In Situ Synthesis of Multivariate Zeolitic Imidazolate Frameworks for C2H4/C2H6 Kinetic Separation

Herein, a new approach for the in situ synthesis of zeolitic imidazolate framework (ZIF) nanoparticles with triple ligands, referred to as Sogang ZIF‐8 (SZIF‐8), is reported for enhanced C2H4/C2H6 kinetic separation. SZIF‐8 consists of tetrahedral zinc metals coordinated with tri‐butyl amine (TBA), 2,4‐dimethylimidazole (DIm), and 2‐methylimidazole (MIm). SZIF‐8(x) with different DIm contents in x (up to 23.2 mol%) are synthesized in situ because TBA preferably deprotonates DIm ligands due to the much lower pKa of DIm over MIm, allowing for the Zn‐DIm coordination. The Zn‐DIm coordination reduces the window size of ZIF‐8 with suppressed linker flipping motion due to bulky DIm ligands and simultaneously enhances the interfacial interaction between 6FDA‐DAM polyimide (6FDA) and SZIF‐8 via electron donor–acceptor interactions. Consequently, 6FDA/SZIF‐8(13) mixed matrix membrane exhibits an excellent C2H4 permeability of 60.3 Barrer and C2H4/C2H6 selectivity of 4.5. The temperature‐dependent transport characterization reveals that such excellent C2H4/C2H6 kinetic separation is attained by the enhancement in size discrimination‐based energetic selectivity. Our hybrid multi‐ligand approach can offer a useful tool for the fine‐tuning of molecular structures and textural properties of other metal organic frameworks. In this work, multivariate zeolitic imidazolate frameworks (ZIFs) are synthesized in situ, using a solution‐based approach for C2H4/C2H6 kinetic separation, denoted as Sogang ZIF‐8 (SZIF‐8). The SZIF‐8 exhibits a smaller pore size with suppressed flipping motion and enhanced interfacial interaction with polyimide chains compared to ZIF‐8. The subsequent polyimide/SZIF‐8 hybrid membrane enhances both C2H4 permeability and C2H4/C2H6 selectivity by 80% and 40%, respectively, compared to polyimide membrane.