Monoclinic Scheelite BiVO4 Research Articles

Improved visible light photocatalytic performance through an in situ composition-transforming synthesis of BiVO4/BiOBr photocatalyst

The monoclinic scheelite (ms) BiVO4 shows great potential applications in the photocatalyst due to its strong light absorption in the visible light region. To improve the separation of photoinduced charge carriers in BiVO4, such as election and hole, BiVO4/BiOBr photocatalyst with a high visible light activity was synthesized using an in situ chemical transformation method with BiVO4 as a matrix and hydrobromic acid (HBr) as a construction agent. The effect of the concentration of BiOBr on the formation of BiVO4/BiOBr nanocomposite was studied. BiVO4/BiOBr nanocomposite was characterized in detail and the results show that the BiVO4 and BiOBr co-present in the system and BiVO4/BiOBr nanocomposite has a well hydrophilic surface. The photocatalytic properties of such nanocomposite were investigated through studying the degradation of a pollutant model (RhB), and meanwhile, the recombination of electron and hole was evaluated by photoluminescence (PL) spectroscopy. The results reveal that incorporation of BiOBr on BiVO4 could contribute to the enhanced separation and transport of photoinduced electrons and hole, leading to improved photocatalysis performance. The BiVO4/BiOBr photocatalyst could be applied as an outstanding photocatalytic material for organic pollutants degradation.

Synthesis of Bismuth Vanadate by a Novel Process and Its Enhanced Photoelectrochemical Performance

Highly crystalline monoclinic scheelite BiVO4 were synthesized by a hydrothermal process from strong redox reaction of VOC2O4 and NaBiO3 solutions over a wide range of pH. A simple electrophoresis process was employed to fabricate the BiVO4 thin films photoelectrochemical cell, which was used as photoanodes for water splitting. It can be found that the photoelectrochemical performance of the BiVO4 thin-film is strongly dependent on the pH used in the synthesis. It demonstrated that the distortion and polarization of the local structure of the synthesized material dependent greatly on the pH condition during the synthesis. Moreover, upon pH=1, the photocurrent density increase. While the Flat band of these bismuth vanadate shifts to positive as the pH decrease, which means the Fermi Energy Level (Ef) is risen as the pH decrease, as well as the conductive band (CB). Electrochemical impedance spectroscopy (EIS) measurements suggested that the sample of pH=1 showed the highest rate of photogenerated charge transfer.

High Photocatalytic Performance of Pd/PdO‐Supported BiVO4 Nanoparticles for Rhodamine B Degradation under Visible LED Light Irradiation

AbstractPd/PdO‐decorated BiVO4 nanoparticles were prepared by two‐step router: (i) monoclinic scheelite BiVO4 nanoparticles were fabricated via the co‐precipitation process in the presence of urea; (ii) Pd/PdO was decorated BiVO4 surface by the combination of by precipitation method and annealing process. The as‐synthesized catalysts were characterized by X‐ray powder diffraction (XRD) analysis, Raman spectra, X‐ray photoelectron (XPS) spectra, UV‐visible diffuse reflectance (UV‐vis DRS) spectra, and photoluminescence (PL) spectroscopy. The photocatalytic performance of Pd/PdO‐decorated BiVO4 samples exhibited excellent photodegradation of rhodamine B as well as the OH• radical generation under LED light irradiation as a comparison with the bare BiVO4. This excellent outcome is due to the reduced electron/hole recombination of Pd/PdO‐decorated BiVO4 samples, which was confirmed by PL characterization. Therefore, the fabrication of semiconductors with a combination of noble metal/oxides are good candidates for enhancement of their photocatalytic performance.

Hybrid-Functional Study of Native Defects and W/Mo-Doped in Monoclinic-Bismuth Vanadate

Monoclinic scheelite (ms) BiVO4 is recognized as one of the most promising photocatalyst materials due to its band gap as well as band-edge positions. Several theoretical and experimental works hav ...

