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 NH_2(0.6)-MFM-136, representing a 55% enhancement more than MFM-136. Concurrently, the CO₂/N₂ selectivity for NH_2(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 NH_2(0.6)-MFM-136 was 34% less than that for MFM-136 after 24 h of exposure to simulated flue gas, making NH_2(0.6)-MFM-136 a promising candidate for the potential application of stable and selective CO₂ capture under industrial flue gas conditions.