CO2 adsorption on single-walled carbon nanotubes (SWCNTs) was carried out at 273 and 298 K, and the BET, Langmuir, and Dubinin-Astakhov equations were employed to represent the isotherms. Only Dubinin-Astakhov equation could describe the CO2 adsorption on SWCNTs. The Astakhov exponent is less than 2 for CO2 adsorption, indicating the presence of heterogeneous porosities. Furthermore, the SWCNTs' surface area calculated using the CO2 Dubinin-Astakhov approach at 273 (or 298 K) is fairly consistent with the surface area obtained from N-2 BET approach at 77 K, indicating that the CO2 molecules are adsorbed on both internal and external surfaces of the tubes. (c) 2006 Elsevier B.V. All rights reserved.