Generation of hydrogen under visible light irradiation with enhanced photocatalytic activity of Bi2WO6/Cu1.8Se for organic pollutants under Vis‐NIR light reign

To make better use of solar light, a new Bi₂WO₆/Cu_1.8Se photocatalyst active to visible and near‐infrared light has been synthesized by a facile hydrothermal method. The composites were characterized by X‐ray diffractometry (XRD), scanning electron microscopy (SEM), UV‐vis diffuse reflectance spectroscopy (DRS), and photoluminescene (PL). The photocatalytic activities of Bi₂WO₆/Cu_1.8Se are evaluated by degrading Congo red solution and hydrogen generation from water. It was found that the molar percentage of Cu_1.8Se had great effects on the morphology and photocatalytic property of the Bi₂WO₆/Cu_1.8Se heterojunctions, and the composite with suitable molar amount of Cu_1.8Se exhibits much enhanced photocatalytic activity for Congo red degradation under visible and near‐infrared light irradiation and for hydrogen generation under visible light compared to Bi₂WO₆. The significant improvement photocatalytic activity of the composite could be attributed to its good light absorption, suitable band gap structure, and effective separation of photogenerated electron‐hole pairs of Bi₂WO₆/Cu_1.8Se heterojunction. This work presents an efficient multifunction photocatalyst owning the activity both for water splitting under visible light and for organic contaminants decomposition under visible‐near‐infrared light.     

Photocatalytic Decomposition of Organic Contaminants by Bi2WO6 Under Visible Light Irradiation

An oxide photocatalyst Bi₂WO₆ with corner-shared WO₆ octahedral layered structure was synthesized. Its band gap was determined to be 2.69 eV from UV–vis diffuse reflectance spectra. The photocatalyst showed not only the activity for photocatalytic O₂ evolution with the initial evolution rate of 2.0 μmol/h but also the activity of mineralizing both CHCl₃ and CH₃CHO contaminants under visible light irradiation. Meanwhile, wavelength dependence of CH₃CHO decomposition was observed, which indicated that the photocatalytic activity of the photocatalyst was in good agreement with its light-absorption ability.     

A Novel Way to Prepare Visible‐Light‐Responsive WO3/TiO2 Composite Film with High Porosity

Amorphous oxide film was prepared on the titanium substrate by plasma electrolytic oxidation (PEO) technology in acidic electrolyte consisting of tungstate and then subject to calcination in air. Films were characterized by scanning electron microscopy, energy dispersive X‐ray, X‐ray diffraction, X‐ray photoelectron spectroscopy, photoluminescence, and UV‐Vis DRS before and after calcination, respectively. Calcined film consisted of anatase and WO₃, showing more open structure compared with uncalcined film. Furthermore, the absorption edge of calcined film was shifted to visible light region and the recombination of photo‐induced carriers was inhibited effectively, resulting that WO₃/TiO₂ composite film produced by PEO technology and calcination should be effective as a visible‐light‐responsive photocatalyst.     

Photocatalytic oxidation of cyanide under visible light by Pt doped AgInS2 nanoparticles

AgInS₂ nanoparticles were prepared by a microwave method, while Pt was doped on the surface of AgInS₂ via photoassisted deposition method. The catalytic performances of the AgInS₂ and Pt/AgInS₂ samples were carried out for photocatalytic oxidation of cyanide under visible light. The UV–vis analysis proved a red shift was detected after the loading of Pt into the AgInS₂. The maximum oxidation efficiency achieved was 100% at 1.5 wt% Pt/AgInS₂ photocatalyst after 35 min reaction time. The catalyst could be reused without any loss in activity during the first five cycles.     

