Mn-, Ru-, Rh-, and Ir-doped SrTiO 3 possessed intense absorption bands in the visible light region due to excitation from the discontinuous levels formed by the dopants to the conduction band of the SrTiO 3 host. Mn-and Ru-doped SrTiO 3 showed photocatalytic activities for O 2 evolution from an aqueous silver nitrate solution while Ru-, Rh-, and Ir-doped SrTiO 3 loaded with Pt cocatalysts produced H 2 from an aqueous methanol solution under visible light irradiation (λ > 440 nm). The Rh(1%)-doped SrTiO 3 photocatalyst loaded with a Pt cocatalyst (0.1 wt %) gave 5.2% of the quantum yield at 420 nm for the H 2 evolution reaction.
The water splitting under visible light irradiation has been achieved by the Z-scheme system constituted of an Fe3+/Fe2+ redox couple as an electron relay and two powdered heterogeneous photocatalysts which we have recently developed. The (Pt/SrTiO3:Rh)–(BiVO4) system showed the highest activity with 0.3% of an apparent quantum yield at 440 nm. It can use visible light up to 520 nm.
The effects upon the photophysical and photocatalytic properties of the codoping of rhodium and antimony
in rutile-type TiO2 were investigated. TiO2 codoped with rhodium and antimony (TiO2:Rh/Sb) had an absorption
band in the visible light region. Its energy gap was 2.1 eV. The TiO2:Rh/Sb powder showed photocatalytic
activity for the oxidation of water to form O2 in the presence of Ag+ ions as an electron acceptor under
visible light irradiation (λ > 440 nm), whereas TiO2 doped with only rhodium showed no activity. The
photocatalytic activity strongly depended on the amount and ratio of the Sb/Rh dopant. Electron spin resonance,
diffuse reflection spectroscopy, and X-ray absorption near-edge structure analyses revealed that the doped
rhodium exists in a trivalent oxidation state in the active photocatalyst. The photocatalytic activity was decreased
remarkably even by a small amount of Rh4+ ions. Antimony played an important role in suppressing the
formation of Rh4+ ions by charge compensation. Thus, it has been clarified that Rh3+ is the species responsible
for the photocatalytic activity under visible light irradiation in the TiO2:Rh/Sb photocatalyst.
Irradiation. -The compounds SrTiO 3 :M (M: Mn, Ru, Rh, Pd, Ir) are characterized by diffuse reflectance spectroscopy. Mn-and Ru-doped SrTiO3 show photocatalytic activities for O2 evolution from an aqueous AgNO3 solution while Ru-, Rh-, and Ir-doped SrTiO3 loaded with Pt cocatalyst produce H2 from an aqueous MeOH solution under visible light irradiation. SrTiO 3 :Rh(1%) loaded with a Pt cocatalyst (0.1 wt%) exhibits 5.2% of the quantum yield at 420 nm for the H 2 evolution reaction. -(KONTA, R.; ISHII, T.; KATO, H.; KUDO*, A.; J.
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