A loose nanofiltration membrane prepared by interfacial radical polymerization for dye/salt separation

In order to recover dyes from practical dye wastewater through loose nanofiltration (NF) membranes, dyes are supposed to be rejected through synergetic effect of sieving and Donnan repulsion while salts are supposed to permeate through membrane under weakened synergetic effect of sieving and Donnan repulsion. Therefore, redox system initiated interfacial radical polymerization was applied to form an integrated negatively charged separation layer with average pore size of 2.2 nm. The surface potential of -50 mV at pH >= 7 was achieved by plenty of -CN, O-C=O, and C-O-C groups. As the results, permeability of 43.1 L/(m2 h bar) and rejection of 99 % to MB for loose NF membrane (PAN-C) was obtained when treating 50 ppm MB aqueous solution under 2 bar, while only rejection of 5.2 % to MO was obtained, confirming the successful separation of MO from MB. Furthermore, the separation factor of MB over Na2SO4 and MgSO4 for PAN-C were 261 and 420, respectively, verifying the potential of PAN-C in application to dyestuff effluent treatment. In addition, PAN-C showed excellent anti-fouling performance with FRR of 0.99 against HA. Overall, this work established a new method to fabricate high performance loose NF membranes designed at molecular level, which could be extended to reverse osmosis, forward osmosis, and other membrane processes.