Temperature and pressure dependence of molecular adsorption on single wall carbon nanotubes and the existence of an adsorption/desorption pressure gap

The interaction of acetone with single wall carbon nanotubes (SWCNTs) was studied by temperature programmed desorption with mass spectrometry (TPD-MS), after reflux, sonication, or exposure to 7.6 Torr of acetone vapors at room temperature. Acetone molecules adsorb strongly on SWCNTs desorbing at similar to 400-900 K, corresponding to desorption energies of similar to 100-225 kJ/mol, as intact molecules. Exchange of intact adsorbed molecules with gas phase species was observed in successive dosing of hydrogenated and deuterated acetone molecules. The desorption energies reported here are in stark contrast to the desorption energies (similar to 75 kJ/mol) reported earlier for SWCNTs interacting with acetone under high vacuum at cryogenic temperatures. This result suggests activated adsorption/desorption, and is also observed for adsorption of ethanol, methane, n-butane and 1,3-butadiene on SWCNTs and on carbon black. Quantum chemical calculations suggest that adsorption in interstitial channels of bundles formed of large-diameter SWCNTs is possible and can account for high desorption barriers, a result of strong dispersion interactions between neighboring SWCNTs. (C) 2009 Elsevier Ltd. All rights reserved.