MOF-Based Chemi-/Physi-Relay Sorbents for High Performance CO₂ Capture under Flue Gas Humidity

Metal–organic frameworks (MOFs) are promising candidates for postcombustion flue gas CO2 capture. MOF-based sorbents are either physisorption-dominating or chemisorption-dominating. The former often lacks strong binding sites for low-pressure CO2 capture or suffers from performance degradation under moisture, while the latter typically requires a high regeneration energy. Herein, we report amine-grafted CPM-200 materials that overcome these limitations through a chemisorption-physisorption relay mechanism. Structural characterization reveals distinct chemisorption and physisorption regions, with dual-stage sorption confirmed by isotherms, heat of adsorption, and 13C NMR. The optimized en-CPM-200 demonstrates exceptional performance: high CO2 uptake (2.62 mmol/g at 0.15 bar), outstanding selectivity (CO2/N2 ∼ 1367), and moderate adsorption heat (54.6 kJ/mol). Remarkably, under realistic flue gas conditions (6% water content), en-CPM-200 shows a 26% increase in dynamic CO2 uptake versus dry conditions while maintaining excellent cycling stability. This humidity-enhanced performance, combined with balanced adsorption heat, positions en-CPM-200 among the most promising sorbents for practical postcombustion carbon capture.