Photocatalytic Activity of Nanotubular TiO2 Films Obtained by Anodic Oxidation: A Comparison in Gas and Liquid Phase

The immobilization of nanostructured photocatalysts is of great importance in the purification of both polluted air and liquids (e.g. industrial wastewaters). Titanium dioxide films with nanotubular morphology and good photocatalytic efficiency in both environments can be produced by anodic oxidation, which avoids release of nanoscale materials in the environment. Here we evaluate the effect of different anodizing process parameters as electrolyte and anodizing time, in order to identify the most efficient and robust technique for the production of TiO2 layers with different morphologies with high photocatalytic activity in both gas and liquid phase. In particular, nanoporous layers were optimized to produce nanotubes made of titanium dioxide, whose specific surface area is much larger than that of a nanoporous oxide, therefore allowing more active sites for photocatalytic reactions. Toluene was used as model reactant for gas phase photocatalytic depuration, while an organic dye, rhodamine B, was chosen as model for wastewater purification. It was found that the role of the electrolyte in particular is crucial: nanoporous or nanotubular structures show remarkably different activities, especially in gas phase degradation reactions, and within nanotubular structures, those produced in non aqueous electrolytes display better photocatalytic activity in both phases of study.