Ammonia adsorption on graphene and graphene oxide: a first-principles study

Motivated by the recent realization of graphene sensor to detect gas molecules that are harmful to the environment, the ammonia adsorption on graphene or graphene oxide (GO) was investigated using first-principles calculation. The optimal adsorption and orientation of the NH3 molecules on the graphene surfaces were determined, and the adsorption energies (Eb) as well as the Mulliken charge transfers of NH3 were calculated. The Eb for the graphene are small and seem to be independent of the sites and orientations. The surface epoxy or hydroxyl groups can promote the adsorption of NH3 on the GO; the enhancement of the Eb for the hydroxyl groups is greater than that for the epoxy groups on the surface. The charge transfers from the molecule to the surfaces also exhibit the same trend. The Brönsted acid sites and Lewis acid sites could stably exist on the GO with surface hydroxyl groups and on the basal, respectively.