Photocatalytic and mechanical properties of immobilized nanotubular TiO2 photocatalysts obtained by anodic oxidation: a novel combined analysis.

Abstract

The photocatalytic and mechanical performance of TiO2 nanotubular coatings obtained by anodic oxidation of commercial titanium, using an NH4F 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 2h. The effects of the anodizing voltage (40-80V) and NH4F concentration (0.06, 0.15, 0.27M) on the formation of the nanotube arrays were evaluated. Nanotube diameters (57 to 114nm), wall thicknesses (4 to 13nm), and lengths (5 to 17µm) increased with the anodizing voltage and the NH4F 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 3h 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 3h of irradiation was obtained for all samples, with a better performance than that of an immobilized P25 sample. The photocatalyst obtained with 0.27M NH4F at 40V 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 TiO2 nanotubular coatings could be successfully used as immobilized photocatalysts in photoreactors for water treatment.