The interaction of sulfuric acid with graphene and formation of adsorbed crystals

Density functional theory has been used to analyse the interaction between sulfuric acid and graphene. Four different coverages, ranging from a nearly isolated sulfuric acid molecule (one H2SO4 molecule per 32 C atoms) to a bilayer (one H2SO4 molecule per 4 C atoms) have been studied calculating geometries, binding energies, charge transfers and band structures. The results show that there is protonation of the graphene sheet by the acid, in accordance with experimental results for H2SO4 adsorbed onto highly oriented pyrolytic graphite and for single-wall carbon nanotubes in concentrated sulfuric acid. Nevertheless the electronic structure of graphene is not heavily affected and its zero-band-gap semiconducting behaviour is preserved. As the coverage increases, the acid molecules rotate approaching their orientation in the pure crystal, showing that graphene can template the growth of a sulfuric acid crystal.