Potential visible WO3/GO composite photocatalyst

Graphene oxide (GO) was synthesized by Hummers method. GO and tungsten oxide (WO₃) composites were successfully prepared by deposition of WO₃ on GO surface to make efficient visible light catalyst. Scanning electron microscopy of pure GO revealed that GO films are folded with kinked and wrinkled edges. The interspaces layers are partially filled by WO₃ nanoparticles with their less wrinkled edges and smooth surface of composite. Moreover, composite sheets are thin and transparent which allow easy penetration of light. EDS showed the presence of C, O, and W in GO/WO₃ composites with no impurity. UV-Vis diffused reflectance spectra showed red shift with the increase in WO₃ contents. Raman spectra of GO and GO/WO₃ composite show G and D bands. These bands reduced in intensity in composite sample due to removal of oxygenated functional groups with some new peaks of WO₃. FT-IR confirmed successful oxidation of graphite into GO with reduction in GO because oxide-related bond groups decrease after reduction. The transmittance peaks of WO₃ in composite sample are appeared indicating W-O-C linkages. The highest visible light activity of the composite is due to easy penetration of light with deposition of WO₃, low band gap, and new linkages.     

Characterization of anodically formed polypyrrole/tungsten trioxide composites

Composite PPy/WO₃ materials were synthesized anodically under various conditions. The cyclovoltammetric switching curves are very close to the blank polypyrrole. The redox behaviour of the filler is only detected through electrochromism, leading to a yellow grey colour at +0.4 V vs SCE and to a green surface at –0.6 V. For overoxidation of the composite, a degree of overoxidation Y = 5 is found, the same as for the matrix alone. Photoelectrochemical response is due to the conducting polymer at negative potentials and even at 0 V vs SCE. A strong effect at positive potentials is due to the WO₃ pigment. From this, a flat band potential of +0.15 V vs SCE is determined for aqueous 0.1 m LiClO₄. Some non-electrochemical properties are also reported. Surface roughness increases with increasing WO₃ concentration, but for thicker layers, from MeCN, it decreases. SEM micrographs reveal homogeneous distribution of WO₃. Large secondary particles are observed in NBu₄BF₄ electrolyte. True and nominal thicknesses differ by up to a factor 1.65 due to the porous structure and this explains differences between densities measured by the flotation and the jump method. X-ray diffraction analysis exhibits unchanged WO₃-lines, but no PPy-lines due to the amorphous character. The conductivity of the composite from MeCN is much lower than expected by the volume filling of the WO₃.     

Preparation and characterization of PVC/CsxWO3 composite film with excellent near-infrared light shielding and high visible light transmission

Near-infrared (NIR) shielding is essential not only in the building and automobile glass films but also in achieving energy conservation. However, effectively shielding NIR and maintaining high transmittance in the visible light region have been great challenges in the past decade. Recently, hexagonal cesium tungsten bronze (Cs_xWO₃) nanoparticles have been widely studied due to the excellent transparency in the visible light region and strong heat-shielding ability in the NIR region. Herein, a design concept of transparent polyvinyl chloride (PVC)/Cs_xWO₃ composite film, as a heat insulation material for glasses, was proposed. To achieve this purpose, the PVC/Cs_xWO₃ composite film was prepared by incorporating Cs_xWO₃ slurry with better dispersion than traditional Cs_xWO₃ nanoparticles powder into a transparent PVC matrix. By the UV-Vis-NIR spectrophotometer characterization, the PVC/Cs_xWO₃ composite film containing 2.1 phr Cs_xWO₃ slurry displays high blocking of NIR (78%) and high transmittance of visible light (76%). In order to further understand the actual heat insulation effect from the PVC/Cs_xWO₃ composite films, the indoor sunlight simulation test and outdoor cooling experiment with solar illumination variations were carried out, which both showed heat insulation that is superior to the antimony tin oxide and indium tin oxide thin films prepared in our previous work. In addition, the mechanical property of PVC/Cs_xWO₃ composite films shows almost no change with the increase of Cs_xWO₃ slurry. The PVC/Cs_xWO₃ composite films simultaneously achieve excellent shielding of NIR and high transmittance of visible light, which makes it an ideal material to alleviate the current building energy consumption issues.     

