Ultramicroporous CO2 adsorbents with tunable mesopores based on polyimines synthesized under off-stoichiometric conditions

• Polyimines with ultramicropores and mesopores were synthesized.
• The porosities of porous polymers were tunable under off-stoichiometric synthetic conditions.
• The porous polymers have high CO2 uptakes and high CO2-over-N2 selectivities.
• The uptake of CO2 on the porous polymers was quite rapid.

A series of porous polymers with ultramicropores and tunable mesopores were synthesized by condensation reaction (Schiff base) of triamine and trialdehyde monomers. They had specific surface areas and pore volumes of up to 694 m2/g and 0.67 cm3/g. The ultramicropores seemed to have been templated by the solvent (DMSO) primarily. The size of the mesopores depended strongly on the amine-to-aldehyde ratio used during synthesis. With a moderate aldehyde excess, the irregular mesopores of the porous polymers increased in size. The polymers' capacities to adsorb CO2 were large (0.93–1.58 mmol/g at 0.15 bar and 2.20–3.28 mmol/g at 1 bar; 0 °C) due to their large ultramicropore volumes, and the estimated CO2-over-N2 selectivities were also relatively high (31–90 for CO2/N2 mixtures with 15 v%/85 v% at 0 °C). The uptake of CO2 on the polymers was quite rapid, and it appears advantageous to have a combination of meso- and ultramicropores in this class of polymers for applications in carbon capture and storage.

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