Low pressure adsorption of CO2 on multi-wall carbon nanotubes

Volumetric techniques were employed to study the adsorption of CO2 on a purified multi-wall carbon nanotubes (MWNT’s) sample, as a mesoporous material, at isothermal conditions of 288, 293 and 298 K and pressures ranging from 30 to 150 kPa. Langmuir, Freundlich and Sips equations were used to represent the isotherms. Also the parameters of these fitted isotherm models have been determined. The isosteric heat of adsorption was calculated using Clausius-Clapeyron equation that resulted in an average value of 10.19 kJ/mol (0.106 eV). Adsorption isotherms behavior with temperature and the average value of heat of adsorption confirmed that CO2 adsorption phenomenon is physisorption at the studied ranges. The observed entropy changes related to the adsorption in the range of surface loading from 0.133 to 0.147 mol/kg were lower than the values of theoretical entropy changes for both of the mobile and localized adsorption models.