Theoretical Study On The Catalytic Decomposition Of Ozone By Defective Graphene

With the intensification of human activities,the concentration of ozone in the troposphere has increased,and ground-level ozone has become one of the world’s major air pollutants.Ozone has strong oxidizing ability and high reactivity,which can directly cause photochemical smog and aggravate air pollution.Long-term living in a high-concentration ozone environment can cause severe lung damage,increase the risk of respiratory diseases and reduce the ability of the immune system.The previous methods of removing ozone mainly include activated carbon adsorption method,chemical adsorption method and catalytic decomposition method.Catalytic decomposition catalysts mostly use metal oxides as active components,but they are easily affected by air humidity and metals,especially heavy metals,can pollute the environment if they are not handled well.At present,graphene is used as a catalyst due to its high specific surface area,good biocompatibility,and high adsorptivity.In this paper,through quantum chemical calculations,density functional theory(DFT)is used to conduct an in-depth research on the catalytic decomposition pathways and effects of perfect graphene,defect graphene,and doped graphene on ozone.In the third chapter of this thesis,the reaction of perfect graphene with ozone in the air is studied through theoretical calculations and the optimal reaction path is explored.DFT calculations show that the stability of graphene makes the reaction energy barrier between graphene and ozone high,but once an epoxy structure is formed on the surface of graphene,it will help ozone decomposition at room temperature.It is designed to form different numbers of epoxy structures on the surface of graphene.Through DFT calculation,it is found that the increase in the number of epoxy helps to further reduce the energy barrier of the reaction between the epoxy structure and ozone.Some experimental documents show that the number of epoxy structures on the surface of graphene oxide after ozone treatment is reduced,which is consistent with our calculation results.In chapter 4,the common defect states(Stone-Wales defect,555-777 double vacancy defect and N-doped)graphene are optimized to determine the highly reactive sites,and calculate the decomposition effect of ozone on the defective graphene.DFT calculations show that in Stone-Wales defect graphene,the most stable epoxy structure has a high energy barrier to react with ozone to catalyze ozone decomposition at room temperature.Vacancy defects can enhance the reaction activity of graphene and ozone,but single-vacancy defect graphene easily combines with water molecules to form a more stable structure,so single-vacancy defect sites on graphene are not conducive to being a catalyst for catalyzing ozone decomposition.555-777 Double vacancy defect does not contain dangling bonds,and the active site can react with ozone at room temperature,and it is difficult to react with common gases(H2O,O2,N2)in the environment,that is,555-777 double-vacancy defect graphene helps to accelerate the decomposition of ozone.In addition,N atom doping can also be used to improve the chemical activity of graphene.Through DFT calculations,it is found that the C atom near the N atom is the most active,and the energy barrier to react with ozone is sufficient to overcome it at room temperature,and the N-doped graphene reacts inertly with common gases in the air,therefore,N-doped graphene can selectively catalyze ozone decomposition.Therefore,555-777 double-vacancy defect graphene and N-doped defect graphene are promising as metal-free catalyst for decomposing ozone.