Optimizing polyamide thin-film composite desalination membranes: simple and performance-effective modification by zwitterionic monohydroxyl monomer

A synthesized zwitterionic monohydroxyl monomer (ZHM) was used as an additive to incorporate zwitterionic sulfobetaine groups into the polyamide (PA) active layers of thin-film composite membranes. Incorporation of ZHM into the PA active layers was achieved through interfacial polymerization, involving the introduction of ZHM and m-phenylenediamine (MPD) into the aqueous phase, and the addition of trimesoyl chloride (TMC) to the hexane phase. The surfaces of the resulting reverse osmosis (RO) membranes were subjected to characterization through water contact angle (WCA) and field emission scanning electron microscopy (FESEM) analyses. The successful incorporation of ZHM into the active PA layers was confirmed by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) analysis. To assess the flux and salt rejection performance of the fabricated membranes, aqueous solutions containing 2000 ppm NaCl or MgSO₄ were filtered in a dead-end filtration system under a pressure of 15 bar. Compared to the control membrane (ZHM-0), the ZHM-modified membranes had significantly enhanced flux without compromising salt retention. In the NaCl solution filtration, the modified membrane (ZHM-1) increased in flux from 6.8 to 9.1 L/m²h while having similar salt rejection (approximately 91%) in comparison to the control membrane (ZHM-0). In the MgSO₄ solution filtration, the modified membranes increased in flux from 6.7 to 9.5 L/m²h, while maintaining a consistent salt rejection rate of 100%, mirroring that of the control membrane.