Photophysical properties of nanosized metal-doped TiO₂ photocatalyst working under visible light

Metal-doped TiO₂ nanoparticles were prepared by the sol-gel and hydrothermal synthesis methods. The estimated quantum yields (QYs) of Pt/Cr-doped TiO₂ nanoparticles was ca. 0.3 %. Cr-, Co- and N-doped TiO₂ showed the photocatalytic activity for IPA degradation to CO₂, but only Cr-doped TiO₂ produced H₂ photocatalytically in the presence of methanol-water aqueous solution under visible light (λ > 420 nm). Thus, in the case of Pt/Co-doped TiO ₂, the electron excited to the conduction band has a sufficient reduction potential to reduce H⁺ ion, but hole in the valence band has lower oxidation potential than required for CH₃OH degradation to CO₂. Therefore, Cr-, Co- and N-doped TiO₂ show the different activity for the photocactalytic reaction of gases and solution phases. The results of the calculated electronic structure and experimental optical properties are correlated to schematically to describe the possible mechanism of the photocatalytic behavior of the system under study.