Molecular and ionic interaction with graphene nanoflakes: a computational investigation of CO₂, H₂O, Li, Mg, Li⁺, and Mg²⁺ interaction with polycyclic aromatic hydrocarbons

Abstract

Understanding the nature of nonbonded interactions on the graphene surface is a problem of outstanding interest. Highly reliable M05-2X/6-311++G**//M05-2X/6-31G* DFT calculations were performed to understand the interaction of small molecules and ionic species with graphenes. Various linear and branched polycyclic aromatic hydrocarbons (PAHs) were taken as models of the graphene surface, and their interaction with small molecules (CO2 and H₂O), metal atoms (Li and Mg), and metal ions (Li⁺ and Mg²⁺) has been studied. The effect of ring size is found to be profound on the interaction energy values and shows an interesting contrast with various species. Our results indicate that the metal atoms and ions are chemisorbed, while CO₂ and H₂O are physisorbed on the PAH surface. H₂O displays a stronger affinity for complexation compared to CO₂. The binding strength of the molecules has been correlated with the nucleus independent chemical shift (NICS), a local aromaticity index, highest occupied molecular orbital (HOMO) energy, and polarizability of PAHs.