Electrokinetic studies on interfaces of group IV-a metal oxides in different electrolytes

ABSTRACT

Experiments were conducted to study the effect of constant concentrations [2.0 mmol] of Sr2+, Ba2+, Mg2+, Ni2+, Mn2+, or Fe3+ ions on the electrokinetic [sigma] potentials of SiO2, GeO2, SnO2 and PbO2 oxides over a wide range of pH. The chlorides of these cations, except Fe3+ decreased the negative electrokinetic potential of the above oxides by 10-15 mv, the effect was more pronounced at pH > 5.0. However, Sr2+ and Ba2+ ions present in all oxides as well as Ni2+, CO2+, and Mn2+ in GeO2 oxides showed no effect on the point of zero charge [PZC] of these oxides, but the presence of Fe3+ ions shifted the PZC values of oxides at pH values from 2.0 +/- 0.25 to 6.7 +/- 0.1, while Ni2+, CO2+ and Mn2+ in GeO2 oxides showed a new PZG at pH = 8.15 +/- 0.35. Furthermore, the effect of Mg2+ ions in SiO2, SnO2 and PbO2 suspensions was sharply different from the other alkaline-earth ions, the sign of the sigma potential was reversed to positive at pH >10.5. The adsorption mechanism of the specific metal ion species on the oxide surfaces is discussed