A facile metal ion pre-anchored strategy for fabrication of defect-free MOF membranes on polymeric substrates

Fabricating metal-organic framework (MOF) membranes on processable and flexible polymeric substrates is of great significance for potential practical application, but remains technically challenging due to the lack of nucleation sites on polymeric substrates. Here, we report an efficient and facile method to render abundant and uniform nucleation sites on the substrate surface by pre-anchoring metal ions through coordination-driven self-assembly of metal-organophosphate. The coordination between the multidentate phytic acid (PA) and the metal ions enables the functionalization of polymeric substrates with a metal-phytic acid layer, which anchors metal ions to promote the subsequent generation of thin and defect-free MOF layers thereon. As an illustration, the ZIF-8 membrane was synthesized on Zn2+-PA functionalized polyacrylonitrile substrate and optimized by regulating the pre-anchored Zn2+ content. The obtained ZIF-8 membrane exhibited a superior separation performance for C3H6/C3H8 mixture, harvesting selectivity up to 150 with C3H6 permeance of 70 GPU. Besides, the polycrystalline ZIF-8 membrane also displays excellent bending and pressure resistance due to the strong combination between the MOF layer and the polymeric substrates from the fortified and robust bridging coordination effect of the metal-organophosphate layer. Our strategy can be extended to diverse MOFs and polymeric substrates, paving a facile and generic way to fabricate MOF membranes.