Theoretical study on adsorption of methane molecule on nanostructured functionalized graphene with hydroxyl and epoxide

In the present work, density functional theory was employed to analyze the effect of functional groups on the adsorption behavior of CH4 in nanostructured functionalized graphene (G). Methane which is abundant in earth is found to be an energy carrier [1] and high use of it would result in the reduction of greenhouse gas emission. It is well known that graphene and derivatized forms of graphene offer applications as gas sensors [2].Two oxygen-containing functional groups such as hydroxyl(OH) and epoxy(O) are applied to modify the graphene surface to clarify the role of a functional group of graphene on the gas adsorption strength. Wood et al demonstrated binding of CO2 and CH4 to model zigzag graphene nanoribbons edge-functionalized with COOH, OH, NH2,H2PO3,NO2, and CH3, while we investigated adsorption of methane molecule on hydroxyl and epoxide on the basal plane of graphene. The interaction mechanism of CH4 with G(OH) and G(O) was demonstrated by using DFT calculation at the special level of B3LYP/6-31G*. The optimized structures of CH4 on G(OH) and G(O) were shown in Figure 1. The adsorption energies (Eads) for CH4 on G-OH and G-O are -3.85 and -3.55 kJ/mol, respectively. Based on the calculated adsorption energy, it can be concluded that the interaction between the gas molecule and the functionalized graphene is weak. Furthermore, values of Eads does not considerably change upon functional groups, indicating the type of functional group has not a significant effect on interaction of the Methane and nanostructures.Moreover, the values of HOMO–LUMO energy gap are G(OH) =0.064 ev Eg G(O) =0.114 ev, CH4/ G(OH)= 0.064 ev and CH4/ G(O)= 0.114 ev respectively, indicating that the adsorption of CH4 has no significant effect on the electronic properties of the functionalized graphene.