Mechanism of Deposition of Vanadium−Oxo Species on the “Anatase/Electrolytic Solution” Interface

The deposition of the V (v) −oxo species on the anatase/electrolyte solution interface was studied over a wide pH and bulk concentration V (v) range using deposition experiments, microelectrophoresis, potentiometric titrations, and an advanced calculation procedure, further developed in the present work. It was found that the mechanism of deposition is quite complicated due to the fact that a change in pH or V (v) bulk concentration causes dramatic changes in the relative concentrations of the V (v) −oxo species in the bulk solution and thus of the corresponding concentrations in the “TiO 2 /electrolyte solution interface”. In fact, 12 equilibria are needed in order to describe the title deposition over the pH range studied. However, a preference was found for the deposition of the monomeric V (v) species (H 2 VO 4 - and HVO 4 2- ) with respect to the deposition of the polymeric V (v) species (V 3 O 9 3-, V 4 O 12 4-, V 10 O 27 4-, HV 10 O 28 5- ). Moreover, a preference was found for deposition through adsorption (reaction) at relatively low (high) pH values on sites created by single TiOH 2 + (TiOH) groups. Significant deposition has not been observed on two adjacent TiOH 2 + groups or TiOH 2 + −O−TiOH groups. The above were quantitatively explained on the basis of an equation derived to describe the deposition. The present work was based on the two-p K /one-site and triple-layer models.