Sealing grain boundary defects in polycrystalline ZIF-8 membranes by graphene oxide coating

• Grain boundary defects of ZIF-8 membranes were sealed by GO coating • GO/ZIF-8 membranes showed significant improvement in C 3 H 6 /C 3 H 8 separation factor • GO-based grain boundary sealing also enhanced the pressure-resistance of ZIF-8 membranes possibly by limiting the framework flexibility • GO did not affect the intrinsic transport properties of ZIF-8 membranes Here we report that a simple graphene oxide (GO) coating can seal the grain boundary (GB) defects of polycrystalline ZIF-8 membranes and thus improve C 3 H 6 /C 3 H 8 separation performance, especially separation factor. The effectiveness of GB defect sealing was investigated in terms of the number of GO coatings, the extent of GB defects in ZIF-8 membranes, and GO coating method (dip-coating under atmospheric pressure vs. dip-coating under vacuum), allowing us to conclude that the strategy can mend ZIF-8 membranes with a wide range of GB defects. Moreover, the GO sealing enhanced the pressure-resistance of a ZIF-8 membrane to some extent. Lastly, the GO-sealed ZIF-8 membrane was thermally stable and the intrinsic transport properties of a ZIF-8 membrane was not influenced by the presence of GO.