Synthesis and characterization of titania-coated silica fine particles by semi-batch process

Monodispersed, spherical titania (TiO2)-coated silica (SiO2) fine particles were synthesized by semi-batch process. By this process, SiO2 fine particles were also prepared and were used as carrier particles for the coating. The mean size of SiO2 particles was 250 nm. The reaction parameters were the concentration of tetraethylorthotitanate (TEOT), the amount of hydroxypropylcellulose (HPC) as a dispersant, the feed rate of starting solution (TEOT+HPC+EtOH) and reaction temperature. As a result, the following results were obtained; particle size of titania-coated silica particles decreased with a decreasing TEOT concentration, slow feed rate and increasing amount of HPC. In addition, it was desirable to maintain a reaction temperature at 15–18 °C in order to obtain the monodispersed fine particles. Consequently, the optimal conditions for the preparation of titania-coated silica particles with narrow size distribution were TEOT (0.03–0.04 M), HPC (0.001–0.0013 g ml−1), feed rate (0.5–0.6 ml min−1), and reaction temperature (15–18 °C). The samples were characterized using FT-IR, EDS, TEM and BET analyzer. The coating thickness of TiO2 particles obtained by using the above conditions was about 5–10 nm.