TiO2 layers on Ti-Au alloy formed by two-step thermal oxidation and their photocatalytic activity in visible-light

Titania (TiO2) layers consisting of anatase and rutile phases were formed on Ti-4at%Au alloy surface, using a two-step thermal oxidation method of carburization followed by air oxidation. Au from the alloy was found in the formed TiO2 layer as metallic Au nanoparticles with diameter <10 nm and dissolved Au3+. The visible-light photocatalytic activity of the TiO2 layer was evaluated by the degradation of stearic acid coating upon irradiation. Marked degradation of stearic acid was observed through the measured decrease in the water contact angle. Possible mechanisms of the visible-light photocatalytic activity are discussed.