Novel high-flux thin film composite nanofiltration membranes fabricated by the NaClO pre-oxidation of the mixed diamine monomers of PIP and BHTTM in the aqueous phase solution

Novel high-flux thin film composite (TFC) nanofiltration (NF) membranes were fabricated by the sodium hypochlorite (NaClO) pre-oxidation of the mixed diamine monomers of piperazine (PIP) and 2,2′-bis(1-hydroxyl-1-trifluoromethyl-2,2,2-triflutoethyl)-4,4′-methylenedianiline (BHTTM) in the aqueous phase solution, and via interfacial polymerization (IP) with trimesoyl chloride (TMC) on the polysulfone (PSF) ultrafiltration (UF) membrane. The chemical change of the pre-oxidation aqueous phase solution was characterized by LC-MS. By optimizing the NaClO and NaOH content in the aqueous phase solution, the pure water flux was improved greatly and the salt rejection kept on a high level (>90%). The properties of NF membranes were characterized by XPS, SEM, AFM and contact angle. Through the NaClO pre-oxidation of the mixed diamine monomers of PIP and BHTTM in the aqueous phase solution, the active layer of NF membrane became thinner and the pore size of NF membrane was enlarged. Besides, after oxidation treatment by 3000 ppm active chlorine solution for 1 h, the NF membrane exhibited pure water flux (PWF) with 161 (LMH) and Na2SO4 rejection of 92.1% under 0.6 MPa. The molecular weight cut-off (MWCO) of the NF membrane was greater than 500, which was calculated from the carbohydrates rejection. The good performance and the satisfactory stability of the novel high-flux NF membrane demonstrated its good potential in the practical application.