Facile one-pot preparation of Bi6O6(OH)3(NO3)3•1.5H2O-Bi2WO6 heterostructure with superior photocatalytic activity

Basic bismuth nitrate Bi₆O₆(OH)₃(NO₃)₃•1.5H₂O (BBN) modified Bi₂WO₆ heterostructures was facilely synthesized by one-pot hydrothermal strategy. The modification of BBN effectively improves the photocatalytic activity of Bi₂WO₆ for degradation and mineralization of Rhodamine B. The enhanced photocatalytic performance is attributed to the increased surface area and effective separation of photogenerated carriers induced by the potential difference at BBN/Bi₂WO₆ interface. Furthermore, the micro-scaled heterostructure is easily recycled with excellent circulating stability. The work provides some new insights for the rational design and synthesis of basic salt modified Bi-system photocatalyst with high efficiency.     

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.     

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.     

Preparation of Bi2WO6 photocatalyst by high-energy ball milled Bi2O3-WO3 mixture

Mechanochemical methods offer a simple and low-cost technique to synthesize nanomaterials. In this work, a new route for preparing Bi₂WO₆ photocatalyst combining high-energy ball milling and solid-state reactions is explored. By using the mechanochemically-activated Bi₂O₃-WO₃ mixture as a starting raw material, the preparation temperature of Bi₂WO₆ is successfully reduced to 400 °C. The obtained Bi₂WO₆ nanopowder as-well-as the mechanochemically-activated Bi₂O₃-WO₃ mixture show a considerable photocatalytic activity for the decomposition of Rhodamine B. Bi₂WO₆ nanopowders calcined at 400 °C exhibited a higher photocatalytic activity respect to powders calcined at a higher temperatures. The small amount of Bi₂O₃ and WO₃ contained in the optimized photocatalysts is thought to be helpful in establishing a complex ternary heterostructure system, allowing for an improved visible-light driven photocatalytic activity. Experimental results show that a combination of high-energy ball milling and solid-state reactions could be a promising technique for fabricating highly efficient photocatalysts.     

The effect of platinum on the performance of WO3 nanocrystal photocatalysts for the oxidation of Methyl Orange and iso‐propanol

BACKGROUND: This research investigated the effect of platinum (Pt) on the reactivity of tungsten oxide (WO₃) for the visible light photocatalytic oxidation of dyes. RESULTS: Nanocrystalline tungsten oxide (WO₃) photocatalysts were synthesised by a sol‐gel process and employed for the photocatalytic degradation of Methyl Orange under visible light. For comparison commercial bulk WO₃ materials were also studied for the same reaction. These materials were fully characterised using X‐ray diffraction (XRD), UV‐visible diffuse reflection spectroscopy and transmission electron microscopy (TEM). The photocatalytic oxidation of iso‐propanol was used as a model reaction to follow the concomitant reduction of molecular oxygen. No reactions occured in the absence of platinum, which is an essential co‐catalyst for the multi‐electron reduction of oxygen. The platinised WO₃ catalysts were stable for multiple oxidation–reduction cycles. The results from the catalytic activity measurements showed that platinised nanocrystalline WO₃ is a superior oxidation photocatalyst when compared with bulk WO₃. Methyl Orange was completely decolourised in 4 h. CONCLUSIONS: The enhanced performance of nanocrystalline Pt‐WO₃ is attributed to improved charge separation in the nanosized photocatalyst. Platinum is an essential co‐catalyst to reduce oxygen. This photocatalyst could be applied to the treatment of organic pollutants in wastewater, with the advantage of using visible light compared with the widely studied TiO₂, which requires UV light. Copyright © 2011 Society of Chemical Industry     

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.

