The double-edged sword effects of in-situ crosslinking in preparing ZIF-8-based mixed matrix membranes for propylene/propane separation

Seamless integration at the interphase is the foremost issue delaying the development of high-performance mixed matrix membranes (MMMs). Here we report an in-situ crosslinking strategy to effectively integrate the solvent-assisted linker exchange (SALE)-derived ZIF-8 with amidoxime-modified PIM-1 (AOPIM-1) for the challenging propylene/propane separation. In this crosslinking system, the AOPIM-1 polymer matrix can chemically anchor to the surrounding ZIF-8 fillers, promoting the formation of core-shell-like structures, thereby improving interfacial compatibility and filler dispersion. As a result, both high propylene permeability and high selectivity are readily achieved at a low filler loading (10 wt%), significantly surpassing the single- and mixed-gas upper bounds. Additionally, we demonstrate a contraction behavior in ZIF-8 unit cells that correlates with filler loading. Despite the persistence of excellent filler dispersion in highly loaded MMMs, excessive unit cell contraction leads to undesirable interfacial debonding and blocked transport through filler, ultimately deteriorating separation performance. Thus, the in-situ crosslinking imparts a ‘double-edged sword’ effect―simultaneously ensuring superior interfacial compatibility while inducing controllable ZIF-8 lattice contraction. These insights are expected to provide valuable guidance for the rational design and performance optimization of MOF-based MMMs via in-situ crosslinking.