Spherical BiVO4 Research Articles

Generation of strong oxidizing radicals from plate-like morphology of BiVO4 for the fast degradation of crystal violet dye under visible light

Highly crystalline bismuth vanadate (BiVO4) powder was prepared by a template-free hydrothermal method under different pH (~ 2, 3, 5, 8, 11) reaction conditions and characterized by X-ray diffraction, scanning electron microscopy, Raman spectroscopy, Brunauer–Emmett–Teller surface area, photoluminescence, and electron spin resonance techniques. It was found that variation in pH of the precursor solution can influence morphology, structure and, consequently, photocatalytic efficiency of obtained products. The spherical BiVO4 nanoparticles were obtained at pH 2 and 3, nanorods at pH 5 and 8, whereas nanoplates were obtained at pH 11. Among the different pH-based BiVO4 samples, the one prepared at pH ~ 11 (BiVO4-11) exhibited surface area 102.74 m2/g and degraded the dye solution completely within 90 min. Therefore, pH-controlled hydrothermal reaction can be useful to synthesize nanostructures with different morphologies efficiently for the enhanced photocatalytic degradation of pollutant under visible light.

Bacitracin-assisted synthesis of spherical BiVO4 nanoparticles with C doping for remarkable photocatalytic performance under visible light

The spherical BiVO4 nanoparticles with C doping were fabricated by using bacitracin as a biological template through hydrothermal-calcination method. And the prepared photocatalysts have excellent photocatalytic performance under visible light.

Effects of morphology on the visible-light-driven photocatalytic and bactericidal properties of BiVO4/CdS heterojunctions: A discussion on photocatalysis mechanism

BiVO4/CdS composites with different morphologies and mass ratios were successfully prepared via a facile deposition-precipitation method by adding different dispersants. Compared with spherical BiVO4 (BS), sheet-like BiVO4 nanoarrays (BA) showed higher (020) exposed areas, as confirmed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). X-ray photoelectron spectroscopy (XPS) revealed further details on the microstructure of the composites namely, CdS was deposited on the surface of BiVO4 forming an S-(111) interface layer. The photocatalytic properties of the samples were tested by studying the degradation of Rhodamine B (RhB) and the sterilization of Escherichia coli (E. coli) under visible-light irradiation. The BAC-60 sample showed the best photocatalytic performance among all the catalysts owing to its: (i) improved high separation efficiency of the photo-induced charge carriers and (ii) high exposure activity of the (020) plane. Electrochemical tests with non-equilibrium carrier injection and free radical trapping experiments are introduced to analyze the mechanism, such as the effects of different crystal planes on the photocatalytic reaction and the flow direction of carriers at the CdS–BiVO4 interface.

Radiative and non radiative recombinations study in the novel nanocomposites BiVO4/3DOM-TiO2, ZnO/3DOM-TiO2 and BiVO4/3DOM-ZnO: Application to the photocatalysis

A theoretical investigation of optical proprieties of three nanostructures such as BiOV4/3DOM TiO2, ZnO/3DOM TiO2 and BiOV4/3DOM ZnO has been presented and discussed. The study based on a one band effective mass approximation model was developed to calculate the charge carrier energies on various parameters of nanostructures including their size. We computed the optical properties for both spherical BiVO4 and ZnO nanoparticles incorporated in the three dimensionally ordered macroporous inverse opal TiO2 nanocomposites (3DOM-TiO2). At first and by solving a three dimension Schrödinger equation we calculated the dependence of charge carriers energies on the size of nanoparticles. Then we investigated the variation of the excitonic energy of BiOV4/3DOM-TiO2, ZnO/3DOM-TiO2 and BiOV4/3DOM-ZnO as function of the radius of these nanostructures into taken account the effects of dielectric and coulomb interaction between charge carriers. We showed that the radiative recombination lifetime is enhanced with decreasing BiVO4 and ZnO quantum dots (QDs) size. It was found that as the size of the dot is reduced the confinement of charge carriers and the optical gap are increased. The optical gap of the ZnO/3DOM-TiO2 is larger than both BiOV4/3DOM-TiO2 and BiOV4/3DOM-ZnO especially for small radius. It was also found that radiative life time in the BiOV4/3DOM-TiO2, ZnO/3DOM-TiO2 and BiOV4/3DOM-ZnO increased by increasing the radius of these nanostructures. In addition, we have also showed that, the radiative lifetime in the ZnO/3DOM-TiO2 nanostructure is less than both BiOV4/3DOM-TiO2 and BiOV4/3DOM-ZnO nanostructures. Finally, we have studied and discussed the Auger process in BiOV4/3DOM-TiO2, ZnO/3DOM-TiO2 and BiOV4/3DOM-ZnO nanostructures. At first, we have showed that the auger process is important when the radiuses of nanostructures are less than 2 nm. Then we have also showed that this process is more important for ZnO/3DOM-TiO2 compared to the other nanostructures.

