Effect Of Nitrogen Doped Graphene In Inducing Peroxydisulfate To Degrade Organic Pollutants In Water

Persulfate(PDS)is an emerging oxidant which can be easily activated by carbon-based materials such as graphene to produce free radicals that degrade organic pollutants.Nitrogen doping is a simple and effective method to modify the physio-chemical properties and structure of graphene.Utilization of nitrogen-doped graphene to activate persulfate for organic pollutant degradation is highly promising.However,the effect and mechanism of the amount and forms of doped nitrogen on the catalytic degradation of organic pollutants by persulfate,activated by nitrogen-doped graphene is still unclear.Furthermore,significant aggregation is often found in nitrogen-doped graphene which obtained by chemical reduction,thus hinds its catalytic activity.In this thesis,the progress of catalysis of persulfate activation to degrade organic pollutants is reviewed.The development of carbon-based materials for activating PDS and degrading organic pollutants is discussed.The synthesis,structure,properties and applications of nitrogen-doped graphene,as well as the modifying methods and application of modified nitrogen doping graphene,are stated.To improve the catalytic performance of nitrogen-doped graphene for activating PDS and figure out its mechanism,and to solve the aggregation problem of nitrogen-doped graphene,a range of nitrogen-doped graphenes and porous nitrogen-doped graphenes were synthesized by hydrothermal method.The so obtained materials are investigated for their catalytic performance,and the relationship between their structure and catalytic performance is clarified.These findings will guide the applications of nitrogen doped graphene as a catalyst and enrich our understanding of the PDS-organic pollutants reaction system.The main conclusions and innovations are as follows:(1)The reactive sites,influencing factors and mechanism of PDS activation catalyzed by nitrogen-doped graphene to degrade organic pollutants are elucidated.This study finds that nitrogen-doped graphene can be obtained by hydrothermal reaction of graphene oxide and a trace amount of nitrogen source.The nitrogen content in nitrogen-doped graphene increases as the amount of nitrogen source increases.Graphite nitrogen is the main active site of nitrogen-doped graphene to activate persulfate to degrade organic pollutants.The catalytic reaction is achieved by two non-radical pathways,i.e.electron transport and singlet oxygen mediated pathway,which degrades phenol into p-hydroxyphenol and p-hydroxybenzoic acid,and finally mineralizes into CO2 and H2O partially,besides,the catalytic efficiency is independent of the initial pH.(2)The relationship between the physiochemical properties and PDS activation catalyzed by porous nitrogen-doped graphene to degrade organic pollutants are revealed.The study finds that controlling the etching time can overcome aggregation of nitrogen-doped graphene,and to obtain the so-called porous nitrogen-doped graphene with more porosity and higher specific surface area.In the process of catalytic degradation of phenol and 2,4-dichlorophenol by porous nitrogen-doped graphene and nitrogen-doped graphene,these pores on the nitrogen doped porous graphene can improve the mass transfer efficiency of persulfate and increase the absorbed pollutants,leading to higher catalytic activity.