Thermodynamics and structure of hydrogen, methane, argon, oxygen, and carbon dioxide adsorbed on single-wall carbon nanotube bundles

Adsorption isotherms, isosteric heats of adsorption, and neutron diffraction measurements of hydrogen, methane, argon, oxygen, and carbon dioxide adsorbed on single-wall carbon nanotube bundles show that all species, except $\mathrm{C}{\mathrm{O}}_2$, condense first on high-energy binding sites, such as the grooves and the widest interstitial channels, and then on the outer rounded surface of the bundles. As for $\mathrm{C}{\mathrm{O}}_2$, only one set of adsorption sites is observed, which is attributed mainly to the grooves. The diffraction results further reveal that the average packing of the bundles is not changed upon adsorption and that no significant overall bundle dilation is observed on our sample. Molecular dynamic simulations confirm and complete our interpretation.