Nanostructured BiVO4 photocatalysts synthesized via a polymer-assisted coprecipitation method and their photocatalytic properties under visible-light irradiation

Nanostructured BiVO₄ photocatalysts were synthesized by a coprecipitation process in the presence of sodium carboxymethylcellulose (CMC), which acts as a steric stabilizer during the formation and growth of the BiVO₄ nanoparticles. Samples with different contents of CMC were prepared in order to study the effect of the polymer on the final morphology of the oxide. The synthesized samples were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), diffuse reflectance spectroscopy (DRS), and adsorption-desorption isotherms (BET). The presence of CMC during the first stage of BiVO₄ synthesis, promoted the formation of granular particles controlling its morphology and favoring its dispersion. The BiVO₄ monoclinic polymorph (m-BiVO₄) was obtained free of the tetragonal crystalline form (t-BiVO₄) by annealing at different temperatures, which were influenced by CMC content: 400 °C (0.5 wt %), 450 °C (3.0 wt %), and 350 °C (6.0 and 9.0 wt %). BiVO₄ nanoparticles showed photocatalytic activity, as they bleached an aqueous solution of rhodamine B (rhB) under visible-light irradiation. The photocatalytic activity of the BiVO₄ samples was directly correlated with the amount of CMC added during the synthesis process.     

A Theoretical Study on the Mechanism of Photocatalytic Oxygen Evolution on BiVO4 in Aqueous Solution

The oxygen evolution reaction (OER) is regarded as one of the key issues in achieving efficient photocatalytic water splitting. Monoclinic scheelite BiVO₄ is a visible‐light‐responsive semiconductor which has proved to be effective for oxygen evolution. Recently, the synthesis of a series of monoclinic BiVO₄ single crystals was reported, and it was found that the (010), (110), and (011) facets are highly exposed and that the photocatalytic O₂ evolution activity depends on the degree of exposure of the (010) facets. To explore the properties of and photocatalytic water oxidation reaction on different facets, DFT calculations were performed to investigate the geometric structure, optical properties, electronic structure, water adsorption, and the whole OER free‐energy profiles on BiVO₄ (010) and (011) facets. The calculated results suggest both favorable and unfavorable factors for OER on the (010) and the (011) facets. Due to the combined effects of the above‐mentioned factors, different facets exhibit quite different photocatalytic activities.     

Hydrothermal Synthesis and Characterization of Visible-Light-Driven Dumbbell-Like BiVO4 and Ag/BiVO4 Photocatalysts

Visible-light-driven dumbbell-like BiVO₄ and Ag/BiVO₄ photocatalysts has been successfully synthesized by a simple hydrothermal method at 180 °C for 24 h. The as-synthesized photocatalysts were characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and UV–Vis absorption spectroscopy. The results obtained showed that ethylenediamine, citric acid, pH and hydrothermal reaction temperature have pronounced effects on the morphology of BiVO₄. Transmission electron microscopy observation shows that the Ag nanoparticles are homogenously dispersed on the surface of the BiVO₄ nanorods. Photocatalytic activities of the dumbbell-like BiVO₄ and Ag-loaded BiVO₄ photocatalysts were also evaluated by using methylene blue as a representative dye indicator under visible light irradiation. It is found that the photocatalytic performance of the as-synthesized BiVO₄ is obviously improved with the incorporation of the Ag nanoparticles. Mechanism for the enhancement of the photocatalytic activity of the Ag/BiVO₄ photocatalyst is also discussed.     

Visible light photocatalytic activity of BiVO4 particles with different morphologies

Bismuth vanadate (BiVO₄) particles with different morphologies were synthesized by a one-step hydrothermal process and their optical and photocatalytic properties were investigated. Their crystal structure and microstructures were characterized using X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). XRD patterns demonstrate that the as-prepared samples are monoclinic cell. FESEM shows that BiVO₄ crystals can be fabricated in different morphologies by simply manipulating the reaction parameters of hydrothermal process. The UV–visible diffuse reflectance spectra (UV–vis DRS) reveal that the band gaps of BiVO₄ photocatalysts are about 2.07–2.21 eV. The as-prepared BiVO₄ photocatalysts exhibit higher photocatalytic activities in the degradation of rhodamine B (Rh B) under visible light irradiation (λ > 420 nm) compared with traditional N-doped TiO₂ (N-TiO₂). Furthermore, wheat like BiVO₄ sample reveals the highest photocatalytic activity. Up to 100% Rh B is decolorized after visible light irradiation for 180 min. The reason for the difference in the photocatalytic activities for BiVO₄ samples obtained at different conditions were systematically studied based on their shape, size and the variation of local structure.     

