Post-synthetic modification of ZIF-8 with AOPIM-1: Enhancing interfacial compatibility and gas-separation performance of mixed matrix membranes via dual interfacial bonding strategy

Mixed matrix membranes (MMMs) composed of polymers and metal-organic frameworks (MOFs) can effectively break the trade-off between selectivity and permeability of pure polymer membranes, thus holding great potential for the development of high-efficiency gas separation membranes. Nevertheless, structural mismatches between polymer matrix and MOF particles easily cause interfacial defects and filler aggregation, which severely hinder efficient gas separation. In this work, a novel interfacial bonding strategy is proposed. Specifically, an amidoxime-modified polymer of intrinsic microporosity (AOPIM-1) with similar structure to polymer matrix (PIM-1) is firstly used to modify and encapsulate the zeolitic imidazolate framework-8 (ZIF-8), generating a composite filler AO@ZIF. Within the resultant MMMs, due to the Zn-N coordination bonds and hydrogen bonds between ZIF-8/AOPIM-1 and PIM-1/AOPIM-1, respectively, low-defect interfaces are obtained. The optimized interfacial compatibility further achieves efficient CO 2 /N 2 separation performance. Particularly, when the filler loading is 2.5 wt%, the CO 2 /N 2 selectivity of the AO@ZIF-2.5/PIM-1 membrane increases by 72.8% and 46.0% compared with pristine PIM-1 and ZIF-2.5/PIM-1 membrane, exceeding the 2008 Robeson upper bound and approaching the 2019 Robeson upper bound. Moreover, the resultant membranes also possess outstanding mechanical properties, anti-plasticization capacity, and excellent anti-physical aging stability. This study provides a feasible strategy for interfacial design and performance optimization of high-performance MOF/polymer MMMs toward advanced gas separation.