Applicability of Dubinin–Astakhov equation to CO2 adsorption on single-walled carbon nanotubes

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 N2 BET approach at 77 K, indicating that the CO2 molecules are adsorbed on both internal and external surfaces of the tubes.