FO membrane fabricated by layer-by-layer interfacial polymerisation and grafted sulfonamide group for improving chlorine resistance and water permeability

This study presents a layer-by-layer interfacial polymerization approach to enhance the chlorine resistance and water permeability of thin-film composite (TFC) polyamide (PA) forward osmosis membranes. The PA film was prepared by self-polymerization using 3,5-Dihydroxybenzoic acid (DHBA) and trimesoyl chloride (TMC) with addition of 4-amino-benzene sulfonamide (4-ABSA), which is a sulfonamide monomer, on a polysulfone (PSF) support layer. The cross-linking structure and surface characterisation of the DHBA-ABSA membrane was studied systematically. FTIR results showed the successful grafting of the sulfonamide group on the membrane surface. Compared with the MPD-TMC membrane, the water flux of three modified membranes—DHBA, ABSA, and DHBA with ABSA—improved by 27.6%, 44.0%, and 67.6%, respectively, and reverse salt flux decreased by 9.9%, 12.3%, and 16.2%, respectively. Furthermore, the chlorine-stability test using 200 ppm NaClO indicated stable long-term performance under different pH values. The stable sulfonamide structure of ABSA with N-H group effectively prevented chlorine from directly attacking the active layer and improve the chlorine-stability of the membrane. In addition, the abundant hydrophilic groups on ABSA and DHBA monomers formed a hydration layer with water molecules on the membrane surface through hydrogen bonding, which enhanced the permeability of the TFC-PA membranes. The findings of this study demonstrate the DHBA-ABSA membrane's wider application potential in water and wastewater treatment processes.