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 crosslinking polymerization of poly(ethylene imine) (PEI) with p‐xylene dichloride (XDC). Then, it was quaternized by methyl iodide (MI) to form a perpetually positively charged layer. The chemical and morphological changes of the membrane surfaces were studied by Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), and atomic force microscopy. To optimize the membrane operation, the PEI solution concentration, PEI coating time, XDC concentration, crosslinking time, and MI concentration were optimized. Consequently, high water flux (5.4 L m−2 h−1 bar−1) and CaCl2 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 cutoff was calculated by the retention of poly(ethylene glycol) solutions with different molecular weights, and finally, the stoke radius was calculated as 1.47 nm. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41988.

Polyphenol Coating as an Interlayer for Thin-Film Composite Membranes with Enhanced Nanofiltration Performance

“…Nanofiltration membranes have been widely used in various fields, including seawater desalination, wastewater treatment, and saline water softening. − These membranes have merits of lower operation pressure and higher water permeation flux as compared with reverse osmosis ones, and they also show high rejection for most multivalent ions and organic molecules with low molecular weight. − In general, nanofiltration membranes are usually fabricated by interfacial polymerization on ultrafiltration substrates to form thin-film composite (TFC) structures. − In these cases, both the top selective layer and the bottom ultrafiltration substrate need to be optimized for desirable properties. , Specifically, the selective layer dominates the service performance of TFC nanofiltration membranes, including water permeation flux, salt rejection, antifouling, and oxidative resistance . Therefore, it is essential to fabricate thin, but defect-free, selective layers for TFC nanofiltration membranes with high performance as their low thickness will greatly promote water permeation flux while their uniform structure can ensure high rejection .…”

Ion separations with membranes

“…Therefore, developing positively charged NF membranes is important for Na + /Ca 2+ , Na + /Mg 2+ , and Li + /Mg 2+ separations, which are important for water softening and lithium production from salt-lake brines. [67][68][69][70] For example, NF membranes functionalized with polyethyleneimine to give a positively charged surface can give 95.8% rejection of CaCl 2 and 67.7% rejection of NaCl. In contrast, an unfunctionalized thin-film composite membrane shows much smaller Na + /Ca 2+ selectivity (96.6% CaCl 2 rejection and 89.4% NaCl rejection).…”

Superior cross-linking assisted layer by layer modification of forward osmosis membranes for brackish water desalination

“…Although, the selective layer was less uniform, compact, and rough, the membrane generated excellent water flux and salt rejection values of 95.1 % for MgCl2, 94.4 % for MgSO4, 80.5 % for Na2SO4 and 85.1 % for NaCl. Akbari et al [14], developed a new strategy involving the coating of PEI on a porous PSF substrate followed by cross-linking using p-xylene dichloride (XDC) and quaternization using methyl iodide (MI). The new selective layer was uniform and was less than 3-4 m thick.…”