Designing multilayer interlocked architectures with vertical LDH nanosheets in ZIF-67 composite membranes for upgrading CO₂ separation

Metal-organic framework (MOF) membranes, by virtue of their high selectivity and low diffusion resistance, make a significant contribution to energy conservation and CO₂ emission reduction via separation technology. Despite possessing substantial potential for propelling the production of high-performance membranes, hurdles persist in the process of constructing MOF membranes that are both highly integrated and structurally sound on flexible polymer substrates. We propose a strategy for constructing highly stable cobalt zeolitic imidazolate framework (ZIF-67) composite membranes on seeded polyacrylonitrile (PAN) substrate. Through a timed-interrupted in-situ growth process, the amino-modified polycrystalline ZIF-67 as a CO₂ affinity layer is precisely and completely confined within the “top sites” and partial “face sites” of the vertical layered double hydroxide (LDH) precursor layer, creating a barrier-low passage for CO₂ as a fast diffusion layer. The substrate and the hybrid ZIF-67@LDH layer were robustly anchored together by the pre-embedded LDH seeds, thereby producing an appealing membrane-multilayer interlocked-support (MMIS) composite architecture. This fast diffusion-CO₂ affinity Pebax/ZIF-67@LDH/PAN membranes with MMIS architecture show average CO₂ permeability of 1487 Barrer and CO₂/N₂ selectivity of above 55.1 after the surface repair coating of polyether-block-amide (Pebax), maintaining stable performance over 150 h, surpassing the Robeson upper bound. The Pebax/ZIF-67@LDH/PAN membranes also exhibit the durability and mechanical robustness, because of the highly inducible activity of LDH precursor layer serving as a linker between the membrane and substrate. These results promote the development of MOF-based membranes in practical separation applications.