N-doped TiO2 by low temperature synthesis: Stability, photo-reactivity and singlet oxygen formation in the visible range

N-doped TiO2 (NDTs) were prepared by sol–gel synthesis at low temperature starting from nanocolloidal TiO2 and triethylamine according to well-known procedures. Diffuse reflectance UV (DRUV) spectroscopy showed a shift of the absorption to the visible range, while diffuse reflectance IRFT (DRIFT) evidenced the presence of a chemisorbed complex involving triethylamine. Powder XRD showed the sole formation of anatase polymorph of TiO2 while XPS indicated successful incorporation of nitrogen. Our data are globally consistent with previous literature results, but emphasize the low thermal and photochemical stability of the nitrogen complex under air. Di-n-butylsulfide photo-oxidation in acetonitrile solution was successfully carried out under irradiation at 420 and 350 nm. The reaction rates were slower under visible light and the product distribution was very dependent upon the wavelength. Our results are discussed in parallel with the literature data assuming the favoured formation of singlet oxygen under visible light.