Preparation,Modification And Cr（Ⅵ） Photoreduction Activity On BiVO₄ Based Materials

Photocatalytic technology based on semiconductor is environment-friendly and low-cost,which is capable to efficiently reduce toxic Cr（Ⅵ）to low-toxic Cr（Ⅲ）using photoinduced electrons by solar energy.However,photocatalytic technology still connot be applied into wastewater treatment for its low efficiency of light absorption and photocatalytic reaction.Monoclinic BiVO₄ is a green and economic semiconductor photocatalyst with excellent visible light response.A slight difference between{010}and{110}surfaces of monoclinic BiVO₄ formed a surface junction,which led to the photogenerated electrons and holes selectively transfer to{010}and{110}surfaces,respectively.The photoreduction and photooxidation were separated and occurred on the{010}and{110}surfaces.In this study,the surface engineering and selective decoration were used to improve the Cr（Ⅵ）photoreduction efficiency and working-life based on the special advantage of BiVO₄surface junction.（1）Monoclinic BiVO₄ with{010}oriented growth was prepared by hydrothermal process.The differences of physical properties between{010}-BiVO₄ and irregular BiVO₄ were analyzed.The effects of pH values and concentrations of phenol in photoreduction of Cr（Ⅵ）were systematically studied.The results indicated{010}-BiVO₄ showed better photocatalytic activity.{010}-oriented growth increased the amount of active sites on BiVO₄,and improved the selective transfer rates of photoinduced electrons and holes between{010}and{110}facets.（2）Pt nanoparticles and MnO₂ were selectively photo-deposited on the（040）and（220）facets of BiVO₄.Pt nanoparticles would significantly extend the absorption of solar light and enhance the Cr（Ⅵ）photoreduction rate.In the process of Cr（Ⅵ）photoreduction,Mn²⁺-MnO₂ conversion on（220）facets played ternary roles:（a）holes scavenger,（b）co-catalyst and（c）anti-acid protective coat,which improved the working life of BiVO₄ in the acid solution required by Cr（Ⅵ）photoreduction reaction.