Development of Novel Positively Charged Nanofiltration Membranes Using Interfacial Polymerization, Followed by Plasma Graft Polymerization

This study demonstrates the feasibility of a novel preparation method for positively charged nanofiltration membranes. First, the interfacial polymerization of piperazine with trimesoyl chloride was conducted to form a base polyamide layer on a polyethylene microfiltration membrane, followed by plasma graft polymerization of [2-(methacryloyloxy)-ethyl]trimethylammonium chloride, containing a quaternary ammonium moiety, on the base membrane to fabricate a positively charged membrane surface. The novel nanofiltration membrane had a pure water permeability of 3.1x10(-12) m(3) m(-2)s(-1) Pa-1 and showed the highest rejection for magnesium chloride, followed by magnesium sulfate, sodium sulfate, and sodium chloride. This is a typical salt rejection trend for positively charged nanofiltration membranes as the rejection of salts containing divalent cations was higher. Finally, the monovalent/divalent ion separation performance was examined using a mixture of magnesium sulfate and sodium chloride, and the results showed that magnesium ion retention was the highest and sodium ion retention was the lowest even when the sodium chloride concentration was considerably high. Therefore, this novel nanofiltration membrane has potential applications in the recovery of divalent cations from desalinated seawater in electrodialysis processes for table salt production.