| At present,graphene has been gradually applied in the field of devices,and a series of new branches of physics have been born,such as valleytronics,twistronics,etc.It,however,is still faced with many problems in device application.For example,the large-scale production technology of graphene remains to be developed,and the change of graphene performance in different service environments needs to be further evaluated.All of these are closely related to the surface/interface performance,which requires a higher level of analysis of these properties and in-depth discussion of the relationship between graphene and environment.Based on these,in this paper,the relationship between surface/interface properties of graphene and environments is studied using first principles.Considering the complexity of environments,this paper mainly studied three scenarios: interactions of air pollutants,halogens and their hydrides,and strong oxidising acids with the surfaces/interfaces of graphene.The above categories cover solid-gas and solid-liquid contacts and involve a series of processes from preparation to use of graphene-based materials.The main contents include the following aspects:(1)Study on gas impermeability of graphene.The high impermeability of perfect graphene has been proved by numerous studies,but in practice,graphene may lose its high impermeability due to a large number of defects caused by mechanical damage and energy and structural fluctuations caused by temperature.Hence,the relationship between non-defect graphene and graphene with point defects and air pollutants(O3,OF2,CO,COCl2,N2 O,NO,NO2,SO,SO2,SO3)was investigated using first principles.The results show that there is only weak physical adsorption between most of the air pollutants and graphene.However,OF2,N2 O and NO2 may have strong adsorption with non-defect graphene at high temperature.For pointdefect graphene,OF2 will break the chemical bond at a lower energy,and thus produce the intermediate OF· which may further dissociate to form oxygen and fluorine free radicals that harm the human body and environment.This work provides rich data and effective guidance for assessing the safety of graphene-based products.This also provides guidance for the further development of safe graphene-based products.(2)Theoretical study on preparation of graphene halide by liquid phase stripping.Halogenated graphene is an important member of graphene family.An in-depth understanding of the preparation process of halogenated graphene by liquid phase exfoliation can help to reduce costs and improve quality.Therefore,the reactions between graphene and halogen hydrides,Br2 and I2 are studied using first principles,in which the relationship between the halogenated graphene and polarity of molecules,the matching degree of molecules to point defects are studied by adsorption energy and charge transfer.The results show that halogenated graphene can only be formed by the reaction of halogen hydride and monolayer graphene containing point defects.At the same time,the products of halogenated and exfoliated can be monolayer halogenated graphene only when the halogen and hydrogen atoms form co-doping on the same monolayer.In this process,polarities between HCl and HBr produce better exfoliation and halogenation results.This work provides abundant theoretical guidance for the preparation of two-dimensional materials,including but not limited to halogenated graphene,by liquid phase exfoliation.(3)Theoretical study on the source of oxygen-containing functional groups of graphene oxide.Study of the source of functional groups will help us to understand and regulate its composition and structure,which will allow us to design the properties of it according to different purposes.Therefore,this section studies the reactions between graphene and H2SO4,HNO3,HMn O4 and HCl O3 using first principles.In this process,we studied the source of functional groups by density of states,adsorption energy and charge transfer.The results show that the oxygen-containing groups can not only come from air and water,but from the dissociation of HMn O4 due to energy fluctuations.Although the topological defects caused by ultrasound can be selective to the generation of groups,this effect is far less than the solvation effect,which makes the HMn O4 potentially a source of groups.This work provides guidance for the source of oxygen-containing functional groups of graphene oxide. |