Facile synthesis of WO3 nanorods/g-C3N4 composites with enhanced photocatalytic activity

In this paper, WO₃ nanorods (NRs)/g-C₃N₄ composite photocatalysts were constructed by assembling WO₃ NRs with sheet-like g-C₃N₄. The as-synthesized photocatalysts were characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, UV–vis diffuse reflectance spectroscopy and photoluminescence. The photocatalytic activity of the photocatalysts was evaluated by degradation of Rhodamine B (RhB) under simulated sunlight irradiation. Compared to pristine WO₃ NRs and g-C₃N₄, WO₃ NRs/g-C₃N₄ composites exhibit greatly enhanced photocatalytic activities. The enhanced performance of WO₃ NRs/g-C₃N₄ composite photocatalysts was mainly ascribed to the synergistic effect between WO₃ NRs and g-C₃N₄, which improved the photogenerated carrier separation. A possible degradation mechanism of RhB over the WO₃ NRs/g-C₃N₄ composite photocatalysts was proposed.     

Efficient photocatalytic activity of water oxidation over WO3/BiVO4 composite under visible light irradiation

A coupled WO₃/BiVO₄ thin film has been deposited on FTO substrate by a spin coating method from precursor solutions. The composite films were characterized by AFM, SEM, XPS and XRD techniques. The incident photon to current efficiency (IPCE) of BiVO₄ electrode was increased by 10 times when a WO₃ film was layered between the BiVO₄ layer and the FTO substrate. The enhanced performance of WO₃/BiVO₄ composite film electrode is mainly ascribed to the effective electron-hole separations at the semiconductor heterojunction. A schematic mechanism of charge transfer was proposed to explain the photocurrent enhancement for the WO₃/BiVO₄ electrode surface.     

Graphene nanosheets-tungsten oxides composite for supercapacitor electrode

Graphene nanosheets-tungsten oxides (tungsten oxide/tungsten oxide hydrate mixture) (GNS-W) composite was successfully synthesized using a facile approach. WO₃/WO₃·H₂O mixtures were deposited on the graphene nanosheets (GNS) to form the GNS-W composite. The GNS-W composite was characterized by X-ray diffraction (XRD), Raman spectrum, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The as-prepared GNS-W composite was directly fabricated into a supercapacitor electrode for potential energy storage application, and electrochemically tested by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy. The GNS-W composite electrode exhibits a better electrochemical performance than that of the WO₃/WO₃·H₂O mixtures electrode. A high specific capacitance of about 143.6 F g⁻¹ at a current density of 0.1 A g⁻¹ for the GNS-W composite delivers significant improvement than that for the WO₃/WO₃·H₂O mixtures and GNS electrodes. The impedance studies also suggest that the GNS-W composite electrode shows the lower resistance and high conductivity due to the good interaction between the graphene nanosheets and the WO₃/WO₃·H₂O mixtures. The good electrochemical performance for the GNS-W composite may be attributed to the interaction between the WO₃/WO₃·H₂O mixtures and the edges of graphene nanosheets, which increases the ion diffusion rate as well as the conductivity.     

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.     

Mechanochemical synthesis of nanoparticulate ZnO–ZnWO4 powders and their photocatalytic activity

In this study, mechanochemical reaction systems with H₂WO₄ as a precursor were investigated for the synthesis of nanoparticulate powders of WO₃, ZnWO₄, and dual-phase (ZnWO₄)_x(ZnO)_1–x. The objective was to establish whether mechanochemical processing can be used to manufacture high activity photocatalysts in the ZnO–WO₃ system. Milling and heat treatment of H₂WO₄ + 12NaCl was found to result in the formation of irregularly shaped platelets of a sodium tungstate rather than nanoparticles of WO₃. Powders of single-phase ZnWO₄ and dual-phase (ZnWO₄)_x(ZnO)_1–x were successfully synthesised by incorporating H₂WO₄ into the ZnCl₂ + Na₂CO₃ + 4NaCl reactant mixture. The photocatalytic activity of these powders was evaluated using the spin-trapping technique with electron paramagnetic resonance spectroscopy. It was found that the photocatalytic activity decreased with the ZnWO₄ content. This decrease in activity was attributed to the larger average particle size of the ZnWO₄ component compared to the ZnO, which reduced the surface area available for interfacial transfer of the photogenerated charge carriers.     

