Epigallocatechin gallate based metal-phenolic network modified covalent organic framework membranes for dye/salt separation

Covalent organic framework (COF) membranes with high porosity and ordered channels possess significant potential for the removal of organic micropollutants from wastewater, offering ultrafast water permeance. This study developed a novel COF-based composite membrane to improve the selectivity of dye/salt separation. The COF layer was initially fabricated via interfacial polymerization using 1,3,5-triformylbenzene and m -phenylenediamine on the hydrolyzed polyacrylonitrile (HPAN) substrate. Subsequently, an in situ grown metal-phenolic network (MPN) layer was formed on the COF layer through the complexation reaction between epigallocatechin gallate (EGCG) and Cu 2+ . The combination of the Cu-EGCG-based MPN layer and the COF layer enhanced the compactness, charge properties, and wettability of the selective layer, thereby improving dye rejection while maintaining relatively low salt rejection. The resulting membrane exhibited rejections of 98.8% for Congo red (CR) and 11.6% for NaCl, with a water permeance of 50.6 L m −2  h −1  bar −1 . In addition, the fabricated membrane exhibited separation stability in the long-term filtration process and demonstrated satisfactory regeneration performance after repeated filtration and cleaning with aqueous ethanol. This work demonstrates an effective post-modification approach for tuning the separation performance of COF membranes.