Alterations of S-doped porous carbon-rGO composites surface features upon CO2 adsorption at ambient conditions

Interactions of CO2 with polymer derived carbon/rGO composites at ambient conditions were studied. Both, dynamic adsorption tests and equilibrium adsorption measurements were analyzed. The samples differed in the porosity, oxidation level and speciation of sulfur on the surface. Even though more CO2 was adsorbed on the oxidized sample than in the unmodified one, the surface chemistry of the latter was found as having more pronounced effect on attracting CO2 to the pore system. That process was accompanied by marked release of water and SO. These compounds are considered as the products of surface reactions/CO2 reduction. It is proposed that CO2 is reduced by sulfur in thiophenic configurations. In this process unstable sulfenic/sulfinic/sulfonic acids are formed and their decomposition results in the release of SO and water. As a result of this the carbon surface was oxidized and small changes in porosity were noticed. These results indicate that CO2 should not be used to determine the porosity of carbons whose surface might promote the reduction of this probe molecule.