Thesis Preparation Of Bismuth Tungstate-based Photocatalyst And Removal Of U(Ⅵ) In Aqueous Solution

Uranium is a fission element and an important resource in the development and utilization of nuclear energy.However,in the process of uranium extraction,smelting,the use of nuclear fuel and reprocessing,a large amount of radioactive waste liquid containing uranium will be produced.If the waste liquid is not treated properly,it will result in waste of nuclear resources and radioactive contamination.Therefore,how to realize the effective separation and enrichment of uranium elements in radioactive waste liquid has important research value and practical significance.In recent years,with the development of photocatalytic technology,it provides a new idea for removing uranium ions from wastewater.Among them,the photocatalyst with bismuth-based structure shows great application prospect because of its obvious absorption in the visible light range.It is of potential application value to use bismuth-based materials to treat uranium-containing radioactive wastewater.The Cu-Bi₂WO₆ and Bi₂O₃/Bi₂WO₆ composite photocatalysts were prepared by hydrothermal method and hydrothermal calcination method.the composite photocatalysts were characterized and analyzed by SEM、EDS、XRD、XPS、FT-IR、BET、Zeta potential,UV-vis、EIS and PEC.The photocatalysts were used to remove U（Ⅵ）from solution.The paper studied the enhancement mechanism of adsorption and photocatalytic activity.（1）The Bi₂WO₆ materials were prepared by hydrothermal and Cu were doped into Bi₂WO₆.The surface morphology,crystal configuration,elemental composition and optical properties of the materials were analyzed from the microscopic level by various characterization methods.The adsorption and photocatalytic reduction of U（Ⅵ）in silution by Cu-Bi₂WO₆ under different conditions were explored.The results showed that at solution p H=5.5,solid-liquid ratio was 0.4g/L,U（Ⅵ）initial concentration was 10 mg/L,the removal rate of U（Ⅵ）at dark reaction（40 min）by 10%-Cu-Bi₂WO₆ material reached 85%,and the U（Ⅵ）was removed by adsorption.Kinetic and Isothermal adsorption studies showed that the adsorption process conforms to the quasi-second-order kinetic model and the Langmuir isothermal adsorption model and is a spontaneous endothermic and entropy increase reaction.Subsequently,when exposed to visible light and 8%methanol was added,the removal rate of U（Ⅵ）reached about 94%.The removal mode was photocatalytic reduction.The reduction kinetic study showed that the photocatalytic reaction was in accordance with the first-order kinetic.At the same time,the first-principles calculation showed that the Cu-Bi₂WO₆ doping system increases the visible light response range and then improves the photocatalytic activity.（2）The Bi₂O₃/Bi₂WO₆ catalysts with different Bi³⁺/WO₄^2-proportions were prepared by hydrothermal calcination.The properties of the catalysts were characterized and analyzed,and the effects of different conditions on the adsorption and photocatalytic reduction of U（Ⅵ）by Bi₂O₃/Bi₂WO₆ catalysts were investigated.The results showed that the removal rate of U（Ⅵ）in dark reaction（40 min）was 88%when the solution p H=5.5,the solid-liquid ratio was 0.6g/L,and the initial concentration of U（Ⅵ）was 10 mg/L,Bi³⁺/WO₄^2-=2.4:1,and the removal mode was mainly adsorption.Kinetic and Isothermal adsorption studies showed that the adsorption process conforms to the quasi-second-order kinetic model and the Langmuir isothermal adsorption model and reaction is a spontaneous endothermic entropy increase.Subsequently,under visible light irradiation and the addition of 6%methanol,the removal rate of U（Ⅵ）in the solution reached 96%.The removal mode was mainly photocatalytic reduction.The reduction kinetics study showed that the reduction process was in accordance with the first-order kinetic law.（3）By comparing the characterization analysis of single semiconductor catalyst and composite catalyst and the removal efficiency of U（Ⅵ）in solution,the results showed that the composite catalyst has a narrower band gap,higher photoelectric conversion efficiency and better optical absorption performance than the single catalyst,and showed a higher removal efficiency for both adsorption and photocatalytic reactions of U（Ⅵ）in solution.