Tailored Design of Mesoporous Aminated Imidazolium Poly(ionic liquid)s: Practical Chemisorption Metric and Detailed Insights into CO ₂ Sorption Behavior

Mitigation against climate change requires efficient and selective CO₂ capture technologies, especially under low-concentration conditions. Herein, we report a reproducible and scalable synthesis of mesoporous aminated imidazolium-based porous poly(ionic liquid)s (PILs) via solvothermal radical polymerization. Despite moderate surface areas, these materials exhibit high CO₂ uptake (up to 2.5 mmol g^-1) and CO₂/N₂ selectivity at low CO₂ pressures, driven by the chemical interaction between CO₂ and the amine-functionalized imidazolium matrix. A practical screening metric, the Low-Pressure Uptake Efficiency (LPUE), was introduced to distinguish sorbents operating via physisorption from those favoring chemisorption. Our aminated porous organic polymers (POPs) displayed relatively high LPUE values (58-66%), indicative of sorption primarily driven by chemisorption. We systematically evaluated the influence of counteranion, cross-linker, amine substitution, and humidity. Solid-state nuclear magnetic resonance (ssNMR) experiments on ¹³CO₂-labeled samples revealed the formation of carbamate-ammonium and carbamic acid species under dry conditions, while water favored carbamate and allowed bicarbonate formation. Breakthrough experiments demonstrated enhanced CO₂ uptake under humid conditions, which is particularly relevant for direct air capture (DAC). Compared to the hydrophobic cross-linker divinylbenzene (DVB), the hydrophilic cross-linker exhibited excessive water uptake, limiting the performance under humid conditions. This dilemma was mitigated by introducing hydrophobic anions such as bis(trifluoromethanesulfonyl)imide (TFSI^-). These findings underscore the versatility of aminated imidazolium PILs for tailored CO₂ capture and highlight their potential for integration into sorption-desorption cycles.