BiVO4 Photocatalyst Research Articles

Photocatalytic degradation and removal mechanism of ibuprofen via monoclinic BiVO4 under simulated solar light

Characterized as by X-ray diffraction, scanning electron microscopy and UV–vis diffuse reflectance spectra techniques, BiVO4 photocatalyst was hydrothermally synthesized. The photocatalytic degradation mechanisms of ibuprofen (IBP) were evaluated in aqueous media via BiVO4. Results demonstrated that the prepared photocatalyst corresponded to phase-pure monoclinic scheelite BiVO4. The synthesized BiVO4 showed superior photocatalytic properties under the irradiation of visible-light. The photocatalytic degradation rate of IBP decreased with an increase in the initial IBP concentration. The degradation process followed first-order kinetics model. At an IBP concentration of 10 mg L−1, while a BiVO4 concentration of 5.0 g L−1 with pH value of 4.5, the rate of IBP degradation was obtained as 90% after 25 min. The photocatalytic degradation of IBP was primarily accomplished via the generation of superoxide radical (O2•−) and hydroxyl radicals (•OH). During the process of degradation, part of the •OH was converted from the O2•−. The direct oxidation of holes (h+) made a minimal contribution to the degradation of IBP.

Controlled synthesis of BiVO4 photocatalysts: Evidence of the role of heterojunctions in their catalytic performance driven by visible-light

Despite heterostructured semiconductors gaining attention as photocatalysts due to their improved activity compared to that of the isolated materials, the role of these heterojunctions in charge separation (electron/hole) remains unclear. Therefore, we studied these aspects in monoclinic/tetragonal BiVO4 (m-BiVO4/t-BiVO4) heterostructures, which was chosen as an active material model under visible irradiation. The synthetic route was based on vanadium peroxo complex preparation as an intermediate step in structure formation using a hydrothermal process. When V2O5 was used at a molar ratio of 5:1 H2O2:(Bi+V) with 24h of annealing, the m-BiVO4/t-BiVO4 heterostructure was obtained, and this material exhibited better photocatalytic performance in methylene blue degradation under visible irradiation than isolated phases. The HRTEM images revealed that heterostructured sample was composed of nanoparticles of m-BiVO4 and t-BiVO4 with size lower than 10 nm, the interface of m-BiVO4/t-BiVO4 was also evidenced. Surprisingly, despite the t-BiVO4 structure being less active than m-BiVO4, the heterostructures with a higher t-BiVO4 content were more photoactive. The m-BiVO4/t-BiVO4 heterostructure showed no significant deactivation even after four successive re-uses for MB photodegradation. Oxidation mechanism of the MB dye was elucidated by mass spectroscopy. Indeed, the species scavenger trapping experimental results reveal the formation of a type-II heterostructure that led to an increase in the charge carrier lifetime, where the holes (h+), superoxide anion radicals (O2−) and hydroxyl radicals (OH) are the main active species.

One-pot synthesis of Ag+ doped BiVO4 microspheres with enhanced photocatalytic activity via a facile hydrothermal method

The Ag+/BiVO4 photocatalyst was fabricated through a facile hydrothermal method by using K6V10O28·9H2O as the vanadium source. The impact of Ag+ on the product's structure and morphology was studied. It was shown that the amount of Ag+ has no effect on the product’s crystal phases but plays an important role on the morphology of the nanoparticles that construct the shell of BiVO4 microspheres. In addition, the Ag+-doped photocatalysts have much higher photocatalytic activities in removing RhB and MB under the UV light illumination than the pure BiVO4. A possible photocatalytic mechanism was proposed in photoexcitation of the BiVO4 electrons which subsequently captured by the dopant. The present work may offer a novel route to reach higher photocatalytic activity by doping the Ag+ in the semiconductor catalysts.

Enhanced photocatalytic properties of molybdenum-doped BiVO4 prepared by sol–gel method

Bismuth vanadate (BiVO4) has been investigated intensively and extensively due to its potential applications in the photocatalytic treatment of organic-containing wastewater. In this study, Mo-BiVO4 samples were synthesized by a facile sol–gel process. These samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and ultraviolet–visible (UV–Vis) diffuse reflectance spectroscopy. It is found that the phase structure of Mo-BiVO4 photocatalyst is monoclinic scheelite. The photocatalytic activities of the obtained BiVO4 samples were investigated by means of the decolorization efficiency of methyl orange (MO). The BiVO4 and Mo-BiVO4 photocatalysts show the response on the visible light. The doped BiVO4 photocatalysts show higher decolorization efficiency than that of bare BiVO4.

