Effect of solution physico-chemistry on the charge property of nanofiltration membranes.

Electrokinetic phenomenon is an important factor in pressure-driven membrane water filtration process. Zeta potential is a measurable and reliable parameter to characterize the charge property of membranes. This study investigated the effects of solution physico-chemistry on the zeta potential of nanofiltration membranes. A comprehensive semi-empirical mathematical model based on the Poisson-Boltzmann equation, Membrane Surface Charge model, was established. The correlations between the zeta potential, surface charge density and solution chemistry were well delineated by this new model. The empirical coefficients in the model are dependent on neither solution pH nor the ionic strength. They only reflect the characteristics of the electrokinetic property of the membrane--solution interface. The point of zero charge (PZC) can be calculated by combination of those empirical coefficients. The Membrane Surface Charge model also provides more information on understanding the charge interaction involved in membrane filtration system. The effects of potential determining ions, indifferent ions and specific adsorption of substances onto the membrane could be revealed by analyzing the coefficients of the model.