| Abstract
| - A Ti-based oxysulfide, Sm2Ti2S2O5, was studied as a visible light-driven photocatalyst. Undervisible light (440 nm ≤ λ ≤ 650 nm) irradiation, Sm2Ti2S2O5 with a band gap of ∼2 eV evolved H2 or O2from aqueous solutions containing a sacrificial electron donor (Na2S−Na2SO3 or methanol) or acceptor(Ag+) without any noticeable degradation. This oxysulfide is, therefore, a stable photocatalyst with strongreduction and oxidation abilities under visible-light irradiation. The electronic band structure of Sm2Ti2S2O5was calculated using the plane-wave-based density functional theory (DFT) program. It was elucidatedthat the S3p orbitals constitute the upper part of the valence band and these orbitals make an essentialcontribution to the small band gap energy. The conduction and valence bands' positions of Sm2Ti2S2O5were also determined by electrochemical measurements. It indicated that conduction and valence bandswere found to have satisfactory potentials for the reduction of H+ to H2 and the oxidation of H2O to O2 atpH = 8. This is consistent with the results of the photocatalytic reactions.
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