Enhanced photocatalytic activity of Pt-doped TiO2 for NOx oxidation both under UV and visible light irradiation: A synergistic effect of lattice Pt4+ and surface PtO

• Pt doped TiO2 was synthesized and used for NOx photocatalytic oxidation.
• Pt–TiO2 exhibited a high activity both under UV and visible light irradiation.
• A new photocatalytic mechanism was proposed.
• Synergistic effect of lattice Pt4+ and surface PtO was clarified.

Various platinum doped TiO2 with different doping ratios was successfully synthesized by a facile sol–gel method. The structural and optical properties of as-synthesized samples were characterized by the X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and UV–vis diffuse reflectance spectroscopy (DRS). The results showed that all samples were anatase crystals and showed extended absorption into visible light region. The Pt states in the samples were investigated by energy dispersive spectrometer (EDS) and X-ray photoelectron spectra (XPS) analyses. The results revealed that Pt4+ ions were doped into TiO2 crystal lattice with a part of PtO deposited on the TiO2 surface. Pt doped TiO2 exhibited a significantly enhanced activity than pure TiO2 and P25 for the photocatalytic oxidation of NOx under irradiation of UV light, simulate sunlight and visible light. An obviously suppressed recombination rate of photo-generated carriers in the Pt doped TiO2 was demonstrated by photoluminescence (PL) spectroscopy measurements. These results suggested that the synergistic effect of two Pt species coexisted in the catalysts played an important role in the improvement of photocatalytic performance. The photocatalytic reaction mechanisms of NOx oxidation on the catalyst under UV and visible light irradiation were discussed in detail.