Enhanced photocatalytic oxidation of arsenite to arsenate in water solutions by a new catalyst based on MoOx supported on TiO2

Photocatalytic oxidation of As(III) to As(V) was investigated using a new catalyst based on molybdenum oxide supported on titania (MoOx/TiO2), under different irradiation intensities and catalyst dosages. Photocatalysts were prepared by incipient wet impregnation of anatase titania with ammonium heptamolybdate solutions. The obtained samples were characterized by thermogravimetric analysis, N-2 adsorption at -196 degrees C, X-ray diffraction, Laser Raman spectra and UV-vis reflectance spectra. UV-vis DRS spectra of the photocatalysts evidenced that the surface coverage with MoOx, did not significantly decrease the equivalent band gap energies. X-ray diffraction analysis showed that up to 8.4 wt% Mo-loading, molybdenum oxide remains on the surface of titania support as amorphous phases. Raman spectra showed the presence of hydrated octahedrally molybdate anchored species interacting with TiO2 surface and a molybdenum oxide monolayer coverage of corresponding to about 9.8 wt% of MoO3. Photocatalytic oxidation tests showed that TiO2 alone is not able to oxidize all As(III) present in solution, while the complete conversion of As(III) to As(V) was achieved in the presence of MoOx/TiO2 catalyst. In particular, the best conversion was observed within 60 min of exposure to UV light irradiation with a Mo-loading corresponding to a monolayer coverage. As(V) produced during the photoreaction was completely released into solution, thus not occupying stably the active sites which results in a photocatalyst with high stability over the time. (C) 2014 Elsevier B.V. All rights reserved.