     

Photocatalytic Splitting of Water Over a Novel Visible-Light-Response Photocatalyst Nd2InTaO7

A new visible-light-response photocatalyst Nd₂InTaO₇ with pyrochlore-type structure crystallized in a cubic system with the space group Fd3m was synthesized by a solid-state reaction method. The H₂ evolution was obtained from Pt/CH₃OH/H₂O solution and pure H₂O, and O₂ evolution was generated from an aqueous AgNO₃ solution under visible light irradiation (λ > 400 nm). The high photocatalytic performance of Nd₂InTaO₇ supported the existing view that the photocatalytic activity correlated with the lattice distortion.     

Photocatalytic inactivation of bacteria by photocatalyst Bi2WO6 under visible light

The photocatalytic inactivation of Escherichia coli under visible light irradiation (λ > 420 nm) was performed with Bi₂WO₆ to investigate the photocatalytic bactericidal capability. Our work shows that the single phase oxide photocatalyst Bi₂WO₆ is effective in photocatalytic inactivation on E. coli. And the results revealed that the photocatalytic inactivation rate of E. coli with Bi₂WO₆ followed pseudo-first-order kinetics. The bactericidal action was directly observed by TEM and further proved by the measurement of K⁺ leakage from the inactive E. coli through the ICP-OES analysis. The results demonstrated that the photocatalysis could cause drastic damage in E. coli cells.     

Band engineering of Ag-Bi12GeO20-Bi2WO6 composite photocatalyst: Interface regulation and enhanced photocatalytic performance

Novel Ag-Bi₁₂GeO₂₀-Bi₂WO₆ heterojunction was developed and demonstrated as an excellent photocatalyst to degrade the Rhodamine B (RhB) aqueous solution with the help of UV–vis light. The Bi₁₂GeO₂₀-Bi₂WO₆ heterojunction was firstly fabricated through a facile partial chemical conversion strategy, employing pre-prepared Bi₂WO₆ nanosheets as Bi³⁺ source. Under the high temperature and high pressure environments, partially released Bi³⁺ ions derived from the Bi₂WO₆ nanosheets could react with Ge source, leading to the formation of Bi₁₂GeO₂₀ tetrahedrons. Meanwhile, the remaining Bi₂WO₆ nanosheets were also anchored in situ onto the surface of the Bi₁₂GeO₂₀ tetrahedrons, thus forming a unique heterojunction with “face-to-face” connection form of heterogeneous interface. After the loading of Ag nanoparticles, the as-obtained Ag-Bi₁₂GeO₂₀-Bi₂WO₆ heterogeneous structure exhibited outstanding catalytic efficiency toward the decomposition of RhB. Due to the structural and compositional features such as matching band structure, intimate interfacial contacts, unique interface contact structure and the well-known “schottky barriers", the photo-generated charges of the resulting ternary composite photocatalyst was efficiently separated and thus exhibited improved catalytic activity. This rational construction of Ag-Bi₁₂GeO₂₀-Bi₂WO₆ ternary photocatalytic system based on energy band engineering is ingenious and can provide a mirror for the fabrication of other photocatalytic materials.     

Facile synthesis of ZnS/WO3 coupled photocatalyst and its application on sulfamethoxazole degradation

In this study, the coupled photocatalysts ZnS/WO₃ were synthesized by a simple co-precipitation method, varying the content of ZnS (1, 5, and 10 wt%). The obtained materials were characterized by X-ray diffraction (XRD), scanning electron microscopy coupled to energy dispersive spectroscopy (SEM-EDS), N₂ physisorption, UV–Vis with diffuse reflectance spectroscopy (DRS), atomic absorption (AAS), infrared (IR), and photoluminescence (PL) spectroscopies. Furthermore, the synthesized photocatalysts were evaluated on the photocatalytic degradation of sulfamethoxazole (SMX) under simulated sunlight. The activity of the different coupled photocatalysts ZnS/WO₃ was significantly improved compared to the individual semiconductors (ZnS and WO₃). This enhancement was attributed to the reduced recombination rate determined through PL analysis. The ZnS_5%/WO₃ photocatalyst exhibited the highest performance in comparison with the other coupled materials, achieving complete SMX degradation in 60 min. In combination, the enhanced specific surface area, high particle dispersion, and reduced recombination rate define the ZnS_5%/WO₃ photocatalyst as a suitable candidate for photocatalytic environmental applications.     

