Tailoring Amine-Functionalized Ti-MOFs via a Mixed Ligands Strategy for High-Efficiency CO₂ Capture

Amine-functionalized metal-organic frameworks (MOFs) are a promising strategy for the high-efficiency capture and separation of CO₂. In this work, by tuning the ratio of 1,3,5-benzenetricarboxylic acid (H₃BTC) to 5-aminoisophthalic acid (5-NH₂-H₂IPA), we designed and synthesized a series of amine-functionalized highly stable Ti-based MOFs (named MIP-207-NH₂-n, in which n represents 15%, 25%, 50%, 60%, and 100%). The structural analysis shows that the original framework of MIP-207 in the MIP-207-NH₂-n (n = 15%, 25%, and 50%) MOFs remains intact when the mole ratio of ligand H₃BTC to 5-NH₂-H₂IPA is less than 1 to 1 in the resulting MOFs. By the introduction of amino groups, MIP-207-NH₂-25% demonstrates outstanding CO₂ capture performance up to 3.96 and 2.91 mmol g^-1, 20.7% and 43.3% higher than those of unmodified MIP-207 at 0 and 25 °C, respectively. Furthermore, the breakthrough experiment indicates that the dynamic CO₂ adsorption capacity and CO₂/N₂ separation factors of MIP-207-NH₂-25% are increased by about 25% and 15%, respectively. This work provides an additional strategy to construct amine-functionalized MOFs with the maintenance of the original MOF structure and high performance of CO₂ capture and separation.