Preparation and characterization of a positively charged nanofiltration membrane based on poly(arylene ether sulfone) with tertiary amine groups

A type of poly(arylene ether sulfone) with pendant tertiary amine groups (PSDA) was synthesized via nucleophilic substitution polymerization of 3,3′-dimethylaminemethylene-4,4′-oxybisphenol (DABP) and 4,4′-bisfluorodiphenyl sulfone(BFDPS). The resulting polymer was used to prepare a nanofiltration membrane via a convenient one-step phase inversion process. The preparation conditions were investigated; the optimum parameters were 30 wt% PSDA, 30 wt% THF, 40 wt% DMF casting solution, and 10 s evaporation time. The zeta potential test indicated that the PSDA membranes were positively charged below pH 11.0. The results of the membrane performance testing showed that the trend for rejection was R_FeCl3 > R_MgCl2 ≈ R_CaCl2 > R_NaCl > R_Na2SO4 (R=rejection), which was a typical positively charged nanofiltration membrane performance. The PSDA membrane also showed excellent chlorine tolerance; no obvious performance change was observed after exposure to an aqueous NaOCl solution (active chlorine concentration no less than 1000 ppm) for 15 days.