Study on Interfacial Electrical Phenomena of Sulfonated Polyethersulfone Nanofiltration Membrane by Electrokinetic Method

Experimental investigations on interfacial electrical phenomena of NTR-7450 nanofiltration membrane that has dissociated functional groups were performed by electrokinetic method. To obtain the accurate zeta potential, the corresponding measures were used; for examples, the determination of the total conductance of the system including the surface conductance, and the membrane body conductance by means of the electrochemical workstation and the alteration of the channel heights. Furthermore, the surface charge density was estimated by the Gouy-Chapmann double-electric layers theory, and the influences of the ionic strength and type of ions (KCl, K2SO4 and K3PO4) on the membrane surface charge were evaluated. On the basis of the preliminary experimental results, the mechanism of charge formation of NTR-7450 membrane was explored. That is, its charge formation was attributed to the dissociation of the functional group in electrolyte solution with a relatively low concentration (0.1–0.5 mol·m−3). However, at the relatively high concentration, the charge formation of NTR-7450 nanofiltration membrane should be ascribed to the specific adsorption of ions. And, the relationship between the volume charge densities, X, and the feed solution concentration, C, agreed well with Freundlich absorption isotherms. That is, for KCl solution, ln|X| (mol·m−3) = 2.337 + 0.722lnC (mol·m−3); for K2SO4 solution, ln|X| (mol·m−3) = 3.584 + 1.119lnC (mol·m−3); for K3PO4 solution, ln|X| (mol·m−3) = 2.988 + 1.067lnC (mol·m−3).