A dual-layer ZnO–Al2O3 hollow fiber for directly inducing the formation of ZIF membrane

Despite many methods available to synthesize MOF membrane, the cost-effective synthesis with high reproducibility and scalability is still a challenge. We present here a homologous support-induced approach for the growth of ZIF membrane supported on the dual-layer ZnO–Al2O3 hollow fibers, which has the potential for applications at larger scales. The developed unique dual-layer hollow fibers consisting of a thin outer ZnO layer firmly attached onto an inner porous alumina substrate were realized through one-step co-extrusion/sintering technique. During the MOF membrane synthesis, ZnO can be used not only as the support, but also as the nucleation sites and growth centers for the ZIF-8 membrane formation. More importantly, ZnO can act as a transitional bridge to direct the membrane growth outward along the support and inward embedded into the support, which significantly improving the binding force between the support and MOF, thus bringing in the outstanding membrane stability. Permeation of single gas and separation of binary mixtures revealed that the prepared membranes were free of defects. The resultant ZIF-8 composite membrane exhibits good hydrogen separation performance and excellent reproducibility. This protocol can achieve an easy and large-scale synthesis. In addition to ZIF-8 membrane, ZIF-67 membrane was also successfully synthesized via this method, which may provide some general guidelines for the preparation of other MOF membranes.