1-pK and 2-pK protonation models in the theoretical description of simple ion adsorption at the oxide/electrolyte interface:: A comparative study of the behavior of the surface charge, the individual isotherms of ions, and the accompanying electrokinetic effects

A number of adsorption models have been considered corresponding to various combinations of the 1-pK and 2-pK charging models, with various models of the oxide/electrolyte interface structure. The corresponding, theoretical descriptions have been developed, along with the relations between the equilibrium constants, suggested by the appearance of the common intersection point. The equations developed for various adsorption models have been applied then to analyze the behavior of the surface charge, individual isotherms of ions, and electrokinetic data reported by Sprycha for the anatase/NaCl solution system. No decisive proof has been deduced in favor of either the 1-pK or 2-pK charging mechanism, but certain important conclusions have been drawn concerning the applicability of various adsorption models. It was shown that to arrive at a reasonable theoretical description, the assumed model of surface charging must necessarily be combined with a certain model of the oxide/electrolyte interface structure.