Ag+- and Pb2+-doped SrTiO3 photocatalysts.: A correlation between band structure and photocatalytic activity

We have prepared the two series of yellowish (PbxSr(1-x))TiO3 (X = 0.01-0.3) and (AgySr1-y(Ti1-yNby)O-3 (y = 0.03-0.1) powders. The UV-vis absorption spectra of these powders indicate that the bandgaps of (PbxSr1-x)TiO3 were narrowed but those of (AgySr1-y)(Ti1-yNby)O-3 were kept constant in comparison with that of SrTiO3. Combining the results of ab initio DOS calculations, we were convinced that the valence band of (PbxSr(1-x))TiO3 consisted of Pb 6s and O 2p and that the top of the valence band shifted to a higher energy, resulting in the visible light absorption. In contrast, (AgySr1-y)(Ti1-yNby)O-3 formed the isolated miniband composed of Ag 4d in the forbidden band above the valence band composed of 0 2p, resulting in the visible light absorption. We investigated the band structure dependence on photocatalytic oxidative activity evaluated by gaseous 2-propanol decomposition under UV (300-400 nm) and visible (400-530 nm) light irradiations. The quantum efficiencies of the photocatalytic reaction with the (PbxSr1-x)TiO3 (x = 0.1) were approximately the same between under UV and visible light irradiations. In contrast, the quantum efficiency under visible light irradiation was approximately one-third of that under UV light for the (AgySr1-y)(Ti1-yNby)O-3 (y = 0.03). Each result in the oxidative activity coincided with respective band structures obtained from the DOS calculations and UV-vis spectra.