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

ABSTRACT 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 Co 2+ 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.