BiVO4 Photocatalyst Research Articles

Facile solid-state synthesis of heteroatom-doped and alkaline-treated bismuth vanadate for photocatalyzing methylene blue degradation and water oxidation

Bismuth vanadate (BiVO4) with suitable band position and visible light responsive properties has been well adopted as the efficient photocatalyst for organic pollution degradation and water oxidation. However, the traditionally used solution process for synthesizing BiVO4 involving dissolving, reacting, crystallizing, and drying is complex and time-consuming. In this study, a facile solid-state synthesis is proposed to fabricate BiVO4 powders via simply mixing the precursors. Heteroatoms doping and alkaline treatment are also realized on BiVO4 by directly incorporating relevant precursors in the solid solution. Methylene blue degradation under visible light for 80 min is enhanced to 81% when 0.1 M NaOH is used to modify BiVO4, due to the possible development of bismuth oxide/BiVO4 heterojunction and the maintenance of rough surface. On the other hand, the W and Mo co-doped BiVO4 electrode shows a higher photocurrent density of 1.17 mA/cm2 at 1.23 VRHE than that for the BiVO4 electrode (0.33 mA/cm2 at 1.23 VRHE) under AM 1.5 solar simulation, owing to the higher carrier density induced by heteroatom-doping for the former case. Different photocatalytic performances of the heteroatom and the alkaline modified BiVO4 toward methylene blue degradation and water oxidation are inferred to be caused by different material compatibilities and the trade-off of the heterojunction and surface roughness. This work not only provides the facile solid-state synthesis but also gives evidences on the varied photoelectrochemical performances toward photodegradation and water splitting for the BiVO4 photocatalysts modified using different manners.

Easy Synthesis of BiVO4 for Photocatalytic Overall Water Splitting.

Developing a photocatalyst system to generate hydrogen from water is a topic of great interest for fundamental and practical importance. In this study, we develop a new Z-scheme photocatalytic system for overall water splitting that consists of Rh/K4Nb6O8 for H2 evolution, Pt/BiVO4 for O2 evolution, and I–/IO3– for an electron mediator under UV light irradiation. The oxygen evolution photocatalyst BiVO4 was prepared by the microwave-assisted hydrothermal method. The method is fast and simple, as compared to conventional hydrothermal synthesis. The catalysts were characterized by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and UV–visible spectroscopy. The photocatalytic water splitting is investigated in (i) aqueous AgNO3 as sacrificial electron scavengers and (ii) a Z-scheme photocatalytic water splitting system. The BiVO4 photocatalysts prepared by the microwave-assisted hydrothermal method not only showed a very high oxygen evolution rate (2622 μmol g–1 h–1) of water splitting reaction in an aqueous AgNO3 solution but also achieved a high H2 evolution rate (340 μmol g–1 h–1) and O2 evolution rate (172 μmol g–1 h–1) in a Z-scheme overall water splitting system.

Patterning of BiVO4 Surfaces and Monitoring of Localized Catalytic Activity Using Scanning Photoelectrochemical Microscopy.

There is a lot of interest in understanding localized catalytic activities at the micro and nanoscale and designing robust catalysts for photoelectrochemical oxidation of water to address the pressing energy and environmental challenges. Here, we demonstrate that scanning photoelectrochemical microscopy (SPECM) can be effectively employed as a novel technique (i) to modify a photocatalyst surface with an electrocatalyst layer in a matrix fashion and (ii) to monitor its localized activity toward the photoelectrochemical (PEC) water oxidation reaction. The three-dimensional SPECM image clearly shows that the loading of the FeOOH electrocatalyst on the BiVO4 semiconductor surface strongly affects its local PEC reaction activity. The optimal photoelectrodeposition time of FeOOH on the BiVO4 photocatalyst was found to be ∼20 min when FeOOH was employed as the electrocatalyst. The electrocatalyst optimization process was conducted on a single photoanode electrode surface, making the optimization process efficient and reliable. The morphology of the formed photocatalyst/electrocatalyst hybrid, inclusive of its localized activity toward the water oxidation reaction, was simultaneously probed. A photoanode surface comprising CuWO4/BiVO4/FeOOH was further prepared in this study and investigated. It was found that the localized photoactivity truly reflects the activity of the local area, differs from region to region, and is contingent on the morphology of the surface. Moreover, the Pt UME is determined as an efficient probe to analyze the photoactivity of the PEC water splitting reaction. This work highlights the novel SPECM technique for enhancement and examination of the catalytic activity of the nanostructured materials.