球形、花形和线状钒酸铋的可控合成及光催化性能

通过无模板、无助剂的可控水热法, 制备出球形、花形和线状钒酸铋(BiVO₄), 研究了其光学和可见光催化性能. 通过X射线衍射(XRD)和透射电镜(TEM)观测其结构和形貌特征. XRD谱线显示, 所制备的样品为单斜晶体结构. TEM结果表明, 通过控制水热过程的反应参数可以得到不同形貌的纳米粉体. 基于不同条件下制备的样品的微结构分析, 提出了这些不同形貌的形成机制. 紫外-可见漫反射光谱(UV-Vis DRS)表明BiVO₄样品的带隙能约为2.19-2.33 eV. 利用可见光(λ>420 nm)照射下的罗丹明B(RhB)降解实验评价了BiVO₄样品的光催化性能. 结果表明, BiVO₄的光催化活性比商用TiO₂催化剂P25 和掺氮TiO₂ (N-TiO₂)高得多. 所制备的球形BiVO₄光催化效率最高, 经可见光照射180 min, RhB溶液的降解率可达100%. 系统地研究了结构和形貌对不同pH值下制备的BiVO₄样品光催化活性的影响.     

Photocatalytic Degradation of Palm Oil Mill Effluent (POME) Waste Using BiVO4 Based Catalysts

Disposal of palm oil mill effluent (POME), which is highly polluting from the palm oil industry, needs to be handled properly to minimize the harmful impact on the surrounding environment. Photocatalytic technology is one of the advanced technologies that can be developed due to its low operating costs, as well as being sustainable, renewable, and environmentally friendly. This paper reports on the photocatalytic degradation of palm oil mill effluent (POME) using a BiVO₄ photocatalyst under UV-visible light irradiation. BiVO₄ photocatalysts were synthesized via sol-gel method and their physical and chemical properties were characterized using several characterization tools including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), surface area analysis using the BET method, Raman spectroscopy, electron paramagnetic resonance (EPR), and UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS). The effect of calcination temperature on the properties and photocatalytic performance for POME degradation using BiVO₄ photocatalyst was also studied. XRD characterization data show a phase transformation of BiVO₄ from tetragonal to monoclinic phase at a temperature of 450 °C (BV-450). The defect site comprising of vanadium vacancy (V_v) was generated through calcination under air and maxima at the BV-450 sample and proposed as the origin of the highest reaction rate constant (k) of photocatalytic POME removal among various calcination temperature treatments with a k value of 1.04 × 10⁻³ min⁻¹. These findings provide design guidelines to develop efficient BiVO₄-based photocatalyst through defect engineering for potential scalable photocatalytic organic pollutant degradation.     

TiO2/BiVO4, a Heterojuncted Microfiber with Enhanced Photocatalytic Performance for Methylene Blue under Visible Light Irradiation

Novel TiO₂/BiVO₄ microfiber heterojunctions were constructed using cotton as biomorphic templates. The as-synthesized samples were characterized by scanning electron microscope, X-ray diffraction, X-ray photoelectron spectroscopy, UV-Vis diffuse reflectance spectra and photocatalytic experiment. The morphology of the as-synthesized TiO₂/BiVO₄ composites was consisted of a large quantity of microfiber structures with diameter from 2.5 μm to 5 μm, and the surface of samples became more coarse and compact with the increase of weight ratio of TiO₂. The TiO₂/BiVO₄ samples with proper content (10.00wt%) showed the highest pho-tocatalytic degradation activity for methylene blue (MB) degradation among all the samples under visible light, and 88.58%MB could be degraded within 150 min. The enhancement of photocatalytic activity was mainly attributed to the formation of n-n heterojunction at the contact interface of TiO₂ and BiVO₄, which not only narrowed the band gap of BiVO₄ for extending the absorption range of visible light, but also promoted the transfer of charge carriers across interface. A possible photodegradation mechanism of MB in the presence of TiO₂/BiVO₄ microfibrous photocatalyst was proposed.     

