Positively charged nanofiltration membranes mediated by a facile polyethyleneimine-Noria interlayer deposition strategy

The development of the positively charged nanofiltration (NF) membrane is of great importance for water softening. The relative low water permeance restricts its widespread application. Up to now, numerous efforts on the interlayer technologies have been implemented to manipulate the interfacial polymerization (IP) process of the negatively charged NF membrane. However, there are few reports on the interlayer-mediated positively charged NF membrane. Herein, an interlayer-mediated positively charged NF membrane is fabricated via an IP process between polyethyleneimine (PEI) and trimesoyl chloride. A facile interlayer is deposited based on the interaction of a macrocycle polyphenol of Noria and PEI. The fabricated NF membrane possesses a unique surface morphology, less intrusion of the polyamide layer, a low lateral mass transfer resistance and adequate separation layer thickness. Consequently, the interlayer-mediated NF membrane exhibits a high water permeance of 110.4 L·m−2·h−1·MPa−1, which is ~2.6 times over the control group of 41.6 L·m−2·h−1·MPa−1, while preserves a considerable rejection of 95.4% towards MgCl2 solution. More importantly, the water permeance is enhanced not at the expense of membrane thickness, which is conducive to the long-term running stability. This study paves a new way to fabricate a high performance positively charged NF membrane through an interlayer manipulation strategy.