Visible-light response Cr-doped TiO2−XNX photocatalysts

Chromium (Cr) and nitrogen (N)-doped titania (TiO2) was prepared using sol–gel method and ammonia thermal treatment. TiO2 co-doped with Cr and N showed intense absorption bands in the visible-light region. The X-ray photoelectron spectroscopy (XPS) detected chromium and nitrogen ions on the surface of catalysts, but no diffractive peak of chromium oxide or titanium nitride was observed in X-ray diffraction (XRD) spectra. The analysis of X-ray absorption near edge spectroscopy (XANES) indicated either Cr3+ or Cr4+ chemical status implying that chromium either substituted Ti4+ site or locally was isolated on the surface of TiO2. The photocatalytic activity was evaluated by the degradation of methylene blue (MB) and isopropyl alcohol (IPA) under visible-light (>460 nm) irradiation using blue-light emitted diode. The rate constants of MB and IPA photodegradation with N-doped TiO2 were 7.7 and 80 μmol l−1 h−1 g−1, which were much higher than those with pure TiO2, 0.15 and 0 μmol l−1 h−1 g−1, respectively. The Cr and N co-doped TiO2 showed less photoactivity than either Cr or N-doped TiO2 due to the extra imperfection of TiO2 lattice during preparation.