Perfluoro-functionalized polyethyleneimine that enhances antifouling property of nanofiltration membranes

In order to improve the antifouling property of nanofiltration membranes, extensive methods have been proposed aiming at enhancing the surface hydrophilicity. In contrast, limited studies focusing on lowering the surface free energy have been reported. In this work, polyethyleneimine (PEI) functionalized with perfluorobutylsulfonyl groups (FPEI) was synthesized and employed as aqueous monomer in interfacial polymerization (IP) process. A novel fluorinated polyamide nanofiltration (FPA/PES NF) membrane was obtained with a rejection to Na₂SO₄ of ~92.6% and a permeation flux of 6.5 L m⁻²· h⁻¹ at 6 bar. The covalently bonded perfluoro groups effectively lowered the surface free energy of the membrane. In addition, the surface of FPEI functionalized membrane was negatively charged at neutral pH, which was completely reversed as compared to the conventional PEI functionalized membrane. Due to these synergic effects, the membrane showed significantly enhanced fouling resistance to bovine serum albumin (BSA) and humic acid (HA), with the total flux decline ratios of 9.9% and 4.9%, respectively. Meanwhile, the corresponding flux recovery ratio (FRR) reached up to 99.1% and 98.0%. The perfluoro functionalization strategy may provide guidelines for designing antifouling nanofiltration membranes for various applications.