Highly Selective CO2 Capture by Triazine-Based Benzimidazole-Linked Polymers

Triazine-based benzimidazole-linked polymers (TBILPs), TBILP-1 and TBILP-2, were synthesized by condensation reaction of 2,4,6-tris(4-formylphenyl)-1,3,5-triazine (TFPT) with 1,2,4,5-benzenetetraamine tetrachloride (BTA) and 2,3,6,7,14,15-hexaaminotriptycene (HATT), respectively. The Ar sorption isotherms at 87 K revealed high surface areas for TBILP-1 (330 m 2 g –1 ) and TBILP-2 (1080 m 2 g –1 ). TBILP-2 adsorbed significantly high CO 2 (5.19 mmol g –1 /228 mg g –1 ) at 1 bar and 273 K. Initial slope selectivity calculations demonstrated that TBILP-1 has very high selectivity for CO 2 over N 2 (63) at 298 K, outperforming all triazine-based porous organic polymers reported to date. On the other hand, the larger surface area of TBILP-2 leads to relatively lower selectivity for CO 2 /N 2 (40) and CO 2 /CH 4 (7) at 298 K. TBILPs showed moderate isosteric heats of adsorption for CO 2: TBILP-1 (35 kJ mol –1 ) and TBILP-2 (29 kJ mol –1 ) enabling high and reversible CO 2 uptake at ambient temperature. In addition, TBILPs displayed promising working capacity, regenerability, and sorbent selection parameter values for CO 2 capture from gas mixtures under vacuum swing adsorption (VSA) and pressure swing adsorption (PSA) conditions.