Preparation of novel NF membrane via interfacial cross-linking polymerization

The goal of present work is the preparation of a novel positively charged nanofiltration (NF) membrane and its development for the cation removal of aqueous solutions. This NF membrane was fabricated by the surface modification of polysulfone (PSf) ultrafiltration support. The active top-layer was formed by interfacial cross-linking polymerization of poly(ethyleneimine) (PEI) with p-xylylene dichloride (XDC) and then quaternized with methyl iodide to form a perpetually positively charged layer. In order to improve the efficiency of nanofiltration membrane, the concentration of PEI, XDC and methyl iodide solutions, PEI coating and cross-linking time have been optimized. As a result, a high water flux and high CaCl₂ rejection (1,000 ppm) was obtained for the composite membrane with values of 18.29 L/m².h and 93.62% at 4 bar and 25&#176;C, respectively. The rejections of NF membrane for different salt solutions followed the order of Na₂SO₄ < MgSO₄ < NaCl < CaCl₂. Molecular weight of cut off (MWCO) was calculated via retaining of PEG solutions with different molecular weights that finally, it revealed the Stokes and hydrodynamic radius of 1.457 and 2.507 nm on the membrane selective layer, respectively. The most efficient positively charged nanofiltration membrane exhibited a Ni²⁺ rejection of 96.26% for industrial wastewater from Shamse Hadaf Co. (Kashan, Iran).