Green-synthesized covalent organic framework membranes for low-pressure high-flux applications

Covalent organic frameworks (COFs) are promising materials for fabrication of defect-free membranes due to their compatibility with polymers. However, harsh synthesis conditions and the use of toxic reagents hinder their practical applications. In this work, a green in-situ interfacial polymerization strategy was developed to fabricate COF/HPAN composite membranes, with ethyl acetate (EA) used as a solvent to replace toxic dichloromethane (DCM). A self-standing COF membrane was prepared via the Schiff-base reaction of m -phenylenediamine (MPD) and benzene-1,3,5-tricarboxaldehyde (TFB), and its crystal structure was characterized to confirm successful synthesis. The resulting membranes demonstrated ultrahigh permeability (462.8 L m −2  h −1  bar −1 ) at a low operating pressure (1 bar), 99% rejection for Congo Red (CR), Methyl Blue (MB) and Methylene Blue (MeB), low rejection of salts (less than 20% for NaCl, MgCl 2 , MgSO 4 and Na 2 SO 4 ), and excellent antifouling performance (a flux recovery rate of 98.7%). This study provides a sustainable strategy for efficient dye/salt separation, which sets an important benchmark for the preparation of next-generation green nanofiltration membranes for industrial applications.