Ternary network derived from polyphenol-inspired sticky nanoparticle: nanofiltration separation efficiency and end-of-life membrane regeneration potential

Nanofiltration (NF) membrane technology is pivotal in water purification, yet commercial membranes degrade over time, reaching end-of-life (EOL) status and requiring costly replacement, which contributes to environmental waste. Herein, a novel strategy is proposed for regenerating EOL NF membranes by constructing a stable ternary crosslinked network incorporating the adhesion characteristics of tannic acid (TA)-polyvinyl alcohol (PVA) self-assembled sticky particles and their metal coordination effect with Fe³⁺. The sticky particle adhesion and Fe³⁺ crosslinking processes were investigated by atomic force microscopy (AFM) and quartz crystal microbalance-dissipation (QCM-D) measurements, which revealed the formation process of TA-PVA-Fe ternary network. Compared to binary networks, the TA-PVA-Fe ternary network exhibited markedly reduced pore size (molecular weight cut-off (MWCO) = 399 Da, average diameter (d_adv) = 0.674 nm), resulting in enhanced monovalent/divalent salt separation performance (Cl^-/SO₄²⁻ separation factor of 54.5). The TA-PVA-Fe regenerated EOL NF membrane demonstrates robust Cl^-/SO₄²⁻ separation capability during extended-duration operation, maintaining Na₂SO₄ rejection at 97.3 ± 0.7% and NaCl rejection at 29.6 ± 0.5%. Additionally, it exhibits superior antifouling properties, reducing flux decline by over 45% relative to TA-Fe membranes under organic foulant challenges. These findings underscore the potential of this eco-friendly approach for recycling EOL membranes and advancing sustainable water treatment technologies.