A novel composite nanofiltration (NF) membrane prepared from graft copolymer of trimethylallyl ammonium chloride onto chitosan (GCTACC)/poly(acrylonitrile) (PAN) by epichlorohydrin cross-linking Original Research Article

A novel composite nanofiltration (NF) membrane was prepared by over-coating the PAN ultrafiltration (UF) membrane with a GCTACC thin layer. The effects of membrane preparation techniques and operating conditions on the performance of the composite membrane were studied. The results indicate that a composite NF membrane from 1.0 wt % GCTACC casting solution, vaporized for 2 h at 50 °C, cross-linked for 20 h at 50 °C and pH ≈ 12 with ethanol/epichlorohydrin (50/0.45 wt/wt) had optimum performance. The resultant GCTACC/PAN composite membrane was positively charged. Scanning electron microscopy showed its asymmetric and composite features. At 25 °C and 30 L/h of cycling flow, the permeability of pure water through this membrane is 6.3 L/h m2 MPa. At 25 °C, 1.2 MPa and 30 L/h of cycling flow, the rejection of 1000 mg/L MgCl2, CaCl2, MgSO4, Na2SO4, and NaCl solutions is 0.976, 0.972, 0.897, 0.65, and 0.407, respectively, with fluxes of 6.8, 6.12, 6.12, 5.57, and 5.51 L/h m2, respectively. The order of rejection of different salts follows the decreasing order of MgCl2, CaCl2, MgSO4, NaCl, KCl, Na2SO4, and K2SO4, which reveals the characteristics of the positively charged NF membrane. In addition, the curve for the streaming potential also illustrates the positively charged characteristics of this membrane, with a pressure osmotic coefficient of 11.7 mV MPa−1.