Research On Graphitic Carbon Nitride Based Hybrid Catalysts For Enhanced Photocatalytic Activity

Graphitic carbon nitride is recently popular as a novel organic photocatalyst for its moderate band gap of 2.7 eV,stability,cost effectiveness and environment friendliness.To date,the photocatalytic property of g-C3N4 is mostly modified by nanostructure design and bandgap engineering,mainly to increase surface area,harvest more visible light or inhibit the bulk re-combination of photogenerated earriers.In this thesis,g-C3N4 is modified through the strategy of integrating semiconductor heterojunction.Two types of traditional semiconductors,manganese oxide(MnOx)and molybdenum disulfide(MoS2),were utilized to be combined with g-C3N4.Through comparative study,it was found that the nano-structural characteristics and surface properties of the two phases would affect the overall photocatalytic properties of the composite material.In the process of constructing the g-C3N4-based composite photocatalyst,in addition to the band structure of the two semiconductors,the combination of the two phases at the microscopic scale is crucial.Loading MnOx directly on the g-C3N4 substrate does not have a significant catalytic effect.Firstly,CeO2 was firstly compounded on the g-C3N4 sheet as a bridging phase,and then the g-C3N4/CeO2/MnOx composites could be successfully constructed by introducing MnOx by chemical impregnation.The Mnox introduced by this method exists in the form of crystals on the edge of the g-C3N4 sheet,and the binding between the MnOx and the base photocatalyst is not tight enough,and the photocatalytic rate does not have a significant increase effect.The two-dimensional/two-dimensional structure of g-C3N4/MoS2 can be successfully obtained by compounding a two-dimensional MoS2 semiconductor on the g-C3N4 substrate,so that the closely-coupled interface promotes the separation of photogenerated carriers and significantly improves the photocatalytic efficiency..Through the experimental conditions,we found that the optimal ratio of g-C3N4/MoS2 was 1.25%MoS2 and the preparation temperature was 550 C.In addition,the pore size structure and the surface properties of the photocatalyst have an important influence on the photocatalytic efficiency.By introducing MoS2 as the second phase,the wrinkles of g-C3N4 are increased microscopically,the number of mesopores of the composites is increased,and the specific surface area of the catalyst is increased,thereby effectively improving the catalytic reaction efficiency.