Determination of the point of zero charge of composite oxides

The variation of the point of zero charge (pzc) as a function of dopant concentration in a composite oxide system has been examined. For the model system, titania-alumina, the surface charge development of the composite material varies systematically in accordance with the relative proportion of each of the pure phases in the composite. The pzc of these composites as well as physical mixtures of TiO2 and A12O3 were determined by mass titration. A model is proposed to explain the results obtained on the basis of a highly dispersed dopant phase. The cluster size estimated from this model is consistent with those estimated by X-ray diffraction analysis. The surface area contributed by each of the individual oxides forming the composite determines the pzc for this composite oxide system.