Zwitterionic ZnO nanoparticles: Novel additives to synthesize high performance and fouling resistance thin-film nanocomposite forward osmosis membrane

Meeting the ever-increasing need for clean water requires developing highly effective thin-film nanocomposite (TFN) membranes with outstanding water permeability, selectivity, and good fouling resistance. In this work, ZnO nanoparticles were synthesized and coated with zwitterionic lysine amino acid (ZnO-lysine) and then incorporated into a polyamide layer to improve their performance as well as to alleviate fouling. The organic shell on the ZnO-lysine surface promoted the PA layer's interaction with ZnO-lysine nanoparticles. TFN membranes demonstrated hydrophilic and smooth polyamide layers with improved permeability and selectivity. In particular, the TFN membranes' enhanced hydrophilicity and smooth surface synergized fouling reduction. In comparison to the bare TFC membrane (12.2 LMH) using 1 M NaCl as the draw solution, the ZnO-lysine-modified TFN-ZL.400 membrane (21.1 LMH) yields a water flux that is 75% greater. In the polyamide layer, the zwitterionic functional groups of ZnO-lysine not only improved the nanoparticles' chemical compatibility, preventing the creation of nonselective gaps, but also enhanced water flux and salt rejection. This study provides insight into the creation of zwitterionic-functionalized nanoparticles that can successfully address fouling issues and trade-off restrictions between selectivity and permeability in TFN membranes.