Oxidant peroxo-synthesized monoclinic BiVO4: Insights into the crystal structure deformation and the thermochromic properties

In this study, a simple and novel hydrothermal approach was developed for the controllable synthesis of monoclinic scheelite BiVO4 using V2O5, Bi(NO3)3 and H2O2 as the starting materials. Diverse morphologies of BiVO4 including rods and branches were obtained by adjusting the H2O2 addition. We characterized these samples using X-ray diffraction, Raman spectroscopy, scanning electron microscopy, in situ UV–vis diffuse reflectance spectroscopy and Fourier transform infrared spectroscopy to investigate the effects of crystal structure deformation on their thermochromic behaviors. The results showed that the greater was the degree of structural distortion, the better was the thermochromic performance. As compared to rod-like morphology, the branch-like BiVO4 material exhibited better thermochromic properties owing to the greater distortion of crystal structure.

Solar-Driven One-Compartment Hydrogen Peroxide-Photofuel Cell Using Bismuth Vanadate Photoanode

One-compartment H2O2-photofuel cells using monoclinic scheelite BiVO4 film deposited on fluorine-doped tin oxide (ms-BiVO4/FTO) as the photoanode, Prussian blue film-coated FTO cathode, and deaerated aqueous electrolyte solution of 0.1 M NaClO4 and 0.1 M H2O2 were constructed. Mesoporous TiO2 photoanode cells with the same cathode and electrolyte solution were also prepared for comparison. The ms-BiVO4/FTO photoanode was prepared by a two-step route consisting of spin coating of a precursor solution on FTO and subsequent heating at 500 °C in the air. The thickness of the ms-BiVO4 film was controlled in the range from 50 to 500 nm by the number of the spin-coating times. There is an optimum thickness of the ms-BiVO4 film in the cell performances under illumination of simulated sunlight (AM 1.5, 100 mW cm–2, 1 sun). Under the optimum conditions, the ms-BiVO4/FTO photoanode cell provides a short-circuit current (Jsc) = 0.81 mA cm–2 and an open-circuit voltage (Voc) = 0.61 V, far surpassing the values of Jsc = 0.01 mA cm–2 and Voc = 0.31 V for the conventional mesoporous TiO2 photoanode cell. The striking cell performance is ascribable to the high visible-light activity of ms-BiVO4 for H2O2 oxidation and its low thermocatalytic activity for the decomposition.

The n-butanol gas-sensing properties of monoclinic scheelite BiVO4 nanoplates

Monoclinic scheelite BiVO4 nanoplates have been prepared via a facile hydrothermal method with monoethanolamine as a surfactant. The obtained BiVO4 nanoplates were characterized by XRD, SEM, Raman microscope and N2 adsorption-desorption analysis. The BiVO4 prepared with MEA is monoclinic scheelite plates which is composed of nanocrystallite with the average size of 100 nm. The sensors based on BiVO4 nanoplates show good sensitivity to alcohols gases, especially to n-butanol. The sensitivity to 100 ppm n-butanol gas is 61.6 at 260 °C, and the sensors exhibit low sensitivity to xylene, formaldehyde and toluene. The BiVO4 nanoplates could be a promising candidate for high selectivity and high sensitivity n-butanol gas-sening materials.

Substrate Temperature Induced (020) Growth Facets of Nebulizer Sprayed BiVO4 Thin Films for Effective Photodegradation of Rhodamine B

AbstractThe high‐efficient and visible‐light active monoclinic BiVO4 thin films with preferentially oriented (020) facets are successfully deposited by nebulizer spray pyrolysis technique. The role of substrate temperature over crystal growth facets and other physical properties of BiVO4 films are analyzed using XRD, HRTEM, UV spectrometer, and Raman analysis. The BiVO4 thin film deposited at 350 °C possesses broad absorbance in the visible region with highly exposed (020) facet is obtained. Room temperature photoluminescence analysis is used to understand the effective charge separation of photogenerated electron‐hole pair in BiVO4 thin films. It is worth to mention that the obtained monoclinic scheelite BiVO4 film with preferentially oriented (020) facet has large surface areas to produce greater number of reactive hydroxyl radicals, for the effective photocatalytic degradation of rhodamine B dye. Total organic content (TOC) study is conducted to examine the mineralization of organic compounds present in rhodamine B dye.

