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 CO2 (5.19 mmol g1/228 mg g(-1)) at 1 bar and 273 K. Initial slope selectivity calculations demonstrated that TBILP-1 has very high selectivity for CO2 over N2 (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 CO2/N-2 (40) and CO2/CH4 (7) at 298 K. TBILPs showed moderate isosteric heats of adsorption for CO2: TBILP-1 (35 kJ mol(-1)) and TBILP-2 (29 kJ mol(-1)) enabling high and reversible CO2 uptake at ambient temperature. In addition, TBILPs displayed promising working capacity, regenerability, and sorbent selection parameter values for CO2 capture from gas mixtures under vacuum swing adsorption (VSA) and pressure swing adsorption (PSA) conditions.