Photocatalytic Ability And Mechanism Of MoS₂/g-C₃N₄ Composite For Reduction Of U（Ⅵ） In Aqueous Soluiton

The removal and recovery of uranium from wastewater is an important issue in the protection of environment.However,the production and reprocessing of nuclear fuel have produced a large amount of uranium-containing radioactive wastewater.U（Ⅵ）and U（Ⅵ）are the main valence state in the aqueous solution,where U（Ⅵ）shows high water solubility and high mobility,but U（Ⅵ）easily forms insoluble oxides.Therefore,reduction of soluble U（Ⅵ）to insoluble U（IV）has been considered as an effective approach for U（Ⅵ）removal from solutions in this study.The photocatalytic reduction of U（Ⅵ）with advantages of the environmental friendliness,mild conditions,low cost and high efficiency has attracted increasing attentions.It is the key to design highly efficient photocatalysts for U（Ⅵ）.Metal-free semiconductor of graphitized carbon nitride（g-C₃N₄）has a medium band gap of 2.7 e V and a corresponding optical wavelength of 460 nm,making it effective in visible light.In addition,it also presents the characteristics of easy preparation,and has become a hot topic of photocatalytic reduction of U（Ⅵ）in recent years.However,g-C₃N₄ has a low specific surface area,a high photoelectron-hole pair recombination rate,low visible light utilization rate and low quantum yield,and difficult to separate the g-C₃N₄ photocatalyst from the solution.Therefore,it is an urgent to improve the photocatalytic activity of g-C₃N₄.In order to solve the problem,the material of molybdenum disulfide（MoS₂）with high specific surface area and strong light-capturing capacity has utilized to form g-C₃N₄/MoS₂composite.And,phosphorus or boron doping of g-C₃N₄ have applied to solve the shortage of low visible light utilization and low quantum yield.The specific research contents of this thesis show as follows:（1）Synthesis,photocatalytic ability and mechanism of MoS₂/g-C₃N₄ composite for reduction of U（Ⅵ）.The MoS₂/g-C₃N₄ composite was prepared by calcination method and ultrasonic method.The MoS₂/g-C₃N₄ photocatalyst has analyzed by a series of characterizations such as XRD,TEM,XPS,and UV-vis.By introducing MoS₂ into g-C₃N₄,the band gap width of was narrowed,and the separation efficiency and carrier mobility of photogenerated electron-hole pairs of photocatalytic material have been improved.And the recombination of photo-generated electron-hole pairs were inhibited,also the band gap of g-C₃N₄ were reduced.The experimental results of photocatalytic reduction of U（Ⅵ）show that the doping of molybdenum disulfide can significantly improve the photocatalytic reduction of U（Ⅵ）.Among them,3%MoS₂/g-C₃N₄ sample material showed the optimal activity.The reduction rate was approximately 2.5 times higher than that of g-C₃N₄,and the degradation rate can reach 95%in 60 minutes.（2）The MoS₂/P-g-C₃N₄composite was prepared by calcination method and ultrasonic method.The MoS₂/P-g-C₃N₄ photocatalyst was analyzed by a series of characterizations such as XRD,TEM,XPS,and UV-vis.By introducing P into g-C₃N₄,the electronic structure was significantly controlled.And the photocatalytic activity was enhanced under visible light.And the recombination of photo-generated electron-hole pairs were inhibited,also the band gap of g-C₃N₄ were reduced.The experimental results of photocatalytic reduction of U（Ⅵ）show that the doping of P can significantly improve the photocatalytic reduction of U（Ⅵ）.Among them,3%MoS₂/P-g-C₃N₄ sample material showed the optimal activity.The reduction rate was approximately 4 times higher than that of g-C₃N₄,and the degradation can reach 93%in 40 minutes.（3）The MoS₂/B-g-C₃N₄ photocatalyst was analyzed by a series of characterizations such as XRD,TEM,XPS,and UV-vis.By introducing B element into g-C₃N₄,the visible light absorption was enhanced,and the charge separation was improved.The experimental results of photocatalytic reduction of U（Ⅵ）show that the doping of B can significantly improve the photocatalytic reduction of U（Ⅵ）.Among them,3%MoS₂/B-g-C₃N₄sample material showed the optimal activity.The reduction rate was approximately 9 times higher than that of g-C₃N₄,and the degradation can reach 95.7%in 20 minutes.The results of above research provide theoretical and experimental basis for the direction of photocatalytic reduction of U（Ⅵ）in future,and also provide technical support for commercial application of photocatalytic reduction of U（Ⅵ）.