Amino‐Acid‐Assisted Interfacial Polymerization Enables Reaction‐Diffusion of COF Membranes for High‐Performance Desalination

ABSTRACT Covalent organic framework (COF) membranes hold significant promise for energy‐efficient desalination, yet achieving precise control over their crystallization and selective‐layer architecture remains a formidable challenge. Herein, we report an amino‐acid‐assisted interfacial polymerization (AAIP) strategy that regulates reaction‐diffusion dynamics to enable the fabrication of highly crystalline, ultramicroporous membranes. L‐cysteine serves as a bifunctional molecular modulator, through cooperative electrostatic and hydrogen‐bond interactions to sequester isophthalic dihydrazide (IPH) monomers, thereby regulating monomer transport toward the reaction interface. The resulting reaction‐diffusion‐controlled growth facilitates the emergence of Turing‐patterned surface structure and promotes an ordered ABC‐stacked framework with high crystallinity. The resulting Tp‐IPH‐Cys 20% membrane exhibits a refined ultramicroporous architecture. When tested with 2000 ppm NaCl feed solution under an operating pressure of 15 bar, the Tp‐IPH‐Cys 20% membrane delivers a NaCl rejection rate of 98.1% and a water permeance of 1.0 L m −2 h −1 bar −1 , outperforming conventional COF membranes while demonstrating exceptional durability under both acidic exposure and 104 h of continuous hydraulic stress. More broadly, this work establishes amino‐acid‐directed reaction‐diffusion engineering as a versatile strategy for controlling the evolution of crystalline porous membranes, offering new pathways for mitigating the permeability‐selectivity trade‐off in advanced separation materials.