Hypercrosslinked natural biopolymers with quasi-unimodal micropores for carbon capture

Ultra-microporous solid sorbents with high CO₂ adsorption capacities and gas selectivity are preferred for carbon capture. Here we deliver such sorbents via a combination of narrow micropores, lack of mesopores and an abundance of CO₂-philic functional groups. This was achieved by crosslinking lignin waste obtained from a local paper factory, in Lewis's acid deep eutectic solvents (DESs) such as [ChCl][ZnCl₂]₂ and [ChCl][FeCl₃]₂, varying crosslinker types and optimizing experimental parameters. Hypercrosslinked polymers (HCPs) prepared in [ChCl][FeCl₃]₂ with 1,4-dichloroxylene crosslinkers comprised quasi-unimodal, ultra-narrow micropores. At 298 K, 1 bar, and using a gas mixture comprising 15 vol.% CO₂ and 85 vol.% N₂ (similar to post-combustion flue gas), the CO₂ adsorption capacity and CO₂/N₂ selectivity of this HCP reached 18.1 cm³ g⁻¹ and 835, respectively. Deployed in temperature swing adsorption and evaluated for vacuum pressure swing adsorption, the CO₂ recovery rates of this HCP were >87 %, outperforming commercial solid sorbents such as zeolite 13X and PSAO2 HP Molsiv™. The optimization of sorbent microporosity with CO₂-philic functional groups could pave the route towards developing bio-derived solid sorbents for carbon capture.