Influence of Porous Texture and Surface Chemistry on the CO₂ Adsorption Capacity of Porous Carbons: Acidic and Basic Site Interactions

Doped porous carbons exhibiting highly developed porosity and rich surface chemistry have been prepared and subsequently applied to clarify the influence of both factors on carbon dioxide capture. Nanocasting was selected as synthetic route, in which a polyaramide precursor (3-aminobenzoic acid) was thermally polymerized inside the porosity of an SBA-15 template in the presence of different H₃PO₄ concentrations. The surface chemistry and the porous texture of the carbons could be easily modulated by varying the H₃PO₄ concentration and carbonization temperature. Porous texture was found to be the determinant factor on carbon dioxide adsorption at 0 °C, while surface chemistry played an important role at higher adsorption temperatures. We proved that nitrogen functionalities acted as basic sites and oxygen and phosphorus groups as acidic ones toward adsorption of CO₂ molecules. Among the nitrogen functional groups, pyrrolic groups exhibited the highest influence, while the positive effect of pyridinic and quaternary functionalities was smaller. Finally, some of these N-doped carbons exhibit CO₂ heats of adsorption higher than 42 kJ/mol, which make them excellent candidates for CO₂ capture