Comparative adsorption of simple molecules on carbon nanotubes: Dependence of the adsorption properties on the nanotube morphology

Adsorption isotherms of krypton between 77.5 and 83.7 K and ethylene between 90 and 100.5 K on carbon multi-walled nanotubes have been measured. The comparison of the results with those obtained under the same conditions on graphite are discussed in the light of the nanotube morphology. The curvature of the graphene sheets constituting the nanotube walls mainly results in higher condensation pressures and a lower heat of adsorption with respect to those on a planar surface. Near the completion of the krypton first condensed layer, a transition to a phase of higher density occurs, the nature of which is discussed. The wetting transition temperature above which a second ethylene monomolecular layer can condense on the surface is higher on nanotubes than on graphite.