Highly visible light active TiO_2-xN_x heterojunction photocatalysts

diaminetetraacetic acid (EDTA) modified sol-gel process.An FT-IR study of EDTA modified TiO₂ gel confirms the existence of an ionic intermediate (as indicated by a Δ value of 233 cm^-1). Differential scanning calorimetry (DSC), X-ray diffraction (XRD), and Raman spectroscopy are employed to study the phase evolution, phase purity, and crystallite size of samples. Formations of O-Ti-N and N-Ti-N bonds in calcined samples are confirmed using XPS and FT-IR spectroscopy. AllEDTAmodified samples show significantly higher visible light photocatalytic activity than the unmodified sample. The most active nitrogen doped heterojunction obtained at 400 °C exhibits 9-fold visible light activity in comparison to the standard photocatalyst Degussa P-25. It is proposed that the photo excited electrons (from the visible midgap level) are effectively transferred from the conduction band of anatase to that of rutile causing effective electron-hole separation, which is responsible for the higher visible light activity and lower photoluminescence (PL) intensity.