Tailoring Properties and Performance of Polyamide Composite Nanofiltration Membranes by LiCl-added Interfacial Polymerization

Polyamide composite nanofiltration membranes prepared by interfacial polymerization have been widely used in brackish water purification, wastewater treatment and solvent recovery. However, it remains a challenge to further enhance the membrane performances by optimizing their structure due to the rapid reaction rate and poor controllability of the conventional interfacial polymerization. In this work, we report a facile strategy to fabricate polyamide composite membranes with improved nanofiltration performance by using lithium chloride as an additive in interfacial polymerization to regulate the membrane structure. The synthesized polyamide layers show a reduced harmonic amide bond density and an increased pore size from 0.51 nm to 0.59 nm, while the morphology, chemical structure, surface charge, and surface hydrophilicity remain almost unchanged under the optimal addition of lithium chloride at 1.25 g<middle dot>L-1. The resulting structure endows the polyamide composite membrane with a 17% enhanced water permeance, reaching up to 216 L<middle dot>m(-2)<middle dot>h(-1)<middle dot>MPa-1, while maintaining a high rejection of Na2SO4 above 98.8%. In addition, nanofiltration membranes prepared demonstrate excellent performance stability when operated under various applied pressures, across a wide concentration range of feed solution, and during a 120-h long-term filtration process, indicating the potential of our membranes in practical applications.