The TiO2/electrolyte solution interface:: Calculation of ζ potential using non-equilibrium theories

The main purpose of this work is to estimate realiably the zeta potential of a TiO2/water interface, establishing the differences with the diffuse potential. Electrophoretic mobility measurements of our interface in terms of three 1 : 1 electrolyte concentrations for a fixed solution pH have been used to determine the zeta potential of the TiO2 particles. Different theories of conversion including those which consider non-equilibrium phenomena have been employed. We have assumed a Nernst behaviour for the surface potential, introducing the ionic concentration dependence via the Debye and Huckel activity coefficients. The diffuse potential was calculated using the site-dissociation/site-binding model and Stern's theory for the electric double layer. The use of the Stern model for the electric double layer gives the most realistic diffuse potential values, which employed in the different theories of conversion from electrophoretic mobility into zeta potential data, offers also the best results.