TiOxNy/TiO2 Photocatalyst for Hydrogen Evolution under Visible Light Irradiation II Degradation of Photocatalytic Activity of TiOxNy/TiO2 with Mild Oxidation

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 .