Visible light photocatalytic activities of nitrogen and platinum-doped TiO₂: Synergistic effects of co-dopants

The visible light photocatalytic activity of nitrogen doped TiO₂ (N-TiO₂) was enhanced with co-doping of Pt ions for the oxidative and reductive degradation of model substrates in gaseous and aqueous phases. The synthesized samples were characterized by various techniques (diffuse reflectance UV-Vis, XPS, XRD, FT-IR, HR-TEM, EDX and laser flash photolysis spectroscopy). The co-doping of N and Pt of TiO₂ (Pt,N-TiO₂) significantly enhanced the degradation of acetaldehyde (gas phase), and trichloroacetate (TCA) (aqueous phase), and the reduction of Cr(VI) (aqueous phase) under visible light (λ>420nm). The observed visible light photocatalytic activity of Pt,N-TiO₂ was markedly higher than the singly-doped TiO₂ (Pt-TiO₂ or N-TiO₂). A time-resolved diffuse reflectance (TDR) study found that the presence of the different oxidation states of Pt (2+ and 4+) plays a crucial role in the charge trapping and transfer dynamics in Pt-TiO₂. The TDR study of Pt,N-TiO₂ further revealed that the synergistic effect of co-doping is attributed to the combined contribution of each dopant. Finally, the first principle calculations for the doped TiO₂ suggested that the electronic interaction of Pt and N in TiO₂ facilitates the charge carrier mobility and reduces the undesired recombination, leading to enhanced photocatalytic activity.