Fabrication of high-performance thin film composite nanofiltration membrane with zwitterionic copolymer as an aqueous additive

Thin film composite nanofiltration (NF) membranes have a wide range of applications in drinking water production and industrial wastewater treatment. However, their performance is constrained by the inherent trade-off between permeability and selectivity, which can be effectively alleviated by regulating interfacial polymerization (IP). In this study, a zwitterionic copolymer (ZPSA), synthesized via one-step free radical polymerization using sulfobetaine ([2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide) and allylamine hydrochloride monomers, was utilized as an aqueous additive to regulate the IP processes for the fabrication of high-performance NF membranes. Adding zwitterionic copolymer retarded the diffusion rate of piperazine monomers due to electrostatic interaction and steric hindrance, resulting in an ultra-thin and relatively loose polyamide selective layer with enhanced surface hydrophilicity. Notably, incorporating zwitterionic copolymer significantly improved water permeability and maintained high rejection of divalent anions. The optimized membrane (i.e., ZPSA-1.5) achieved a water permeability around 18.8 L m −2  h −1 bar −1 , which was threefold higher than that of the control membrane, along with 98.0 % Na 2 SO 4 rejection. Additionally, the X-ray photoelectron spectroscopy results suggest that the added hydrophilic ZPSA could hinder PIP diffusion rate and decrease its reaction rate at interface, which was further confirmed by molecular simulation. The ZPSA-regulated membrane enhanced water permeability while preserving salt rejection, demonstrating its potential for nanofiltration applications.