The Study On Structure And Properties Of Graphene-like Materials And Metal Oxides Composites

In this paper,the first-principles calculation was used to study the properties of graphite-like materials and metal oxide composite.The geometrical structures,electronic properties,optical properties and enhanced photocatalytic mechanism of TiO₂/graphene-like materials and h-BN sheet and reduced graphene oxide?RGO?or reduced graphene fluorid?GF?were studied by the first-principles method on the basis of the graphite-like material?including graphene,g-C3N4,MoS2 and black phosphorus?models.And the adsorption mechanism of Cr???by Fe₃O₄/graphene composites was studied.They can be summarized as the follows:1.Graphene-like materials?GLM?have attracted intense attention in the research on photocatalytic technology due to their superior properties.First-principles calculations based on density functional theory?DFT?were used to explore the photoactivity and electronic properties of graphene-like materials and TiO₂ composites in this work.It was found that TiO₂/GLM composites might be demonstrated for high thermodynamic stability.The electronic properties of TiO₂/GLM,such as geometric structure,density of states,charge density,charge density difference and optical properties,were characterized.There were interactions between GLM sheets and TiO₂,which caused charge accumulation on the GLM surface and charge depletion on the other side of TiO₂ in the heterojunction.Electrons in the highest occupied molecular orbital?HOMO?consisted of the O-2p orbital from TiO₂ could be directly excited or dispersed to the lowest unoccupied molecular orbital?LUMO?composed of the hybridized orbital from GLM and TiO₂ under irradiation.The produced well-separated electron-hole pairs induced an enhanced photocatalytic performance of TiO₂/GLM.The theoretical results pointed out the electron migration and transfer path at the interface,which might illustrate the mechanism of enhanced photocatalytic activity of TiO₂/GLM.2.First-principles calculation based on DFT was used to investigate the enhanced photocatalytic mechanism and electronic properties of hexagonal boron nitride?h-BN?and reduced graphene oxide?RGO?or fluorinated graphene?GF?sheets,as well as the connection between such interaction in this work.Herein,it is demonstrated that the role,which O or F atoms play,was a necessarily beneficial factor for stability of the h-BN/RGO?GF?composites.We testified that the internal electron recombination promoted the separation of electron-hole pair on those composites interface and restrained photo-generated carrier recovery.The valence and conduction band edge positions of h-BN/RGO?GF?composites relative to the Fermi level could be changed due to the morphological structure of RGO?GF?sheet.Moreover,by analyzing the change of photo-electron transition paths and the absorption edge red-shift,the enhanced photocatalytic ability of h-BN/RGO?GF?composites was demonstrated.Most importantly,different morphologies were bound to different standard heterostructure,and those composites exhibited the superior oxidation.These findings could provide valuable information for thoroughly understanding the molecular mechanism of the exceptional performance of h-BN/RGO?GF?composites compared to the h-BN sheet.3.The first-principles calculation of DFT was used to explore the electronic structure and adsorption properties of Fe₃O₄/graphene composite.The adsorption of Cr???by Fe₃O₄/graphene composite was calculated and the adsorption mechanism of Cr???on Fe₃O₄/graphene composite was elucidated.We demonstrated that Fe₃O₄/graphene composite has good thermodynamic stability.Meanwhile,it could be concluded that the adsorption energy of Cr???on Fe₃O₄/graphene composite could show that the adsorption process was relatively stable chemical adsorption.In addition,we analyzed in detail the migration path of charge from Cr???to surface material.Finally,by analyzing the charge density and the differential charge density,it was concluded that the introduction of a large amount of charge on the graphene had a positive effect on the whole adsorption process.This work explained a microscopic adsorption mechanism and provided a theoretical basis,while Fe₃O₄/graphene composite might be expected to be used for industrial adsorption of Cr??? applications.