Plasmonic Z-scheme Pt-Au/BiVO4 photocatalyst: Synergistic effect of crystal-facet engineering and selective loading of Pt-Au cocatalyst for improved photocatalytic performance

Constructing Z-scheme photocatalysts is one of the most effective technologies to enhance the photocatalytic reduction or oxidation ability in artificial photosynthesis. For the BiVO4 photocatalyst, it usually shows limited photocatalytic ability because of the severe bulk recombination of photogenerated carriers and the poor reduction reaction of photogenerated electrons. In this paper, a novel plasmonic Z-scheme Pt-Au/BiVO4 single-crystal photocatalyst was constructed to solve the above issues. Here, Au nanoparticles are selectively deposited on the electron-rich (0 1 0) facet of BiVO4, while Pt nanoparticles are selectively modified on the Au surface. Photocatalytic results indicated that the resultant Pt-Au/BiVO4 Z-scheme photocatalyst exhibits an obviously higher photocatalytic performance than pure BiVO4, Au/BiVO4, randomly deposited BiVO4(Pt-Au/BiVO4(R)) and conventional Pt-Au/BiVO4. More importantly, compared with the well-known Pt/BiVO4(2.0 wt%), the Pt-Au/BiVO4 not only exhibits a higher photocatalytic performance, but also loads a lower amount of high-cost Pt cocatalyst. The excellent photocatalytic activity of the plasmonic Z-scheme Pt-Au/BiVO4 photocatalyst can be attributed to the synergistic effect of crystal-facet engineering and selective loading of Pt-Au, which results in the orientation transfer of photogenerated carriers in the single-crystal BiVO4, the enhanced reduction power of photogenerated electrons, and the rapid oxygen-reduction reaction on Pt cocatalyst.

Synthesis of g-C3N4/BiVO4 and Its Photocatalytic Performance for Hydrogen Production

In this study, ultrasonic hybridization was used to improve the photocatalytic efficiency and stability of the g-C3N4/BiVO4 photocatalyst, which was synthesized using Bi(NO3)3·5H2O and NaVO3 via the hydrothermal method to obtain BiVO4, and further modified by g-C3N4. Moreover, the obtained photocatalyst was studied using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, energy-dispersive spectroscopy, transmission electron microscopy, Brunauer–Emmett–Teller, ultraviolet–visible spectroscopy and electrochemical impedance spectroscopy. Subsequently, the photocatalytic performance for hydrogen production of the obtained photocatalyst was determined in a photocatalytic reactor under visible light, with methanol as the sacrificial agent and chloroplatinic acid as the promoter. The experimental results showed that the photocatalytic activity of BiVO4 considerably improved under visible light condition when its surface was modified with g-C3N4. When the amount of g-C3N4 was 5% of the amount of BiVO4, the hydrogen production rate was 53.25 μmol/h, which was 77.17 times higher than that of pure BiVO4. This improved performance can be attributed to the larger specific surface area, the better electron transfer efficiency and the electron–hole pair separation efficiency of g-C3N4/BiVO4. A possible mechanism model for the formation of g-C3N4/BiVO4 composite photocatalyst has also been proposed.

Effect of Operational Parameters on the Degradation of Methylene Blue Using Visible Light Active BiVO4 Photocatalyst

Visible light active bismuth vanadate (BiVO4) nanoparticles were fabricated by the facile hydrothermal method. The crystal structure and formation of the prepared BiVO4 were examined by X‐ray diffraction and Fourier‐transform infrared spectroscopy. The optical absorption property of BiVO4 was measured by ultraviolet–vis diffuse reflectance spectroscopy. The photocatalytic activity of the as‐prepared BiVO4 photocatalyst was assessed for the photodegradation of methylene blue (MB) under visible light irradiation (VLI). About 91.9% degradation in 90 min was observed when BiVO4 was used as a photocatalyst. Furthermore, the effect of varying the experimental parameters such as the catalyst amount, pH, and dye concentration were studied. Finally, the possible mechanism for MB degradation is presented.

