Engineering nanofiltration membranes based on a two-step modification process with enhanced antifouling and salt separation performance

Nanofiltration (NF) membranes with impenetrable hydration layers and hydrophobic inserts can integrate multiple antifouling properties. This work used a two-step modification process to construct NF membranes with hydrophilic surfaces and low-surface energy inserts innovatively. The construction of antifouling surface consisted of two steps, including sequential grafting of triethanolamine (TEOA) and perfluorooctyltrimethoxysilane (POTS). Due to modification process by adjusting the pore size distribution and reducing the membrane surface negative charge, the Cl-/SO42- separation selectivity (α) of the modified membrane P-T-PA/PSF reached 49.53, which was 2.31 times higher than the virgin membrane. During the filtration of multiple modelled contaminants, irreversible flux decreases were reduced, and flux recovery after pure water backwashing was above 95% in all cases. Operational stability tests confirmed that P-T-PA/PSF membrane has superior pH stability, chlorine resistance, stability under high contaminant loading, and recoverability. Interfacial thermodynamic analysis quantitatively described the antifouling mechanism that increases the energy barrier of membrane-foulant interaction. This work lays the foundation for preparing NF membranes with enhanced antifouling and salt separation.