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

The surface of TiO 2 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 TiO 2 @SiO 2 “core-shell” particles are shown to exhibit a significant enhancement of singlet oxygen generation compared with the initial TiO 2 . 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. Graphical abstract Highlights The surface modification of TiO 2 NPs with SiO 2 did not cause any phase composition changes. SiO 2 shell formation led to a significant decrease in the size NPs and their agglomerates. The formation of SiO 2 shell resulted in a more than double increase in the NPs specific surface area. The ТiO 2 @SiO 2 composite nanoparticles are characterized by a higher surface-fractal dimension. SiO 2 shells improve the stability of the aqueous suspensions of TiO 2 NPs.