In this work, anodic oxidation of Ti-40 wt.% Zr alloy in EG/NH4F/H2O electrolyte was done to produce anodic self-aligned oxide nanotube arrays. The nanotubes were amorphous but upon annealing at 400° C they were crystallized into ZrO2-TiO2 nanotubes and ZrTiO4-TiO2 nanotubes at 600 °C. The nanotubes were used to reduce 60 ppm Cr(VI) ions under sunlight or UV irradiation. 100% removal of Cr(VI) was achieved on ZrTiO4-TiO2 nanotubes after 5 h of exposure to UV light but only 53% removal was obtained on ZrO2-TiO2 nanotubes. The higher photocatalytic activity of the ZrTiO4-TiO2 nanotubes can be related to the presence of the ZrTiO4 phase which has good acid-base properties as well as the junction formation between ZrTiO4 and TiO2 that can further enhance the reduction process.
