The pH-dependent surface charging of tellurium (IV) oxide has been studied. The isoelectric point (IEP) of tellurium (IV) oxide was determined by microelectrophoresis in various 1-1 electrolytes over a concentration range of 0.001-0.1 M. In all electrolytes studied and irrespective of their concentration the zeta potential of TeO2 was negative over the pH range 3-12. In other words the IEP of TeO2 is at pH below 3 (if any). TeO2 specifically adsorbs ionic surfactants, and their presence strongly affects the zeta potential. In contrast the effect of multivalent inorganic ions on the zeta potential of TeO2 is rather insignificant (no shift in the IEP). In this respect TeO2 is very different from metal oxides.
Keywords: electric double layer; isoelectric point; point of zero charge; specific adsorption; zeta potential.