A composite material consisting of tantalum oxynitride (TaON) and monoclinic zirconium oxide (m-ZrO 2 ) is prepared by a surface modification method as a photocatalyst with enhanced activity for H 2 evolution from water under visible light ( > 420 nm). The composite is prepared by loading particulate Ta 2 O 5 with nanoparticulate m-ZrO 2 followed by nitridation at 1123 K for 15 h under NH 3 flow. The activity of the m-ZrO 2 /TaON composite for H 2 evolution from aqueous methanol solution is higher than that of either m-ZrO 2 or TaON when loaded with nanoparticulate ruthenium as a H 2 evolution site. The highest activity is obtained using a composite prepared with a Zr/Ta molar ratio of 0.1. The optimized material also provides elevated activity when used as an H 2 evolution photocatalyst in Z-scheme overall water splitting in combination with Pt-loaded WO 3 as an O 2 evolution photocatalyst and an IO 3 À /I À shuttle redox mediator. The improvement in activity is attributed to the suppression of surface defect formation by inhibiting tantalum reduction during nitridation.

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The effect of photoirradiation on adsorption of NO on ZnO powder was examined at 303 K, and the photoconductivity change of ZnO during adsorption of NO was also determined. Photoirradiation gave rise to a marked chemisorption of NO on ZnO. The photochemisorption led to an initial decrease and the following increase in the photoconductivity. In situ FT-IR examination showed the formation of oxidized species of NO upon photochemisorption. These results indicate two processes of the trapping of a photogenerated electron by the chemisorbed NO and the pseudo-oxygen defect formation on oxidation of NO.

Photoassisted Chemisorption of NO on ZnO.-Photoirradiation of ZnO exposed to NO of 2.7 kPa leads to an irreversible chemisorption of NO. The rate of photoinduced NO adsorption increases with the pressure in the range 0.13-2.7 kPa and with the light intensity. The light-induced chemisorption is accompanied by an initial decrease and subsequent increase in the photoconductivity of ZnO. These changes of the electrical conductivity are attributed to trapping of a photogenerated electron by chemisorbed NO and formation of a pseudo-oxygen defect on oxidation of NO. -(KASE, K.; YAMAGUCHI, M.; SUZUKI, T.; KANEKO, K.; J.