Structural and surface characterization of nanostructured spray dried titanosilicate microspheres

The aim of the present study was to synthesize by spray drying titanosilicate microspheres of less than 5 μm in diameter and to induce by thermal treatment the growth of nanocrystalline phases in amorphous matrices. The microspheres obtained by this process belong to the xTiO2:ySiO2 system, with x:y ratios of 1:2, 1:1 and 2:1, doped with 1% Gd2O3. Anatase and rutile nanocrystals were developed by increasing the calcination temperature from 700 to 1100 °C, and both are desired phases concerning their applications. Structural and surface characterization before interaction with biological and/or environmental media are an important issue for the expected behaviour in such milieus. The changes induced by the thermal treatments with respect to structure, morphology and Ti/Si ratio on the surface of the samples were investigated using thermogravimetrical (TGA), differential thermal analyses (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Surprisingly, for as-prepared microspheres the surface atomic composition relative to Ti and Si is quite similar for all three systems, while for the heat treated samples the Si content increases, that reflects that the developed titania nanocrystals are covered by a thin layer of amorphous silica.