A novel and facile solvothermal-and-hydrothermal method for synthesis of uniform BiVO4 film with high photoelectrochemical performance

This paper reports a facile method for synthesis of highly photoresponsive flower-like monoclinic scheelite BiVO4 on FTO glass. The whole processes include a solvothermal step and a subsequent hydrothermal step with bismuth nitrate hydrate and ammonia metavanadate as the bismuth and vanadium sources, respectively. Based on experimental parametric analyses, the optimal condition has been obtained for fabrication of highly responsive flower-like BiVO4 films. The BiVO4 films produced have stronger hardness than those prepared by conventional physical methods. The BiVO4 films exhibit superior photocatalytic activity under simulated solar irradiation. In a photoelectrochemical system, using the present BiVO4 film for electricity generation, the applied bias photon-current efficiency is achieved 0.39% under the optimal conditions at 0.7 V vs. RHE.

Core–Shell Heterostructured BiVO4/BiVO4:Eu3+ with Improved Photocatalytic Activity

To enhance the photocatalytic activity of monoclinic scheelite (ms) BiVO4 for dye degradation, the heterostructured core (BiVO4)/shell (BiVO4:Eu3+) samples were synthesized by sol–gel method. The samples were characterized by UV–Vis diffuse reflectance spectroscopy, X-ray diffraction (XRD) and X-ray photoelectron spectra (XPS). The results reveal that as-synthesized photocatalysts are characteristic of ms core/shell structure, responsive to visible light. The XPS spectra confirm that the doped Eu3+ mainly distributed in the outside layer of BiVO4 particle. The valence band (VB) spectra indicate the shell (BiVO4:Eu3+) exhibits a high carrier mobility. The core/shell photocatalysts showed higher photocatalytic activity than pure BiVO4 through degrading Rhodamine B and Methylene blue. The better performance of core/shell heterojunction mainly results from that the Eu3+ ions selectively present on shell layer, increasing the VB value of shell layer (forming a interface electric field with core) and carrier mobility. It is considered that the half-filled 7f–electron configuration of Eu3+ can improve the electron trapping and transfer. Besides, the low PL intensity and high SBET of BiVO4/BiVO4:Eu3+ contribute to enhanced photocatalytic performances.

Electrochemical performance and enhanced photocatalytic activity of Ce-doped BiVO4 under visible light irradiation

Ce-BiVO4 composites have been synthesized via a simple precipitation-impregnation method and were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectrum (DRS), electrochemical impedance spectrum (EIS) and photocurrent. All the BiVO4 and Ce-BiVO4 samples are composed of monoclinic scheelite BiVO4. Compared to BiVO4, the increased photocurrent and decreased diameter of the semicircle have been observed for Ce-BiVO4, indicating that the Ce-doping can enhance interfacial electron transfer for Ce-BiVO4. Ce-BiVO4 composites show enhanced activity in the photocatalytic degradation of rhodamine B under visible light irradiation in comparison with P25 and pure BiVO4, and 1.0%Ce-BiVO4 shows the best photocatalytic activity because of its enhanced light absorption, narrowed bandgap and improved separation of the photogenerated electron–hole pairs, which was achieved as a result of photogenerated electrons transfer from the BiVO4 to the Ce4+ ions.

Low-heating solid-state chemical synthesis of monoclinic scheelite BiVO4 with different morphologies and their enhanced photocatalytic property under visible light

The monoclinic scheelite BiVO4 with different morphologies were synthesized by low-heating solid-state chemical reaction method without template or organic surfactant. The addition of weak base NaHCO3 can change the morphology of BiVO4 from polyhedrons to peanut-like and rice-like shape because that the base changed the microenvironment of the reaction system, increased the nucleation rate of product and hindered the further growth of the original product particle in process of solid-state reaction. Among the as-fabricated BiVO4 samples, the rice-like sample showed the best photocatalytic activity of 98.2% degradation for methylene blue solution after irradiation of 2h under visible light, which attributed to the efficient separation of photoexcited electrons and holes that improved the quantum efficiency during the photodegradation process. With the help of scavengers, OH and O2− were proved to be the main reactive species for the degradation of methylene blue.

