Visible light active platinum-ion-doped TiO₂ photocatalyst

Platinum-ion-doped TiO₂ (Pt_ion-TiO₂) was synthesized by a sol-gel method, and its visible light photocatalytic activities were successfully demonstrated for the oxidative and reductive degradation of chlorinated organic compounds. Pt_ion-TiO₂ exhibited a yellow-brown color, and its band gap was lower than that of undoped TiO₂ by about 0.2 eV. The flat band potential of Pt _ion-TiO₂ was positively shifted by 50 mV compared with that of undoped TiO₂. X-ray absorption spectroscopy and X-ray photoelectron spectroscopy analyses showed that the Pt ions substituted in the TiO₂ lattice were present mainly in the Pt(IV) state with some Pt(II) on the sample surface. Pt_ion-TiO₂ exhibited higher photocatalytic activities than undoped TiO₂ under UV irradiation as well. The visible light activity of Pt_ion-TiO₂ was strongly affected by the calcination temperature and the concentration of Pt ion dopant, which were optimal at 673 K and 0.5 atom %, respectively. Under visible irradiation, Pt_ion-TiO₂ degraded dichloroacetate and 4-chlorophenol through an oxidative path and trichloroacetate via a reductive path. The activity of Pt_ion-TiO₂ was not reduced when used repeatedly under visible light. However, visible-light-illuminated Pt_ion-TiO₂ could not degrade substrates such as tetramethylammonium and trichloroethylene, which are degraded with UV-illuminated TiO₂. The characteristics and reactivities of Pt_ion-TiO₂ as a new visible light photocatalyst were investigated in various ways and discussed in detail.