Preparation and characterization of poly(piperazineamide) composite nanofiltration membrane by interfacial polymerization of 3,3′,5,5′-biphenyl tetraacyl chloride and piperazine

Most nanofiltration (NF) membranes are composite and have a polyamide thin film prepared by interfacial polymerization. Their performances mainly correlate the structure of the thin film and monomers used for its preparation. In this work, a novel thin-film composite (TFC) nanofiltration membrane was successfully prepared from 3,3′,5,5′-biphenyl tetraacyl chloride (mm-BTEC) and piperazine (PIP) through interfacial polymerization. Attenuated reflectance infrared (ATR-IR) and X-ray photoelectronic spectroscopy (XPS) were used to characterize the chemical composition of the membrane surface. The membrane performance was optimized by studying preparation parameters including monomer concentration, reaction time, and pH of aqueous phase. The resulting NF membrane exhibited significantly enhanced water permeability while maintaining high rejection to salt. The flux and rejection of NF membrane to Na2SO4 (500 ppm) reached to 51.5 L/(m2 h) and 95% under 0.5 MPa. The streaming potential tests indicated that the TFC membrane surface had high charge density and very low isoelectric point which situated between pH 1 and 2.