Hydrothermal Synthesis of Graphene/Bi2WO6 Composite with High Adsorptivity and Photoactivity for Azo Dyes

Graphene/Bi₂WO₆ composites have been synthesized by hydrothermal reduction at 160°C for 24 h using ethanol as the reducing agent. All as‐prepared composites were characterized using X‐ray diffraction (XRD), UV–vis diffuse reflectance spectroscopy, FT‐IR spectroscopy, Raman spectroscopy, scanning electron microscopy, high‐resolution transmission electron microscopy, N₂ adsorption, and photocatalytic activity evaluation. The effective charge separation of graphene/Bi₂WO₆ composites was caused by the electrical conduction of graphene which is the most important factor. The results have proved the formation of interfacial contact between graphene nanosheets and Bi₂WO₆ nanoplates. The adsorptivity for azo dyes was enhanced greatly with the introduction of graphene. The oxy‐functional groups located at the edges of graphene were responsible for the enhanced adsorptivity. As‐prepared graphene/Bi₂WO₆ composites exhibited enhanced light absorption from UV to visible‐light region. In addition, the introduction of graphene would also result in smaller crystalline size and lower crystallinity of Bi₂WO₆. Graphene/Bi₂WO₆ composites containing an appropriate amount of graphene were proved to exhibit higher adsorptivities and photocatalytic activities for azo dyes. High photocatalytic activities of graphene/Bi₂WO₆ composites were considered to be the synergetic effects of high adsorption, high light absorption, and high electrical conduction induced by the introduction of graphene.     

Tailored synthesis of macroporous Pt/WO3 photocatalyst with nanoaggregates via flame assisted spray pyrolysis

High‐surface‐area macroporous WO₃ particles with deposited Pt (Pt/WO₃) were successfully synthesized for the first time, using flame‐assisted spray pyrolysis. Nanoparticle aggregates‐like structures (nanoaggregates) were formed, although a salt precursor was used for the synthesis. The macroporous structure was tailored by changing the mass ratio of the polystyrene template to ammonium tungstate pentahydrate. The cavities between the nanoaggregates formed mesopores, which increased the surface area. The presence of meso‐ and macro‐pores in the synthesized Pt/WO₃ particles improved their photocatalytic activities in visible‐light‐induced photodegradation of rhodamine B. The combination of a high surface area and the presence of an in situ‐deposited Pt cocatalyst gave a high photodecomposition rate, approximately 9.6 times higher than that achieved with dense WO₃ particles. This research provides a promising strategy for synthesizing submicron particles with high surface areas at a high production rate, and is suitable for industrial applications. © 2016 American Institute of Chemical Engineers AIChE J, 62: 3864–3873, 2016     

Hydrogen Tungsten Bronze‐Supported Platinum as Electrocatalyst for Methanol Oxidation

Hydrogen tungsten bronze (H_xWO₃)‐supported platinum was prepared by electrodeposition and used as an electrocatalyst for methanol oxidation. The prepared electrocatalyst was characterized by Raman spectrum, X‐ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), cyclic voltammetry (CV), and chronoamperometry (CA). It is found that the support, H_xWO₃, not only reduces the platinum particle size and thus reduces the platinum loading, but also provides platinum with the anti‐poison ability to carbon monoxide and thus improves the activity of platinum toward methanol oxidation.     

Solvothermal synthesis of CNTs–WO3 hybrid nanostructures with high photocatalytic activity under visible light

The CNTs–WO₃ hybrid nanostructures were fabricated by solvothermal synthesis. The morphologies, phase structures and optical properties of the nanostructures were investigated by TEM, XRD, UV–vis DRS and XPS respectively. The CNTs–WO₃ hybrid nanostructures exist higher photocatalytic activity than pure WO₃ nanosheets and the mechanical mixture of WO₃ and CNTs for the degradation of methyl blue (MB) under visible light. This is attributed to their large surface area, absorption enhancement in visible light region and effective separation of electrons and holes. The presence of radical scavengers such as KI, Fe^3 + and methanol in photocatalytic experiments demonstrates that photogenerated electrons are responsible for the photocatalytic degradation of MB on CNTs–WO₃.     