Comparison of Synthetic Routes for Large-scale Synthesis of Spherical BiVO4 with Photocatalytic and Superhydrophobic Properties

The spherical BiVO4 in tetragonal and monoclinic scheelite phases have been prepared through five general methods by using K6V10O28·9H2O as self-sacrifice templates. Morphology of these BiVO4 is kept spherical because of K6V10O28·9H2O as self-sacrifice templates. The microwave-assisted synthesis of tetragonal BiVO4 is convenient and ultrasonic synthesis is the best choice for the synthesis of monoclinic BiVO4.

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.

Experimental and theoretical study of optical properties and quantum size phenomena in the BiVO4/TiO2 nanostructures

Novel BiVO4/3DOM TiO2 nanostructure has been synthesized by hydrothermal method. BiVO4 nanoparticles and TiO2 inverse opal structure have also been prepared as reference. The prepared samples were characterized by Diffuse reflectance UV–Visible and photoluminescence (PL) spectroscopy. The absorption spectra of BiVO4/TiO2 nanocomposite samples show an absorption edge in the visible region, suggesting the potential application of this composite as an active visible-light driven photocatalysts. Theoretically quantum confinement phenomena and size dependent optical properties of BiVO4 quantum dots have been also studied. Using the effective mass approximation model, we computed the optical properties for spherical BiVO4 nanoparticles incorporated in TiO2 matrix. The size dependent of charge carrier’s energies were calculated. The result shows that the confinement energy decreases with increase the size of BiVO4 nanoparticles. Dielectric properties of the BiVO4 nanoparticles were investigated and it was found that the dielectric constant decreases significantly as the size is reduced as a result the exciton energy decreases. It has been also found that the radiative recombination lifetime is concurrently enhanced with decreasing BiVO4 QDs size.

Visible light photocatalysis and electron emission from porous hollow spherical BiVO4 nanostructures synthesized by a novel route

Hollow spheres of BiVO4, made of pyramid like nanocrystals have been synthesized in an aqueous medium through a precursor solution mediated growth method with appropriate amount of polyvinyl alcohol (PVA). It was found that concentration of PVA in the precursor solution played a crucial role in determining the morphology of the product. Hollow spherical BiVO4 was formed with PVA concentration of 64mg/mL in the precursor solution while with 32mg/mL PVA concentration mixed morphology of hollow spherical and cubical structure was formed. Without adding PVA, only cubical (bulk like) BiVO4 powder was obtained. The structures have been characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), Fourier-transformed infrared (FTIR) spectroscopy, UV–Vis spectroscopy, thermogravimetry analysis (TGA) and differential thermal analysis (DTA). As-prepared hollow spherical BiVO4 samples were having monoclinic structure with energy band gap 2.42eV. The hollow spherical BiVO4 exhibited excellent visible-light-driven photocatalytic efficiency for degrading N,N,N′,N′-tetraethylated rhodamine (RhB) organic dye, which was nearly 13 times efficient than that of the samples prepared by the same method but without PVA in the precursor solution. After five recycles, the hollow spherical BiVO4 catalyst did not exhibit any significant loss of photocatalytic activity, confirming the photocatalyst is essentially stable. The BiVO4 hollow spheres also exhibited electron field emission indicating that BiVO4 with tailored morphology can be used as a multi-functional material.

Controllable Synthesis and Photocatalytic Activity of Spherical, Flowerlike and Threadlike Bismuth Vanadates