Generation of mesoporous n-p-n (ZnO–CuO–CeO2) heterojunction for highly efficient photodegradation of micro-organic pollutants

In this research, a mesoporous rod-shaped ZnO/CuO/CeO₂ n-p-n heterojunction has been designed via a two-step co-precipitation technique for photocatalytic applications. Characterization by powder X-ray diffraction (PXRD), fourier transform infrared spectroscopy (FTIR), UV–Vis, and Scanning Electron Microscopy (SEM) techniques confirmed the formation of mesoporous rod-shaped ZnO/CuO/CeO₂ n-p-n heterojunction having preferred interface developing between the ZnO, CuO, and CeO₂ phases, thus extended the light-absorption window up to 800 nm. Under sunlight, the ability of a mesoporous ZnO/CuO/CeO₂ n-p-n heterojunction to act as a photocatalyst was tested with methyl orange (MO) and crystal violet (CV) as target molecules. We found the degradation efficiencies of CV and MO dyes on mesoporous ZnO/CuO/CeO₂ to be 96% and 88%, respectively, after 90 min of sunlight irradiation. The estimated rate constants (k, min^?1) for deterioration of CV and MO under sunlight over ZnO/CuO/CeO₂ composite were 0.039 and 0.022 min^?1, respectively. We endorsed the greater photo-response, the well-aligned band-structure, and practical usage of the photo-induced carriers of the mesoporous photocatalyst to be the leading causes for the outstanding photocatalytic properties of ZnO/CuO/CeO₂ n-p-n heterojunction. The ultimate oxidizing species that destroyed dyes were O₂￣ and ·OH over ZnO/CuO/CeO₂ photocatalyst under sunlight illumination. Besides, the recycling tests confirmed the high photostability of the ZnO/CuO/CeO₂ photocatalyst. Hopefully, the mesoporous rod-shaped architecture of the n-p-n heterojunction with anticipated interface manufacturing will assist the photocatalyst strategy with better photocatalytic action under sunlight irradiation.     

Hydrothermal and post-heat treatments of TiO2/ZnO composite powder and its photodegradation behavior on methyl orange

The composite powder of TiO₂/ZnO with an atomic ratio of Ti to Zn of 3/1 was prepared through sol–gel process followed by hydrothermal and post-heat treatments. The as-prepared powder was characterized in detail by means of XRD, TG/DTA, DLS, and SEM. The XRD results showed that by applying the hydrothermal process the crystallinity of the composite powder was significantly improved. The SEM and DLS results revealed no visible variations on particle morphology and size owing to the hydrothermal and post-heat treatments. The enhancement of the photocatalytic activity of the composite powder evaluated through methyl orange (MO) degradation under UV light irradiation was, therefore, attributed to its high crystallinity that was achieved during the hydrothermal process under a rather low temperature.     

Color-tunable photoluminescence in Bi3.6Eu0.4Ti3O12/ZnO nanorods composite films

Color-tunable photoluminescence has been realized by constructing Bi_3.6Eu_0.4Ti₃O₁₂/ZnO (BEuT/ZnO) nanorods composite films. The composite films were prepared by a hybrid chemical solution method. Effects of ZnO nanorods on photoluminescence of BEuT were studied. On one hand, the near-band-edge ultraviolet emission of ZnO nanorods can greatly improve the red emission of Eu³⁺ ions in BEuT, and on the other hand, ZnO nanorods can also produce a strong green deep-energy-level luminescence. Our study demonstrates that the color of photoluminescence in the composite films can be tuned from green to yellow to red, through suitable control of ZnO nanorods. The BEuT/ZnO nanorods composite films with the color-tunable photoluminescence may have potential applications for white light emission and other integrated optoelectronic devices.     

