A chlorine-tolerant nanofiltration membrane prepared by the mixed diamine monomers of PIP and BHTTM

Using Polysulfone (PSF) ultrafiltration (UF) membrane as porous support, a chlorine-tolerant nanofiltration (NF) membrane was prepared by interfacial polymerization of piperazine (PIP) and 2,2'-bis(1-hydroxyl-1-trifluoromethyl-2,2,2-triflutoethyl)-4,4'-methylenedianiline (BHTTM) mixture with trimesoyl chloride (TMC). The XPS, SEM, AFM and contact angle methods were employed to characterize the physicochemical properties and morphology of the prepared NF membranes. The effects of preparation conditions such as reaction time, monomers mixing ratio and oxidation treatment on NF membrane performance were investigated. The salt rejection of the NF membrane met the order of Na2SO4>MgSO4>NaCl, indicating the membrane possessed a negative surface charge. The results showed the NF membrane prepared under the optimum conditions exhibited pure water flux (PWF) with 79.1 (L/m2 h) and Na2SO4 rejection of 99.5% under 0.6 MPa. The optimized post oxidation condition was treated by 3000 ppm NaClO solution for 1 h. The best NF membrane had a molecular weight cut-off (MWCO) less than 300 Da, corresponding to the pore size of 1 nm, which was calculated from the rejection of carbohydrates. The robustness of the NF membrane was proven by showing satisfactory stability in the long time running.