TiO(x)N(y)/TiO(2) Photocatalyst for Hydrogen Evolution under Visible Light Irradiation II Degradation of Photocatalytic Activity of TiO(x)N(y)/TiO(2) with Mild Oxidation

[Image: see text] We have studied degradation of photocatalytic activity of TiO(x)N(y) for water splitting under visible light irradiation with heat treatment in O(2)/N(2) mixed gas. The reduction of the N content by oxidation through the formation of O–N–O species (NO(x)) was confirmed as the result of the reduction of the catalytic activity. The catalytic activity is not simply related to the amount of N remained but that of N taking the chemical state of O–Ti–N in TiO(x)N(y), which is the active species for visible light responsiveness on hydrogen evolution. N in TiO(x)N(y) is first oxidized to NO(2) species during the oxidation, which reduces the activity. Then, O–N–O species (NO(x)) is removed as NO(x) gas from the surface. Because the formation of O–N–O in TiO(x)N(y) could induce an impurity energy level to enhance charge recombination, the loss of catalytic activity might be influenced by the formation of O–N–O species (NO(x)) rather than the loss of the N content from TiO(x)N(y).