Synthesis and characterization of water-soluble SiO1.5/TiO2 hybrid nanoparticles by hydrolytic co-condensation of triethoxysilane containing hydroxyl groups

Novel R–SiO1.5/TiO2 hybrid nanoparticles were synthesized by hydrolytic co-condensation of titanium alkoxides (Ti(OR′)4, R′ = ethyl, isopropyl, and butyl) with a triethoxysilane precursor, R–Si(OCH2CH3)3, R = –CH2CH2CH2N(CH2CH2COOCH2CH2OH)2, derived from 2-hydroxyethyl acrylate. Co-condensation of a titanium alkoxide with the triethoxysilane precursor was investigated at different feed ratios, suggesting that water-soluble nanoparticles were obtained only at less than 30% of Ti(OEt)4 molar ratio in the feed. In contrast, the co-condensation of titanium tetraisopropoxide, Ti(OiPr)4, with the triethoxysilane precursor in the presence of acetylacetone proceeded as a homogeneous system until 70% of Ti(OiPr)4 molar ratio to afford water-soluble organic–inorganic hybrid nanoparticles containing titania–silica mixed oxides, as confirmed by NMR, FT-IR, elemental and ICP analyses. Scanning force microscopy (SFM) measurements of the product prepared at Ti(OiPr)4/triethoxysilane = 50/50 mol% with acetylacetone indicated the formation of the nanoparticles having relatively narrow size distribution with average particle diameter less than 2.0 nm without aggregation. The refractive index of the hybrid nanoparticle was 1.571. The isolated nanoparticles distributed homogeneously were visualized by transmission electron microscopy (TEM), and the size of the hybrid nanoparticle (1.9 nm) was determined by X-ray diffraction (XRD).