New route to synthesize highly active nanocrystalline sulfated titania-silica: Synergetic effects between sulfate species and silica in enhancing the photocatalysis efficiency

A simple and efficient approach has been set up for fabricating highly active sulfated titania-silica (SO42-/TiO2-SiO2): Ti(SO4)(2) was hydrolyzed in the presence of silica, making it possible to sulfate titania and form titania-silica mixed oxide in one step. This study was focused on investigating the roles of sulfate species and silica in improving the physicochemical properties and photoactivity of SO42-/TiO2-SiO2 through comparison with sulfated titania (SO42-/TiO2) and sulfate-free catalysts (TiO2 and TiO2-SiO2). Various characterization methods, including X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and surface photovoltage spectroscopy (SPS), were employed to test these materials. The results revealed that for SO42-/TiO2 and TiO2-SiO2 the sole presence of either sulfate species or silica imposes negative effects on the photocatalysis behavior of titania, leading them to have negligible photoactivities. On the contrary, in the case of SO42-/TiO2-SiO2, sulfate species and silica were proved to act in a cooperative manner; therefore, the following enhanced structure and surface properties of SO42-/TiO2-SiO2 were obtained: (i) relatively well-crystallized and smaller-size (15.4 nm) anatase-phase titania was formed upon 500 C calcination without forming rutile phase and (ii) the formation of active surface sulfate species promotes the separation of photoinduced electron-hole pairs and therefore accelerates the photocatalysis reaction. Therefore, its photoactivity is enhanced as a result of the favorable synergetic effects between sulfate species and silica due to their simultaneous presence.