Zwitterionic liquid hydrogel sustained-release strategy for high-performance nanofiltration membrane

Controlling the diffusion of amine monomers plays a crucial role in fabricating well-defined architecture and high-performance nanofiltration (NF) membranes through interfacial polymerization (IP). Herein, a sustained-release strategy was proposed to regulate the interfacial polymerization through a zwitterionic liquid hydrogel transition layer. The hydrogel (Gel) was fabricated via in-situ one-step UV photo-initiated free-radical polymerization between 1-vinyl-3-ethylimidazolium chloride ([VEIm][Cl]) and 3-sulfopropyl methacrylate potassium salt (SMP) on the polyethersulfone (PES) substrate. The polyamide (PA) layer was then formed on the Gel layer by mitigating the diffusion of amine monomers. Low-field time-domain nuclear magnetic resonance (TD NMR) analysis demonstrated that the Gel layer significantly enhanced the water-absorbing capacity of the composite membrane. Positron annihilation lifetime spectroscopy (PALS) also confirmed the Gel-PA composite membrane possessed enlarged free volumes. The obtained Gel-PA composite membrane displayed a permeance of 13.22 L m−2 h−1 bar−1, a high Na2SO4 rejection of 98.23 %, a favorable NaCl/Na2SO4 selectivity of 49.75, outstanding long-term operational stability, and membrane antifouling properties. This sustained-release strategy provides a facile and feasible approach to controlling the IP process and obtaining high-performance nanofiltration membranes.