WO3–based photocatalysts: A review on synthesis,performance enhancement and photocatalytic memory for environmental applications

A significant drawback of the traditional photocatalysts such as titanium dioxide (TiO₂) is their inability to absorb visible light from the solar spectrum due to their wide band gap energy. They are only photoactive in the ultraviolet (UV) region which is just a little fraction of the solar spectrum and could be harmful with much exposure to it. Due to its abundance in the solar spectrum, visible light needs to be harnessed for environmental applications. However, we lack visible light driven photocatalysts with long-lasting energy storage capacity for “round-the-clock photocatalytic” (RTCP) applications. For this reason, there is a growing need to find new photocatalysts that can mitigate these bottlenecks. It is evident from some carefully selected published articles (1976–2021) that tungsten oxide (WO₃) and its composites have attracted popularity in recent years because of its outstanding properties and particularly its smaller band gap energy of 2.8 eV. However, pristine WO₃ is limited due to relatively low energy density and smaller specific surface area. These drawbacks can be addressed by developing various WO₃ – based materials to improve their performance. This paper reviews and discusses their recent development in surface advancement, morphology control, modification of nanostructured WO₃ and its composites, and their RTCP energy storage for photocatalytic activities in visible light and the dark for environmental applications. Specific aspects focused on its nature, structure, properties, synthesis, coatings, deposition, approaches at modifying and enhancing its visible light photoactivity for enhanced performance and energy storage potential.     

Synthesis of Ternary Heterostructure Semiconductor Photocatalyst and Its Photocatalytic Performance Under Visible Light Irradiation

Introducing magnetic metal onto semiconductor materials has been proven to be an attractive strategy for enhancing the photocatalytic activity in the visible region. In this work, ternary heterostructure magnetic semiconductor photocatalyst RGO/ZnFe₂O₄/Ag₂WO₄ was successfully synthesized through a simple hydrothermal method and was evaluated by photodegradation of Rhodamine B (RhB) under visible light irradiation. The composition, structure, morphology, and optical absorption properties of the as-prepared photocatalyst were investigated by XRD, FT-IR, SEM, and UV–Vis DRS, respectively. It was found that the photocatalytic activity under visible light irradiation was in the order of RGO/ZnFe₂O₄/Ag₂WO₄?>?ZnFe₂O₄?>?Ag₂WO₄?>?RGO/ZnFe₂O₄ and RGO/ZnFe₂O₄/Ag₂WO₄. The enhancement of photocatalytic performance could be attributed to the reduced graphene oxide sheets can function as an electron collector and transporter to lengthen the lifetime of the charge carriers, improving the whole photocatalytic activity. The reaction kinetics, possible degradation pathway, and catalyst stability, as well as the roles of ZnFe₂O₄ and Ag₂WO₄ in photoreaction, were comprehensively studied. The obtained results indicate that the prepared magnetic and effective catalytic materials could be potentially applied in environmental organic pollutants purification.

     

Sonochemical preparation and photocatalytic properties of CdS QDs /Bi2WO6 3D heterojunction

Hierarchical CdS quantum dots (QDs)/ Bi₂WO₆ three-dimensional (3D) heterojunction photocatalyst was successfully synthesized by a facile green ultrasonic method for the first time. Photocatalytic activities under visible light irradiation were tested by the degradation of Rhodamine B (RhB) and tetracycline hydrochloride (TC), and the reduction of Cr(VI) in aqueous solution. As compared to pure CdS and Bi₂WO₆, CdS QDs/ Bi₂WO₆ heterojunctions manifested a significantly enhanced photocatalytic activity for these treatments. When the effect of the mass ratio of CdS QDs to Bi₂WO₆ was investigated, 3% CdS QDs/ Bi₂WO₆ heterojunction showed the highest photocatalytic efficiency: the efficiency for RhB degradation was 94.5% for 30?min and this value was about 6 times and 1.5 times higher than those of pure Bi₂WO₆ and CdS QDs. This enhancement was majorly accredited to the synergetic effect between Bi₂WO₆ and CdS QDs, which included intimate contact and matched band gap potentials between 0D CdS QDs and 3D Bi₂WO₆, which contributed to the efficient electron-hole separation and fast transfer of charge carriers between CdS QDs and Bi₂WO₆. A possible Z-scheme photocatalytic mechanism was proposed, in which the sample was provided with the efficient charge transfer pathway and was endowed with excellent oxidation and reduction ability.     

