A general method to coat colloidal particles with titania.

We describe a general one-pot method for coating colloidal particles with amorphous titania. Various colloidal particles such as silica particles, large silver colloids, gibbsite platelets, and polystyrene spheres were successfully coated with a titania shell. Although there are several ways of coating different particles with titania in the literature, each of these methods is applicable to only one type of material. The present method is especially useful for giving the opportunity to cover many types of colloidal particles with titania and forgoes the use of a coupling agent or a precoating step. We can produce particles with a smooth titania layer of tunable thickness. The monodispersity, which improves during particle growth, and the high refractive index of titania make these particles potential candidates for photonic crystal applications. We also describe various ways of fabricating hollow titania shells, which have been intensively studied in the literature for their applications in electronics, catalysis, separations, and diagnostics. Note that our method initially produces amorphous shells on the particles, but these can be easily turned into crystalline titania by a calcination step. We also find that the growth of titania is a surface-reaction-limited process.