Preparation and characterization of N,O-carboxymethyl chitosan (NOCC)/polysulfone (PS) composite nanofiltration membranes

N,O-carboxymethyl chitosan (NOCC) composite nanofiltration membranes having a polysulfone (PS) UF membrane as the substrate were prepared using a method of coating and cross-linking, in which a glutaraldehyde (GA) aqueous solution was used as the cross-linking agent. Attenuated total reflection infrared spectroscopy (ATR-IR) was employed to characterize the resulting membrane. The effects of the composition of the casting solution of the active layer, the concentration of the cross-linking agent, and the membrane preparation techniques on the performance of the composite membrane were investigated. At 13–15 °C and 0.40 MPa the rejections of the resulting membrane to Na2SO4 and NaCl solutions (1000 mg L−1) were 92.7 and 30.2%, respectively, and the permeate fluxes were 3.0 and 5.1 kg m−2 h−1, respectively. The rejection of this kind of membrane to the electrolyte solutions decreased in the order of Na2SO4, NaCl, MgSO4, and MgCl2. This suggests that the membrane active layer acquires a negative surface charge distribution by the adsorption of anions from the electrolyte solution and this charge distribution mainly determines the membrane performance.