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Critical Evaluation of the Surface Complexation Model for Metal Oxide Aqueous Interface Based on Measurements of Surface Potential

Ionic equilibria at metal oxide aqueous interface is commonly interpreted on the basis of the Surface Complexation Model that takes into account mechanism of specific interfacial reactions, their equilibrium constants, and the structure of electrical interfacial layer. Several variations of the basic model were used for interpretation of experimental data. The common experimental techniques are acid base titrations of suspension providing surface charge density in the inner plane, counter ion adsorption measurements and electrokinetics. It was found that these experimental data may be successfully interpreted by several different variations of the model so that one needs to introduce a new experimental technique that might help in solving the problem. There were several attempts to measure surface potential at the inner plane by metal electrodes covered by layer of a metal oxide. However, due to the porosity of oxide layer the data were not reliable. Recently, we have constructed an electrode made of monocrystaline hematite enabling the reliable measurements. These data, together with other data obtained by classical methods, enables evaluation of all parameters characterizing the interface and critical test of the assumptions involved in the application of the Surface Complexation Model.

metal oxide aqueous interface; surface complexation model; surface potential; metal oxide monocrystal electrode

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