A Visible‐Light‐Driven Photocatalyst of NASICON Li2Ni2(MoO4)3 Nanoparticles

A visible‐light‐driven photocatalyst based on the well‐known cathode material of NASICON‐type Li₂Ni₂(MoO₄)₃ was prepared by a modified Pechini method. The sample was characterized by X‐ray diffraction, scanning electron microscope, transmission electron microscopy, and UV‐vis absorption spectrum. The average size of Li₂Ni₂(MoO₄)₃ particle is below 50 nm. NASICON nanoparticles Li₂Ni₂(MoO₄)₃ has an efficient absorption in the UV‐visible light wavelength region with a direct allowed electronic transition of 2.07 eV. The photocatalytic properties of Li₂Ni₂(MoO₄)₃ were evaluated by the photodegradation of methylene blue (MB). Li₂Ni₂(MoO₄)₃ has an efficient photocatalytic activity and could be a potential photocatalyst driven by visible‐light. The photocatalytic activity was discussed on the optical absorption and special hexagonal tunnel structure connected by optical active centers of MoO₄ and NiO₆ and its good conductivity.     

Graphene–WO3 nanobelt composite: Elevated conduction band toward photocatalytic reduction of CO2 into hydrocarbon fuels

Graphene oxide (GO), tungsten trioxide (WO₃) and graphene–WO₃ nanobelt composites (GW) were synthesized and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), UV–vis diffuse reflection spectra (DRS) and X-ray photoelectron spectroscopy (XPS) valence band spectra. We demonstrated that the graphene can elevate the conduction band of WO₃ toward photocatalytic reduction of CO₂ into hydrocarbon fuels under visible-light irradiation. And the photocatalytic activity of GW is higher than that of GO, WO₃ and P25 TiO₂.     

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.     

Indoor air purification using heterogeneous photocatalytic oxidation. Part I: Experimental study

Heterogeneous photocatalytic oxidation (PCO) has shown to be a promising air purifying technology in outdoor conditions using TiO₂ as photocatalyst activated with UV light. Also to indoor air quality more and more attention is paid because of the very important role it plays on human health, and it can be influenced by many factors like ventilation system, building materials, furniture, cooking, and outdoor pollutants.The present work addresses the indoor air purification using photocatalytic oxidation. The photocatalytic reaction setup is introduced for the assessment of the indoor air quality. A modified TiO₂ that can be activated with visible light (VIS) is used as photocatalyst due to the shortage of UV light in indoor condition. One special wall paper is applied as the substrate for the coating of the photocatalyst in the present study.Nitric oxide (NO) is one typical indoor air pollutant, which is used as target pollutant for the photocatalytic oxidation with indoor concentration level. Influential parameters like initial NO concentration, flow rate, relative humidity of the experimental environment, irradiance, photocatalyst dosage that can affect the PCO are studied. Furthermore, the second part content of the present study is introduced at the end of this paper.     

Laser-induced anchoring of WO3 nanoparticles on reduced graphene oxide sheets for photocatalytic water decontamination and energy storage

In this work, the synthesis of tungsten oxide/reduced graphene oxide (WO₃-rGO) nanocomposite, using a simple method of pulsed laser ablation in liquids (PLAL) is reported. The pulsed laser beam of 355 nm wavelength carries out two simultaneous processes: the reduction of graphene oxide and at the same time the anchoring of nanostructured WO₃ on reduced graphene oxide. In the photo-catalytic application, WO₃-rGO shows much better visible light absorption and less photo-generated charge recombination than pure WO₃, as indicated by optical absorption and photoluminescence spectra. These improved features in WO₃-rGO significantly enhanced the photo-catalytic decontamination of methylene blue (MB) dye in the water, compared to the use of pure WO₃ as a photocatalyst. A Poly 2-acrylamido-2-methyl-1-propanesulfonic acid (PAMPS) based electrolyte together with the high electrical conductance and porosity of rGO which were produced after anchoring WO₃ on the graphene oxide, were harnessed for the energy storage application using this material for a supercapacitor. The specific capacitance for WO₃-rGO based device is achieved to be 577 F g⁻¹ measured by the galvanostatic charge-discharge (GCD) method. Also, at a power density of 1000 W kg⁻¹, the as-synthesized WO₃-rGO demonstrated a large energy density value of 76.3 Wh Kg⁻¹ that is much larger than obtained, using WO₃ alone. Besides these photocatalytic and energy storage performance evaluation of WO₃-rGO, the optical, morphological and elemental characteristics of synthesized WO₃-rGO were also investigated to study the improved performance of the nanocomposite in these two applications.     

