Molecular physisorption on graphene and carbon nanotubes: A comparative ab initio study

The results of ab initio density functional theory calculations of molecular physisorption on a number of different adsorption sites on a graphene sheet and on a (10, 0) single walled carbon nanotube are discussed. Both the Vosko-Wilk-Nusair (VWN) local density approximation (LDA) functional and the Perdew-Wang (PW91) generalized gradient approximation (GGA) functional were employed in calculating the binding energy of a hydrogen molecule to the appropriate carbon nanostructure as well as the optimal molecule – nanostructure separation. Both exterior and interior nanotube adsorption sites were examined and it is shown that the binding energy associated with interior adsorption sites is larger than exterior adsorption on the nanotube or onto the graphene layer. The use of carbon nanostructures for hydrogen storage is also discussed.