Molecular simulations were used to shed light on a controversy concerning where gases were adsorbed on single-walled carbon nanotube bundles. Simulations were performed using models of carbon nanotube bundles composed of tubes that were all of the same diameter (homogeneous) and tubes of differing diameters (heterogeneous). Simulation data were compared with experimental data in order to identify the best model for describing experimental data. Adsorption isotherms, isosteric heats of adsorption and specific surface areas were computed for Ar, CH4 and Xe on closed, open and partially opened homogeneous and heterogeneous nanotube bundles. Experimental data on nanotubes prepared using two different methods (electric arc, HiPco) were examined. Experimental adsorption isotherms and isosteric heats for nanotubes prepared by using the electric arc method were in best agreement with simulations of heterogeneous bundles of closed nanotubes. Models which included adsorption in defect interstitial channels were required to achieve good agreement with experiment. Experimental isosteric heats and specific surface areas on HiPco nanotubes were best described by a model which consisted of heterogeneous bundles with approximately 11% of the nanotubes opened.

Adsorption of Gases in Carbon Nanotubes: Are Defect Interstitial Sites Important? M.R.LaBrosse, W.Shi, J.Karl Johnson: Langmuir, 2008, 24[17], 9430-9