Aged titania nanoparticles. The simultaneous control of local and long range properties

TiO2 nanoparticles are obtained by combining a sol-gel preparative route with hydrothermal aging steps, performed in mild conditions, of varying time lengths. Both aged and un-aged samples are thermally treated at 300 and 600 °C, for the same length of time. The crystal structures, the phase composition, and crystallite sizes are analyzed by powder X-ray diffraction. Raman spectra of anatase nanocrystals with average sizes of 7-10 nm are reported and the correlation between the Raman band shape of the main feature at 144 cm-1 and the crystallite size is discussed. Nitrogen physisorption by Brunauer-Emmett-Teller (BET) method is adopted to evaluate the particles surface area and mesopore size and size distribution. The role played by the hydrothermal step in affecting the physicochemical properties of the powders is discussed also with respect to the H2O/TiO2 interactions as apparent from Raman spectroscopy investigations of the O-H stretching range (3000-3800 cm-1).