Microwave-Hydrothermal Synthesis And Characterization Of Bismuth Ferrite Powders

With the development of semiconductor photocatalysts, bismuth vanadate,with its superior chemical properties have recently attracted considerableattention. Scholars committed to developing its potential in the field of catalyticdegradation of pollutants, especially in the photocatalytic activity under visiblelight. The band gap of bismuth vanadate is about2.3-2.4eV, the oxidationpotential is located near2.4eV, in theory, it can be achieved in the visiblepollutants to degrade.In this paper pure monoclinic BiVO₄、tetragonal BiVO₄and mixed crystalwith monoclinic phases and tetragonal phases were synthesized bymicrowave-hydrothermal method by adjusting alkali concentrations of theprecursor solution, reaction temperature and pH value; Cu²⁺has been loaded onBiVO₄to improve the photocatalytic activities, Cu/BiVO₄catalyst has beenprepared by microwave hydrothermal method. TiO₂and BiVO₄has beencompounded obtaining TiO₂/BiVO₄composite photocatalyst. BiVO₄films weresynthesized to solve the problem of photocatalyst load. The phases, structures,morphologies, specific surface area and the light absorption capacity ofphotocatalysts were characterized respectively by XRD, FE-SEM, BET, andUV-vis methods. The photocatalytic activity of the different powders wereinvestigated, and Conclusions are as follows:1pure monoclinic BiVO₄、tetragonal BiVO₄and mixed crystal withmonoclinic phases and tetragonal phases were synthesized bymicrowave-hydrothermal method by adjusting alkali concentrations of theprecursor solution, using Bi（NO₃）₃·5H₂O and NH₄VO₃powders as raw materials.The powder prepared under the precursor dissolved deionized water was BiVO₄mixed crystal with monoclinic phases and tetragonal phases; When the precursorwas dissolved into HNO₃and NaOH solutions, the as-prepared powder wasmonoclinic phases; When the concentration of NaOH was increased to4mol/L,the powder became the mixed crystal. The photocatalytic activity of the mixed crystal with monoclinic and tetragonal phases highter than pure monoclinicphases.2Different BiVO₄phase were synthesized by microwave-hydrothermalmethod at160-220℃, using Bi（NO₃）₃·5H₂O, NH₄VO₃and citric acid as rawmaterials. When the temperature at160℃and180℃，Products was tetragonalphases BiVO₄. The mixed crystal with monoclinic phases and tetragonal phasesBiVO₄was obtained at200℃and220℃.The BiVO₄powders synthesized at160℃was spherical with some floc structure. The degradation rate of RhBsolution was97.8%under the UV light after100min.3Pure monoclinic BiVO₄was synthesized by microwave-hydrothermalmethod at different pH value, using Bi（NO₃）₃·5H₂O and NH₄VO₃powders asraw materials. The samples prepared at pH=1.40-7.04were mixed phases. WhenpH value increased to10.07，the products were pure monoclinic phases. WhenpH=1.40, tetragonal and monoclinic mixed phase BiVO₄crystal, has bestphotocatalytic activity, the degradation rate of RhB up to90.0%under the visiblelight after240min. Usingthe pure monoclinic BiVO₄prepared at pH=7.04asphotocatalysis，the degradation rate was88.2%.4Cu/BiVO₄catalyst has been prepared by microwave hydrothermal method,at200℃using Bi（NO₃）₃·5H₂O, NH₄VO₃and citric acid as raw materials. Thecrystal was not changed after introducing Cu²⁺. The absorption band has red shiftto550-560nm, and enhances the absorption in the visible light range.TheCu/BiVO₄of doping content of2at.%under UV and visible light, the RhBdegradation rate respectively up to95%for4.5h,90%for6h.5TiO₂/BiVO₄catalyst has been prepared by microwave hydrothermalmethod, at200℃using Bi（NO₃）₃·5H₂O, NH₄VO₃and citric acid as raw materials.The absorption band located at550-560nm, and enhances the absorption in thevisible light range. The TiO₂/BiVO₄of doping content of20at.%under UV andvisible light, the RhB degradation rate respectively up to85%for5.5h,85%for6h.6BiVO₄films were synthesized by sol-gel method under different molarratios of Bi and V. The pure mBiVO₄films could be synthesized under thesolutions with Bi: V of1:1and1:1.2. As the molar ratios of Bi and V wasincreased to1.5, the films were composited with BiVO₄and V₄O₉;Bi₂O₂.75/ BiVO₄photocatalysts could obtain when Bi: V=1:0.8. Compared with pureBiVO₄，the composite films prepared at Bi:V=1:0.8and Bi:V=1:1express thehigher photocatalytic efficiency.