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

Abstract

We have studied degradation of photocatalytic activity of TiOxNy for water splitting under visible light irradiation with heat treatment in O2/N2 mixed gas. The reduction of the N content by oxidation through the formation of O-N-O species (NOx) 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 TiOxNy, which is the active species for visible light responsiveness on hydrogen evolution. N in TiOxNy is first oxidized to NO2 species during the oxidation, which reduces the activity. Then, O-N-O species (NOx) is removed as NOx gas from the surface. Because the formation of O-N-O in TiOxNy 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 (NOx) rather than the loss of the N content from TiOxNy.