Highly Visible Light Active TiO2-xNx Heterojunction Photocatalysts

Nitrogen doped anatase-rutile heterojunctions are successfully synthesized through an ethylenediaminetetraacetic 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 Delta v 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. All EDTA modified samples show significantly higher visible light photocatalytic activity than the unmodified sample. The most active nitrogen doped heterojunction obtained at 400 degrees 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.