Contribution of photocatalytic and Fenton-based processes in nanotwin structured anodic TiO nanotube layers modified by Ce and V.

In the present work, nanotwin structured TiO nanotube (TNT) layers are prepared by the electrochemical anodization technique to form the anatase phase and by surface modification spin-coating of Ce and V precursors to form Ce-TNT and V-TNT, respectively. The surface and cross-sectional images by SEM revealed that the nanotubes have an average diameter of ∼130 nm and a length of ∼14 μm. In addition, the TEM images revealed the nanotwin structures of the nanotubes, especially the anatase (001) and (112) twin surfaces, that increase the transport of photogenerated charges. The photoinduced degradation of caffeine (CAF) by TNT, Ce-TNT, and V-TNT led to a degradation extent of 16%, 26% and 33%, respectively, whereas it increased to 26%, 38%, and 46% in the presence of HO, owing to the involvement of Fenton-based processes (in addition to photocatalysis). The effect of the Fenton-based processes accounts for about 10% of the total degradation extent of CAF. Finally, the mechanism of the photoinduced degradation of CAF was investigated. The main oxidative species were the hydroxyl radicals, and the better efficiency of V-TNT over Ce-TNT and TNT was ascribed to its negative surface, thus improving the interactions with CAF.