Formation of TiO2 layers on commercially pure Ti and Ti–Mo and Ti–Nb alloys by two-step thermal oxidation and their photocatalytic activity

Abstract Anatase-containing TiO 2 layers were formed on commercially pure (CP) Ti and Ti–25mass%Mo (Ti–25Mo) and Ti–25mass%Nb (Ti–25Nb) alloys by two-step thermal oxidation. The first-step treatment was conducted in an Ar–1%CO atmosphere at 1073 K for 3.6 ks, and the second-step treatment was conducted in air at 673–1073 K for 10.8 ks. The second-step temperature range for anatase formation was wider in the Ti alloys than in CP Ti. Photo-induced superhydrophilicity under UV irradiation was observed for the TiO 2 layers with anatase fractions ≥0.6 on CP Ti and the Ti–25Mo alloy, and with anatase fractions ≥0.18 on the Ti–25Nb alloy. The TiO 2 layers on the Ti–25Nb alloy exhibited excellent photocatalytic activity in the low anatase fraction region, which is considered to be caused by the incorporation of 1–3 at% Nb into the TiO 2 layers. The rate constant of methylene blue degradation showed maxima at anatase fractions of 0.6–0.9.