Synthesis and photocatalytic activity of g-C3N4/ZnO composite microspheres under visible light exposure

In this paper, a novel g-C₃N₄/ZnO composite microspheres (CZCM) with enhanced photocatalytic activity under visible light exposure were successfully prepared by a self-assembly method followed by calcination in the air. A hierarchical structure in which ZnO microspheres were closely covered with g-C₃N₄ nanosheets was constructed. The microstructure and photocatalytic activities of the CZCM were characterized. The photocatalytic property of CZCM was evaluated by degrading solution Methyl Orange (MO) and Tetracycline (TC). The effects of varied contents of g-C₃N₄ on the photocatalytic capability of CZCM were systematically investigated and the results show that the optimized CZ-15% sample exhibit much higher photocatalytic degradation efficiency than that of bare g-C₃N₄ or ZnO under identical conditions. The analysis of Photoluminescence (PL) and photocurrent (PC) independently conformed that the photo-induced electron-hole (e^?-h⁺) pairs in the CZCM were effectively generated and responsible for the observed photocatalysis. The enhanced adsorption of visible-light and the effective charge separation on the surface of CZCM enabled significant improvement of photocatalytic performance. According to the experimental results and relative energy band levels of the two semiconductors, a possible photocatalysis mechanism for the reaction process is proposed.     

ZnO nanorods surface-decorated by WO3 nanoparticles for photocatalytic degradation of endocrine disruptors under a compact fluorescent lamp

Nanoscaled tungsten oxide (WO₃) particles coated on ZnO nanorods (ZNRs) were newly synthesized by combining a hydrothermal technique with a chemical solution process. The structure, morphologies and compositions of the as-prepared WO₃–ZNR nanocomposites were characterized through XRD, FESEM, TEM and Raman measurements. The results revealed that pure monoclinic WO₃ nanoparticles with an average size range of 18–26 nm were distributed on the surfaces of ZNRs and attached strongly. Particularly, the optical properties as well as photocatalytic characteristics of pure ZNRs and WO₃–ZNR nanocomposites with different loadings of WO₃ were also examined. The absorption of WO₃–ZNR nanocomposites was redshifted due to effective immobilization of WO₃ on ZNRs. Under irradiation of a 55 W compact fluorescence lamp, the photocatalytic activities of the WO₃–ZNR nanocomposites were superior to those of pure ZNRs and P25 in the degradation of resorcinol (ReOH). Furthermore, WO₃–ZNR nanocomposites showed very favorable recycle use potential and high sedimentation rate. Other endocrine disrupting chemicals (EDCs) such as phenol, bisphenol A (BPA) and methylparaben were also successfully photodegraded under identical conditions. These characteristics showed the practical applications of the WO₃–ZNR nanocomposites in indoor environmental remediation.     

Enhanced NO2 sensing properties of Pt/WO3 films grown by glancing angle deposition

In this work, WO₃ films were synthesized by glancing angle deposition (GLAD) and conventional planar deposition respectively. By depositing Pt on WO₃ by GLAD, the NO₂ sensitivity of WO₃ films were significantly improved. The structural characteristics and NO₂ sensing properties of the films were investigated in order to establish the enhancement mechanism. The results show WO₃ films prepared by GLAD have porous nanorod-like structure, and isolated Pt clusters are distributed on WO₃. The nanostructured Pt/WO₃ films show high sensitivity to NO₂ at 150 °C, detecting as low as 80 ppb NO₂ with a response of 1.23. Meanwhile, the films also exhibit high NO₂ selectivity against NH₃, CO, acetone and ethanol. The excellent NO₂ sensing properties of the Pt/WO₃ films can be explained due to large specific surface area of nanorod-like WO₃, catalysis of Pt and Schottky barriers at interfaces. The reliable Pt/WO₃ nanostructure prepared by GLAD could be potentially applied in low-temperature, highly sensitive NO₂ sensor for micro-electro-mechanical system (MEMS).     

Photocatalytic activity of TiO2 supported on multi-walled carbon nanotubes under simulated solar irradiation

TiO₂ particles supported on multi-walled carbon nanotubes (MWCNTs) were prepared using a sol–gel method to investigate their photocatalytic activity under simulated solar irradiation for the degradation of methyl orange (MO) in aqueous solution. The prepared composites were analyzed using XRD, SEM, EDS and UV–vis absorption spectroscopy. The results of this study indicated that there was little difference in the shape and structure of MWCNTs/TiO₂ composite and pure TiO₂ particles. The composite exhibited enhanced absorption properties in the visible light range compared to pure TiO₂. The degradation of MO by MWCNTs/TiO₂ composite photocatalysts was investigated under irradiation with simulated solar light. The results of this study indicated that MWCNTs played a significant role in improving photocatalytic performance. Different amounts of MWCNTs had different effects on photodegradation efficiency, and the most efficient MO photodegradation was observed for a 2% MWCNT/TiO₂ mass ratio. Photocatalytic reaction kinetics were described using the Langmuir–Hinshelwood (L–H) model. The photocatalyst was reused for eight cycles, and it retained over 95.2% photocatalytic degradation efficiency. Possible decomposition mechanisms were also discussed. The results of this study indicated that photocatalytic reactions with TiO₂ particles supported on MWCNTs under simulated solar light irradiation are feasible and effective for degrading organic dye pollutants.     

