Comparative study of sol–gel-hydrothermal and sol–gel synthesis of titania–silica composite nanoparticles

Titania–silica composite nanoparticles were prepared by sol–gel-hydrothermal and sol–gel routes, respectively, and their physico-chemical and photocatalytic properties were compared. The results of XRD, TEM and BET surface areas showed that sol–gel-hydrothermal route led to anatase titania–silica composite nanoparticles with large specific surface area, but the sol–gel route tended to form mixture of anatase and rutile. The composite nanoparticles prepared by sol–gel-hydrothermal route had better thermal stability against phase transformation from anatase to rutile, agglomeration and particle growth than those prepared by sol–gel route. On the basis of XRD, FT-IR, XPS and 29Si MAS-NMR, a strong interaction was found between SiO2 and TiO2, and Ti–O–Si bonds formed during both the two routes. But more Ti–O–Si bonds formed in the composite nanoparticles prepared by sol–gel-hydrothermal route than those prepared by sol–gel route. As a result, the titania–silica composite nanoparticles prepared by sol–gel-hydrothermal route exhibited higher photocatalytic activity in decomposition of methylene blue than that prepared by sol–gel route, and it had excellent photocatalytic activity even after calcined at 1000 °C.