Functionalized Dual/Multiligand Metal–Organic Frameworks for Efficient CO2 Capture under Flue Gas Conditions

Reducing carbon dioxide (CO2) emissions has become increasingly urgent for China, particularly in the industrial sector. Striking a balance between a high CO2 adsorption capacity and long-term stability under practical conditions is crucial for effectively capturing CO2 from flue gas. In this study, a series of functionalized MFM-136 adsorbents were synthesized in which -NO2 and -NH2 groups were grafted onto the kagome lattice of MFM-136. Modifications with -NH2 groups were found to be highly effective for CO2 adsorption, specifically, the CO2 adsorption capacity peaked at 4.35 mmol/g for NH2(0.6)-MFM-136, representing a 55% enhancement more than MFM-136. Concurrently, the CO2/N2 selectivity for NH2(0.6)-MFM-136 was increased 1.57 times. Verification of novel adsorption sites introduced by NH2–H2L4 was conducted by using in situ DRIFT analysis and DFT calculations. It turns out that NH2–H2L4 modification can effectively mitigate the chemical deposition from the impurity gases and significantly improve the adsorbent’s hydrophobicity and its tolerance to impurity gases. Remarkably, the reduction in the CO2 absorption capacity for NH2(0.6)-MFM-136 was 34% less than that for MFM-136 after 24 h of exposure to simulated flue gas, making NH2(0.6)-MFM-136 a promising candidate for the potential application of stable and selective CO2 capture under industrial flue gas conditions.