Interface tailoring of SnO₂–TiO₂ photocatalysts modified with anionic/cationic surfactants

SnO₂–TiO₂ nanocomposites are prepared by growing TiO₂ nanoparticles onto the preformed SnO₂ nanoparticles. The SnO₂ core nanoparticles ware obtained in the presence of two different surfactants, namely hexadecyltrimethyl ammonium bromide and polyethylene glycol 600 (PEG600), by chemical precipitation followed by a thermal treatment at 500 °C. The TiO₂ was obtained directly on modified SnO₂ nanoparticles by a sol–gel process. A sample without surfactants was prepared in the same conditions. The processes involved during annealing of precursors were revealed by TGA-FTIR. The crystalline and mesoporous structures of samples were evidenced by XRD, HRTEM and by N₂ adsorption–desorption isotherms. XPS investigations highlighted the interface modifications due to the presence of cationic or anionic moieties resulted from the thermal decomposition of surfactants. Combined UPS and UV–Vis measurements allowed the determination of the oxidation energies, band gaps and energy bands alignment of nanocomposites. The photocatalytic activity based on reactive oxygen species (ROS) generation was studied toward degradation of RhB under visible-light irradiation and by the use of EPR coupled with spin-trapping technique. It was found that the generated ROS are only of ^·OH type and, this specific process, is analyzed in terms of energy bands alignment.