Facile solvothermal synthesis of monoclinic-tetragonal heterostructured BiVO4 for photodegradation of rhodamine B

We synthesized BiVO4 photocatalysts using a facile solvothermal router and three different mixed solvents, 2-methoxyethanol (MEOH), 1,2-ethanediol (EDOH), and 1,2,3-propanetriol (PTOH) with water, which we then characterized by XRD, XPS, FE-SEM, and UV–vis DRS. The XRD results show that we obtained single-phase monoclinic scheelite (m-s BiVO4) in the EDOH/water and PTOH/water systems and monoclinic/tetragonal heterostructure BiVO4 (m-t BiVO4) in the MEOH and water mixture. m-t BiVO4 with a monoclinic/tetragonal heterostructure prevents the recombination of photoexcited electron-hole pairs. As such, of the three samples, the m-t BiVO4 material showed the highest activity in the photodecomposition of rhodamine B.

The improvement of photocatalysis O2 production over BiVO4 with amorphous FeOOH shell modification

A novel amorphous FeOOH modified BiVO4 photocatalyst (A-FeOOH/BiVO4) was successfully produced and characterized by various techniques. The results showed that amorphous FeOOH with about 2 nm thickness evenly covered on BiVO4 surface, which caused resultant A-FeOOH/BiVO4 exhibiting higher visible light photocatalytic performance for producing O2 from water than BiVO4. When the covered amount of amorphous FeOOH was 8%, the resultant photocatalyst possessed the best photocatalytic performance. To find the reasons for the improvement of photocatalytic property, electrochemical experiments, DRS, PL and BET, were also measured, the experimental results indicated that interface effect between amorphous FeOOH and BiVO4 could conduce to migration of photogenerated charge, and exhibit stronger light responded capacity. These positive factors promoted A-FeOOH/BiVO4 presenting improved the photocatalytic performance. In a word, the combination of amorphous FeOOH with BiVO4 is an effective strategy to conquer important challenges in photocatalysis field.

Z-scheme g-C3N4/BiVO4 photocatalysts with RGO as electron transport accelerator

BiVO4 is known for its ability to decompose water under visible light irradiation. However, BiVO4 overall suffers from rapid recombination of photogenerated carriers, low photochemical conversion efficiency, low specific surface area, poor conductivity, and weak adsorption capacity of dye. These features limited its application in photocatalysis. In this work, ternary Z-scheme g-C3N4/RGO/BiVO4 nanocomposites were successfully fabricated by in situ electrostatic adsorption of g-C3N4 sheets on RGO/BiVO4 surface using hydrothermal and thermal oxidations processes. The ternary Z-scheme g-C3N4/RGO/BiVO4 nanocomposites were then tested for photodegradation of Rhodamine B. The introduction of graphene into direct Z-scheme g-C3N4/BiVO4 nanocomposites as an electronic accelerator efficiently enhanced the photocatalytic properties. The as-prepared g-C3N4/RGO/BiVO4 composites exhibited optimal visible light responses with significantly improved photocatalytic performances toward degradation of Rhodamine B. The degradation efficiency using ternary photocatalyst reached 100% after 20 min of irradiation time. The reaction rate constant was estimated to 1.537, which was almost 29- and 20-folds higher than those of pure g-C3N4 and binary g-C3N4/BiVO4, respectively. The synergistic effect between BiVO4, RGO and g-C3N4 yielded g-C3N4/RGO/BiVO4 composites with Z-scheme charge transfer mechanism, promoting rapid separation and slow recombination of photogenerated electron–hole pairs with strong photocatalytic activity. Overall, these findings look promising for design of future Z-scheme photocatalysts for environmental degradation of organic dyes.

