TiO2 colloidal nanocrystals surface modification by V2O5 species: Investigation by 47,49Ti MAS-NMR and H2, CO and NO2 sensing properties

Abstract

TiO2 and TiO2–V2O5 nanocrystals were prepared by coupling sol–gel and solvothermal methods, followed by heat-treatment at 400°C, after which the mean nanocrystal size was about 5nm. The materials were characterized by X-ray diffraction, transmission electron microscopy and solid state nuclear magnetic resonance spectroscopy. It was shown that while the TiO2 phase was always anatase even after heat-treatment at 500°C, the presence of the vanadium oxide species enhanced the surface re-configuration of the Ti ions. Hence the coordination environment of surface Ti atoms was drastically changed, by formation of further bonds and imposition of a given local geometry. The final hypothesis was that in pure titania surface rearrangement occurs, leading to the new NMR signal, but this modification was favored in the TiO2–V2O5 sample, where the Ti surface atoms were forced into the final configurations by the bonding with V atoms through oxygen. The materials heat-treated at 400°C were used to process chemoresistive sensors, which were tested to hydrogen, CO and NO2, as examples of gases with peculiar sensing mechanisms. The results evidenced that the surface deposition of V2O5 onto the anatase TiO2 nanocrystals was effective in modifying the adsorption properties of the anatase nanocrystals.