Polyamide Nanofiltration Membrane through Aqueous Phase Additive-Mediated Interfacial Polymerization for Ion Separation

Polyamide (PA) membranes prepared by the interfacial polymerization (IP) process enjoy wide applications in ion separation; however, they face the bottleneck of the permeability-selectivity trade-off. Herein, we used 1-butyl-3-methylimidazolium chloride (BMIM-Cl) as an aqueous phase additive to control piperazine (PIP) diffusion to construct a PA membrane for ion separation. BMIM-Cl possessed weak interaction with PIP, reducing the diffusion speed of PIP during the IP process. Accordingly, membrane thickness and cross-linking degree decreased, leading to increased water permeance from 15.8 L m–2 h–1 bar–1 to 25.5 L m–2 h–1 bar–1. Meanwhile, abundant acyl chloride groups were left and hydrolyzed to increase the membrane hydrophilicity and electronegativity. Hence, the membrane exhibited a high rejection of 99.9% for Na2SO4 and a separation factor of 40 for Cl–/SO42– under an 8000 ppm mixed-salt feed. Moreover, the membrane could retain stable water permeance and Na2SO4 rejection of 99.3% after 7 days of continuous cross-flow test. Therefore, our study provided an efficient method for preparing PA membranes for rapid and precise ion separation.