RESUMEN
TiO x N y /TiO2 was synthesized by nitriding of TiO2 in NH3 gas. TiO x N y /TiO2 generated hydrogen from methanol aqueous solution under visible-light irradiation. It was revealed by N K-edge XANES and N 1s XPS measurements that the N species contributing to visible-light responsiveness was the O-Ti-N species. The structure of TiO x N y /TiO2 showing the photocatalytic activity was a double shell type with thin layers of TiO x N y that covers the TiO2 core. Although N content on the surface decreased during the photocatalytic reaction, N was supplied from the deeper side to keep the TiO x N y phase at the surface and the activity as well.
RESUMEN
We have studied degradation of photocatalytic activity of TiO x N y 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 (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 NO2 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 .
RESUMEN
We have examined the photocatalytic activity of Ga2O3 supported on Al2O3 (Ga2O3/Al2O3 catalyst) without a noble metal cocatalyst for water splitting and reduction of CO2 with water under UV light irradiation by changing the loading amount of Ga2O3. All prepared Ga2O3/Al2O3 catalysts show photocatalytic activities for both water splitting and CO2 reduction, and their activities are significantly improved compared to those of nonsupported Ga2O3 and Al2O3. The water splitting is dominated for Ga2O3/Al2O3 with less than 1.0 vol % of Ga2O3 loaded, whereas the CO2 reduction, for higher Ga2O3-loaded samples (2.6, 4.2 vol %). Crystalline structure characterizations of Ga2O3/Al2O3 catalysts indicate that active sites for both reactions are different. The water splitting proceeds on nanometer-sized Ga2O3 rods dispersed on an Al2O3 support consisting of a little distorted α-Ga2O3 phase. On the other hand, the CO2 reduction proceeds on sub-micrometer-sized Ga2O3 particles consisting of mixed phases of α-Ga2O3 and γ-Ga2O3 or with appearance of boundaries between the α and γ phases, which plays a critical role. Al2O3 used as the support of the Ga2O3 particles does not seem to play an important role in the photocatalytic CO2 reduction.