Stepwise growth for preparing highly loaded ZIF-8 ultrathin mixed matrix membranes towards efficient CO2/N2 separation

Metal-organic framework (MOF)-based membranes show promising potential for gas separation. However, it remains challenging to fully exploit the synergistic advantages of MOF crystals and polymers for fabricating highly loaded mixed matrix membranes (MMMs). Herein, a highly loaded ZIF-8 ultrathin MMM was prepared in situ via a stepwise growth strategy. Driven by the diffusion rate difference between the ligand and polyethyleneimine (PEI-600), preferentially formed ZIF-8 crystals served as the dominant phase, while the subsequently developed PEI-Zn 2+ crosslinked network acted as an intergranular densification phase. Owing to the reduction in ZIF-8 crystal size induced by PEI, the MMMs exhibited an ultrathin thickness of only 160 nm. Furthermore, PEI enhanced the molecular sieving ability of crystals and membrane's CO 2 /N 2 solubility selectivity by regulating the pore structure and membrane composition. With a high ZIF-8 loading of 84.3 %, the resulting MMMs demonstrated an excellent CO 2 permeance of 3177.4 GPU, accompanied by a CO 2 /N 2 selectivity of 36.9. Notably, it maintained stable separation performance after bending and during long-term operation, showing good processability and industrial application potential. This strategy not only reinforces the advantages of MOF-based gas separation membranes but also provides a new paradigm for fabricating highly loaded MMMs.