Metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) hybrids are novel porous composite materials with potential applications in advanced membrane separations. However, the preparation of defect-free and self-standing separation membranes remains challenging. Here, we report a COF-MOF composite membrane with a sandwich layer structure and a two-dimensional (2D) intergrown nanosheet morphology. This was achieved by inducing the secondary growth of a layer of MOF (ZIF-67) membrane using a two-dimensional COF (TpPa1) membrane as a seed layer and porous support. It is worth noting that a rare ZIF-67 membrane consisting of 2D nanosheets was grown on the TpPa1 porous support. The [TpPa1]-[ZIF-67] membranes exhibited excellent permeance for organic solvents, pure water (95.3 L m h bar), with high rejection rates (>97 %) towards dyes larger than 700 Da, while maintaining a low rejection rate for hydrated salt ions (<14 %) and outstanding dye/salt selectivity. The membranes also displayed considerable long-term operational stability and could be easily transferred to other substrates without damaging their integrity. The excellent separation properties achieved through layer-by-layer filtration are mainly due to the sandwich structure and the synergistic effect of the components.

中文翻译：

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用于染料分离的高渗透性自支撑COF-MOF复合夹层膜


金属有机框架（MOF）和共价有机框架（COF）杂化物是新型多孔复合材料，在先进膜分离中具有潜在应用。然而，制备无缺陷且自支撑的分离膜仍然具有挑战性。在这里，我们报道了一种具有夹层结构和二维（2D）共生纳米片形态的COF-MOF复合膜。这是通过使用二维 COF (TpPa1) 膜作为种子层和多孔支撑物诱导 MOF (ZIF-67) 膜层的二次生长来实现的。值得注意的是，由 2D 纳米片组成的罕见 ZIF-67 膜是在 TpPa1 多孔支撑上生长的。 [TpPa1]-[ZIF-67] 膜对有机溶剂、纯水 (95.3 L m h bar) 表现出优异的渗透性，对大于 700 Da 的染料具有高截留率 (>97%)，同时保持低截留率用于水合盐离子 (<14%) 和出色的染料/盐选择性。该膜还表现出相当大的长期运行稳定性，并且可以轻松转移到其他基材上，而不会损坏其完整性。逐层过滤所实现的优异分离性能主要得益于夹层结构和各组分的协同效应。