Fabrication of Hollow Hybrid Microspheres Coated with Silica/Titania via Sol−Gel Process and Enhanced Photocatalytic Activities

In this paper, we reported a facile and effective approach for fabrication of polystyrene (PS)/silica/titania hybrid microspheres and their resultant hollow double shell hybrid spheres with a smooth and uniform shell of SiO 2 /TiO 2 . In this approach, the cationic polystyrene spheres were first synthesized by emulsifier-free emulsion polymerization using the cationic initiator. Subsequently, the PS/SiO 2 /TiO 2 multilayer hybrid spheres were successfully formed by two-step sol−gel methods. The as-prepared hybrid spheres were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy (EDS), thermogravimetric analysis, ζ potential measurement, and N 2 adsorption/desorption isotherm analysis. The effects of the titanium tetrabutoxide content, surfactant content, and the midlayer of silica on the morphology, porosity and mean pore size, specific surface area, and thermal property of the obtained hybrid spheres were systematically evaluated. The photocatalytic activity of the prepared hollow SiO 2 /TiO 2 hybrid spheres under ultraviolet light irradiation was compared to that of commercial p-25 powder using the photocatalytic degradation of methylene blue (MB) as a model reaction. The photocatalytic activity of hybrid spheres with three layers of titania was slightly higher than that of P-25. Moreover, the photocatalytic activity of nitrogen-doped hollow SiO 2 /TiO 2 hybrid spheres was also investigated under visible light irradiation. The photocatalytic degradation rate of nitrogen-doped hollow hybrid sphere was about two times that of nitrogen-doped P-25 powder in 5 h for the degradation of MB.