Physical Interactions Tune the Chemisorption of Polar Anions on Carbon Nanostructures

Density functional tight-binding calculations of the adsorption of OH- and other related diatomic anions on carbon nanotubes and graphene show that two adsorption states coexist: a physisorption state caused by Debye interactions and a chemisorption state at shorter distances dominated by ionic-covalent interactions. For all anions, both adsorption energies scale linearly with the curvature of the carbon surface and increase with decreasing anion polarizability but also, in metallic nanotubes, with chiral angle. At short distances, charge transfer modifies the attractive Debye forces into repulsive forces of the dipole-dipole type, tuning the strength of the chemisorption state, and may determine its existence and stability.