DES assisted synthesis of hierarchical nitrogen-doped carbon molecular sieves for selective CO2versus N2 adsorption

Abstract

Deep eutectic solvents (DESs) composed of resorcinol, 3-hydroxypyridine and tetraethylammonium bromide were used for the synthesis of hierarchical nitrogen-doped carbon molecular sieves. DESs played multiple roles in the synthetic process, as the liquid medium that ensures reagent homogenization, the structure-directing agent responsible for the achievement of the hierarchical structure, and the source of carbon and nitrogen for the solid sorbent obtained after carbonization. Thus, the synthesis offers an economy of reagents that emphasizes the green nature and low cost of conventional polycondensation. Interestingly, while macropores facilitated mass transport and access to the surface area, the combination of the molecular sieve structure and nitrogen functionalization provided, respectively, excellent CO₂ adsorption capacities of up to 3.7 mmol g⁻¹, and outstanding CO₂–N₂ selectivities of up to 14.4 from single component gas data. Nonetheless, the CO₂–N₂ selectivity in the Henry law regime – representative of post-combustion flue-gas streams – of some of our carbons was particularly remarkable (e.g. 96), comparable to or even higher than those described for most recent carbons, and only surpassed by those of certain zeolites.