Theoretical Characterization Of The Local Structure Of Nitrogen And Oxygen Doped Graphyne By X-ray Spectroscopy

Graphyne is a new allotrope of carbon,which composed of the hexatomic ring of graphene and carbine.It has abundant carbon chemical bonds,excellent chemical stability,wide plane spacing and large conjugated system.Successful synthesis of high polymer graphyne film on the surface of the copper by Li et al.in 2010 opened up an important research field of graphenyne,and has brought a hot-spot of graphyne theoretical research.Because of the different composition of carbon atoms,graphenyne can be divided into various forms according to its structure and period.At present,many different configurations of graphyne have been synthesized by experiments and studied in depth.Compared with traditional carbon materials such as fullerenes and graphene,graphyne with special hybrid network structure has better electronic structure and performance,and shows important applications in electronics,catalysis,optoelectronic devices,semiconductors,new energy,and other fields.Graphyne can produce a large number of heteroatomic defects and active sites after doping nitrogen and oxygen atoms.It can be used as oxygen reduction reaction and has good catalytic performance.The catalytic activity of carbon materials mainly depends on the form of doped atoms,and the different positions of doping atom will produce many different structures,which have a great influence on the performance of various doping structures.It is difficult to detect these different doping types in situ through experiments,however,we can identify and characterize the doped graphenyne molecular structures through theoretical simulations.X-ray photoelectron spectroscopy is one of the most important and widely used spectral techniques in chemical analysis about surface.Using the energy distribution of electron excitation and de-excitation in nuclear orbitals,X-ray spectra can effectively be used to measure the composition of doped elements,and the chemical and electronic states of each element.The X-ray spectra in this paper include X-ray photoelectron spectroscopy(XPS)and near-edge X-ray absorption fine structure spectroscopy(NEXAFS).XPS is sensitive to the local chemical environment of elements and can be used to identify the configurations of different doping types.NEXAFS corresponds to the state where the electron from the 1s orbital is excited to the unoccupied orbital,which can improve the information for the unoccupied orbital.NEXAFS spectra can be used to effectively detect the electron and chemical structures of the molecular system,which is obviously dependent on the local chemical environment of different doping structures.Therefore,we can use XPS and NEXAFS to identify and characterize the local structure of nitrogen and oxygen doped graphyne.In this study,based on the density functional theory(DFT),we simulated XPS and NEXAFS of the local structure of graphyne doped with nitrogen and oxygen.Through the simulation of these two spectra,we carried theoretical characterization on the two different doped graphyne.The content and conclusion of this paper mainly include the following two points:There are five typical structures of nitrogen-doped grapyne,and the N 1s of XPS and NEXAFS spectra of these five local structures have been simulated theoretically.By comparing the calculated ionization energy with the experimental XPS,we obtained the relative contents of different nitrogen doping types,and further used in the simulation of NEXAFS spectra.We reassigned the main characteristic peaks of the experimental spectra and explained the changes in the energy position and intensity of the main characteristic peaks.In addition,the NEXAFS spectra shows a strong dependence on the local structures of the five doping configurations,so the main nitrogen doped graphyne structures can be identified by using the NEXAFS spectra.In this paper,we also calculated the effective charge and enthalpy changes of five doped configurations,and analyzed the oxygen reduction reaction catalytic activities of several configurations.We reviewed the literature and summarized the experimental results of all available X-ray spectra of oxygen-doped graphyne,and clearly listed the differences in spectral peaks in different papers.Based on the first-principles method,we simulated the C and O 1 s XPS and NEXAFS spectra of seven oxygen doped graphyne.The XPS shows a rough dependence on seven local structures doped with oxygen atoms,so it can not be used adequately to identify seven types doping structures.However,compared with XPS,the NEXAFS spectra of the seven oxygen doped graphyne systems show a strong dependence on the local structure of excited atom.Furthermore,the accurate structure-spectral relationships established in two-dimensional carbon materials can be used to identify the major doping forms.The NEXAFS spectra of each configuration can be used to identify seven oxygen doped structures.This paper consists six chapters.The first chapter is the foreword,which mainly describes the prospect of X-ray spectrum of graphyne doped with nitrogen and oxygen.The second chapter mainly describes the basic theory of quantum chemistry involved in the research work.The third chapter mainly recommends the theory of X-ray spectrum.The fourth chapter mainly recommends the theoretical characterization of X-ray spectra of the local structure of nitrogen doped graphyne.In chapter five mainly recommends the theoretical characterization of X-ray spectra of the local structure of oxygen doped graphyne.The oxygen doped configuration can be determined and identified by the relationship between spectra and structure.The chapter six is the summary and prospect of the main work of this paper.