Fine‐Tuned Ultra‐Microporous Metal–Organic Framework in Mixed‐Matrix Membrane: Pore‐Tailoring Optimization for C₂H₂/C₂H₄ Separation

Abstract Effective separation of ethyne from ethyne/ethylene (C₂H₂/C₂H₄) mixtures is a challenging and crucial industrial process. Herein, an ultra‐microporous metal–organic framework (MOF) platform, Cd(dicarboxylate)₂(ditriazole), with triangular channels is proposed for high‐efficiency separation of C₂H₂ from C₂H₄. The targeted structures are constructed via a mixed‐ligand strategy by selecting different‐sized ligands, allowing for tunable pore sizes and volumes. The pore properties can be further optimized by additional modification via pore environment tailoring. This concept leads to the successful synthesis of three ultra‐microporous Cd‐MOFs (JLU‐MOF87–89). As intended, C₂H₂ uptake and C₂H₂/C₂H₄ selectivity gradually increase with progressively optimizing the pore structure by adjusting ligand length and substituents. JLU‐MOF89, functionalized with methyl groups, features the most optimal pore chemistry and shows selective recognition of C₂H₂ over C₂H₄, owing to the framework–C₂H₂ host–guest interactions. Furthermore, JLU‐MOFs are fabricated into mixed‐matrix membranes for C₂H₂/C₂H₄ separation. C₂H₂ permeability and C₂H₂/C₂H₄ permselectivity are substantially enhanced by ≥400% and ≥200%, respectively, after hybridization of JLU‐MOF88 and JLU‐MOF89 with a polyimide polymer (6FDA–ODA). These membranes can work efficiently and are stable under different conditions, demonstrating their potential in actual ethyne separation.