The pH-controlled {040} facets orientation of BiVO4 photocatalysts with different morphologies for enhanced visible light photocatalytic performance

Hierarchically structured m-BiVO4 samples with different morphologies have been synthesized via a template-free solvothermal route by adjusting the pH value of the precursor solution. The effects of pH value on structure, morphology and photocatalytic activity were investigated. The results showed that the pH value played a great influence not only on the formation of the hierarchical structures with different morphologies, but also on the preferential crystal growth of the BiVO4 oriented along {040} facets. The pinwheel-like sample with the highest relative intensities of the diffraction peaks I040/I–121 exhibited the best photocatalytic activity for the photodegradation of MB under visible light irradiation. According to the Ostwald ripening process, a possible oriented aggregation mechanism was proposed.

Photoanodes on titanium substrates: one-step deposited BiVO4 versus two-step nano-V2O5 films impregnated with Bi3+

One-step deposition of photoelectrochemically active BiVO4 (monoclinic) from a polyethylene glycol (PEG300) precursor paint onto titanium substrates is demonstrated to lead to more complex multioxide phase films. Photocurrents in 0.5 M Na2SO4 remain relatively low when compared to those reported on tin-doped indium oxide (ITO) substrates, possibly due to the effect of detrimental underlying titanium oxide phases or mixed phases. For comparison, the one-step deposition is demonstrated also for the direct formation of V2O5 nanocrystalline films, which also exhibited low photoelectrochemical activity. Impregnation of nanocrystalline V2O5 with aqueous Bi3+ is shown to cause substantial recrystallization with formation of much more photoactive BiVO4. In particular, on low-temperature (high surface area) nano-V2O5 (400 °C) and after further mild annealing at 400 °C much improved photoelectrochemical water oxidation activity (ca. 0.3 mA cm−2 at 1.0 V vs Ag/AgCl (KCl (3 M) at 0.1-W cm−2 xenon lamp radiation) is observed. This opens up a new mild temperature two-step route for BiVO4 photocatalysts on practical titanium substrates.

Effects of citric acid and urea on the structural and morphological characteristics of BiVO4 synthesized by the sol–gel combustion method

Micro-sized spherical BiVO4 photocatalysts composed of nanoparticles were synthesized by the sol–gel combustion method. The effects of citric acid and urea on the structural and morphological characteristics of samples were studied by X-ray diffraction, field emission scanning electron microscopy, N2 adsorption and desorption and UV–Vis spectroscopy. The photocatalytic activity was evaluated by the photocatalytic degradation of rhodamine B under visible light. The results showed the sphere-shaped BiVO4 sample to have excellent photocatalytic performance compared with the bulk sample prepared by solid-state reaction. This enhancement could be attributed to the special spherical morphology, which enhanced the absorption ability, increased the separation efficiency of photon-generated carriers and improved surface reaction sites for consumption of photon-generated carriers. Uniform micro-sized spherical BiVO4 samples composed of nanoparticles were successfully synthesized by the sol–gel combustion method. The relationships between the morphologies and citric acid with urea contents were studied by using the field emission scanning electron microscopy (FE-SEM) technology.

Green-synthesized W- and Mo-doped BiVO4 oriented along the {0 4 0} facet with enhanced activity for the sun-driven water oxidation

A green hydrothermal synthesis approach, which employs almost neutral pH conditions and ammonium carbonate as a structural directing agent, has been used for the preparation of W- and Mo-doped BiVO4 powders with a monoclinic scheelite-like structure and preferential growth along the {040} facet. The crystal structure and morphology of the samples have been studied by means of XRD and FESEM analyses. The proper introduction of the W and Mo dopants in the lattice of BiVO4 crystals has been confirmed from XRD and XPS analyses. Moreover, it has been shown that the superficial amount of W and Mo dopants (obtained by means of XPS) plays a more important role than the overall (bulk and surface) dopant quantities in the BiVO4 (estimated by means of ICPMS analysis). The best of the so prepared materials demonstrated an extraordinary enhancement of the water oxidation rate under simulated sunlight (i.e. 942μmol/g.h O2), which is about two-fold and 100 times higher than those of a state-of-art Mo-doped and the non-doped BiVO4 reference materials, respectively. The here reported BiVO4 photocatalysts are highly promising for different applications such as renewable energy production systems (i.e. solar fuels production form water and sunlight) and to resolve environmental issues (i.e. photocatalytic degradation of organic pollutants, water remediation, among others).

