Binding energy and monolayer capacity of Xe on single-wall carbon nanotube bundles

We have determined the adsorptive capacity of Xe on the different groups of binding sites available to this atom on a sample of single-walled carbon nanotube (SWNT) bundles. The SWNT's used were not treated after production: hence, the cap, at the ends of each of the tubes remain intact. By comparing these experimental values to the values computed for the different portions of the bundles obtained from geometrical considerations, we conclude that Xe adsorption takes place only on the outer surfaces of the SWNT bundles. We have also measured Xe adsorption isotherms on the same SWNT sample at a low coverages for nine different temperatures (between 210 and 295 K) to determine the isosteric heat of adsorption of Xe on the SWNT's; this quantity is directly related to the binding energy of the adsorbate to the substrate. We determined that the binding energy of Xe on the SWNT's is 282+/-11 meV. This value is 74% larger than that for Xe on planar graphite.