Research On Photocatalytic Reduction Of Carbon Nitride Hollow Spheres And Its Composites

In solving the two problems of energy shortage and environmental pollution,photocatalytic technology has broad application prospects.In this thesis,a series of researches are carried out on carbon nitride hollow spheres.Carbon nitride hollow spheres not only have the advantages of carbon nitride itself being metal-free,cheap,and non-toxic,but also have better physical and chemical stability and thermal stability,excellent surface properties and stronger visible light response,which can be used in photolysis water,carbon dioxide reduction,photocatalytic degradation of organic pollutants and other aspects have shown excellent performance.Although the carbon nitride hollow sphere has many good physical and chemical properties,it still has many problems.The nature of carbon nitride polymer makes it have a serious photo-generated electron-hole pair recombination phenomenon in the reaction process,and the high exciton binding energy limits the kinetics of the catalytic reaction.These problems restrict the development of this material.In view of these problems,this article mainly studies the following contents in order to improve the photocatalytic performance of the catalyst:（1）Open hollow microsphere carbon nitride with nitrogen defectsIn order to fully tap the surface performance potential of carbon nitride hollow spheres,based on the template method synthesis of hollow carbon nitride microspheres,the open hollow microsphere carbon nitride with nitrogen defects（OHCNs）were obtained by controlling the amount of precursors.And explore the changing laws of its surface properties and catalytic activity.The results show that OHCNs not only have a larger surface area and porosity,but also form nitrogen defects on the surface of the catalyst,which improves the photoelectric conversion performance and the separation efficiency of electron-hole pairs,and significantly improves the photocatalytic activity.The photocatalytic activity is the best when the mass ratio of the material to the template is 1:1.（2）1T-MoS₂ modified hollow carbon nitride microspheresPolymeric carbon nitride excitons have high binding energy and low catalytic reaction kinetics rate,and generally require the assistance of a promoter.Therefore,this study uses a two-dimensional transition metal sulfide MoS₂ as a promoter to modify the surface of carbon nitride hollow spheres,and explore the mechanism of MoS₂ affecting the catalytic reaction.The research results show that MoS₂ reduces the hydrogen overpotential of the carbon nitride microspheres and improves the kinetics of the photolysis water reaction.In addition,the excellent conductivity of MoS₂ improves the separation efficiency of photogenerated carriers,thereby improving the performance of photocatalytic hydrogen production.（3）Low-temperature copolymerization of carbon nitride hollow spheresThe thiophene monomer is selected and the copolymerization method is adopted to control the polymerization process of the carbon nitride hollow sphere.Considering that the hollow spheres of carbon nitride prepared by high-temperature polymerization collapse seriously,a low-temperature solvothermal copolymerization method was used to synthesize the hollow sphere catalyst.The results show that the successful grafting of thiophene into the carbon nitride molecular framework not only improves the visible light absorption performance,but also improves the serious problem of photo-generated carrier recombination of the catalyst.Through copolymerization modification,CNS photodegradation activity of methyl orange is significantly improved,which is 1.34 times that of CN.