Ultrastable Nanofiltration Membranes Engineered by Polydopamine-Assisted Polyelectrolyte Layer-by-Layer Assembly for Water Reclamation

The layer-by-layer (LBL) electrostatic assembly is an effective method for fabricating high-performance nanofiltration (NF) membranes. However, the structural integrity of the separation layers can be compromised in strong acid and alkaline conditions, which limits their applications in water reclamation. Herein, we presented novel ultrastable LBL-based NF membranes engineered by mussel-inspired "bio-glue" polydopamine (PDA)-assisted polyelectrolyte LBL deposition (PDA-a-LBL) technique. Through alternative deposition of PDA/polyethylenimine (PEI) and poly(sodium 4-styrenesulfonate) (PSS) layers onto polyethersulfone (PES) ultrafiltration substrates, tailorable pore size and tunable surface chemistry were achieved. The hydrophilicity and surface charge properties of the NF membranes were dependent on the functionality of the outermost layer. The novel PDA-a-LBL NF membranes presented molecular weight cut-off (MWCO) of 275–430 Da and more than 94% rejections against divalent anions along with pure water permeability of 7–13 L m–2 h–1 bar–1, which were competitive with the currently reported LBL-based NF membranes and commercial FilmTec NF-270 membrane. Significantly, the newly developed NF membrane (PES-50-3L) exhibited remarkable chemical stability in the pH range of 2–11, ascribing to the synergistic effects of covalent bonds, electrostatic interaction, and π–π stacking between PDA/PEI and PSS layers. In addition, the membrane exhibited robust performance in a continuous, 1 week long-term operation, demonstrating its great potential for sustainable water reclamation. Our findings may shed light on the future design of novel LBL-based NF membranes with enhanced chemical stability.