Synthesis of BiVO4 photocatalyst via cyclic microwave irradiation method

Visible light-active BiVO4 photocatalyst was successfully synthesized through a cyclic microwave irradiation method without further calcination process. The synthesized powder was characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS). The BiVO4 powder revealed an excellent photocatalytic degradation of methylene blue under visible light irradiation. The degraded methylene blue was monitored by both UV-Vis spectrophotometer and absorbance in RGB channels. Similar decolorization percentage as well as pseudo first-order rate constant were achieved with high accuracy and sensitivity. The light absorption in RGB channels is an alternative simple and cartable way requiring lower amount of sample for detecting the dye degradation photocatalytic activity.

Evaluating the photocatalytic efficiency of the BiVO4/rGO photocatalyst

The present study reported the preparation of BiVO4 by co-precipitation method. The as-prepared BiVO4 photocatalyst were deposited on rGO sheets to form BiVO4/rGO via the hydrothermal method. The crystalline structure, morphological, optical properties, and surface properties of the synthesized pure BiVO4 compared to BiVO4/rGO composite were studied using X-ray diffraction (XRD), scanning electronmicroscopy (SEM), photoluminescence (PL) spectrophotoscopy, UV–vis spectrophotometer with an integrating sphere, and N2 adsorption-desorption isotherm based on BET theory. The photocatalytic activity of the prepared samples were evaluated by the degradation of MB dye in aqueous medium under visible light irradiation. The result showed that the BiVO4/rGO composite exhibited greater photocatalytic efficiency compared to pure BiVO4 with the photocatalytic degradation efficiency remains stable up to fifth cycle. The improved activity of the BiVO4/rGO composite might be attributed to the high surface area available to adsorb more MB molecules, and efficient charge separation of BiVO4 through π electron on the rGO structure. According to experimental results, the possible photocatalytic mechanism of the BiVO4/rGO composite were determined and the active species hydroxyl radical were reported. Based on photocatalytic activity inhibition in the presence of both h+ (VB) and O2•− (CB) scavengers over the BiVO4 photocatalyst, it can be proposed that the hydroxyl radical generated during the photocatalytic degradation mechanism is mainly responsible by the main active species of h+ and O2•− at VB and CB positions, respectively.

Tailoring the morphological structure of BiVO4 photocatalyst for enhanced photoelectrochemical solar hydrogen production from natural lake water

Solar hydrogen production via natural lake water was investigated via monoclinic bismuth vanadate (BiVO4) photocatalyst in a tandem photoelectrochemical cell (PEC), which was made up via integrating a PEC system with a dye-sensitized solar cell (DSSCs) in a series. Herein, the visible-light-driven BiVO4 photocatalysts were synthesized via a simple hydrothermal treatment reaction. A mathematical representation for optimizing the synthesizing condition of BiVO4, namely pH and the hydrothermal temperature was successfully generated via response surface methodology (RSM). The BiVO4 sample prepared at pH = 1.96 and hydrothermal treatment at 120 °C (Run 4) exhibited remarkable photocatalytic hydrogen performance of 9.52 mmol/h within 7 h. In addition, the observed photocurrent density and photoconversion efficiency were 5.66 mA/cm2 at 0.7 V and 0.056%, respectively. The profound performance observed was attributed to the low photocharge carrier resistance and a more negative flat band potential for PEC water splitting system. This work demonstrates the feasibility of producing hydrogen from abundant natural lake water via BiVO4 photocatalyst.

Crystal violet degradation over BiVO4 photocatalyst under visible light irradiation

