CO$_{2}$ adsorption on single-walled dahlia-like carbon nanohorns*

The adsorption of CO$_{2}$ on spherical aggregates of as-produced (i.e., closed) dahlia-like single-walled carbon nanohorns was investigated. We conducted volumetric adsorption measurements at five temperatures between 147 and 180 K. The shape of the isotherms for CO$_{2}$ is very different from those measured with neon and CF$_{4}$. For CO$_{2}$ there is a single, smeared step in the adsorption data between the lowest coverages and saturation. By contrast, Ne and CF$_{4}$ show two distinct substeps on the same substrate. The isosteric heat was also obtained and its dependence on coverage also showed an usual behavior: it increased with increasing coverage. The isosteric heat decreases with coverage both for Ne and CF$_{4}$. The stronger intermolecular interactions present for CO$_{2}$ probably are responsible for this adsorbate's unusual behavior. Comparisons with the behavior reported in the literature for CO$_{2}$ on SWNTs, which shows similar unusual characteristics, will also be made.