Adsorption of polycyclic aromatic hydrocarbons onto graphyne: Comparisons with graphene

Density functional theory calculations were implemented to expand the knowledge about graphyne and its interaction with polycyclic aromatic hydrocarbons (PAHs). Due to the porous character of graphyne, the adsorption strength of PAHs onto graphyne surfaces is expected to be lower with respect to graphene (a perfect pi-extended system). However, there are not quantitative evidences for this assumption. This work shows that the adsorption strength of adsorbed PAHs onto gamma-graphyne nanosheets (GY) is weakened in 12 - 23% with respect to the adsorption onto graphene, with a decrease of 10 - 20% in the dispersive interactions. The adsorption energies (in eV) of the GY-PAH systems can be straightforward obtained as E-ads/eV approximate to 0.033N(H) + 0.031N(C), where N-H and N-C is the number of H and C atoms in the aromatic molecule, respectively. This equation predicts the binding energy of graphene-graphyne bilayers with a value of similar to 31 meV/atom. Analysis of the electronic properties shows that PAHs behaves as n-dopants for GY, introducing electrons in GY and also reducing its bandgap in up to similar to 0.5 eV. Strong acceptor or donor substituted PAHs decrease the bandgap of g-graphyne in up to similar to 0.8 eV, with changes in its valence or conduction band, depending on the chemical nature of the adsorbate. Finally, these data will serve for future studies related to the bandgap engineering of graphyne surfaces by nonaggressive molecular doping, and for the development of graphyne-based materials with potential applications in the removal of persistent aromatic pollutants.