Photo-induced properties of non-annealed anatase TiO2 mesoporous film prepared by anodizing in the hot phosphate/glycerol electrolyte

In this study, anatase crystalline TiO2 mesoporous film was formed by anodizing of titanium specimens without annealing procedures. The specimens were anodized at 3 and 20 V in 0.6 mol dm−3 K2HPO4 and 0.2 mol dm−3 K3PO4/glycerol electrolyte at 433 K. The obtained films had mesoporous structures with pore diameters as small as ∼10 nm. The mesoporous film formed at 20 V without annealing (MP-20V) was a mixture of amorphous phase and nanograined anatase, which clearly showed strong 〈0 0 1〉 preferred orientation, whereas that at 3 V was completely amorphous. Even without annealing, the MP-20V showed high photocatalytic activities for decomposition of water and methylene blue. In contrast, the anodic TiO2 nanotube film formed in NH4F/ethylene glycol electrolyte revealed photocatalytic activities only after annealing at 723 K, because of the amorphous nature of the as-anodized nanotube film. The MP-20V film also showed superhydrophilicity with UV light irradiation.