Direct Imaging of Highly Anisotropic Photogenerated Charge Separations on Different Facets of a Single BiVO4 Photocatalyst.

Spatially resolved surface photovoltage spectroscopy (SRSPS) was employed to obtain direct evidence for highly anisotropic photogenerated charge separation on different facets of a single BiVO4 photocatalyst. Through the controlled synthesis of a single crystal with preferentially exposed {010} facets, highly anisotropic photogenerated hole transfer to the {011} facet of single BiVO4 crystals was observed. The surface photovoltage signal intensity on the {011} facet was 70 times stronger than that on the {010} facets. The influence of the built-in electric field in the space charge region of different facets on the anisotropic photoinduced charge transfer in a single semiconductor crystal is revealed.

Photodegradation of Alachlor Using BiVO4 Photocatalyst Under Visible Light Irradiation

In this study, BiVO4 powder is prepared and used as a visible-light catalyst for the photocatalytic degradation of alachlor. The as-prepared BiVO4 photocatalyst is characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–vis diffuse reflectance spectra (DRS), and BET surface area analysis. Alachlor could be successfully degraded in the presence of both H2O2 and BiVO4 catalyst under visible-light irradiation. With optimal operating parameters, its degradation efficiency could reach 97 % in 6 h. Factors such as solution pH, catalyst dosage, and the presence of anions are found to influence the degradation rate. To scrutinize the mechanistic details of the alachlor photodegradation, the intermediates of the process are separated, identified, and characterized by solid-phase microextraction (SPME) and gas chromatography/mass spectrometry (GC/MS). Results suggest that possible transformation pathways may include oxidation of the arylethyl group, cleavage of the N-methoxymethyl group, and N-chloroacetyl moiety.

Novel synthesis and photocatalytic performance of BiVO4 with tunable morphologies and macroscopic structures

BiVO4 photocatalysts with tunable morphologies and macroscopic structures were successfully achieved by a facile combined alcohol-thermal and CNFs templates route, based on the adjustment of solvent composition. The phase structures, morphologies, and optical absorption properties of the as-prepared BiVO4 samples were characterized by X-ray diffraction, field emission scanning electron microscopy, and ultraviolet-visible diffuse reflectance spectroscopy in detail. In addition, the results show that the photocatalytic activities of the as-prepared BiVO4 samples for the degradation of rhodamine B under visible-light irradiation are dependent on the solvent used in the synthesis. Note that the BiVO4 sample which derived from the mixture solvent (ethanol: EG=1:1, volumetric ratio), has the highest photocatalytic activity (up to 92% within 3h), due to its fusiform-like morphology and macroscopic structure, better crystallization, relatively larger specific surface area, suitable band gap energy and good permeability.

Template-Engaged In Situ Synthesis of Carbon-Doped Monoclinic Mesoporous BiVO4: Photocatalytic Treatment of Rhodamine B

In this paper, carbon-doped monoclinic scheelite mesoporous bismuth vanadate was synthesized through template-engaged in situ method. The bismuth nitrate pentahydrate and ammonia metavanadate were used as bismuth and vanadium precursors, respectively, glucose as carbon source, and mesoporous SiO2 aerogel as a hard template. Carbon-doped monoclinic mesoporous BiVO4 were obtained by heat treatment of BiVO4/glucose/template to carbonize glucose and form monoclinic crystal, followed by etching with NaOH solution to remove the SiO2 template. The samples were characterized by x-ray diffraction, N2 adsorption and desorption, UV-visible spectroscopy, Energy dispersive spectrometry, Raman spectroscopy, and Transmission electron microscopy. It was found that the sample with a carbon content of 0.5 wt.% possesses a specific surface area of 10.2 m2/g and has mesoporous structure with the most probable pore size of 13.9 nm. The band gap of carbon-doped monoclinic mesoporous BiVO4 was estimated to be 2.33 eV, indicating the superior photocatalytic activity under visible light. The photocatalytic efficiency of carbon-doped monoclinic mesoporous BiVO4 for the degradation of Rhodamine B under visible light (λ > 400 nm) in 120 min reaches 98.7%, Besides, the carbon-doped monoclinic mesoporous BiVO4 photocatalyst still showed high stability: 85% for Rhodamine B degradation after ten recycles.

