Preparation and photocatalytic performance of ZrO2 nanotubes fabricated with anodization process

Anodization process is a facile method to prepare structured nano-material. In this research, anodization process of zirconium in (NH4)2504/NH4F solution was studied systematically and the anodized zirconia was applied to degrade methyl orange (MO) solution under UV irradiation and compared with anodized titania nanotubes to determine the photoactivity of zirconia nanotubes. After anodization in aqueous electrolyte containing 1 M (NH4)2504 and 0.25 wt% NH4F for 120 min at 20V, zirconia nanotubes (ZNT) with diameters of about 20 nm and lengths of about 600 nm were formed. The growth mechanism of ZNT was studied with SEM and TEM. The hypothesis of ZNT growth, in which electric etching process started at the pits and further to deepen in situ to form nanotubes, was confirmed by the SEM. The anodization process on the sanded rough Zr foil verified this assumption since the growth of ZNT occurred at the bottom of the ripples on Zr foil and gathered to form bundles at the peaks. The as-grown ZNT is a mixture of monoclinic and tetragonal Zr02 crystals, which transforms into pure monoclinic structure after annealed at 300 C. The unannealed ZNT has excellent photocatalytic performance with a MO photo-degradation rate of 94.45% after 4 h, even if contrasting to anodized titania. Reusing experiments confirmed that the decaying of photocatalytic performance of ZNT can be negligible in 6 times recycling. (C) 2014 Elsevier B.V. All rights reserved.