Spherical, flowerlike, and threadlike bismuth vanadates (BiVO4 ) were synthesized via a controllable hydrothermal method without using any surfactant or template. The optical and photocatalytic properties of the BiVO4 samples were investigated. The phase structures of the BiVO4 samples were observed by X-ray diffraction (XRD), which indicated that the as-prepared samples possessed monoclinic cells. Transmission electron microscope (TEM) observations showed that BiVO4 crystals with different morphologies were fabricated simply by manipulating the parameters of the hydrothermal reaction. On the basis of the structural analysis of samples obtained under different conditions, a possible mechanism for the formation of these distinct morphologies was proposed. UV-visible diffuse reflectance spectra (UV-Vis DRS) of the samples revealed that the band gaps of the BiVO4 photocatalysts were about 2.19-2.33 eV. The as-prepared BiVO4 photocatalysts exhibited higher photocatalytic activities toward the degradation of rhodamine B (RhB) under visible light irradiation (λ 420 nm) than commercial P25 TiO2 and traditional N-doped TiO2 (N-TiO2 ). Spherical BiVO4 showed the highest photocatalytic activity of the samples, decolorizing up to 100% of RhB upon visible light irradiation for 180 min. The reason for the different photocatalytic activities of the BiVO4 samples fabricated at different pH was systematically studied by considering their structure and morphology.

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.

Hydrothermal fabrication and visible-light-driven photocatalytic properties of bismuth vanadate with multiple morphologies and/or porous structures for Methyl Orange degradation

Monoclinic BiVO4 with multiple morphologies and/or porous structures were fabricated using the hydrothermal strategy. The materials were characterized by means of the XRD, Raman, TGA/DSC, SEM, XPS, and UV-Vis techniques. The photocatalytic activities of the BiVO4 materials were evaluated for the degradation of Methyl Orange under visible-light irradiation. It is observed that pH value and surfactant exerted a great effect on the morphology and pore structure of the BiVO4 product. Spherical BiVO4 with porous structures, flower-cluster-like BiVO4, and flower-bundle-like BiVO4 were generated hydrothermally at 100°C with poly(vinyl pyrrolidone) (PVP) and urea (pH = 2) and at 160°C with NaHCO3 (pH = 7 and 8), respectively. The PVP-derived BiVO4 showed much higher surface areas (5.0–8.4 m2/g) and narrower bandgap energies (2.45–2.49 eV). The best photocatalytic performance of the spherical BiVO4 material with a surface area of 8.4 m2/g was associated with its higher surface area, narrower bandgap energy, higher surface oxygen vacancy density, and unique porous architecture.

Microemulsion synthesis and photocatalytic activity of visible light-active BiVO4 nanoparticles

A water-in-oil microemulsion made up of a cyclohexane/n-hexyl alcohol/Polyethylene glycol tertoctylphenyl/aqueous solution including Bi3+ and VO3+ ions yields the spherical BiVO4 precursors with the size from 5 to 300 nm. Well-crystallized monoclinic scheelite BiVO4 particles with nanometer or micrometer size are fabricated in control by heating microemulsion precursors under various temperatures. The corresponding nucleation and growth process of as-prepared samples has also been investigated via TEM, which demonstrates the detailed morphological evolution of nuclei inside the precursors. As-prepared BiVO4 photocatalysts exhibit enhanced photocatalytic activity under visible-light irradiation in comparison with the bulk BiVO4 prepared by solid-state reaction. The highest RB degrading efficiency of 98% in 180 min under visible-light irradiation is observed for the sample calcined at 600 °C.

Flame-assisted synthesis of nanoscale, amorphous and crystalline, spherical BiVO4 with visible-light photocatalytic activity

The synthesis of bismuth vanadate (BiVO4) nanoparticles has drawn considerable attention to their application as a visible-light-driven photocatalyst. Several techniques are addressing the enlargement of surface area, but some of them can cause impurities and lower the performance of the material. In this work, flame spray synthesis technique was used as a simple, easy upscalable technique to produce BiVO4 powders. The effect of process parameters on particle properties such as size, morphology and crystallinity were investigated by several techniques: BET, XRD, DSC, TEM, DRS and ζ potential. Spherical BiVO4 nanoparticles with either amorphous or monoclinic phase-pure crystal structure, along with specific surface areas (SSA) between 10 and 75m2g−1 were obtained by a setup including an in situ crystallization step at T≥ 270°C on the powder collection site, sometimes followed by a mild or severe annealing post-treatment. Traditional synthesis routes usually require such annealing post-treatment which implies considerable loss of SSA. The photocatalytic activity of the as-prepared powders was investigated by the degradation of the cationic dye methylene blue (MB). N-demethylation of the dye was clearly identified as one of the degradation pathways, while ring cleavage was only observed with crystalline samples. Crystallinity and SSA were crucial parameters for the photocatalytic activity of different samples of BiVO4 depending on the pH of the solutions. The control of these two parameters during the synthesis of BiVO4 qualifies this method for a potential large scale production.