Rational design,fabrication, optical properties and high-efficiency visible-light photocatalytic degradation performance for organic pollutants of Eu:Bi2WO6/CdS nanostructures

Over the past few years, semiconductor materials (especially bismuth tungstate) exhibiting unique environment purification and energy conversion capacities arouse huge attention as impacted by issues of environmental pollution and energy shortage, whereas its application is restricted by the problems of high carrier recombination rate and unsatisfactory degradation efficiency. In this study, Eu:Bi₂WO₆ nanostructures containing Eu ions of different concentrations were synthesized with a chemical solution method, and CdS was generated on the surface of Eu:Bi₂WO₆ nanostructures in situ epitaxial to synthesize the Eu:Bi₂WO₆/CdS composites. The effects of Eu doping concentration on the crystal structure, chemical composition, local structure, optical properties and visible-light photocatalytic properties exhibited by Eu:Bi₂WO₆/CdS nanostructures were studied more specifically, and the Eu doping behavior on the improvement mechanisms for optical and photocatalytic performance exhibited by Eu:Bi₂WO₆/CdS nanostructures was clarified. The robust PL emission peak at about 390 nm and weak emission peak at nearly 450 nm are attributed to the exciton emission and defect state of Bi₂WO₆/CdS nanostructure, respectively. As indicated from the mechanism insights, the reasonable introduction of Eu³⁺ could alter the band gap of the photocatalyst, and the epitaxial CdS could decrease the recombination probability of electron and hole in the Bi₂WO₆/CdS, while improving the photocatalytic activity. This study supplies new occasions for rational excogitation and better comprehending of atomic-scale complicated structures for applications in numerous fields (e.g., energy and environmental protection).     

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.

     

Effect of carbon doping on WO3/TiO2 coupled oxide and its photocatalytic activity on diclofenac degradation

The improved photocatalyst carbon-doped WO₃/TiO₂ mixed oxide was synthesized in this study using the sol–gel method. The catalyst was thoroughly characterized by X-ray diffraction (XRD), diffuse reflectance UV–vis spectroscopy, N₂ adsorption desorption analysis, scanning electron microscopy coupled with energy dispersive X-ray analysis (SEM/EDX), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The photocatalytic efficiency of the prepared materials was evaluated with respect to the degradation of sodium diclofenac (DCF) in a batch reactor irradiated under simulated solar light. The progress of the degradation process of the drug was evaluated by high-performance liquid chromatography (HPLC), whereas mineralization was monitored by total organic carbon analysis (TOC) and ion chromatography (IC). The results of the photocatalytic evaluation indicated that the modified catalyst with tungsten and carbon (TWC) exhibited higher photocatalytic activity than TiO₂ (T) and WO₃/TiO₂ (TW) in the degradation and mineralization of diclofenac (TWC>TW>T). Complete degradation of diclofenac occurred at 250 kJ m⁻² of accumulated energy, whereas 82.4% mineralization at 400 kJ m⁻² was achieved using the photocatalytic system WO₃/TiO₂-C. The improvement in the photocatalytic activity was attributed to the synergistic effect between carbon and WO₃ incorporated into the TiO₂ structure.     

Synthesis of flake-like bismuth tungstate (Bi2WO6) for photocatalytic degradation of coomassie brilliant blue (CBB)

Bismuth tungstate (Bi₂WO₆) flake-like nanostructures with zigzag periphery and 30–40 nm thickness in high yield were produced by facile and efficient modified hydrothermal technique. The as-synthesized nanostructures were characterized by X-ray diffraction (XRD), energy dispersive x-ray spectroscopy (EDX), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). Bi₂WO₆ nanostructures were investigated as visible light photocatalyst to degrade model dye coomassie brilliant blue (CBB). The role of hydrogen peroxide (H₂O₂) used as initiator was also studied by varying concentrations during photocatalysis. It was observed that photocatalytic activity significantly enhanced for lower initiator concentrations. The growth mechanism for nanostructures was also discussed briefly.     