Structural characteristics and photoinduced carrier behaviors of the mixed-phase BiVO4: a first-principles theoretical study

Nowadays, it is an attractive strategy to promote the efficiency of photocatalytic reactions by introducing the heterojunctions. Bismuth vanadate (BiVO4), one of the promising non-titania-based visible light-driven semiconductor photocatalysts, possesses three different crystal phases which can transform from one phase to another under appropriate conditions. The heterophase junction built by the monoclinic scheelite (s-m) and tetragonal zircon (z-t) phase BiVO4 has been demonstrated to have high photocatalytic activity than the single-phase BiVO4. Here we presented a step-by-step protocol based on the first-principles density functional theory calculations to explore the origin of high photocatalytic activity existed in BiVO4 heterojunction. The mixed-phase geometrical structures, density of states, electrostatic potential, electron localization function and band offsets of optimal interface have been calculated. For the heterojunction, the calculated valence band maximum and conduction band minimum of z-t BiVO4 are 0.29 and 0.32 eV above those of s-m BiVO4, respectively, indicating that the presence of interface in monoclinic/tetragonal heterophase provides a spatial condition for charge carrier separation and promotes the separation of photoinduced electron–hole pairs. Further calculations reveal that the direction of electron migration across the phase boundary is from z-t to s-m, consistent with the experimental observation.

Control of crystal phase of BiVO4 nanoparticles synthesized by microwave assisted method

Different crystalline phases BiVO4 nanoparticles (tetragonal-zircon, monoclinic-scheelite, and tetragonal-zircon/monoclinic-scheelite heterophase) have been prepared by fast microwave assisted method and annealing treatment. For the heterophase, the ratio of tetragonal-zircon and monoclinic-scheelite phases can be well controlled by controlling the annealing temperature. Furthermore, a tight interface junction has been formed between tetragonal-zircon BiVO4 and monoclinic-scheelite BiVO4 in a nanosize level. This tight interface junction can modify the electronic structure of BiVO4 nanoparticles, which would be very helpful for achieving high photocatalytic activity.

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.

Facile preparation of highly cost-effective BaSO4@BiVO4 core-shell structured brilliant yellow pigment

BiVO4 as an environmentally-friendly yellow pigment has been received increasing attention over the past two decades. Unfortunately, the relatively high cost hinders its large-scale applications. Herein, core-shell structured BaSO4@BiVO4 yellow pigments with a mean particle size of 193 nm were successfully synthesized, in which the BiVO4 coating has a pure monoclinic scheelite structure and a thickness of ∼5 nm. It is found that the appropriate particle size and monoclinic scheelite BiVO4 coating give this pigment a brilliant greenish-yellow color. For the BaSO4@BiVO4 micro-composite loaded with 16.3 wt.% BiVO4, its color coordinate L* and b* values can reach up to 76.53 and 75.46, much higher than the corresponding values 64.50 and 60.11 of pure BiVO4. Consequently, our strategy can save at least 83.7 wt.% BiVO4 without any detriments to color properties and also shows great potential in cutting down the cost of other expensive pigments.

Facile microwave assisted synthesis of floral-shaped BiVO4 nano particles for their photocatalytic and photoelectrochemical performances

