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

Abstract

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 m 2 MPa. At 25 °C, 1.2 MPa and 30 L/h of cycling flow, the rejection of 1000 mg/L MgCl 2, CaCl 2, MgSO 4, Na 2SO 4, 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 m 2, respectively. The order of rejection of different salts follows the decreasing order of MgCl 2, CaCl 2, MgSO 4, NaCl, KCl, Na 2SO 4, and K 2SO 4, 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.