Formation of grassy TiO2nanotube thin film by anodisation in peroxide electrolyte for Cr(VI) removal under ultraviolet radiation

Arrays of TiO(2)nanotubes (TiO2NTs) with grassy surfaces were observed on titanium foil anodised at 60 V in fluorinated ethylene glycol (EG) with added hydrogen peroxide (H2O2). The grassy surface was generated by the chemical etching and dissolution of the surface of the TiO2NTs walls, which was accelerated by the temperature increase on the addition of H2O2. Upon annealing at 600 degrees C, the grassy part of the TiO2NTs was found to consist of mostly anatase TiO(2)whereas the bottom part of the anodic oxide comprised a mixture of anatase and rutile TiO2. The TiO2NTs were then used to reduce hexavalent chromium (Cr(VI)) under ultraviolet radiation. They exhibited a rather efficient photocatalytic effect, with 100% removal of Cr(VI) after 30 min of irradiation. The fast removal of Cr(VI) was due to the anatase dominance at the grassy part of the TiO2NTs as well as the higher surface area the structure may have. This work provides a novel insight into the photocatalytic reduction of Cr(VI) on grassy anatase TiO2NTs.