Influence of anodizing variables on Cr(VI) photocatalytic reduction using TiO2 nanotubes obtained by anodic oxidation

Abstract

The effect of growth conditions of TiO2 films with nanotubular structures produced by anodic oxidation in electrolytes containing NH4F in glycerol and water was investigated. The effect of anodizing voltage, time, NH4F concentration and initial surface preparation on the formation of nanotube arrays was evaluated. In these cases, the structure was characterized by using scanning electron microscopy, X-ray diffraction and UV–Vis diffuse reflectance spectroscopy. The photocatalytic activity was evaluated using hexavalent chromium in the presence of EDTA (EDTA/Cr(VI) = 1.25 M ratio). The results show that uniform nanotube arrays were only formed with an applied voltage of 20 V, independently of the value of the other parameters studied. The photocatalytic activity increases with the NH4F concentration and the anodizing time, due to the increase in the length of the nanotubes, achieving the highest Cr(VI) transformation (93.8%) after 5 h UV irradiation under the optimal conditions.