Synthesis and photocatalytic performances of BiVO4 by ammonia co-precipitation process

This paper reports the preparation and photocatalytic performance of Bismuth vanadate (BiVO₄) by a facile and inexpensive approach. An amorphous BiVO₄ was first prepared by a co-precipitation process from aqueous solutions of Bi(NO₃)₃ and NH₄VO₃ using ammonia. Followed by heating treatment at various temperatures, the amorphous phase converted to crystalline BiVO₄ with a structure between monoclinic and tetragonal scheelite. The crystallization of BiVO₄ occurred at about 523 K, while the nanocrystalline BiVO₄ were formed with a heat-treatment of lower than 673 K. However, when the heat-treatment was carried out at 773 K, the accumulation of nanocrystals to bulk particles was observed. The photocatalytic performances of the materials were investigated by O₂ evolution under visible-light, and MB decomposition under solar simulator. The results demonstrated that the crystalline structure is still the vital factor for the activities of both reactions. However, the crystallinity of BiVO₄ gives a major influence on the activity of O₂ evolution, whereas the surface area, plays an important role for photocatalytic MB decomposition.     

Fabrication of ternary dual Z-Scheme AgI/ZnIn2S4/BiVO4 heterojunction photocatalyst with enhanced photocatalytic degradation of tetracycline under visible light

In this study, a novel ternary AgI/ZnIn₂S₄/BiVO₄(AZB) composite photocatalyst was successfully prepared by hydrothermal method and in-situ precipitation method. The as-synthesized samples were characterized by XRD, SEM, TEM, XPS and so on, and the photocatalytic activity was evaluated through photocatalytic degradation of tetracycline (TC) under visible light irradiation. When the molar ratio of Bi to Ag was 1:1, the degradation rate of TC can reach 91.44 % within 150 min. The AZB heterojunction demonstrated outstanding efficiency with the apparent reaction rate constants of 0.02118 min^?1 for TC removal, was 4.68, 3.27 and 3.27 times higher than that of pure BiVO₄, AgI and ZnIn₂S₄. Based on active species trapping experiments and ESR analysis, a dual Z-Scheme pathways among BiVO₄, AgI and ZnIn₂S₄ for effective separation of photogenerated charges was recommended. This work provided a promising insight for the design of ternary dual Z-scheme heterojunction with multilevel electron transfer to present greater photo-absorption, charge separation, and photodegradation for environmental decontamination.     

One-pot synthesis of peony-like Bi2S3/BiVO4(040) with high photocatalytic activity for glyphosate degradation under visible light irradiation

In this work, samples consisting of BiVO₄ with exposed (040) facets coupled with Bi₂S₃ (Bi₂S₃/BiVO₄) were prepared through a one-pot hydrothermal method, using ethylenediaminetetraacetic acid as directing agent and L-cysteine as sulfur source and soft template. X-ray diffraction, field emission scanning electron microscopy, and high-resolution transmission electron microscopy measurements indicated that the Bi₂S₃ content had a significant influence on the growth of (040) and (121) facets as well as on the morphology of the Bi₂S₃/BiVO₄ samples. When the Bi₂S₃ content reached 1 mmol, the Bi₂S₃/BiVO₄ samples exhibited a peony-like morphology. The results of transient photocurrent tests and electrochemical impedance spectroscopy measurements confirmed that a more effective charge separation and a faster interfacial charge transfer occurred in Bi₂S₃/BiVO₄ than BiVO₄. The enhanced photocatalytic activity of the Bi₂S₃/BiVO₄ samples could be attributed to the improved absorption capability in the visible light region and the enhanced electron-hole pair separation efficiency due to the formation of the Bi₂S₃/BiVO₄ heterostructure. In addition, the Bi₂S₃/BiVO₄ samples showed relative stability and reusability. The simple method presented in this work could be used to fabricate composite photocatalysts with high activity for different applications, such as photocatalytic degradation of organic pollutants, photocatalytic splitting of water, and photocatalytic reduction of carbon dioxide.     

Porous F-doped BiVO4: Synthesis and enhanced photocatalytic performance for the degradation of phenol under visible-light illumination

Fluoride-doped BiVO₄ with the F/Bi molar ratios of 0, 0.09, 0.13, and 0.29 (denoted as BiVO₄–F0, BiVO₄–F0.09, BiVO₄–F0.13, and BiVO₄–F0.29, respectively) were synthesized using the hydrothermal strategy with the hydrothermally derived BiVO₄ as the precursor and NH₄F as the fluoride source. Physicochemical properties of the materials were characterized by means of a number of analytical techniques. Photocatalytic activities of the fluoride-doped BiVO₄ samples were evaluated for the degradation of phenol under visible-light irradiation. It is shown that compared to the undoped BiVO₄–F0 sample, the fluoride-doped BiVO₄ samples retained the monoclinic structure, but possessed higher surface areas and oxygen adspecies concentration, better light-absorbing performance, and lower bandgap energies. Among the four samples, the porous spherical BiVO₄–F0.29 sample exhibited the best photocatalytic activity for the degradation of phenol in the presence of a small amount of H₂O₂ under visible-light illumination. It is concluded that the higher surface area and oxygen adspecies concentration, stronger optical absorbance performance, and lower bandgap energy were responsible for the excellent photocatalytic performance of BiVO₄–F0.29 for the photocatalytic degradation of phenol.     

