Visible light responsive iodine-doped TiO2 for photocatalytic reduction of CO2 to fuels Original Research Article

Iodine-doped titanium oxide (I-TiO2) nanoparticles that are photocatalitically responsive to visible light illumination have been synthesized by hydrothermal method. The structure and properties of I-TiO2 nanocrystals prepared with different iodine doping levels and/or calcination temperatures were characterized by X-ray diffraction, transmission electron microscopy and diffraction, X-ray photoelectron spectroscopy, and UV–vis diffuse reflectance spectra. The three nominal iodine dopant levels (5, 10, 15 wt.%) and the two lower calcination temperatures (375, 450 °C) produced mixture of anatase and brookite nanocrystals, with small fraction of rutile found at 550 °C. The anatase phase of TiO2 increased in volume fraction with increased calcination temperature and iodine levels. The photocatalytic activities of the I-TiO2 powders were investigated by photocatalytic reduction of CO2 with H2O under visible light (λ > 400 nm) and also under UV–vis illumination. CO was found to be the major photoreduction product using both undoped and doped TiO2. A high CO2 reduction activity was observed for I-TiO2 catalysts (highest CO yield equivalent to 2.4 μmol g−1 h−1) under visible light, and they also had much higher CO2 photoreduction efficiency than undoped TiO2 under UV–vis irradiation. I-TiO2 calcined at 375 °C has superior activity to those calcined at higher temperatures. Optimal doping levels of iodine were identified under visible and UV–vis irradiations, respectively. This is the first study that investigates nonmetal doped TiO2 without other co-catalysts for CO2 photoreduction to fuels under visible light.