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 (lambda > 420 nm). 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. (C) 2013 Elsevier B.V. All rights reserved.