Mixed-linker ZIF-8 analogue membranes with improved O2/N2 and C2H4/ C3H6 separation performances synthesized by evaporation-induced rapid thermal deposition

초록

Here we report mixed linker ZIF-8 analogue membranes composed of dual ligands of 2-methylimidazole (mIm) and 2,4-dimethylimidazole (dmIm), which targets to improve the kinetic separation of gases of a ZIF-8 membrane by reducing effective pore aperture size. The rapid thermal deposition technique, which is based on evaporation-induced crystallization, was adopted to synthesize the membranes due to its simplicity. The reduction in effective pore aperture size with the addition of bulkier dmIm into ZIF-8 was indirectly confirmed by N2 isotherm measurements at 77 K and diffusion coefficients calculated from membrane permeation data. As a result, the O2/N2 and C2H4/C3H6 selectivities of the ZIF-8 analogue membrane containing 37.1 mol% dmIm were improved from 4.4 to 6.7 and from 16.9 to 24.3, respectively, compared to the ZIF-8 membrane due to the enhanced kinetic separation and the membrane showed sufficiently high O2 and C2H4 permeances of-140 GPU and-50 GPU despite the reduced pore size. Lastly, the performance was superior to those of previously reported polymer and MOF membranes.

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