Influence of temperature and heating time on growth rate and phase transition of titania nanocrystals embedded in amorphous silica

In this work we studied the thermal stability of TiO2 nanocrystals (∼15 nm) embedded and dispersed in an amorphous silica nanoparticle, aiming its application in photocatalysis at high temperatures. The SiO2/TiO2 samples were made by the H2-O2 flame hydrolysis method. The nanostructural evolution of TiO2 nanocrystals, (phase transformation anatase -> rutile and the growth of nanocrystals) was investigated in relation to the temperature (500 to 1400 deg C) and heating time (2 to 48 hours). The as deposited and heat-treated powders were characterized by XRD, SEM and XRF. We observed that the silica acted as a strong inhibitor of the nanocrystals growth and phase transformation even for long periods at high temperatures treatment. The final size and time required for the stability of nanocrystals for given temperature and concentration of TiO2 were estimated. For a temperature of 1050 deg C and t=48 hours the nanocrystals did not exceed 30 nm, while the anatase phase was maintained stable. (author)