(662b) Experimental and Theoretical Comparison of Gas Desorption Energies On Metallic and Semiconducting Single Walled Carbon Nanotubes

Single walled carbon nanotubes (SWNTs) have been widely studied as adsorbents from both simulations and experiments due to their high surface areas and precisely defined pores. It is widely known that SWNTs can be either metallic or semiconducting based on differences in the chiral indices, (n,m), which determine how the carbon hexagons are arranged on the surface of the SWNT. All simulations of adsorption on SWNTs using classical potentials have implicitly assumed that the adsorption potential between a molecule and a SWNT is independent of whether the SWNTs are metallic or semiconducting. However, it is reasonable to assume that metallic SWNTs, which have extremely high longitudinal polarizabilities, would exhibit stronger van der Waals forces with adsorbate molecules than semiconducting SWNTs. We use precise temperature programmed desorption experiments and van der Waals-corrected density functional theory to probe the differences in binding energies for gas molecules adsorbed on the surfaces of metallic and semiconducting SWNTs. We have measured and calculated the binding energies for Xe, a spherical adsorbate, and the highly anisotropic n-heptane molecule on metallic and semiconducting-SWNTs having about the same diameter. Binding energies computed from van der Waals corrected density functional theory are in good agreement with experiments.