Polyamine-based thin-film composite nanofiltration membrane embedded with catalytic chemical additive for enhanced separation performance and acid stability

Nanofiltration (NF) membranes with excellent acid stability and enhanced separation performance are of great benefit in treating acid wastewater and meeting freshwater demand. In this study, terephthalic acid (TPA) molecules with unique catalytic reactivity were directly incorporated as a chemical additive into the membrane selective layer via interfacial polymerization reaction to form a novel polyamine-based nanofiltration membrane. The resultant membrane morphology, chemical and functional composition, hydrophilicity, surface charge, separation performance, thermal stability and acid resistance were all investigated. The results showed improved hydrophilicity, electronegativity and cross-linking degree of the membranes. Compared with the bare membrane, the TPA incorporated membrane performance was best at 0.15% TPA concentration with improved water permeability of 14.1 LMH.bar⁻¹ which was 1.6 times the control with an excellent salt rejection of 96.7% for MgCl₂. Furthermore, after exposure to 5% (w/w) HCl and 20% (w/w) H₂SO₄ acid solutions at 25 °C for 60-days, the membranes displayed excellent acid stability with appreciable increase and a corresponding decrease in water fluxes and salt rejections. No obvious change was observed in the membrane surface as revealed by the SEM, FTIR and XPS analysis after exposure period expiration. In addition, the membrane showed excellent pressure resistance and long-term stability after acid exposure for 30 days. Overall, incorporating TPA into the membrane provides a scalable system with great potential in water desalination and acid wastewater treatment.