Deep Eutectic Solvent–Water Interfacial Polymerization: A Scalable Route to Tailorable Covalent Organic Framework Membranes

The synthesis of thin, large-area, and highly ordered covalent organic framework (COF) membranes with high flux and selectivity toward targeted separations remained a vital challenge. Herein, we propose a deep eutectic solvent (DES)-water platform with suppressed Marangoni effect and tailorable interfacial properties to construct diversified freestanding and crystalline COF membranes, and the fabrication process can be scaled to an area of 600 cm². A "bilateral constraint" strategy mediated by the high viscosity of DES and hydrogen bonds in both phases to mediate the diffusion of monomers was validated. We further demonstrate that the nucleation and reaction kinetics were drastically suppressed by tailoring the Brønsted acidity of DES, leading to a slow polycondensation rate and thermodynamically controlled crystallization at the interface. Benefiting from the periodic 1D open porous structure, the obtained COF membranes exhibited high selectivity in antibiotics or dye separations with unprecedented water permeance (up to 307.5 L m^-2 h^-1 bar^-1), which is 3 times higher than most of the state-of-the-art systems. This discovery advances the scalable production of robust crystalline membranes and broadens the scope of interfacial polymerization.