Photocatalytic properties of BiVO4 synthesized by microwave-assisted hydrothermal method under simulated sunlight irradiation

BiVO4 with monoclinic-type structure were successfully synthesized by microwave-assisted hydrothermal method (BiMH) and hydrothermal reaction (BiH500) in aqueous medium. The materials were characterized by X-ray diffraction, scanning electron microscopy, Barrett–Emmett–Teller technique, diffuse reflectance spectroscopy, and UV–Vis spectroscopy. The photocatalytic activity of samples was evaluated by the degradation of different pollutants such as xanthene (rhodamine B), indigoids (indigo carmine), and antibiotics (tetracycline) under simulated sun-light irradiation. The relation among surface area, morphology, particle size, charge recombination, and photocatalytic performance of the powders was also discussed. The degradation of the antibiotic solution (TC) over BiVO4 photocatalyst was quickly reached for with half-life time (t 1/2) minor than 12 min. On the other hand, in the case of organic dyes (RhB and IC) the best results were t 1/2 = 79 and 150 min under simulated sun-light irradiation, respectively. BiVO4, had a good stability, did not present photocorroded under irradiation. The degree of mineralization of the organic compounds was determined by total organic content (TOC) analysis, which revealed that mineralization by the action of BiMH is feasible in 83 % (RhB), 58 % (IC), and 50 % (TC) after 96 h of irradiation.

The pH-controlled morphology transition of BiVO4 photocatalysts from microparticles to hollow microspheres

Through adjusting the reaction pH, monoclinic BiVO4 hollow microspheres have been prepared from a novel vanadium source K6V10O28·9H2O without any additives via a facile one-step hydrothermal method. The effects of pH on structure, morphology and photocatalytic activity were investigated. The results suggest that the pH of reaction mixture played a key role in the formation of BiVO4 with different and controllable morpholoyies. The products of monoclinic BiVO4 exhibited remarkable photoactivity for the photodegradation of RhB under the UV irradiation at room temperature. Based on the evolution process of morphology, a possible formation mechanism was proposed according to Ostwald’s step rule.

Microwave-assisted synthesis of monoclinic–tetragonal BiVO4 heterojunctions with enhanced visible-light-driven photocatalytic degradation of tetracycline

In this study, BiVO4 photocatalysts of different crystalline phases (monoclinic scheelite (M-phase), tetragonal zircon (T-phase) and monoclinic–tetragonal heterojunction (M–T)) have been successfully synthesized via a facile microwave-assisted method.

ChemInform Abstract: Advanced Chemical Compositions and Nanoarchitectures of Bismuth Based Complex Oxides for Solar Photocatalytic Application

AbstractReview: emphasis on BiVO4, Bi2WO6, and Bi2MoO6‐based photocatalysts; 206 refs.

Synthesis and the enhanced visible-light-driven photocatalytic activity of BiVO4 nanocrystals coupled with Ag nanoparticles

