Bulk, Surface and Morphological Features of Nanostructured Tin Oxide by a Controlled Alkoxide-Gel Path

SnO2 particles and films were prepared by following a common sol-gel preparative route using tin (IV) alkoxide as the starting compound; the xerogels were thermally treated at 300, 500 and 700 degrees C. The materials were characterized for phase composition-crystallinity, by X-ray diffraction, and for surface area and porosity, by N-2 adsorption isotherms. Both structural and morphological characterizations showed, at all temperatures, the formation of nanostructured SnO2. By cyclic voltammetry and by electrochemical impedance spectroscopy the typical semiconductive behaviour of nanostructured materials was observed; the presence of Sn surface states with lower valence with respect to Sn(IV) was supported by both impedance and XPS analyses performed, also, in the valence band region. The isoelectric point (i.e.p.) of the material and its dependence on the temperature of calcination was obtained by means of electrophoretic mobility determinations as a function of the solution pH.