Abstract

The CO2 adsorption on porous carbon materials (PCM) samples prepared under different conditions of alkaline activation and, consequently, having different pore hierarchy and specific surface area was studied. It was shown that at atmospheric pressure (1bar), CO2 adsorption on carbon adsorbents occurs in narrow micropores, while at high pressures (up to 40bar), large micropores and small mesopores participate in the adsorption. The maximum CO2 adsorption (39.58mmol/g at 40bar and a temperature of 298K) was demonstrated by the PCM 6/1 sample, which had the maximum volume of micropores and narrow mesopores (corresponding to a pore width of <7nm). In the region of low pressures (up to 1bar), the most active CO2 adsorbent (4.4mmol/g) is the PCM1/1 sample, which had the maximum volume of ultramicropores (corresponding to a pore width of <0.7nm). The applicability of the Langmuir and Freundlich models to the sorption process on the obtained PCM sample was assessed in the temperature range of 298-318K up to a pressure of 40bar. The values of the adsorption heat (q) and the entropy change (?S) were calculated for different values of CO2 on the prepared PCM. The changes in q and ?S for the CO2/ PCM6/1 system depending on the temperature and the amount of adsorbed CO2 were explained by the transitions of the adsorbate in the micropores and narrow mesopores of PCS6/1 from the bound state near the high-energy adsorption centers to molecular associates. © 2025 Elsevier Ltd.