Study On The Properties And Mechanism Of Photocatalytic Reduction Of UO₂²⁺ By S,P-doped G-C₃N₄

The nuclear industry has brought great development of modern economy,which also produces a large number of nuclear waste.Uranium is a mainly high chemical toxicity and high radioactive nuclear waste,which is harm to human health.How to efficiently and effectively remove uranium pollution is a major environmental problem to be solved urgently.In this project,we will use the photocatalytic reduction technology to remove radioactive uranyl contamination.S and P are introduced in the g-C₃N₄ structure,and electronic structure characteristics of g-C₃N₄ photocatalyst materials have been modified by introducing S and P for effectively reduction elimination of uranyl pollutant under visible-light irradiation.In this project,we developed the doped g-C₃N₄ preparation method through thermal polymerization,and we also studied the effect of doped atom composition,introducing morphology,and content on the light response range and intensity,the valence and conduction band potential,photoelectron generation,migration and use efficiency of the doped g-C₃N₄ in the photocatalytic reduction of uranyl pollution,furthermore the relationship between electron structure and uranyl pollution efficiency of aromatic g-C₃N₄ were determined by qualitative and quantitative characterization,which revealed its photocatalytic reduction mechanism.The results will provide the basis for designing highly effieicnt photocatalyst materials to effectively eliminate uranyl pollutant by photocatalytic reduction technology.The main contents are as follows:?1?Owing to the unique electronic and optical properties,the graphene-like carbon nitride?C₃N₄?materials have attracted widespread interest.However,the exfoliation of bulk C₃N₄ into graphene-like structure is inhibited by the planar hydrogen bond between strands of polymeric melon units with NH/NH2,due to the higher electronegativity of N with respect to C atoms.Herein,graphene-like sulfur-doped C₃N₄?SC₃N₄?samples were successfully prepared by introducing sulfur into C₃N₄ to weaken the planar hydrogen bonding,and investigated as catalysts to photoreductively eliminate uranyl ion in aqueous media.Both experimental and computational perspectives confirmed that S-doping in SC₃N₄ can modify its electronic structure,reflected by the elevated conduction and valence band levels,as well as the improved transportation capability of photogenerated electrons.As a result,the photoactivity for UO₂²⁺ photocatalytic reduction over the optimal SC₃N₄ was significantly improved,with apparent rate value reaching 0.16 min-1 under visible-light irradiation,which was 2.28 times that over C₃N₄.This study provides an effective strategy for designing efficient visible-light-responsive photocatalysts for environmental remediation.?2?P-doped g-C₃N₄ samples were prepared with using tributyl phosphate and urea as precursors.In the experiment,it is found that the photocatalytic activity of g-C₃N₄ based photocatalysts was significantly improved by introducing P into the structures of g-C₃N₄ for the photocatalytic reduction of UO₂²⁺,and the optimum photocatalytic activity was achieved to be 0.11 min-1 under visible light irradiation.Series characterizations revealed that,the wavelength range and the absorption intensity of g-C₃N₄ based photocatalytic materials were enhanced by the doped phosphorus.Moreover,the doped effect can also improve the photogenerated electron-hole separation efficiency and utilization efficiency,and thus increase the activity for photocatalytic reduction of UO₂²⁺.