Porous Titanium Dioxide Coatings Obtained by Anodic Oxidation for Photocatalytic Applications

The aim of this work is to obtain porous titanium dioxide with good efficiency for photocatalytic environmental applications. TiO2 coatings were obtained by anodic spark deposition, at constant applied potential (150 V), using a platinum cathode and 0.5 M sulfuric acid as electrolyte. Samples of titanium Grade 2 were used as substrate, metallographically prepared until 1 μm diamond surface finishing. The variables of the process were temperature (25 and 40 °C) and anodization time (5 and 10 min). Samples obtained at 40 °C showed a higher current density than those obtained at 25 °C and the potential reached by these samples was lower than those obtained at 25 °C. These results are attributed to an increased electrolyte conductivity. Optical microscopy images of the oxides obtained at 40 °C showed heterogeneity in color, indicating a non-uniform oxide thickness. This coincides with the images obtained by scanning electron microscopy that revealed “valleys” where the material did not present porosity. On the other hand, the oxides obtained at 25 °C showed a complete homogeneous porous structure. The average pore diameter was reduced with the increased oxidation time and temperature of the electrolyte. An increase of the crystalline anatase phase was observed with an increase of the anodization time; besides, rutile formation was observed, probably due to the final potential achieved by the samples.