Photocatalytic oxidation of aniline over MO/TiO2 (M = Mg, Ca, Sr, Ba) under visible light irradiation

MO/TiO2 (M = Mg, Ca, Sr & Ba; TiO2: Evonik Aroxide P25) composites were prepared for photocatalytic aniline oxidation under visible light irradiation. The conversion efficiencies of aniline over the samples are revealed as follow order: BaO/TiO2 > SrO/TiO2 > CaO/TiO2 > MgO/TiO2. The combined results of XPS and CO2 TPD indicate that the electron density of lattice oxygen and the surface basicity for the photocatalysts became higher and higher with the atomic number increase of the alkaline metal elements, in accordance with the order of the conversion efficiency. The sample SrO/TiO2 shows the highest nitrosobenzene selectivity. BaO/TiO2 with highest surface basicity may facilitate the further aniline transformation to nitrobenzene and azobenzene, resulting in lower selectivity for nitrosobenzene. Surface complexes formed on the basic sites of the catalysts via aniline chemsorption would be acted as active sites and be excited for the photocatalytic oxidation of aniline under visible light irradiation.