Zinc Coordination‐Polymer‐Mediated Self‐Assembly of Nanoparticles into “Brick‐and‐Mortar” Membranes for Hydrogen Separation

Abstract Zeolitic imidazolate framework‐8 (ZIF‐8) with high stability and porosity is a promising candidate for hydrogen separation membranes. However, most ZIF‐8 polycrystalline membranes exhibit low H 2 /CO 2 (kinetic diameters of 2.9/3.3 Å) mixed gas selectivity, due to the intercrystalline defects and the unprecise molecular sieving originated from framework flexibility of ZIF‐8 structure with a theoretical aperture size of 3.4 Å. Here, inspired by nacre's “brick‐and‐mortar” structure, we develop mixed matrix type composite membranes in which dominant crystalline ZIF‐8 nanoparticles (bricks) are interconnected by ultrathin zinc coordination polymer interlayers (mortar) via self‐assembling. Driven by coordination bonds between Zn 2+ from precursor colloid and branched polyethyleneimine (PEI), a zinc coordination polymer network is formed to connect ZIF‐8 nanoparticles through interactions between Zn 2+ of coordination polymer and surface terminal groups on ZIF‐8 nanoparticles, thus eliminating intercrystalline void defects and providing a highly selective H 2 transport pathway. Meanwhile, the micropores and large cavities in ZIF‐8 allow fast H 2 transport. Benefitting from both highly selective pathway and fast H 2 transport through porous ZIF‐8, the optimized ZIF‐8‐PEI membrane exhibits a record‐high H 2 permeability of ~1.78×10 5 Barrer with a high mixed gas H 2 /CO 2 selectivity of 176, surpassing state‐of‐the‐art performance. This bioinspired multifunctional membrane expands the scope of molecular sieving membrane.