The sorption of butanes over carbon nanotubes

Single- and multi-walled carbon nanotubes (SWCNT and MWCNT) were synthesized by the catalytic decomposition of methane and acetylene, respectively. The catalyst/carbon mixtures were submitted to various procedures to obtain samples, enriched in nanotubes. Adsorption isotherms and gas sorption frequency response (FR) spectra of butanes were determined between 273 and 373 K at different equilibrium pressures in the 1 - 6 kPa range. The adsorption capacities were found to increase with increasing (i) carbon nanotube content, (ii) available surface area, and (iii) concentration of O-containing surface functional groups that are sites for strong butane adsorption. The FR studies demonstrated that the rate-governing mechanism of butane sorption depends both on the morphology and the surface properties of the nanotubes. The FR method was shown to be a powerful technique for the characterization of the carbon nanotube products.