In this study, sulfonated nanofiltration membranes were synthesized via interfacial polymerization (IP) of aqueous-phase piperazine (PIP), 3-amino-1-propanesulfonic acid (APA), and organic-phase trimesoyl chloride (TMC) monomers on porous substrates. Membranes with different APA contents were thoroughly characterized to determine how APA affected the physicochemical characteristics and permselectivity of the membranes. Membrane characterization confirmed the incorporation of APA into the generated polyamide (PA) layer. The optimal membrane performance was obtained at a 0.8 w/v% aqueous-phase APA content, where the enhanced membrane molecular weight cutoff (MWCO) and surface hydrophilicity resulted in a pure water permeability of 11.9 L m À2 h À1 bar À1 , approximately 13.1% higher than that of the blank membrane. Enhanced electrostatic repulsion of the APA-modified membrane on Na 2 SO 4 resulted in up to a 96.2% Na 2 SO 4 rejection rate. The 24.3% NaCl rejection rate resulted in NaCl/Na 2 SO 4 selectivity for the mixed-salt solution of the optimized membrane of 19.9, which was a significant increase over that of the blank. The embedding of APA did not affect the long-term stability of the NF membrane. The combined effects of the hydrophilicity, charge, and roughness of the membrane surface slightly enhanced the antifouling ability of the APA-modified membrane over that of the blank. This study provides a facile strategy for the fabrication of NF membranes with high perm-selectivity.
K E Y W O R D S3-amino-1-propanesulfonic acid, nanofiltration, perm-selectivity, sulfonation 1 | INTRODUCTION Nanofiltration (NF) membranes have been used extensively for brackish water desalination, potable water purification, and industrial wastewater treatment, as these membranes occupy a small space, do not undergo phase changes during purification, and are environmentally friendly and easy to operate. [1][2][3][4] The emergence of NF membranes is associated with the interfacial polymerization (IP) reaction that was first proposed by Morgan and Kwolek 5 in 1965. Cadotte et al 6 subsequently used IP to prepare the first polyamide (PA) membrane. Thus far, the most extensively used "loose" NF membrane with an ultra-thin PA layer was synthesized via IP between PIP and TMC on a porous substrate surface.The operating pressure and membrane pore size of NF (NF membranes can reject solutes with a size of approximately 1 nm) are between those of ultrafiltration (UF) and reverse osmosis (RO). 7,8 NF membranes have better flux and rejection capabilities than low-flux RO membranes and low-rejection-capability UF membranes and have been widely used for water treatment. 9The perm-selectivity of NF membranes considerably limits their application. [10][11][12] Consequently, researchers have designed and