Development of nanofiltration membrane with high salt selectivity and performance stability using polyelectrolyte multilayers

A selective nanofiltration membrane was engineered layer-by-layer (LBL) from polydiallyldimethylammonium chloride (PDADMAC) and polysodium-4-styrenesulfoate (PSS) polyelectrolytes. Thickness for 5 bilayers of PDADMAC/PSS was 321.00 ± 11 nm and showed 73.87 ± 7% rejection of MgSO4, 22.52 ± 2% rejection of NaCl and satisfactory flux of 12.33 L.m− 2.h− 1 at 5 bar. Formation of PDADMAC/PSS multilayers using 1.5 M of supporting electrolyte produced nanofiltration membrane with the best NaCl/MgSO4 selectivity of 2.97. In addition, the stability of polyelectrolyte multilayers was evaluated through membrane back-flushing. Modified membrane using polyelectrolyte solutions of moderate ionic strength (by adding 1.5 M NaCl) displayed the best performance stability in which the MgSO4 retention capability reduced for only 4%.