In-situ growth of ZIF-8 in amphiphilic graft copolymer for mixed matrix membranes with simultaneous improvement of permeability and selectivity

The fabrication process of mixed matrix membranes (MMMs) typically involves the solution mixing of pre-synthesized fillers and polymer matrix; however, its application is limited by poor dispersion of fillers and interfacial adhesion. Herein, we report the preparation of high-performance MMMs based on the in-situ growth of ZIF-8 nanoparticles within an amphiphilic graft copolymer matrix, poly(vinyl chloride)-graft-poly(oxyethylene methacrylate) (PVC-g-POEM). The process involves the formation of PVC-g-POEM/Zn(NO₃)₂ complex membranes, followed by their immersion into 2-methylimidazole (2MI) organic linker solution. Zn²⁺ ions have strong coordination interactions with the hydrophilic POEM domains, resulting in a reduced free volume and decreased gas permeability. Upon the infiltration of MI, the ZIF-8 nanoparticles are in-situ grown in the matrix, resulting in the simultaneous improvement of permeability and selectivity. The in-situ grown MMM with 28.7% loading shows a high CO₂ permeability of 244.9 Barrer, CO₂/N₂ selectivity of 39.3, and CO₂/CH₄ selectivity of 14.0. This performance is much better than those of pristine PVC-g-POEM and conventional MMMs with pre-synthesized ZIF-8. This novel in-situ approach will encourage the development of next generation MMMs.