Sigle phase scheelite-monoclinic BiVO4 materials with different morphologies were successfully fabricated via a facile hydrothermal process by controlling pH of the precursor. The photocatalytic properties of the as-prepared materials were assessed via the photodecomposition of crystal violet (CV) solution under a 60 W LED (Cree-L6) visible light irradiation. The Langmuir-Hinshelwood model was utilized to present kinetic behavior. The obtained BiVO4 exhibited a monoclinic crystalline structure and narrow bandgap energy (Eg = 2.3–2.6 eV), which were confirmed by the X-ray diffraction (XRD), Raman and UV-vis diffuse reflectance spectra (UV-vis DRS) results. From the scanning electron microscopy (SEM) results, BiVO4 morphologies could be facilely controlled by turning the pH value of the precursor. When pH = 0.3, the BiVO4 products showed spherical morphologies with particle sizes in the range of 1–5 µm. Rod- and spherical like-BiVO4 products were obtained when the pH of the precursor was adjusted to 3. Moreover, BiVO4 with nanoparticles could be prepared under the pH of 5–7, whereas leaf-like morphologies could be achieved when pH = 9. The photocatalytic test showed that the adsorption equilibrium constant depended on the morphologies of the BiVO4 products and the reaction rate constant was reached the highest level at pH = 3. This outcome indicated that the enhanced performance of BiVO4 significantly depended on the morphologies of the BiVO4 products and the effective suppression of photo-excited electrons and holes.

A nitrogen-rich BiVO4 nanosheet photoanode for photoelectrochemical water oxidation

In this work, a nitrogen-rich BiVO4 nanosheet sample prepared by one-step hydrothermal method and characterized by XRD, TEM, Raman, XPS. With the introduction of N, partial oxygen atoms of BiVO4 were replaced by N to form Bi–N and V–N bonds, lead to the deviation of binding energy and the right shift of Raman peak. PEC measurements show that photocurrent density of nitrogen-rich BiVO4 photocatalyst is nearly two times higher than the pristine BiVO4, have longer electronic life and higher carrier concentration. These are mainly attributed to the Bi–N and V–N bonds are serve as the main OER catalytic active sites, and facilitate the transmission of electrons from the semiconductor surface to the FTO. The possible catalytic mechanism of nitrogen-rich BiVO4 system has also been proposed.

Fabrication of high surface area AgI incorporated porous BiVO4 heterojunction photocatalysts

The low surface area and photogenerated charge carrier recombination rate severely affects the usability of a photocatalysts. In this work, a visible light active AgI/BiVO4 photocatalyst was fabricated via a low temperature one step hydrothermal method. Low temperature preparation results in a porous and very high surface area (114 m2/g) BiVO4 photocatalysts. XRD, FTIR, Raman and BET surface area analysis revealed that AgI is bonded as well as embedded in the porous structure of BiVO4, which causes shrinking of the BiVO4 lattice. Compare to bare BiVO4, the AgI/BiVO4 photocatalyst shows nearly 1.7 times higher photocurrent response and 43% higher photocatalytic activity. The significantly high photocatalytic activity ascribed to the very high surface area, and the effective charge separation at the AgI/BiVO4 p-n heterojunction. Further, based on UV-DRS and Mott-Schottky measurements, a plausible charge transfer mechanism is proposed.

The photocatalytic activity of GO-modified BiVO4 for the degradation of phenol under visible light irradiation

In recent years, using graphene to modify BiVO4 has become a research hotspot. However, there are few reports on the effects of the graphene size and the loading content on the photocatalytic activity of the graphene-modified BiVO4. In this work, a series of BiVO4 photocatalysts modified by oxide graphene (GO) of different sizes and loadings were prepared, characterized and their activities were investigated. The results showed that when the size of GO was 5–7 μm and the loading was 0.5 wt%, the phenol degradation rate over the GO-modified BiVO4 was the best and reached 65.2% after 5 h visible light irradiation.

Constructing a novel hierarchical β-Ag2MoO4/BiVO4 photocatalyst with Z-scheme heterojunction utilizing Ag as an electron mediator

A novel β-Ag2MoO4/BiVO4 heterojunction photocatalyst was synthesized via a simple precipitation method. The photocatalytic activity of photocatalysts was assessed by RhB (Rhodamine B) and TC (tetracycline hydrochloride) degradation. Furthermore, the Ag nanoparticles were produced during the photocatalytic degradation process facilitates the construction of Z-scheme system. The XRD, XPS, SEM, EDX, TEM, HR-TEM and BET measurements revealed the structure and morphology properties and the UV–Vis DRS, PL, PT and EIS were used to investigate the optical properties. The results exhibited that the β-Ag2MoO4/BiVO4 heterojunction photocatalyst possess higher photocatalytic activity than individual BiVO4 and β-Ag2MoO4. Furthermore, h+ was the most crucial active species in the β-Ag2MoO4/Ag/BiVO4 Z-scheme system according to the reactive species trapping experiments. The potential Z-scheme photocatalytic mechanism also was discussed based on experimental and characterization results. This work shows a simple method to construct Z-scheme heterojunction photocatalyst by self-assembly and demonstrates that photocatalytic technology has great application prospects for water purification.

