Adsorption Characteristics of CO2 and N2 on Chitosan-based Nano-structured Porous Activated Carbon

In this work, nano-structered porous activated carbon (AC), prepared from chitosan through KOH chemical activation procedures, exhibits favorable adsorption characteristics for both CO₂ and N₂. The distinct physicochemical properties of the prepared ACs were primarily characterized using nitrogen adsorption analysis, SEM, and XPS. A clear correlation was observed between the textural properties and the KOH mixing ratio, whereas no consistent pattern was identified between the chemical composition and the KOH mixing ratio. Pure component adsorption isotherm data revealed that a greater ultra-micropore volume (V<0.9 nm) corresponds to increased adsorption of CO₂ and N₂. Additionally, the adsorption characteristics of these gases demonstrated correlation with quadrupole moment, polarizability and kinetic diameter. The Sips equation provided the best fitting results for the measured isotherm data. Furthermore, the adsorption affinity and the adsorption energy distribution functions prove valuable in comparatively assessing the surface heterogeneity of the prepared ACs. Calculated CO₂/N₂ selectivities using the ideal adsorbed solution theory(IAST) suggest that ACs with well-developed ultramicropores hold significant potential for adsorptive separations, including applications in flue gas and direct air capture.