Preparation and characterization of a novel positively charged nanofiltration membrane based on polysulfone

Abstract

The goal of this study was to prepare positively charged nanofiltration(NF) membranes to remove cations from aqueous solutions. A composite NF membrane was fabricated by the modification of a polysulfone ultrafiltration support. The active top layer was formed by the interfacial cross linking polymerization of poly(ethyleneimine) (PEI) with -xylene dichloride (XDC). Then, it was quaternized by methyliodide (MI) to form a perpetually positively charged layer. The chemical and morphological changes of the membrane surfaces were studied by Fourier transform infra red spectroscopy, scanning electron microscopy (SEM), and atomic force microscopy. To optimize the membrane operation, the PEI solution concentration, PEI coating time, XDC concentration, cross linking time, and MI concentration were optimized. Consequently, high water flux (5.4L/m2 h bar ) and a Cl rejection (94%) values were obtained for the composite membranes at 4 bars and 30 C. The rejections of the NF membrane for different salt solutions, obtained from pH testing, followed the order Na2SO4 <MgSO4 <NaCl<CaCl2 . The molecular weight cut off was calculated by the retention of poly(ethyleneglycol) solutions with different molecular weights, and finally, the stoke radius was calculated as 1.47nm.