Interface-Induced Growth of Macroscopic, Free-Standing, and Flexible Monolithic Pure MOF Membrane With Adaptive Porosity.

Membrane-based separation technologies have emerged as energy-efficient and environmentally sustainable alternatives to traditional industrial separation processes. However, the development of high-performance separation membranes faces fundamental material challenges, as amorphous polymeric materials typically exhibit poorly controlled pore size distributions while crystalline porous materials encounter intrinsic difficulties in forming continuous, defect-free membranes at the macroscopic scale owing to inevitable crystal boundaries. Despite their exceptional structural tunability and separation potential, MOF membranes face fundamental challenges in defect-free fabrication due to intrinsic crystallinity constraints. Integrating the structural precision of crystalline MOFs with the adaptivity of polymers, we successfully fabricated a macroscopic, free-standing, and flexible monolithic pure MOF membrane through interface-induced coordination of Co2+ with the flexible multidentate amino acid ligand 2,6-diaminopimelic acid (DAP). The flexible alkyl-chain backbone suppresses long-range crystallization and reduces interfacial strain during continuous membrane growth. Locally defined Co-amino-acid coordination units preserve a framework scaffold, while conformationally flexible alkyl segments impart guest-responsive latent free volume. The flexible Co-DAP membrane exhibits guest-responsive dynamic porosity, in which hydration generates water-accessible transport pathways that regulate hydrated-state molecular and ionic transport, enabling osmotically driven water/ion separation through coupled transport and interfacial electrostatic effects under conditions relevant to forward osmosis.