Confined synthesis of ionic covalent organic framework membranes for efficient sub-nanosized liquid molecular separations

Ionic covalent organic frameworks (iCOFs) with long-range ordered pore structures and chemical versatility have emerged as promising materials for engineering advanced membranes to tackle challenging separation demands. Nevertheless, the facile and controllable fabrication of continuous free-defect iCOF membranes (iCOFMs) for sub-nanosized molecular separation remains a critical challenge. Herein, the continuous iCOFMs have been fabricated on flexible polymer supports via the confined contra-diffusion interfacial polymerization strategy. Through adjusting the monomer concentration and reaction time, the conformal growth of iCOF along the polymer supports can be well-regulated to form continuous defect-free iCOFMs. The iCOFMs featuring hydrophilic ionic groups are in favor of generating sieving channels that promote water-selective transport. The optimal iCOFM exhibits superior butanol dehydration separation efficiency with a permeation flux of 12,620 g m −2  h −1 and a separation factor up to 3161, surpassing the most state-of-the-art membranes. Meanwhile, it maintains stable separation performance in long-term operation due to its exceptional chemical and mechanical stability. This study provides new insights for the construction of iCOFMs in precise sub-nanosized molecular separations.