An improved Parks equation for prediction of surface charge properties of composite ceramic membranes

An improved Parks equation was proposed to predict the surface charge properties of composite ceramic membranes, which establishes the relationship between the chemical composition and the molarity of H+ ions at isoelectric point. Focus was put on investigation of the effects of chemical composition on membrane surface charge properties. The surface charge properties of a series of TiO2-doped Al2O3 composite microfiltration membranes were investigated by applying transmembrane streaming potential measurements. When the TiO2 contents are 5%, 10%, 15%, 40% and 60%, the isoelectric points of the composite membranes are 6.1, 5.7, 4.8, 4.3 and 4.1, respectively. With increasing of TiO2 content, the isoelectric point shifts towards lower pH. Comparing the theoretical predictions of the improved Parks equation and Parks equation with the experimental results shows that the improved equation could provide significantly more accurate predictions with the error of 8.4% than the Parks equation with the error of 39.2%, which verifies the validity of the improved Parks equation.