Oxysulfide photocatalyst for decomposition of water by visible light

A photocatalyst which comprises an oxysulfide containing at least one transition metal; a preferable photocatalyst which also comprises a rare earth element such as Sm in addition to the above and wherein the transition metal is at least one selected from the group consisting of Ti and Nb; a more preferable photocatalyst which further comprises a promoter comprising a transition metal such as Pt loaded on each of the above photocatalyst; and a catalyst for use in the decomposition of water by a light which comprises one of the above oxysulfide photocatalysts.