Arsenic photocatalytic oxidation over TiO2-loaded SBA-15

Versatile materials for oxidizing As(III) into less hazardous As(V) species has triggered increasing attention. In this work, 7% anatase TiO2 was coated on pre-formed SBA-15 by means of impregnation to produce Ti-SBA-15. The materials were characterized by XRD, Raman, FTIR, N2 adsorption, DRS and TEM techniques. Photo-oxidation tests at different pHs were carried out. In the dark, the As(III) adsorption equilibrium on Ti-SBA-15 was reached, showing a moderated adsorption capacity at pHs 4, 7, and 9 (7%, 11%, and 30%, respectively), being more evident at alkaline conditions. This fact was attributed to the presence of surface hydroxyl groups on the deposited TiO2, which promotes the formation of surface monodentate As(III) complexes on Ti-SBA-15. Moreover, Ti-SBA-15 showed to be an efficient photocatalyst in all pHs, being more than 98% of As(III) photo-oxidized into As(V). Results demonstrated that the oxidation process is induced by reactive oxygen species, including •OH and 1O2, generated onto the TiO2 nanoparticles loaded on SBA-15 during the irradiation. SBA-15 instead showed a negligible impact on adsorption and photo-oxidation, indicating that these processes are the effect of the presence of TiO2 deposited on it. However, the use of SBA-15 as support promotes an adequate dispersion of TiO2, favoring these processes. Thus, a mechanism for the adsorption and photo-oxidation of As(III) on Ti-SBA-15 was proposed. Finally, despite the fact that TiO2 covers only a few percent of the overall Ti-SBA-15 surface it showed an unprecedented photocatalytic behavior, demonstrating to be a prominent photocatalyst for the removal of arsenic from water.