 6-h exposure in dark. On the other hand, the pre-discharged film exhibited no significant bactericidal effect. The moderate bactericidal effect may restrain bacteria from increasing during the night, and the survived bacteria may be killed by TiO₂ due to its strong bactericidal effect in the next day. The photo-charged film generated H₂O₂ by reducing oxygen. The bactericidal effect of the photo-charged film was close to that of H₂O₂ of the generated amount. Thus, the bactericidal effect of the photo-charged TiO₂–WO₃ film can be explained chiefly in terms of the generated H₂O₂.     

Sol–gel synthesis of mesoporous WO3–TiO2 composite thin films for photochromic devices

Mesoporous WO₃–TiO₂ composite films were prepared by a sol gel based two stage dip coating method and subsequent annealing at 450, 500 and 600 °C. An organically modified silicate based templating strategy was adopted in order to obtain a mesoporous structure. The composite films were prepared on ITO coated glass substrates. The porosity, morphology, and microstructures of the resultant products were characterized by scanning electron microscopy, N₂ adsorption–desorption measurements, μ-Raman spectroscopy and X-ray diffraction. Calcination of the films at 450, and 500 °C resulted in mixed hexagonal (h) plus monoclinic phases, and pure monoclinic (m) phase of WO₃, respectively. The degree of crystallization of TiO₂ present in these composite films was not evident. The composite films annealed at 600 °C, however, consist of orthorhombic (o) WO₃ and anatase TiO₂. It was found that the o-WO₃ phase was stabilized by nanocrystalline anatase TiO₂. The thus obtained mesoporous WO₃–TiO₂ composite films were dye sensitized and applied for the construction of photochromic devices. The device constructed using dye sensitized WO₃–TiO₂ composite layer heat treated at 600 °C showed an optical modulation of 51 % in the NIR region, whereas the devices based on the composite layers heat treated at 450, and 500 °C showed only a moderate optical modulation of 24.9, and 38 %, respectively. This remarkable difference in the transmittance response is attributed to nanocrystalline anatase TiO₂ embedded in the orthorhombic WO₃ matrix of the WO₃–TiO₂ composite layer annealed at 600 °C.     

Erratum to: Sol–gel synthesis of mesoporous WO3–TiO2 composite thin films for photochromic devices

Mesoporous WO₃–TiO₂ composite films were prepared by a sol gel based two stage dip coating method and subsequent annealing at 450, 500 and 600 °C. An organically modified silicate based templating strategy was adopted in order to obtain a mesoporous structure. The composite films were prepared on ITO coated glass substrates. The porosity, morphology, and microstructures of the resultant products were characterized by scanning electron microscopy, N₂ adsorption–desorption measurements, μ-Raman spectroscopy and X-ray diffraction. Calcination of the films at 450, and 500 °C resulted in mixed hexagonal (h) plus monoclinic phases, and pure monoclinic (m) phase of WO₃, respectively. The degree of crystallization of TiO₂ present in these composite films was not evident. The composite films annealed at 600 °C, however, consist of orthorhombic (o) WO₃ and anatase TiO₂. It was found that the o-WO₃ phase was stabilized by nanocrystalline anatase TiO₂. The thus obtained mesoporous WO₃–TiO₂ composite films were dye sensitized and applied for the construction of photochromic devices. The device constructed using dye sensitized WO₃–TiO₂ composite layer heat treated at 600 °C showed an optical modulation of 51 % in the NIR region, whereas the devices based on the composite layers heat treated at 450, and 500 °C showed only a moderate optical modulation of 24.9, and 38 %, respectively. This remarkable difference in the transmittance response is attributed to nanocrystalline anatase TiO₂ embedded in the orthorhombic WO₃ matrix of the WO₃–TiO₂ composite layer annealed at 600 °C.     

