Preparation Of G-C₃N₄-Bi₂O₃/Al₂O₃ Material And Characteristics Of Visible Light Catalytic Reduction Of U（Ⅵ） In Water

Uranium in the wastewater discharged from uranium mining,processing and enrichment is mainly hexavalent uranium,which mostly exists in the form of uranyl ion(UO₂²⁺).Existing reduction method to remove its pollution.In the process of the treatment of uranium-containing wastewater,the hexavalent uranium U（Ⅵ）with strong mobility and easy solubility in water is reduced to the tetradent uranium U（IV）with weak mobility and hard solubility in water,thus achieving the separation of U（Ⅵ）from water.The graphite-phase carbon nitride（g-C₃N₄）has a typical 2D lamellar structure and a suitable band gap（2.70e V）.However,the shortcomings of pure g-C₃N₄,such as high electron-hole recombination rate,low visible light utilization efficiency and low specific surface area,restrict the photocatalytic application of g-C₃N₄.We first prepared g-C₃N₄material by calcination method,and then prepared carbon nitride-bismuth oxide-alumina（g-C₃N₄-Bi₂O₃/Al₂O₃）photocatalyst by thermal polymerization method,which will be used for photocatalytic reductionExperimental results of photocatalytic reduction of U（Ⅵ）of g-C₃N₄-Bi₂O₃/Al₂O₃under visible light irradiation show that when the mass ratio of Al₂O₃,g-C₃N₄and Bi₂O₃is 3:2:1,p H=5,the dosage of ternary composite was 0.50g/L,and the U（Ⅵ）removal rate reached98.71%after dark reaction for 30min and light reaction for 60min.Its removal rate is 3.27 times that of uncomplicated material g-C₃N₄and Bi₂O₃,and 1.32 times that of binary composite g-C₃N₄-Bi₂O₃.On this basis,the active species in the U（Ⅵ）photocatalytic process of g-C₃N₄-Bi₂O₃/Al₂O₃composite photocatalyst were captured.The experimental results show that the addition of p-benzoquinone（BQ）and potassium persulfate obviously reduces the photocatalytic reduction efficiency of U（Ⅵ）.XPS characterization of the ternary composites showed that U（Ⅵ）in the solution was reduced to U（IV）.Photogenerating electron（e^-）and superoxide radical（·O₂^-）are the main factors involved in the reduction of U（Ⅵ）to U（IV）.The repeatability test results of g-C₃N₄-Bi₂O₃/Al₂O₃show that the photocatalytic reduction efficiency of U（Ⅵ）can reach 85.13%after 5cycles,which indicates that the catalyst has good stability and cycling ability.g-C₃N₄-Bi₂O₃/Al₂O₃provides a new idea for the subsequent high-efficiency photocatalytic reduction of low-concentration uranium-containing wastewater.