Surface and photocatalytic properties of sol–gel derived TiO₂@SiO₂ core-shell nanoparticles

The surface of TiO₂ nanoparticles was modified with silica prepared by acid hydrolysis of tetraethoxysilane followed by polycondensation. A comparative characterization of the initial and modified nanoparticles by TEM, XRD, specific surface area and ζ-potential measurements as well as the estimation of the surface acid-base properties via dynamic pH measurements revealed that the applied surface modification provided almost no changes in the phase composition, crystallite size range (~16 nm) and mesostructure of the initial anatase nanoparticles, but resulted in a more than twofold increase in the specific surface area and change of the surface functionality from a prominent Lewis acidity toward a relatively weak Broensted acidity. The resulting TiO₂@SiO₂ “core-shell” particles are shown to exhibit a significant enhancement of singlet oxygen generation compared with the initial TiO₂. In conjunction with increased specific surface and modification of the surface centers, this effect promoted a drastic growth of photocatalytic activity indicated by an almost 90% degradation of methylene blue dye upon UV irradiation.