Interplay between oxygen doping and ultra-microporosity improves the CO2/N2 separation performance of carbons derived from aromatic polycarboxylates

Microporous carbons were prepared starting from a series of benzene polycarboxylic acids following two strategies: (i) activation- and template-free pyrolysis and (ii) ion-exchange pyrolysis. The proposed synthetic strategies are facile approaches to produce highly microporous carbons that avoid the use of large amounts of corrosive and expensive chemical activators or templates. By varying the number of carboxylic acid groups, the charge balancing species and the degree of deprotonation of the precursors, microporous carbons with diverse morphologies, textural properties and oxygen contents were obtained and their CO2 and N2 sorption properties were assessed. The abundant micropores made the materials suitable for CO2 adsorption at low pressure and ambient temperature, achieving CO2 uptake as high as 4.4 mmol g−1 at 25 °C and 1 bar, competitive with those reported for porous carbons produced using large excess of alkali metal based activating agents. It was found that high performance, in terms of CO2 uptake and CO2/N2 selectivity, was linked to the simultaneous presence of large ultra-micropore volume and high oxygen content in the sorbents. This suggests that the interplay of ultra-microporosity and oxygen doping matters more than the two features taken singularly in determining the CO2/N2 separation properties of porous carbons at low pressure.