BiVO4 nanocrystals coupled with Ag nanoparticles (Ag–BiVO4 heterogeneous nanostructures) have been prepared by a new strategy via combining a hydrothermal route with a polyol process, in which BiVO4 nanocrystals were first synthesized by a hydrothermal route, and then, Ag nanoparticles were grown on the surfaces of the presynthesized BiVO4 nanocrystals through a polyol process. The photocatalytic evaluations demonstrate that BiVO4 nanocrystals coupled with Ag nanoparticles exhibit the enhanced visible-light-driven photocatalytic activity for the degradation of methylene blue (MB) and rhodamine B (RhB). The energy alignment and diffuse reflectance property of Ag–BiVO4 heterogeneous nanostructures demonstrate that Ag nanoparticles attached on the surfaces of BiVO4 nanocrystals play double roles for the enhanced visible-light-driven photocatalytic activity. First, the Ag nanoparticles grown on the surfaces of BiVO4 nanocrystals may act as electron sinks to retard the recombination of the photogenerated electrons and holes in BiVO4 so as to improve the charge separation on its surfaces. Second, the Ag nanoparticles increase the visible light absorption of the Ag–BiVO4 photocatalyst due to surface plasmon resonance (SPR) of Ag nanoparticles. These double roles of Ag nanoparticles make Ag–BiVO4 heterogeneous nanostructures to exhibit the enhanced photocatalytic activity to decompose MB and RhB under visible light irradiation, compared to the pure BiVO4 nanocrystals. The enhanced photocatalytic activity is attributed to the charge transfer from BiVO4 to the attached Ag nanoparticles as well as SPR absorption of Ag nanoparticles. The present work not only provides an efficient route to enhance visible-light-driven photocatalytic activity of BiVO4, but also offers a new strategy for fabricating metal–semiconductor heterogeneous nanostructure photocatalysts, which are expected to show considerable potential applications in solar-driven wastewater treatment and water splitting.

Visible-Light-Induced Photocatalytic Activity of Boron-Doped BiVO4

Boron-BiVO4 samples were synthesized by sol-gel method. They were characterized by UV-vis diffuse reflectance spectroscopy, X-ray diffraction. Photocatalytic activity of the obtained BiVO4 samples was investigated through degrading methylene blue (MB). The results reveal that boron-BiVO4 catalysts have monoclinic scheelite structure. The BiVO4 and Co-BiVO4 photocatalysts were responsive to visible light. Co-BiVO4 photocatalyst showed higher photocatalytic activity than pure BiVO4, resulting in the significantly improved efficiency of degradation of MB.

Hydrothermal preparation of BiVO4 photocatalyst with perforated hollow morphology and its performance on methylene blue degradation

Monoclinic scheelite type BiVO4 samples with high photocatalytic activity were successfully synthesized by a hydrothermal method in the presence of ethylenediamine tetraacetic acid (EDTA). Monoclinic scheelite structure was obtained at a hydrothermal temperature as low as 140°C, which was much lower than 210°C in the absence of EDTA. Experimental results indicate that the morphology of the BiVO4 changed from sphere, polygon with hole, perforated hollow polygon, to particle with fragment with the increase of EDTA amount, and the particle size also decreased. On the conditions of the hydrothermal temperature of 170°C, pH of 7.0, hydrothermal time of 4h and the amount of EDTA of 3.0mmol, BiVO4 samples with perforated hollow polygon structure and low band gap of 2.48eV were obtained. Catalyzed by the perforated hollow polygon BiVO4, the discoloration rate of methylene blue (MB) reached 90.84% in simulated sunlight. The high discoloration rate of BiVO4 was successfully explained by the experiment results of crystal structure, morphology, UV–vis diffuse reflectance spectroscopy and band gap.

Effects of structure, morphology, and up-conversion on Nd-doped BiVO4 system with high photocatalytic activity

Nd-doped BiVO4 photocatalysts with high photocatalytic activities have been synthesized by the microwave hydrothermal method. The effects of Nd doping on structural transformation, morphology, chemical valence, optical properties, and photocatalytic activities of Nd-doped BiVO4 photocatalysts were investigated systematically. It is found that Nd doping and pH of the reaction precursor can induce the stabilization of tetragonal zircon BiVO4, and Nd3+ ions have been incorporated into the BiVO4 lattice. The structure and morphology of BiVO4 play a significant role in the photocatalytic activity. The UV–vis diffuse reflectance spectra of Nd-doped BiVO4 present four absorption peaks at 532, 590, 690 and 750nm due to the excitation of Nd3+ species. The strong up-conversion fluorescence spectra of Nd-doped BiVO4 suggest the existence of up-conversion process, and the value of k/BET could reflect the effect of up-conversion lively and directly in Nd-doped BiVO4 system. The contribution of high photodegradation activities to Nd-doped BiVO4 catalysts under simulated sun-light is mainly from UV-light region. The mechanism of up-conversion upon sun-light excitation is proposed in favor of the improved photocatalytic activities of Nd-doped BiVO4.