Characterization and performance of Ag nanoparticles on TiO2 for the photocatalytic oxidation of dibenzothiophene compounds

Ag nanoparticles on TiO₂ were synthesized and characterized to determine its potential use as photocatalysts and then were assessed in the photocatalytic oxidation of dibenzothiophene compounds. The incorporation of Ag onto the TiO₂ structure was investigated as a function of Ag loading. The catalysts were prepared with Ag loadings of 1, 3, 5 and 10 wt% and were characterized by scanning electron microscopy (SEM-EDX), transmission electron microscopy (TEM), X-ray diffraction (XRD), UV–vis diffuse reflectance spectroscopy (DRS), photoluminescence (PL) spectroscopy and electrochemical impedance spectroscopy (EIS). The characterization results showed that Ag was incorporated as nanoparticles onto TiO₂ anatase and that their incorporation decreased the bandgap energy and the recombination rate of photogenerated [e^-/h⁺] species. In addition, it was determined that the proximity of the conduction band energy of the catalysts to the reduction potential of O₂/•O₂^- triggered the generation of •O₂^- radical on the catalytic surface. It was due to the localized surface plasmon resonance effect, improving the charge-carrier capacity and therefore the interfacial electron transfer. The photocatalytic oxidation of DBT, 4-MDBT and 4,6-DMDBT was successfully achieved in 90 min under a combined UV–vis irradiation. Noteworthy, the most recalcitrant compound was more reactive, in the opposite trend to that reported in the conventional non-photocatalytic desulfurization system.