Solid-phase Synthesis of Visible-light-driven BiVO4 Photocatalyst and Photocatalytic Reduction of Aqueous Cr(VI)

This communication reports a pioneering study on the synthesis of BiVO4 and photocatalytic reduction of Cr(VI)-polluted wastewaters. Monoclinic phase BiVO4 micron-crystals with adjustable morphology were synthesized via a solid-phase route. The structures, morphology, optical properties of the BiVO4 micron-crystals were characterized by X-ray diffraction, field emission scanning electron microscopy, UV-vis diffuse reflectance spectra, Fourier transform infrared spectroscopy spectra, and photocurrent measurements. Besides, their photocatalytic properties were tested for the reduction of aqueous Cr(VI) under visible light (l > 420 nm) irradiation. The photocatalytic tests showed that the photocatalytic activities of BiVO4 powders in aqueous Cr(VI) depended on the dark adsorption amount for Cr(VI) and number of photogenerated carriers. BiVO4-(c) exhibited the highest photocatalytic reduction efficiency that attributed to highest separation and transfer efficiency of photogenerated electrons and holes. Besides, effects of photocatalytic experiment parameters (including dosage of photocatalyst and coexistent anions and cations) on the Cr(VI) removal rate by BiVO4-(c) were also investigated, and •OH play an important role in the BiVO4 photocatalytic reduction Cr(VI).

The effect of crystal facets and induced porosity on the performance of monoclinic BiVO4 for the enhanced visible-light driven photocatalytic abatement of methylene blue

In this study, a unique two-step approach has been developed to synthesize mesoporous BiVO4 (m-BiVO4) photocatalysts. The synthesized photocatalysts were characterized by means of XRD, SEM, EDS, UV–vis, Raman, PL, DRS, and N2-physiosorption analysis techniques. The hybrid BiVO4/KIT-6 composite and m-BiVO4 particles exhibited selective growth of the (040) crystal facet, a smaller size, high surface areas, a large pore volume as a result of the porosity induced by KIT-6 and, a greater number of active sites. The charge recombination rate of m-BiVO4 was remarkably lower than that of conventional BiVO4. In addition, the bandgap energy of m-BiVO4 was 2.2 eV, which is suitable for visible light irradiation. It was observed that the photocatalytic activity of m-BiVO4 was superior to that of conventional BiVO4 under visible-light illumination, due to the synergistic effect of the highly active monoclinic phase and large surface area of m-BiVO4. Furthermore, the monoclinic m-BiVO4 was also tested for photocatalytic degradation ability by using an anonymous industrial effluent for 3 h under visible light irradiation.

Ternary BiVO4/NiS/Au nanocomposites with efficient charge separations for enhanced visible light photocatalytic performance

The design and synthesis of efficient photocatalysts for organic pollutant degradation has been regarded as a hopeful approach for environmental protection and remediation. Herein, ternary BiVO4/NiS/Au nanocomposites are successfully synthesized via a simple two-step hydrothermal and photo-reduction method for organic pollutant degradation based on efficient charge separations. Taking the merits of electron collector property of Au and advantages of formed p-n junction between NiS and BiVO4, the prepared BiVO4/NiS/Au composites shows remarkable improvement of organic pollutant degradation compared with pure BiVO4 photocatalyst or binary composites (BiVO4/NiS or BiVO4/Au). Noticeably, the photodegradation efficiency of the optimal ternary BiVO4/NiS/Au composites toward tetracycline (TC) is 4.25 times higher than pure BiVO4. A possible mechanism and degradation pathway for TC was proposed based on the trapping experiments and liquid chromatography–mass spectrometry (LC–MS) analysis.