Evaluation of CO2 interactions with S-doped nanoporous carbon and its composites with a reduced GO: Effect of surface features on an apparent physical adsorption mechanism

Adsorption of CO2 at temperatures close to ambient and up to 1.5 MPa was measured on nanoporous polymer-derived carbon, on its composite with reduced graphene oxide (rGO), and on their air oxidized counterparts. The isotherms were fitted by the LBET class models and the adsorption mechanisms were described in terms of parameters derived from the mentioned models including the amount adsorbed, adsorption energy distribution, maximum CO2 adsorption energy in the first layer, heterogeneity level parameter in the first adsorbed layer, cluster heights, and changes in the volume adsorbed in the first layer upon cycling experiments. The results were analyzed in conjunction with adsorbents' porosity and surface chemistry. Even though the volume of small pores is a main parameter governing the extent of the adsorption process, surface chemistry was found as important for the energetics of adsorption and for the clustering patterns the CO2 molecules in the pore system. Regarding the quantity and quality of surface species, the results suggest that the latter might have more dominant effect on the mechanism of the adsorption process.