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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.

A novel thin-film composite (TFC) nanofiltration membrane containing hydrophilic organic additives was fabricated via interfacial polymerization. Three organic acids, i.e., lactic, maleic, and citric acid, served as aqueous-phase additives and their role in membrane structure and nanofiltration membrane flux enhancement was investigated. Fourier transform-infrared (FT-IR) analysis confirmed the presence of organic acids in the polyamide (PA) layer. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) analyses were applied to investigate the membrane morphology. The more carboxylic functional groups present in the additive resulted in higher hydrophilicity and porosity and flux was enhanced significantly compared to the neat PA membrane, while salt rejection was influenced only to a minor extent.

A novel polyamide thin film composite (PATFC) as a nanofiltration (NF) membrane was prepared by a modified interfacial polymerization (IP) reaction. Herein trimesoyl chloride and piperazine as the reagents, dimethyl sulfoxide (DMSO) as additive and polysulfone (PSF) ultrafiltration membrane as support were used respectively. The main goal of the present study is to improve TFC membrane water flux by addition of DMSO into the aqueous phase of IP reaction, without considerable rejection loss. Morphological, roughness, and chemical structures of the PATFC membrane were analyzed by scanning electron microscopy, atomic force microscopy (AFM), and Fourier transform infrared spectroscopy (FT-IR),respectively. The AFM analysis demonstrated that as DMSO was added to the aqueous phase, the surface roughness of PATFC membrane increased. Results showed that the pure water flux of modified-PATFC membranes increased up to 46%, compared to nonmodified-PATFC membrane, while salt rejection was not sacrificed considerably. The results elucidated that the addition of DMSO leads to an increase in the number of cross-linking bonds between monomers and pore diameter, which results in enhancement of the membrane flux. Finally, the results showed that the newly developed PATFC membrane is a highperformance NF membrane which augments the efficiency of conventional PATFC membrane.