Preparation Of Nitrogen-oxygen Double Defect Carbon Nitride For Photocatalytic Water Splitting To Produce Hydrogen

In recent years,non-metallic photocatalysts have received extensive attention from many scholars in the field of photocatalysis.Among them,carbon nitride has the advantages of simple synthesis,low raw materials,no pollution and good stability,and has been extensively studied by researchers.However,its shortcomings such as easy recombination of photogenerated electron-hole pairs,small specific surface area and low catalytic efficiency severely limit its practical application.Therefore,in order to further improve its photocatalytic activity,this paper adopts an effective strategy to modify the non-metallic photocatalyst carbon nitride,which lays a solid foundation for its practical application in the photolysis of water for hydrogen production.Firstly,carbon nitride(CN)was prepared by sintering melamine,and CN was modified by different methods to obtain nitrogen vacancy modified carbon nitride(DCN),oxygen doped modified carbon nitride(OCN)and Oxygen doped and nitrogen vacancy co-modified carbon nitride(ODCN).The photocatalytic activity and stability of the material were evaluated under visible light irradiation.The experimental results showed that ODCN has the best hydrogen production rate of 364μmolg-1h-1.The hydrogen production rates of samples CN,DCN,and OCN are 52,252,and 122μmolg-1h-1,respectively,which are all lower than the hydrogen production rate of ODCN.And the hydrogen production rate of ODCN is 7,1.4 and 3 times that of CN,DCN,and OCN,respectively.This can be attributed to the synergistic effect of oxygen doping and nitrogen vacancies,thereby increasing the specific surface area,promoting the rapid separation of photo-generated electron-hole pairs,and significantly improving its photocatalytic hydrogen production activity.Secondly,carbon nitride(CN),oxygen-modified carbon nitride(ACN)and double-vacancy carbon nitride(DACN)were prepared by different methods.Under visible light irradiation,the photocatalytic activity and stability of water were evaluated by the photocatalytic activity and stability of the material.The experimental results show that DACN-2 performs the best hydrogen production performance,and its hydrogen production rate was 595 μmolg-1h-1.The hydrogen production rates of CN,ACN,DACN-1 and DACN-3 are 51,103,552 and 532 μmolg-1h-1,respectively.The hydrogen production rate of DACN-2 is 11.7 and 5.8 times that of CN and ACN,respectively,which greatly promotes the photocatalytic hydrogen production activity of carbon nitride.The structure of nitrogen vacancy and oxygen vacancy not only increases the photocatalytic active sites,but also greatly promotes the transfer and separation of photo-generated charges.In this thesis,two nitrogen-oxygen double defects co-modified carbon nitrides were prepared by different methods,and a series of related characterizations and experimental evaluations of the photocatalysis of the prepared materials were carried out to study their photocatalysis.In this way,the reason for the improvement of its photocatalytic activity is studied,which has important practical significance for promoting the photocatalyst to split water to produce hydrogen.