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 H2/CO2 (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 Zn2+ from precursor colloid and branched polyethyleneimine (PEI), a zinc coordination polymer network is formed to connect ZIF-8 nanoparticles through interactions between Zn2+ of coordination polymer and surface terminal groups on ZIF-8 nanoparticles, thus eliminating intercrystalline void defects and providing a highly selective H2 transport pathway. Meanwhile, the micropores and large cavities in ZIF-8 allow fast H2 transport. Benefitting from both highly selective pathway and fast H2 transport through porous ZIF-8, the optimized ZIF-8-PEI membrane exhibits a record-high H2 permeability of ~1.78×105 Barrer with a high mixed gas H2/CO2 selectivity of 176, surpassing state-of-the-art performance. This bioinspired multifunctional membrane expands the scope of molecular sieving membrane.
Published Version
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