Tunable triptycene-pyrazine porous polymers for highly selective CO₂ capture

Effective carbon dioxide capture from flue gas and natural gas streams requires adsorbents with high capacity, selectivity, and stability. Porous organic polymers are promising because of their adjustable porosity and functional versatility. In this study, we present a series of porous organic polymers (TPZ-1, TPZ-2, TPZ-3), synthesized through Friedel–Crafts alkylation of triptycene and 2,6-diaminopyrazine. By combining the intrinsic free volume of triptycene with nitrogen-rich CO₂-binding sites from 2,6-diaminopyrazine, the TPZ networks achieve high Brunauer–Emmett–Teller (BET) surface areas (up to 791 m²/g) and predominantly microporous structures. These polymers exhibit significant CO₂ adsorption capacity (up to 2.74 mmol/g at 273 K) and strong selectivity for CO₂ over CH₄ and N₂. Under conditions mimicking post-combustion flue gas, the IAST (CO₂/N₂) selectivity reaches 144 at 273 K and 108 at 298 K. An IAST (CO₂/CH₄) selectivity of 22.1 and 18 is also observed under natural gas purification conditions at 273 K and 298 K, respectively. The isosteric heat of CO₂ adsorption (∼27 - 30 kJ/mol) indicates favorable physisorption, making regeneration easy. Along with their sturdy covalent frameworks and high thermal stability, these features make the TPZ series promising for energy-efficient carbon capture.