Titania coated silica core-shell spheres with dual grain size as efficient photocatalysts

The TiO2 nanoclusters were modified into the pores of silica core-shell particles (SiO2@dSiO2) by the sol-gel method, and the loading amount reached 47%. Based on the Ostwald ripening theory, by simply extending the reaction time, a part of the TiO2 in the pores of the shell was dissolved and then re-deposited on the outer surface of the shell to form a TiO2 layer. Using this method, TiO2 crystalline grains of different sizes were obtained simultaneously inside and outside the shell of silica core-shell spheres. Small-sized crystalline grains were located in the pores of the shell, and they had a strong quantum size effect. The large crystalline grains were located in the TiO2 layer on the outer surface of the shell of SiO2@dSiO2. Due to the formation of larger-sized crystalline grains, the recombination probability of photogenerated electron-hole pairs was reduced. When used as photocatalysts for the degradation of Rhodamine B under UV irradiation, the catalytic activity of SiO2@dSiO2@TiO2 was 5.4 times higher than that of the commercial P25 TiO2 photocatalyst.