Surface properties and thermal stability of SiO2-crystalline TiO2 nano-composites

TiO2/SiO2 nanocomposites are synthesized and fully characterized after thermal stabilization at temperatures between 400 degrees C and 800 degrees C. The control of the impregnation media is crucial to obtain nanocomposites of satisfactory quality, i.e. presenting no segregation of titania particles outside the silica pore structure. Characterization shows that pore size and pore volume decrease linearly with an increase in titania loading, and remain close to the theoretical values calculated assuming the formation of a non-porous coating. Surface area remains unchanged whatever the titania loading (always comprised between 450 and 480 m(2) g(-1)), and micropore volume evolution suggests the formation of nanometric particles within the silica pores. While X-ray diffraction is inefficient to identify the titania phase, Raman spectroscopy showed the formation of anatase particles, with crystal sizes in the nanometric range (<4.5 nm, when stabilized at 400 degrees C). Satisfying thermal stability is obtained on the low titania loading nanocomposites (20 wt% TiO2), with only minor anatase crystal growth up to 800 degrees C. Further characterization by FT-IR of the surface chemical properties of the nanocomposites showed properties similar to that of conventional titania, while improved oxygen mobilities (as evaluated by the O-18/O-16 exchange reaction) are reported on the low titania loading, thermally stable, composites.