Chitosan-assisted interfacial diffusion strategy for fabricating continuous ionic COF membranes

Ionic covalent organic frameworks (iCOFs) are promising materials for nanofiltration (NF) due to their ordered nanochannels and permanently charged pore surfaces. However, the introduction of ionic groups may affect the crystallization behavior and membrane assembly, which can make the construction of continuous iCOF membranes more demanding. In this work, Chitosan-assisted interfacial diffusion (ID) strategy was developed to fabricate continuous TpPa-SO₃H iCOF membranes on porous nylon substrates. The pre-deposited chitosan establishes a stabilized interfacial environment and facilitates the formation of a continuous selective layer with reduced defects. Structural characterizations confirm that chitosan effectively improves membrane continuity and suppresses interfacial defects. The optimized membrane achieves a high pure water permeance of 223 L·m −2 ·h −1 ·bar −1 with a Congo red (CR) rejection of 98.6% and low salt rejection (<10%), demonstrating excellent dye-salt separation performance.