Preparation And Modification Of Graphitic Carbon Nitride For Photocatalytic Evolution Of Hydrogen

With the excessive exploitation and utilization of the fossil energy,the energy crisis and environmental pollution have become the most serious and urgent need to address these problems.Solar energy becomes one of the ideal energy since it is a clean,renewable and cheap energy.Photocatalytic technology has become an ideal way to solve the energy crisis and environmental pollutions.However,the practical applications of the traditional TiO2 photocatalytic material is greatly limited due to its low quantum efficiency and wide bandgap,which lead to that it can only absorb ultraviolet light and cannot absorb the visible light in the sunlight as the main part.Therefore,it is a hot research topic to study the photocatalytic nanomaterials with strong photocatalytic activity and responsive to visible light.The photocatalytic performance of the bulk graphite-like carbon nitride(g-C3N4)is low due to its small surface area and the quick recombination of photogenerated electron-hole pairs.In order to improve the photocatalytic hydrogen evolution performance of g-C3N4,the preparation,characterization and photocatalytic performance of cobalt-doped g-C3N4 and two-dimensional g-C3N4 nanosheets were studied in this dissertation.The details of this thesis are summarized as follows:(1)Cobalt-doped graphitic carbon nitride(Co-CN)was synthesized by one-step thermal polycondensation using cobalt phthalocyanine(CoPc)and melamine as precursors.The prepared samples were characterized by XRD,FTIR,SEM,TEM,XPS,UV-Vis DRS and PL to disclose their crystal structures,morp hologies,specific surface areas and chemical states,and their photocatalytic performance towards hydrogen evolution was investigated under visible light irradiation.Compare with pure g-C3N4,the specific surface area of the optimized cobalt-doped graphitic carbon nitride(0.46% Co-CN)increases from 13.2 m2/g to 33.1 m2/g,which provides more active sites.The photocatalytic hydrogen evolution rate of 0.46% Co-CN is 3.0 times of that of the pure g-C3N4.This study provides a valuable strategy to modify CN with enhanced photocatalytic performance.(2)The graphite-like carbon nitride nanosheets were prepared by thermal polycondensation of solvothermally-pretreated melamine with N,N-dimethylformamide.The prepared samples were characterized by a series methods to reveal their crystal structures,morphologies,specific surface areas and chemical states,and their photocatalytic performance towards hydrogen evolution was investigated.Under irradiation of visible light,the average H2 evolution rate over the optimized g-C3N4 nanosheets is 53.8 ?mol·h-1,which is 8.3 times of that over the bulk g-C3N4(6.5 ?mol·h-1).The enhancement of photocatalytic performance of the g-C3N4 nanosheets can be attributed to the large specific surface area,the enhanced reduction potential of the photogenerated electrons and efficient separation of photo-generated electron-hole pairs.