“Living Nanosheets” of Covalent Organic Frameworks Aligned into Laminar Membranes for Sharp and Durable Molecular Separations

Abstract Organic solvent nanofiltration (OSN) requires membranes to have exquisite pore structures and excellent solvent resistance to alter energy‐intensive separation processes. Here, we report a scalable “living nanosheet” strategy for synthesizing covalent organic framework (COF) membranes with robust laminar structures. COF nanosheets and residual monomers are collectively cast onto smooth substrates, followed by heating in an enclosed environment. The slow shear‐flows make COF nanosheets accurately aligned into laminar structures while avoiding possible distortion. The COF nanosheets are still “living”, so that they can continue to react with remaining monomers upon heating, further healing the intercrystalline defects and stabilizing the laminar membranes. This strategy allows upscalable preparation of membranes with a large area of up to 600 cm 2 . The resulting COF membranes exhibit ultrahigh permeability (1.1 × 10 4 L m −2 h −1 bar −1 nm for methanol) and a sharp molecular weight cutoff (360 Da), outperforming state‐of‐the‐art OSN membranes. Notably, it achieves a sharp and durable separation process of photosensitizers (e.g., 98.3% rejection of TMPyP4 tosylate) and >92% solvent recovery. This work establishes a versatile approach for scalable synthesis of COF membranes, enabling energy‐efficient molecular separations in pharmaceutical and chemical industries.