Photocatalytic Degradation of Tetracycline by Z-Scheme Bi2WO6/ZIF-8

To improve the photocatalytic activity of Bi₂WO₆, ZIF-8 was successfully introduced with the in-situ growth for the first time. The addition of ZIF-8 effectively inhibited the recombination of photogenerated electron–hole pairs with further improved electron utilization efficiency. The superoxide anion, .O₂^?, generated, greatly improved the photocatalytic activity. The performance of Bi₂WO₆/ZIF-8 in the photodegradation of tetracycline (TC) was studied under different conditions, including the proportions of ZIF-8, the dosage of catalyst, and the concentration of TC. The results indicated that 10 mg of B/Z/5/1 offered the best photocatalytic activity under UV light, achieving 97.8% degradation of TC (20 mg/L) within 80 min. The measured rate constant (k) for TC degradation was almost 3 times that of pure Bi₂WO₆. The effects of pH, HA, and inorganic anions on the degradation of TC were also studied for the simulated real water. Further, B/Z/5/1 could be reutilized up to five cycles without reduction of the catalysis performance. Therefore, the Bi₂WO₆/ZIF-8 heterojunction composite material can be utilized as an efficient photocatalyst for remediation of environmental pollution.

     

Electrochemical synthesis of WO3/PANI composite for electrocatalytic reduction of iodate

Composite film of polyaniline (PANI) and tungsten oxide (WO₃) was electrodeposited by cyclic voltammetric technique from a solution of aniline and tungstic acid. The obtained WO₃/PANI film displayed a significant enhancement of electrocatalytic activity for iodate reduction and a better stability than that of pure WO₃ and PANI films. Result of amperometric experiment revealed a good linear relationship with concentration of IO₃⁻ from 20 to 500 μM, with a high sensitivity of 0.54 μA/μM and a detection limit of 2.7 μM for the determination of iodate. This composite film was also successfully applied in determination of iodate in commercial table salt.     

Effect of ZnO–WO3 additives on sintering behavior and microwave dielectric properties of 0.95MgTiO3–0.05CaTiO3 ceramics

The effect of WO₃ addition on the phase formation, the microstructures and the microwave dielectric properties of 1 wt% ZnO doped 0.95MgTiO₃–0.05CaTiO₃ ceramics system were investigated. Formation of second phase MgTi₂O₅ could be effectively restrained through the addition of WO₃, but should be in right amount. WO₃ as additives could not only effectively lower the sintering temperature of the ceramics to 1310 °C, but also promote the densification. A dielectric constant ε_r of 20.02, a Q×f value of 62,000 (at 7 GHz), and a τ_f value of −5.1 ppm/°C were obtained for 1 wt% ZnO doped 0.95MgTiO₃–0.05CaTiO₃ ceramics with 0.5 wt% WO₃ addition sintered at 1310 °C.     

Preparation and characterization of TiO2, ZnO,and TiO2/ZnO nanofilms via sol–gel process

The preparation of the TiO₂, ZnO, and TiO₂/ZnO nanofilms was conducted on glass via sol–gel process. The prepared film was detailedly characterized by means of OM, SEM, XRD, and EDS. The results showed that the obtained pure TiO₂ was composed of nanoparticles. For pure ZnO it consisted of nanoparticles and large agglomerates. Both the microstructural morphology and the crystallization of the prepared TiO₂/ZnO composite film were strongly related to the Ti/Zn ratio in the film. With a Ti/Zn ratio less than 1/1, the composite film was absence of cracks. Poor crystallization was definitely observed for the composite film with Ti/Zn ratio of 3/1 and 1/1. The EDS analysis revealed homogeneous distribution of Ti and Zn elements in the film.