Molecular Simulation Study On Healing Mechanism Of Multi-Vacancy Defective Graphene

Graphene is a kind of two-dimensional crystal made of one layer of C atoms.Perfect graphene excels in electricity,optics,thermodynamics and mechanics,but it is difficult to obtain defect-free graphene in ordinary factories.Defects will lead to the significant degradation of all aspects of graphene properties,so the repair of defective graphene is a subject worthy of attention.In this paper,the irradiation repair process of defective graphene was studied by large-scale molecular dynamics simulation of injecting C atoms on a multi-vacancy graphene sheet.Apart from that,we studied the catalytic behavior and mechanism of metal atoms in the process of graphene repair.The main research contents are as follows:(1)We prepared a graphene model with multi-vacancy defects on the surface,adopted the ReaxFF force field to describe the C/H system,and simulated the irradiation repair process of the defective graphene by injecting C atoms on the multi-vacancy defective graphene.In combination with the evolution curve of graphene potential energy during the irradiation process,the coupling effect of the system temperature and the incident energy of injected C atom on the repair behavior of multi-vacancy defective graphene was revealed.Our simulations show that a relatively high temperature is prerequisite for perfect healing of defective graphene.Moreover,an appropriate incident energy for injected atoms is also necessary for perfect healing,even under a suitable temperature for perfect healing.If the incident energy of the carbon radiation is too high,defect structures will occur and hinder the healing process.(2)By calculating the potential energy landscape near the surface of the defective graphene and the potential energy evolution curve of the probe C atom when getting close to the graphene vertically,the adsorption phase of the graphene repair process was studied.It was found that the adsorption phase was mainly determined by the incident velocity of the injected C atoms.In addition,we simulated the simplified graphene reconstruction phase by relaxing the intact graphene with C atoms adsorbed on the surface,and found that the process has significant temperature dependence.By calculating the variation of the number of microstructures during the simulation,the different roles of the two repair mechanisms(mechanism of “edge grow” and “atom insertion”)at different temperatures are revealed.(3)We prepared the larger size of the multi-vacancy defect graphene model,adopted the ReaxFF force field to describe the C/Ni system and the C/Pt system,and simulated the process of defective graphene repairing under the catalysis of Ni and Pt atoms.By observing the atomistic structure obtained at the end of the simulations,the different catalytic repair effects were studied.And we calculated the variation of 5,6 and 7-member rings of graphene during the repair process,it was found that the two kind of metal atoms have different catalytic capabilities.(4)Some typical structure evolutions were simulated.We found that Ni and Pt atoms respectively lead to local structural transformations of “jump from the ring” and “bond breakage”,and exhibit different degrees of ability to capture carbon chains at different temperatures.In addition,we mapped the migration route of metal atoms and calculated the migration distance.By observing the different migration behaviors of the two metal atoms in and out of the plane,the different catalytic mechanisms were further studied.The research content of this paper helps us to understand the intrinsic microscopic mechanism of multi-vacancy defective graphene repair process,as well as the catalytic mechanism of metal atoms on the repair of defective graphene.It is of theoretical significance to the selection of external conditions and catalysts for the repair of defective graphene.