Facile preparation of BiVO4 thin film by screen-printing technique for its photocatalytic performance in the degradation of tetracycline under simulated sunlight irradiation

BiVO₄ films were prepared by a screen-printing technique on Corning glass substrate. The material employed to prepare the films was synthetized by the hydrothermal method. For comparative purposes, the BiVO₄ was synthesized via solid state reaction and deposited in film form by the same technique. From the X-ray diffraction structural characterization it has been stated that BiVO₄ films crystallized in the monoclinic structure. The characterization of BiVO₄ films was complemented with scanning electron microscopy, which revealed a morphology of irregular form and dendritic type depending on the starting material. The thickness of the BiVO₄ films were determined by profilometry. The film obtained from the hydrothermal method showed minor photoluminescence, i.e., the sample showed low recombination of electron–hole pairs. The highest photocatalytic activity in the degradation of tetracycline (TC) was presented for the BiVO₄ films obtained from hydrothermal powders under simulated sunlight irradiation; attributed mainly to the surface area value, smaller particle size and lower recombination of electron–hole pairs. Mineralization degree of TC by BiVO₄ films was determined by the total organic carbon analysis, reaching 50% after 24 h of irradiation. The main oxidizing species that was most influenced in the degradation of TC was the hydroxyl radical (OH^·).

     

Concentration specific and tunable photoresponse of bismuth vanadate functionalized hexagonal ZnO nanocrystals based photoanodes for photoelectrochemical application

In the present work, dual layer BiVO₄/ZnO photoanode is instigated for photo-electrochemical (PEC) water splitting applications. Two different photocatalytic layers ZnO and BiVO₄, reduces charge carrier recombination and charge transfer resistance at photoanode/electrolyte junction. The concentration-specific, tunable and without ‘spike and overshoot’ features, photocurrent density response is originated by varying BiVO₄ concentration in the BiVO₄/ZnO photoanode. The crystal structure of ZnO (hexagonal wurtzite structure) and BiVO₄ (monoclinic scheelite structure) is confirmed by X-ray diffraction studies. The band gap of BiVO₄/ZnO was estimated to be ca. 2.42 eV through Kubler-Munk function F(R_∞) using diffuse reflectance spectroscopy. Electrochemical behavior of samples was analyzed with photocurrent measurements, electrochemical impedance, Mott-Schottky plots, bulk separation efficiency and surface transfer efficiency. The maximum photocurrent density of BiVO₄/ZnO photoanode was found to be 2.3 times higher than pristine ZnO sample.0.038 M BiVO₄/ZnO exhibited the highest separation efficiency of 72% and surface transfer efficiency of 64.7% at +1.23 V vs. RHE. Mott-Schottky study revealed the maximum charge carrier density in the same sample.     

Density functional theory study on the electronic and optical properties of three crystalline phases of BiVO4

The differences in the photocatalytic activity of bismuth vanadate in three crystalline phases have been investigated through calculating their electronic structures and optical properties based on density functional theory. Our results indicate that zircon-tetragonal BiVO₄ has a direct and wide band gap, while monoclinic BiVO₄ and scheelite-tetragonal BiVO₄ has indirect and narrow band gaps. The density of states and atom populations of monoclinic and scheelite-tetragonal phases are similar, but slightly different from those of zircon-tetragonal phase. Among three phases, the monoclinic BiVO₄ possesses the largest dipole moment and the lightest effective mass of carriers, which can promote the generation and separation of photo-induced carriers, and subsequently may improve photocatalytic activity.     

Excellent photocatalytic reduction of nitroarenes to aminoarenes by BiVO4 nanoparticles grafted on reduced graphene oxide (rGO/BiVO4)

