Deposition of titania nanoparticles on spherical silica

Titania coated silica nanoparticles were prepared through a sol-gel process using peptized TiO2 nano-sols. The TiO2 sols were obtained by peptization, the process of redispersing a coagulated colloid, and were coated on SiO2 particles by the control of the weight ratio of TiO2/SiO2 and the pH of the mixture in aqueous solution. At pH 4.5 the difference of zeta-potential between SiO2 and TiO2 maximized and then the TiO2-coated SiO2 particles with highest TiO2 contents (∼20%) were obtained without the self-aggregation of TiO2 sols. The morphologies of particles were characterized with field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) and the isoelectric points (IEP) of particles were measured by zeta potential. The nature of exposed titanium ions on the surface of titania-coated silica nanoparticles was elucidated by X-ray photoelectron spectroscopy (XPS).