Abstract: The invention is directed to a catalyst having activity under the irradiation of a visible light, the catalyst being an oxide semiconductor such as an anatase type titanium dioxide, having stable oxygen defects. A method for producing a catalyst having activity under the irradiation of a visible light which comprises treating an oxide semiconductor with hydrogen plasma or with a plasma of a rare gas element, comprising performing the treatment in a state substantially free from the intrusion of air into the treatment system is also provided. An article comprising a base material having the catalyst above provided on the surface thereof and a method for decomposing a substance, comprising bringing an object to be decomposed into contact with the catalyst above under the irradiation of a light containing at least a visible radiation are disclosed.

Abstract: A photocatalyst with visible light activity in which TiC is supported at least partially on a surface of TiO2 is claimed. This is obtained by subjecting TiO2 to a CVD treatment in a plasma with a mixed gas of hydrocarbon and methane. A method for decomposing material wherein a material to be decomposed such as formaldehyde is made in contact with the above-mentioned catalyst to which light including at least visible ray is radiated. According to the present invention, a photocatalyst with visible light activity capable of making harmless organic compounds such as formaldehyde, a method for making harmless organic compounds such as formaldehyde by the use of the photocatalyst and a method for photo-decomposition of organic compounds such as tar are provided.