Influence of anodization mode on the morphology and photocatalytic activity of TiO2-NTs array large size electrodes

Properties of nanotubular titania structures (TiO2-NTs) have been widely evaluated in small electrodes at lab scale. A novel experimental approach to overcome the limitations for the anodization of large size electrodes is presented. Several potentiostatic and galvanostatic anodization procedures have been tested, and their impact on the morphological features of the TiO2-NTs analyzed. A clear relationship between the applied voltage and current density and the NTs length and diameter is confirmed. Photocatalytic activity of the TiO2-NTs structures was evaluated in the methanol oxidation reaction. From these results, it was obtained that kinetic constant for the photocatalytic oxidation of methanol is higher when the reaction is carried out with NTs of higher length/diameter aspect ratio. This is related to a higher TiO2 active surface area available to generate photo-induced electron-hole pairs and for the adsorption of the reactants. This work confirms the viability of formation of photocatalytically active large size TiO2-NTs electrodes when high voltage or current density is applied under controlled conditions. Availability of fluoride in the electrolyte can be ensured by the use of a novel concept of continuous flow anodization reactor allowing the renovation of the electrolyte to keep under control not only the composition but also the temperature of the solution.