Role of platinum-like tungsten carbide as cocatalyst of CdS photocatalyst for hydrogen production under visible light irradiation

To investigate the role of platinum-like tungsten carbide as a cocatalyst for photocatalytic hydrogen production under visible light irradiation, we fabricated for the first time a composite material consisting of WC and CdS by a precipitation/hydrothermal method. The composite prepared by this procedure consisted of well-dispersed WC and CdS, as confirmed by TEM mapping analysis. The WC/CdS composite photocatalyst exhibited a high rate of hydrogen production, comparable to that of Pt/CdS, under visible light irradiation (λ ≥ 420 nm) from water containing sulfide and sulfite ions as hole scavengers. Like Pt cocatalyst loaded on the surface of CdS, WC provides active sites for proton reduction and causes fast diffusion of photoelectrons generated from CdS toward WC, leading to high photocatalytic activity of hydrogen production.     

S–N Co-Doped TiO2 Photocatalysts with Visible-Light Activity Prepared by Sol–Gel Method

S–N co-doped anatase nanosized TiO₂ photocatalyst was successfully prepared by simple sol–gel method. The samples were characterized by XRD, XPS, UV–Vis. From the results of UV–Vis, a red shift of the absorption edge was brought out owing to the S and N codoping. XPS and UV–Vis studies revealed that N and S were in situ codoped in the lattice of TiO₂ and the absorbance in visible light region decreased with the calcination temperature increased. The photocatalytic activity was evaluated by the photocatalytic oxidation of penicillin solution under visible light irradiation. The results show that visible-light induced photocatalytic activities of the as-prepared TiO₂ powders were improved by S–N copoing. The high activity of S–N co-doped TiO₂ can be related to the results of the synergetic effects of strong absorption in the UV–Vis region, red shift in adsorption edge.     

Photocatalytic reduction of carbon dioxide on NiO/InTaO4 under visible light irradiation

Developing a photocatalyst system for the conversion of solar energy to electric energy or chemical energy is a topic of great interest with fundamental and practical importance. The semiconductor catalysts, such as InTaO₄, have been extensively used for water splitting under visible light irradiation. However, it has not been used for photoreduction of carbon dioxide with water. InTaO₄ was synthesized by solid-state reaction. NiO was added by incipient-wetness impregnation method as the cocatalysts. The catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet–visible spectroscopy (UV–Vis) and X-ray photoelectron spectroscopy (XPS). The photocatalytic reduction was carried out in a Pyrex reactor under visible light illumination using 500 W halogen light as the light source. The band gap of InTaO₄ was estimated, from UV–Vis spectrum, to be 2.6 eV, showing that these catalysts have ability to reduce CO₂ into methanol. The effects of the NiO cocatalyst and pretreatment process on the photocatalytic reduction of the catalyst to methanol were investigated. The methanol yield increased with the amount of NiO cocatalyst. The reduction–oxidation pretreatment had a positive effect on the catalyst.     

WO3 Nanoparticles Synthesized Through Ion Exchange Route as Pt Electrocatalyst Support for Alcohol Oxidation

Tungsten oxide (WO₃) nanocrystals with the diameter <5 nm supported on porous carbonized resin (denoted as C‐WO₃) are synthesized. The WO₃ precursors are dispersed at ion level through ion exchange route, then reduced to WO₃ nanocrystals. Pt nanoparticles are loaded on the porous C‐WO₃ matrix (denoted as Pt/C‐WO₃) and used as electrocatalyst in fuel cell for alcohol oxidation, in which WO₃ is found efficient promotion effect on Pt electrocatalyst in the electrochemical activity and stability. Thereinto, Pt/C‐WO₃ gives 1.63 times higher current densities than the commercial Pt/C (TKK) for methanol oxidation at the same Pt loadings. Moreover, Pt/C‐WO₃ electrocatalyst shows excellent properties in mass transfer than Pt/C (TKK). The present method can be readily scaled up for the production of other nanomaterials as well as WO₃.