Preparation of magnetic composite photocatalyst Bi2WO6/CoFe2O4by two-step hydrothermal method and itsphotocatalytic degradation of bisphenol A

Easily separable magnetic photocatalyst Bi₂WO₆/CoFe₂O₄ was synthesized by a two-step hydrothermal method. Pure spinel CoFe₂O₄ in nano-scale was prepared by a hydrothermal method, which was followed by a second hydrothermal process to coat CoFe₂O₄ with Bi₂WO₆. The prepared Bi₂WO₆/CoFe₂O₄ kept the magnetic property of CoFe₂O₄ and high efficient photocatalytic activity of Bi₂WO₆ as well. The photoactivity of Bi₂WO₆/CoFe₂O₄ (mass ratio 10:1) to degrade bisphenol A (BPA) was close to that of pure Bi₂WO₆ after 120 min of simulated solar light irradiation. After reaction, the catalyst particles could be easily harvested from the suspension by applying an external magnetic field.     

In-situ room-temperature synthesis of amorphous/crystalline contact Bi2S3/Bi2WO6 heterostructures for improved photocatalytic ability

We developed a facile in-situ growth method to construct amorphous-based Bi₂S₃/Bi₂WO₆ heterostructures at room temperature. As demonstrated by HRTEM, XPS and EDX-mapping, amorphous state Bi₂S₃ dispersed uniformly on the surface of crystalline Bi₂WO₆ hollow spheres. The photocatalytic activities of prepared Bi₂S₃/Bi₂WO₆ heterostructures were evaluated by the photodegradation of RhB and TC under visible light irradiation, indicating that the introduction of appropriate amorphous Bi₂S₃ significantly improved the photocatalytic activity of Bi₂WO₆. The amorphous/crystalline contact in Bi₂S₃/Bi₂WO₆ heterostructures played a crucial role in the enhancement of photocatalytic efficiency. Based on DRS, photoluminescence spectra, photocurrent intensity, electrochemical impedance spectroscopy and OCVD measurements, it was proposed that the enhanced performance could be ascribed to increased visible light utilization, promoted separation efficiency and prolonged life time of photogenerated electron-hole pairs by the introduction of amorphous Bi₂S₃. This work may provide new insights into the construction of amorphous-based composited heterostructures for improving photocatalytic activity.     

Photocatalytic behavior of a new composite ternary system: WO3/SiC-TiO2. Effect of the coupling of semiconductors and oxides in photocatalytic oxidation of methylethylketone in the gas phase

It has been found that the photocatalytic activity of classical TiO₂ for the purification of polluted effluents containing volatile organic compounds (VOCs) can be greatly improved using the effect of the coupling of semiconductors and oxides. Thus, a new mixed photocatalyst has been prepared leading to a composite ternary system, WO₃/SiC–TiO₂. The results indicate that this combination can result in an enhancement in the photocatalytic activity toward methylethylketone (MEK) oxidation at room temperature by a factor greater than four with a total mineralization into CO₂ and H₂O, without creating toxic by-products. The efficiency of the composite system strongly depends on the relative amounts of WO₃ and SiC in the various samples because an optimum in photo-activity is observed when the weight ratios WO₃ and SiC are about 3.5 and 20%, respectively. The increase and synergy in photo-oxidation activity, in comparison to TiO₂ and to the binary TiO₂-based systems, WO₃/TiO₂ and SiC–TiO₂, are obtained as the simultaneous effect of WO₃ and SiC. Addition of WO₃ mainly results in the retarding of electron-hole recombination process by an electron trapping effect and in the modification of surface acidity compared to the case of pure TiO₂. On the other hand, the coupled system of the two illuminated semiconductors, TiO₂ and SiC, leads to a simultaneous electron transfer from SiC to TiO₂ and hole transfer from TiO₂ to SiC, increasing spatial charge separation and thus preventing charge recombinations, detrimental to photocatalytic efficiency.     

