Formation of Micro- and Nanostructured TiO2 Films by Anodic Oxidation for Enhanced Photocatalytic Activities

This paper presents growth of micro- and nanostructured TiO2 layers on Ti6Al4 V by thermal and anodic spark oxidation for photocatalysis. Effects of anodization parameters on surface morphology and photocatalytic behavior were investigated. The photocatalysts divided into two groups consisting of four samples were prepared for growth of micro- and nanostructured TiO2 layer on Ti6Al4 V. The microstructured surfaces were obtained in 1 M H2SO4 electrolyte in 5 min at the anodization voltage in the range of 100-400 V, whilst the nanostructured TiO2 layers were prepared in 1% HF solution in the range of 10-40 V in equal time. Surface morphology, phase structure, band gap and surface roughness values of the micro- and nanostructured TiO2 photocatalysts were analyzed by scanning electron microscope, X-ray diffraction, UV-Vis diffuse reflectance spectroscopy and surface profilometer, respectively. Photocatalytic performances of TiO2 photocatalysts obtained with different anodization parameters were investigated via methylene blue aqueous solution. It was observed that the anodization voltage has a great effect on photocatalytic performances due to the formation of different crystallinity and morphology. Among the samples, the layer prepared at 100 V exhibited the best photocatalytic activity with 91.15% degradation efficiency and 95.5 x 10(-4) min(-1) kinetic rate constant. Moreover, the further investigation determining active species were carried out using ammonium oxalate, benzoquinone, and isopropyl alcohol. In this process, the photocatalytic mechanism revealed that the superoxide radicals (O-center dot(2)-) play a very important role during the photodegradation process. The TiO2 layer on Ti6Al4 V anodized at 100 V also showed high activity and stability, suggesting its potential for wastewater treatment.