Engineering a nanofiltration membrane with high mono-/divalent anion selectivity and antifouling properties via L-histidine incorporation

The limited mono−/divalent anion selectivity and inadequate antifouling properties of polyamide (PA) nanofiltration (NF) membranes restrict their use in water treatment. Herein, L-histidine (L-His)-modified NF membranes were prepared through interfacial polymerization on a polyethersulfone porous substrate. The aqueous-phase comonomers were piperazine and L-His, which contain both amino and carboxyl groups, while the organic-phase monomer was trimesoyl chloride. Compared with the NF0 membrane without addition of L-His, all of the L-His-modified membrane was characterized by a higher surface roughness, a thinner PA layer, greater hydrophilicity, a more negative surface charge and a larger mean pore size. Among them, the optimal NF0.5 membrane with the addition of 0.5% ( w / v ) L-His demonstrated a pure water permeability of 17.9 L/(m 2 ·h·bar) and a 2.7-fold higher NaCl/Na 2 SO 4 selectivity (up to 102.0). In particular, the NaCl/Na 2 SO 4 selectivity improved with higher operating pressure, but decreased with increasing single-salt concentration or NaCl/Na 2 SO 4 mass ratio in the feed solution. In addition, the NF0.5 membrane demonstrated superior resistance to protein fouling and outstanding long-term operational stability throughout a continuous 7-day filtration process. This study could provide valuable insights into the development of NF membranes with high mono−/divalent anion selectivity and excellent antifouling properties.