Ag3PO4/Bi2WO6 hierarchical heterostructures with enhanced visible light photocatalytic activity for the degradation of phenol

The Ag₃PO₄/Bi₂WO₆ hierarchical heterostructures were prepared by a combination of hydrothermal technique and in situ precipitation method for the first time. The Ag₃PO₄/Bi₂WO₆ hierarchical heterostructures displayed enhanced visible-light photocatalytic activity against phenol. The enhanced photocatalytic activity could be attributed to the effective separation of photogenerated carriers driven by the photoinduced potential difference generated at the Ag₃PO₄/Bi₂WO₆ heterojunction interface. Repetitive tests showed that the Ag₃PO₄/Bi₂WO₆ hierarchical heterostructures maintained high catalytic activity over several cycles, and it had a better regeneration capability under mild conditions.     

Fabrication of direct Z-scheme FeIn2S4/Bi2WO6 hierarchical heterostructures with enhanced photocatalytic activity for tetracycline hydrochloride photodagradation

A series of direct Z-scheme FeIn₂S₄/Bi₂WO₆ hierarchical heterostructures with intimate interface contacts were synthesized by in-situ growth route and characterized by systematical analyses. All as-prepared FeIn₂S₄/Bi₂WO₆ nanocomposites showed significantly enhanced photocatalytic activity towards photodegradation for the removal of tetracycline hydrochloride (TCH) in comparison with individual FeIn₂S₄ and Bi₂WO₆. Meanwhile, the highest photocatalytic degradation activity can be achieved by modulating adding amount of FeIn₂S₄ in FeIn₂S₄/Bi₂WO₆ nanocomposites and the optimized component ratio of FeIn₂S₄ to Bi₂WO₆ is determined to be 10 wt%. The enhanced photocatalytic activity could be ascribed to efficient separation between photogenerated holes and electrons based on the construction of direct Z-scheme system. The high photocatalytic stability of resultant 10 wt% FeIn₂S₄/Bi₂WO₆ nanocomposites was revealed through six successive recycling reactions. The main intermediate generated during TCH photodegradation was explored by HPLC-MS. Besides, the direct Z-scheme photocatalytic mechanism was confirmed by band position analysis, electron spin resonance (ESR) and active species capture experiment.     

Ag/Bi2WO6 plasmonic composites with enhanced visible photocatalytic activity

Three-dimensional flower-like Bi₂WO₆ microspheres with the diameter of about 4 μm were prepared by a facile hydrothermal method using bismuth nitrate pentahydrate and sodium tungstate dihydrate as raw materials. A novel Ag-modified Bi₂WO₆ was synthesized through a simple and practical photoreduction process. The UV–vis diffuse reflectance spectra indicate that the Ag/Bi₂WO₆ samples have a significantly enhanced optical absorption in the visible light region than that of pure Bi₂WO₆ microspheres due to the surface plasmon resonance (SPR) of Ag nanoparticles on the surface of pure Bi₂WO₆. The photocatalytic activities of the as-prepared samples were evaluated by the decolorization of rhodamine B under simulated sun-light irradiation. The results reveal that the photocatalytic activities of the Ag/Bi₂WO₆ samples increase first and then decrease with increasing amount of loading Ag and the 1.0 wt% Ag-loaded Bi₂WO₆ sample exhibits the best photocatalytic activity compared with the other samples. The enhanced photocatalytic activity could be attributed to the synergistic effect of the strong SPR and the effective separation of photogenerated electrons and holes caused by Ag nanoparticles.