Anodic film on Ti: Nanotubes formation and application for Cr(VI) and Cd(II) removal

Self-organized titanium dioxide, TiO2 nanotube (TNT) arrays were fabricated by two steps anodic oxidation of titanium foil in fluoride/EG electrolyte. First step anodization was done for template formation at low applied voltage (20 V) while second step anodization was done to grow TNTs at high voltage (60 V). The template was formed by removing initial anodic layer by sonication. The TNTs produced were ∼ 7 μm long, and with diameter of 99.28 nm. Crystallization of the TNTs by annealing led to the formation of anatase-TiO2. The annealed TNTs were then used as photocatalyst for removal of toxic Cadmium, Cd(II) and hexavalent chromium, Cr(VI) under two different source of light; ultraviolet (UV) and sunlight. The results show that TNT was able to remove 58 % and 55 % of Cd(II) under sunlight and UV, respectively within 120 min. For the removal of Cr(VI), 100 % removal was successfully recorded using the TNT after 45 min of exposure of the Cr(VI) solution to UV radiation. However, only 50 % Cr(VI) was removed under the sunlight irradiation.