Multistep coating of thick titania layers on monodisperse silica nanospheres

Titania coating on monodisperse silica spheres was carried out with a multistep method using titanium n-butoxide. Titania-coated silica spheres were characterized with transmission electron microscopy and energy-dispersive X-ray flourescence spectroscopy. Electrophoretic properties and size distributions of the particles were also measured. Starting from monodisperse silica spheres of 550 nm in mean diameter, the thickness of titania coatings achieved with five coating steps was up to 46 nm, or 125 monolayers of titania, equivalent to a titania weight loading of 54.7 wt %. The uniformity of the titania coating was confirmed by the precise agreement in the electrokinetic mobility of the resulting spheres with that of bulk titania particles. High monodispersity was maintained with a relative standard deviation in diameter of less than 5%. The aggregation extent of the coated spheres was only increased slightly from 11.8% for the silica spheres to 17.2% after three steps of titania coating.