Photocatalytic and mechanical properties of immobilized nanotubular TiO photocatalysts obtained by anodic oxidation: a novel combined analysis.

The photocatalytic and mechanical performance of TiO nanotubular coatings obtained by anodic oxidation of commercial titanium, using an NHF and 3.5% v/v water in ethylene glycol solution as electrolyte was investigated. After the anodization, the coatings were thermally treated at 450 °C for 2 h. The effects of the anodizing voltage (40-80 V) and NHF concentration (0.06, 0.15, 0.27 M) on the formation of the nanotube arrays were evaluated. Nanotube diameters (57 to 114 nm), wall thicknesses (4 to 13 nm), and lengths (5 to 17 µm) increased with the anodizing voltage and the NHF concentration. The photocatalysts were characterized by scanning electron microscopy, glancing incidence X-ray diffraction, and UV-Vis diffuse reflectance spectroscopy. The mechanical properties of the photocatalysts were determined: adhesion using the tape test (ASTM D3359) and erosion resistance through a 3 h accelerated test. The photocatalytic activity of the nanotubes under UV irradiation was evaluated using hexavalent chromium (Cr(VI)) in the presence of ethylenediaminetetraacetic acid (EDTA), using a 1.25 EDTA/Cr(VI) molar ratio solution at pH 2. A complete Cr(VI) transformation after 3 h of irradiation was obtained for all samples, with a better performance than that of an immobilized P25 sample. The photocatalyst obtained with 0.27 M NHF at 40 V presented a good behavior in adherence and erosion resistance, together with a very good photocatalytic activity. This novel analysis, combining photocatalytic and mechanical tests, proved that the new TiO nanotubular coatings could be successfully used as immobilized photocatalysts in photoreactors for water treatment.