Facile dual-functionalization of NF membranes with excellent chlorine resistance and good antifouling property by in-situ grafting of zwitterions

During water treatment, the chlorination degradation by active chlorine and membrane fouling seriously threaten the service life of nanofiltration (NF) membranes. In this work, dual-functionalized NF membranes were facilely fabricated by in-situ grafting of zwitterions, which were generated by in-situ grafting 2,4,6-Triaminopyrimidine (TAP) onto the separation layer and the subsequential quaternization. The introduction of zwitterions was confirmed by ATR-FTIR and XPS. Under constant chlorine exposure (24000 ppm·h), chlorine with high concentration proved to be more corrosive. After harsh 24000 ppm·h chlorination in different environments (pH = 4.0, 7.0, and 10.0, respectively), all the salt rejections of the zwitterion-grafted NF membranes (the QTAP NF membranes) were higher than 98.0% and barely decreased. The flux of the QTAP NF membranes was 23.5% higher than that of the pristine NF membranes in acid chlorine environment after chlorination. The SEM and ATR-FTIR results indicated that no obvious change occurred to the surface morphologies and chemical structures for the QTAP NF membranes after chlorination. Flux recovery ratio (Bovine serum albumin) of the QTAP NF membranes was 91.2%, which indicated good antifouling property. The quaternization process slightly increased the rejection for inorganic salts. The zwitterions endowed the membranes with excellent chlorine resistance and good antifouling property. This study could provide a facile and effective strategy for constructing dual-functional NF membranes with chlorine-resistance and antifouling property.