Pore volume regulated CO2 adsorption in C–C bonded porous organic frameworks

Abstract

Three C–C bonded porous organic polymers are assembled by reacting rigid monomers (triformylphenol, triformylphloroglucinol, triformylresorcinol) with pyrrole in a catalyst-free solvothermal reaction. The resulting black-colored amorphous polymers yield moderate Brunauer–Emmett–Teller surface areas (213 m² g⁻¹ to 277 m² g⁻¹). All the polymers exhibit the same pore size but different pore volumes. The impact of pore volume on the adsorption capacity has been investigated. The POFs show excellent CO₂ adsorption properties with moderate heat of adsorption values (31.9–37.6 kJ mol⁻¹) and good IAST selectivity for CO₂/N₂ and CO₂/CH₄ separation. The working capacity of the POFs determined using mixed gas IAST calculations shows that these POFs can preferentially adsorb CO₂ from the CO₂/N₂ gas mixture. POFs show facile adsorption kinetics with a self-diffusion coefficient on the order of 10⁻⁹ m² sec⁻¹. The POFs offer excellent stability under acidic conditions and retain their working capacity after long humidity exposure. The stability of POFs under harsh acidic conditions has also been established by 273 K CO₂ adsorption, which shows a negligible fall in the CO₂ saturation capacity.