Advances in nanofiltration membrane design for water purification: Enhancing micropollutant rejection and salt passage

The occurrence of micropollutants (MPs) in water systems has become a growing global concern due to their persistence and potent biological activity. Nanofiltration (NF) has gained significant attention as an effective treatment technology because it enables high MP removal at relatively low operating pressures. Nevertheless, its broader application is limited by an intrinsic selectivity trade-off, as conventional NF membranes tend to reject both MPs and salts. Recent advancements in NF membrane fabrication and modification via interfacial polymerization (IP), nanoparticle incorporation, and layer-by-layer (LbL) assembly have demonstrated improved permeability, enhanced antifouling properties, superior stability, and high MP rejection while allowing the passage of desirable salts. Progress in membrane design, particularly through tailoring active-layer chemistry, controlling crosslinking density, engineering transport pathways, and modifying surface functionalities, has enabled the fabrication of ultrathin polyelectrolyte selective layers with tunable charge and hydration characteristics. These advancements position NF membranes among the most promising technologies for water purification. Despite this progress, comprehensive reviews in this field remain scarce. Addressing this gap, the present review systematically explores recent advances in NF membrane fabrication, outlines key challenges, and discusses future research directions. It begins with the fundamental properties of NF membranes, followed by an overview of their separation mechanisms. The review further evaluates membrane stability, including performance in real water matrices and resistance to fouling. Finally, it provides perspectives on the future development of NF technologies, with a focus on enhancing MP removal while maintaining adequate salt permeability.