▎ 摘　　要

The investigation of methane adsorption on surface of graphene is of high interest as graphene can be tuned as required, also the favorable adsorption properties may be employed to create cost-effective novel storage devices. In the present study, we investigate the adsorption characteristics of methane (CH4) on eight different kinds of hydrogen-capped graphene sheet with variable and high number of carbon atoms using density functional theory methods. Our results infer that the methane adsorption is high on defected graphene than that of pristine and less charge transfer between CH4 and graphene. The physisorbed methane molecule on graphene sheet has enhanced adsorption energy with a high number of carbon atoms and the value is -0.184 and -0.185 eV (pristine graphene) and -0.188 and -0.191 eV (defected graphene). Due to high barrier, the transfer of electrons from graphene to methane is hard rather than methane to graphene. Further, it is found that the energy gap value of the hydrogen-capped graphene sheets decreases upon adsorption of methane. The reduced density gradient (RDG) scatter graph shows the interaction to be weak van der Waals interaction with the steric repulsion in the graphene sheet.