Floral shaped monoclinic scheelite BiVO4 (ms-BiVO4) have been successfully synthesized by a facile microwave assisted method using domestic micro oven. The synthesized material has been subjected to characterized using XRD, SEM, TEM, XPS, BET, IR, Raman, PL and UV–Vis DRS techniques to describe the crystalline and morphology nature and photochemical properties of the sample. The floral shaped ms-BiVO4 possessed strong photoabsorption properties in the visible light with a band gap of ca. 2.3 eV. The analysis report of the ms-BiVO4 was stated that the catalyst has monoclinic crystalline and high surface area of ca. 24.0 m2 g−1. This study denotes that the microwave plays a major impact on the morphology and crystal size. The photocatalytic activity was evaluated by the degradation of a methylene blue and phenol aqueous solution in the presence of a small amount of H2O2 under visible light illumination. The photocurrent density and more negative flat band potentials also supported to photoelectrochemical (PEC) water splitting performance of ms-BiVO4 and the two features could have to improve the recombination life time, electron donor density. The floral shaped ms-BiVO4 maintained stability with better photocatalytic efficiency even at fifth cycles. The improved photocatalytic activity for methylene blue, phenol degradation and PEC activity of ms-BiVO4 was associated with the unique crystalline, optical property and morphology.

Enhanced visible-light photocatalytic activity of BiVO4 microstructures via annealing process

The peanut-shaped monoclinic scheelite BiVO4 crystals were synthesized via a facile one step hydrothermal method without using any templates, followed by annealing at different temperatures. The as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), Brunauer-Emmet-Teller (BET) and UV–vis diffuse reflectance spectra (DRS), showing that the annealing procedure could not only change the surface morphology and crystallinity of BiVO4 but also increase the specific surface area without damaging the peanut shape. The band gap values of the samples annealed at different temperatures could be reduced to 2.44–2.46 eV as compare with that of 2.47 eV of the original sample. The photocatalytic activities of BiVO4 crystals were evaluated by degradation of methylene blue in aqueous solution under artificial solar-light. Results demonstrated that the sample annealed at 450 °C exhibited the highest activity, and the photocatalytic conversion of methylene blue could reach above 94% after 150 min of irradiation.

Microwave assisted synthesis of sheet-like Cu/BiVO4 and its activities of various photocatalytic conditions

The Cu/BiVO4 photocatalyst with visible-light responsivity was prepared by the microwave-assisted hydrothermal method. The phase structures, chemical composition and surface physicochemical properties were well-characterized via X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance absorption (UV–vis/DRS), scanning electron microscopy (SEM), and N2 adsorption–desorption tests. Results indicate that the crystal structure of synthetic composite materials is mainly monoclinic scheelite BiVO4, which is not changed with the increasing doping amount of Cu. In addition, the presence of Cu not only enlarges the range of the composite materials under the visible-light response, but also increases the BET value significantly. Compared to pure BiVO4, 1% Cu/BiVO4-160 performs the highest photocatalytic activity to degrade methylene blue under the irradiation of ultraviolet, visible and simulated sunlight. In addition, the capture experiments prove that the main active species was superoxide radicals during photocatalytic reaction. Moreover, the 1% Cu/BiVO4-160 composite shows good photocatalytic stability after three times of recycling.

Preparation and efficient visible light-induced photocatalytic activity of m-BiVO4 with different morphologies

The monoclinic scheelite BiVO4 crystals with peanut-like, oval, twin-quadrangle and twin-four-pointed star morphologies were synthesized via a facile one step hydrothermal method by using sodium citrate as the chelating agent. The X-ray diffraction and scanning electron microscopy were employed to elucidate the structures and mophologies of the as-prepared BiVO4 samples. The results showed that the formation of m-BiVO4 with different morphologies relied on the pH value of the precursor solution. The band gaps values (Eg) of all the BiVO4 samples were around 2.37–2.45eV according to the UV–vis diffuse reflectance spectrum, which indicated that samples could strongly absorb in the visible light region. The photocatalytic activities of BiVO4 crystals were evaluated by degradation of MB in aqueous solution under artificial solar-light. The BiVO4 samples obtained at different pH values showed different photocatalytic activities during the sunlight-driven photodegradation of methylene blue (MB). The sample with peanut-like-shape prepared at pH=1 exhibited the highest activity, and the photocatalytic conversion could reach above 90% after 3h of irradiation. The result suggested that m-BiVO4 with peanut-like-shape could be used as an effective photocatalyst in practical application for organic pollutants degradation.