Influence of Sn4+ on the structural and electronic properties of Ti1-xSnxO2 nanoparticles used as photocatalysts

Ti1-xSnxO2 nanocrystalline materials employed for photocatalysis have been characterised by means of X-ray diffraction, Raman, X-ray absorption (XANES and EXAFS) and UV-Vis spectroscopy and high resolution transmission electron microscopy. Single-phase samples with anatase or rutile type structures and similar tin contents permitted a separate study of the effect of Sn4+ ions on these crystalline forms, whereas materials composed of anatase and rutile mixtures were used to investigate the distribution of the dopant cations when both phases coexist. The results obtained from the single-phase doped TiO2 samples indicate that the presence of tin causes a different effect when doping anatase or rutile in both their structural and electronic properties. While a random substitution of Sn4+ for Ti4+ seems plausible for the rutile phase, some kind of gradient in Sn4+ concentration is possible in anatase. On the other hand, when anatase and rutile coexist, effects of doping are visible in both phases. Regarding chemical composition, a homogeneous distribution of tin was found in both calcined and hydrothermal multiphase samples. Photocatalytic experiments show that both tin-doping and coexistence of different phases have a beneficial effect on the activity of the catalysts.