Diameter and chirality effects of narrow SWCNTs on molecular hydrogenation

Density functional theory (DFT) has been employed to investigate hydrogen physisorption on very narrow (diameter: d < 6 Å) single wall carbon nanotubes (SWCNTs). Equilibrium deposition sites and binding energy for a single hydrogen molecule have been studied through exo- and endo-hydrogenations. Effects of chirality, diameter and also the orientation of the molecule against the SWCNTs, have been under consideration, as well. The narrow SWCNTs with different chiralities and roughly same radius have very different binding energies for the H2 adsorption in endo-hydrogenation. Incidentally, the calculations show that the binding energy for hydrogen molecule inside the nanotubes is approximately two times higher than the outside adsorption.

► HEX is the most stable configuration forexo-hydrogenation on narrow SWCNTs.
► The H2 binding energy on narrow nanotube is much higher than on the wider ones.
► Narrow tube endo-hydrogenation is very sensitive to curvature and also chirality.
► Binding energy for endo-hydrogenation is approximately two times of the exo-cases.
► H–H bound length in endo-hydrogenation changes depending on curvature of narrow SWCNTs.