Alkali- and chlorine-resistant nanofiltration membranes via surface-enhanced crosslinking.

Conventional polyamide (PA) nanofiltration membranes suffer from poor chemical tolerance, being particularly susceptible to degradation in alkaline and chlorine-containing environments. This inherent nature leads to membrane performance deterioration, severely limiting their practical applications. To overcome these limitations, we developed a surface-enhanced crosslinking strategy involving the sequential grafting of ethylenediamine (EDA) and polyacrylic acid (PAA) onto a piperazine-trimesoyl chloride (PIP-TMC) polyamide layer. The modified IP-EDA/PAA membrane demonstrated altered surface zeta potential, reduced pore size distribution, and a more compact functional layer structure, resulting in both excellent nanofiltration performance and remarkable long-term stability under harsh chlorine and alkaline conditions. The surface-enhanced crosslinking could eliminate the chlorination-active sites through molecular grafting and capping. Besides, the crosslinking also endowed the active layer with improved mechanical stability, enhanced electrostatic repulsion effects, and a sacrificial protection layer. Therefore, the IP-EDA/PAA membrane maintained a rejection rate of ∼86.8 % for Na2SO4 following 5-day immersion in a pH 13 NaOH solution and retained ∼93.8 % rejection after cumulative chlorine exposure of 80,000 ppm·h (1000 ppm for 80 h). This work successfully demonstrated the design and fabrication of a robust nanofiltration membrane with excellent alkali- and chlorine-resistance.