| The novel photocatalysts of bismuth compouds have aroused great attention in recent years.Many studies have focused on BiVO4and Bi2WO6for their unique crystal structures, narrowbandgap and excellent photocatalytic performance in the field of catalysis. BiVO4exists in threecrystalline phases, namely monoclinic scheelite, tetragonal zircon, and tetragonal scheelite.Among the three forms, monoclinic scheelite BiVO4(m-BiVO4) exhibits much betterphotocatalytic activity under visible light irradiation for its narrow band gap (2.4eV). Herein,porous BiVO4and BiVO4/Bi2WO6photocatalysts with regular morphologies were synthesized byhydrothermal method and alcohol-hydrothermal method. The as-prepared samples werecharacterized by X-ray powder diffraction (XRD), field-emission scanning electron microscopy(FE-SEM), specific surface area determinator, energy dispersive X-ray analysis (EDS) andUV–vis diffuse reflectance spectra (DRS). The photocatalytic activities of BiVO4andBiVO4/Bi2WO6were investigated through the degradation of RhB under visible light irradiation.The main study results are as follows:(1) BiVO4microcrystals with decahedral and porous spherical morphologies weresuccessfully fabricated via the hydrothermal method using bismuth nitrate and ammoniummetavanadate as raw materials, tetradecyl trimethyl ammonium bromide (TTAB) as surfactant,HNO3or NaOH as pH adjustor.The hydrothermal reaction temperature, time, usage of TTAB andpH value were investigated during the experiment, among which the amount of TTAB and pHvalue had a significant influence on the crystal structure, particulate morphology and even theporous structure of the product. It is found that m-BiVO4with uniform morphology wassynthesized under the optimum reaction temperature of180℃and the optimum reaction time of180min. The monoclinic scheelite BiVO4with different morphologies (irregular granule,polyhedron and decahedron), which had shown bigger specific surface area and better optical absorption and photocatalytic performance than the surfactant free sample of BVO-T0, could beobtained with the TTAB amount of0.5g,1g and1.5g. The RhB photodegradation rates of theas-prepared samples were above26%with the catalyst dosage of50mg. Besides, as for the impactof pH, the results indicate that the BiVO4samples prepared in pH range of1.5-9had differentphases and morphologies. With the increase of pH value, the phase of the crystalline transformedfrom monoclinic BiVO4(pH=1.5-3) to mixture of monoclinic and tetragonal BiVO4(pH=5-9),while the morphology changed from polyhedron (pH=1.5-3) to porous microsphere (pH=5-9).With the pH value of5-7, the as-prepared samples (BVO-T1-5and BVO-T1-7) showed superiorphotocatalytic performance (with the degradation rate of90.4%and catalyst amount of50mg) forthe unique morphology, high specific surface area and good porous structure.(2) Porous hollow microspheres of BiVO4were successfully synthesized with the assistanceof ethylenediamine tetraacetic (EDTA) and sodium dodecylbenzene sulfonate (SDBS) viaalcohol-hydrothermal method using bismuth nitrate and ammonium metavanadate as rawmaterials, ethanol and isopropanol as solvent, HNO3or NaOH as pH adjustor.The hydrothermalreaction temperature, time, ratio of EDTA/SDBS and pH value were investigated during theexperiment. It is found that m-BiVO4with regular morphology was synthesized under theoptimum reaction temperature of180℃and the optimum reaction time of180min. Duringfabrication, the monoclinic crystalline structure was mainly controlled by EDTA, while themorphology was influenced by both of EDTA and SDBS. Aslo, results indicate that an increase inthe amount of EDTA (EDTA/SDBS=2:1-4:1) was helpful to m-BiVO4formation, but too much(EDTA/SDBS=5:1) use might cause a certain degree of inhibition. The porous hollow sphericalsample of BVO-E1-S0.5prepared with the EDTA/SDBS ratio of2:1, which had bigger specificsurface area and better optical absorption and photocatalytic performance (with the degradationrate of46.2%and catalyst amount of50mg) than the surfactant free sample of BVO-E0-S0. Inaddition, with the pH range of1.5-7, the samples of BVO-E0.5-S0.5-1.5, BVO-E0.5-S0.5-3,BVO-E0.5-S0.5-5and BVO-E0.5-S0.5-7were composed of microspheres with loosen particlesstacked inside. As for BVO-E0.5-S0.5-9and BVO-E0.5-S0.5-11(pH=9-11), the spherical structureshad particles stacked closely inside. Among the products, BVO-E0.5-S0.5-11with high proportionof m-BiVO4, small size of microspheres and low band gap energy had shown better photocatalyticactivity (with the degradation rate of54.1%and catalyst amount of50mg) than the other products.(3) BiVO4/Bi2WO6heterojunctions with flower-like and flake-like morphologies weresuccessfully fabricated through the alcohol-hydrothermal method using bismuth nitrate,ammonium metavanadate and sodium tungstate as raw materials, ethanol and isopropanol assolvent, EDTA and SDBS as templates by adjusting the co-growth molar ratios of BiVO4andBi2WO6. The results indicate that with the BiVO4/Bi2WO6ratios of1:1and2:1, the samples of BVO/BWO-E1-S0.5-R1:1and BVO/BWO-E1-S0.5-R2:1were both composed of loosen flower-likestructures. As for BVO/BWO-E1-S0.5-R3:1and BVO/BWO-E1-S0.5-R4:1(BiVO4/Bi2WO6=3:1-4:1),the morphologies existed in flake with porous structures. Besides, all the BiVO4/Bi2WO6heterojunctions with high specific surface area (above9m2·g-1) and narrow band gap had shownbetter RhB degradation rate (catalyst amount of20mg) than BVO-E1-S0.5(with the degradationrate of46.2%and catalyst amount of50mg) prepared under the same condition. Among thecomposite photocatalysts, the product of BVO/BWO-E1-S0.5-R2:1(BiVO4/Bi2WO6=2:1) with highproportions of m-BiVO4and Bi2WO6, loosen flower-like structure, high specific surface area andnarrow band gap, had shown excellent photocatalytic performance (with the degradation rate of69.4%and catalyst amount of20mg). |
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