A Study Of Charge Performance On The Surface Of Nanofiltration Membrane

Surface charge performance of nanofiltration membrane affects the flux, permselectivity and the anti-pollution ability. It is becoming a hot subject on the study of the membrane property recently.The stream potential measurements of SG nanofiltration membrane were carried out under aqueous solution of NaCl,Na2CO3 and CuCl2 at different concentration, operating pressure, cross-flow velocity, and operating temperature. The zeta potential and surface charge density of the membrane were estimated on the basis of Helmholtz -Smoluchowski equation and the Gouy-Chapmarn theory. The results show that the SG membrane has a weak negative charge, and the absolute value of the zeta potential and surface charge density increase with the increment of the operating pressure, solution concentration and temperature, and with the decrement of the cross-flow velocity of the solution. In addition, the absolute value of the stream potential, surface zeta potential and charge density increase with the increment of cation valence and anion valence of solute. Under high operation pressure, high solution concentration and low cross-flow velocity, the ion valence, especially the the same valence cation have more obviou effect on the membrane charge property.Comparing zeta potential calculated by the stream potential to that measured by known the concentration of NaCl solution, the solute concentration on the surface of membrane can also be estimated, and is close to theoretical result relatively. According to the charge property and the surface solute concentration of the membrane, the permeation flux and retention rate were also analysed.