Fabrication of an efficient ternary TiO2/Bi2WO6 nanocomposite supported on g-C3N4 with enhanced visible-light- photocatalytic activity: Modeling and systematic optimization procedure

In this study, a ternary TiO₂/g-C₃N₄/Bi₂WO₆ nanocomposite was prepared via a facial approach. The final structure was applied as a new photocatalyst for the removal of brilliant green (BG) dye, as a model of organic pollutants, from the aqueous solution. The results of FESEM, EDS with mapping, XRD, FTIR, UV–vis DRS, PL, and EIS analyses further demonstrate the successful establishment of heterojunction between TiO_2, g-C₃N₄, and Bi₂WO₆. Integration of g-C₃N₄ and Bi₂WO₆ with TiO2 was remarkably decreased the band gap energy of TiO₂ to 2.68 eV (from 3.15 eV). The effects of various experimental factors such as TiO₂/g-C₃N₄/Bi₂WO₆ dosage, initial BG concentration, visible irradiation time, and pH on the photocatalyst behavior of TiO₂/g-C₃N₄/Bi₂WO₆ were investigated by 2 ^k-1 factorial design. The results of the analysis of variance demonstrate these experimental factors are effective on the BG degradation efficiency. The response surface methodology was applied to achieve the optimization procedure of BG degradation. According to these results, the complete BG removal efficiency was obtained for the optimal conditions of 15.76 mg of TiO₂/g-C₃N₄/Bi₂WO₆ nanocomposite, an initial BG concentration of 10 ppm, pH of 9, and time duration of 70 min. The improved photocatalytic performance of ternary TiO₂/g-C₃N₄/Bi₂WO₆ nanocomposite was related to the formation of heterojunction between TiO_2, g-C₃N₄, and Bi₂WO₆, significant light adsorption ability, and low recombination of photogenerated carriers.     

负载金属对WO3-TiO2光催化剂结构与催化性能的影响

用溶胶-凝胶和浸渍-还原相结合的方法制得M/WO₃-TiO₂ (M＝Pd, Cu, Ni, Ag)光催化剂. 利用X射线衍射(XRD)、程序升温还原(TPR)、红外(IR)、程序升温脱附(TPD)、紫外-可见漫反射光谱(UV-Vis-DRS)和光反应器等技术研究了复合半导体负载金属的物相结构、光吸收性能和光催化反应性能. 结果表明: 金属负载在复合半导体上延迟了TiO₂由锐钛矿向金红石相转化, 增强W与载体TiO₂的相互作用, 使TiO₂光吸收限发生蓝移, 对可见光部分的吸收明显增加; 固体材料吸光性能强弱顺序Pd/WO₃-TiO₂＞Cu/WO₃-TiO₂＞Ag/WO₃-TiO₂＞Ni/WO₃-TiO₂; 金属Pd对CO₂吸附能力过强, 卧式吸附态脱附温度高, 光催化效率不高; 金属Cu对CO₂吸附能力适中, CO₂与C₃H₆脱附温度较接近, 实现了“光-表面-热”协同作用, 光量子效率最高, 达到19.7%.     

An all-solid photoelectrochemical cell for the photooxidation of organic vapours under ultraviolet and visible light illumination

An all-solid photoelectrochemical cell has been tested in the photooxidation of methanol vapours as a proof-of-concept for the application of electrochemically enhanced photocatalysis in air treatment. The cell was based on a Nafion^®-impregnated microporous membrane that served as the solid polymer electrolyte. The working and reference electrodes (a TiO₂/WO₃-coated stainless steel mesh and AgCl-coated Ag wire, respectively) were adhered with the addition of a Nafion^® solution onto one face of the membrane, while the counter electrode (a plain stainless steel mesh) was attached to its opposite face. The use of an electrosynthesized TiO₂/WO₃ photoelectrode allowed the utilization of both UV and visible light. The device was tested by constant potential photoamperometry in air streams saturated with water or water–methanol vapours and the obtained photocurrent increased with increasing methanol levels, confirming the photoelectrochemical oxidation of methanol vapours under UV and visible light illumination.