A novel heterogeneous composite material based on reduced graphene oxide (rGO) and bismuth vanadate (BiVO₄) was prepared and characterized by various techniques such as powder XRD, HRTEM, EADX, UV–Vis‐DRS, FT‐IR, Raman, BET and XPS analyses. The characterization results reveal that the rGO well decorated by BiVO₄. The electrochemical impedance spectroscopy (EIS) shows the increasing of charge transfer of rGO/BiVO₄ in presence of light irradiation. In this research, the pure BiVO₄ and rGO/BiVO₄ composite have been explored for photocatalytic reduction of nitroarenes. Among the prepared nanocomposites, rGO loaded with 10% BiVO₄ catalyst (noted as rGO/BiVO₄–10%) shows the best performance for the photo‐reduction of various nitroaromatic molecules to their corresponding amine compounds under visible‐light irradiation at room temperature. The catalyst exhibited in particular excellent photocatalytic activity for the conversion of 1,4‐dinitrobenzene to 4‐nitroanilline (100% conversion) in 20 min, 4‐chloronitrobenzene to 4‐chloroaniline and 2‐nitrophenol to 2‐aminophenol (100% conversion) in only 30 min. In addition, the conversion of 4‐bromonitrobenzene, 4‐iodonitrobenzene to their corresponding amine compounds (100% conversion) was achieved in 60 min. The catalyst was recovered for several times and reused without decreasing of its efficiency.     

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.     

磁性BiVO4可见光催化材料的制备及光催化性能

采用水相沉淀法,以Fe3O4粒子为核心,令BiVO4沉淀附着于其上,制备了一种更易于从溶液中分离的磁性BiVO4可见光催化材料,以XRD、SEM、UV-Vis DRS、低温氮吸附-脱附等对其进行了表征。结果表明制备的磁性BiVO4为单斜白钨矿型,颗粒呈片状,粒径比普通BiVO4有所增大,在可见光区的吸收更强,吸收边红移程度随Fe3O4含量增加而增大,但比表面积并没有明显改变。并以可见光(λ≥400 nm)为光源,以亚甲基蓝溶液模拟染料废水,考察了其可见光催化活性,发现与纯BiVO4相比,磁性BiVO4具有更为良好的催化性能。通过考察各催化剂的DRS图谱以及暗反应后亚甲基蓝的浓度,发现这种降解效率上的提高是禁带宽度(Eg)降低、可见光吸收增加和对亚甲基蓝吸附量增大综合作用所导致的。这种吸附量的提升与比表面积无关,本工作以等电点的影响来解释此原因。     

四角星形BiVO4/Bi2O3催化剂的制备及性能

采用水热法合成具有四角星形貌的钒酸铋,再将钒酸铋浸渍在碱溶液里二次水热,制备出BiVO_4/Bi_2O_3催化剂。采用X射线粉末衍射(XRD)、扫描电子显微镜(SEM),紫外-可见漫反射(UV-Vis DRS)等方法对样品进行表征。可见光下,BiVO_4/Bi_2O_3复合物的光催化降解罗丹明B性能及光电流响应均优于纯BiVO_4。这是由于BiVO_4/Bi_2O_3复合材料形成了异质结构,有效抑制了光生电子与空穴的复合效率。     

四角星形BiVO4/Bi2O3催化剂的制备及性能研究

采用水热法合成具有四角星形貌的钒酸铋,再将钒酸铋浸渍在碱溶液里二次水热,制备出BiVO₄/Bi₂O₃催化剂。采用X射线粉末衍射(XRD)、扫描电子显微镜(SEM),紫外-射(UV-Vis DRS)等方法征。可见光下,BiVO₄/Bi₂O₃复合物的光催化降解丹明B性能及光电优于纯BiVO₄。BiVO₄/Bi₂O₃复合材料形成了异质结构,有效抑制了光电子与空穴的复合效率。     

Enhanced visible-light photocatalytic activities of porous olive-shaped sulfur-doped BiVO4-supported cobalt oxides

Porous S-doped bismuth vanadate with an olive-like morphology and its supported cobalt oxide (y wt% CoO_x/BiVO_4−δS_0.08, y = 0.1, 0.8, and 1.6) photocatalysts were fabricated using the dodecylamine-assisted alcohol-hydrothermal and incipient wetness impregnation methods, respectively. It is shown that the y wt% CoO_x/BiVO_4−δS_0.08 photocatalysts were single-phase with a monoclinic scheetlite structure, a porous olive-like morphology, a surface area of 8.8–9.2 m²/g, and a bandgap energy of 2.38–2.41 eV. There was the co-presence of surface Bi⁵⁺, Bi³⁺, V⁵⁺, V³⁺, Co³⁺, and Co²⁺ species in y wt% CoO_x/BiVO_4−δS_0.08. The 0.8 wt% CoO_x/BiVO_4−δS_0.08 sample performed the best for methylene blue degradation under visible-light illumination. The photocatalytic mechanism was also discussed. We believe that the sulfur and CoO_x co-doping, higher oxygen adspecies concentration, and lower bandgap energy were responsible for the excellent visible-light-driven catalytic activity of 0.8 wt% CoO_x/BiVO_4−δS_0.08.