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

Highlights: • Novel sensing architecture is presented, made by V₂O₅ modification of TiO₂ surface. • MAS NMR techniques are a powerful tool for studying the influence of the V₂O₅ layer. • The V₂O₅ surface deposition enhanced the adsorption properties with respect to pure TiO₂. - 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 5 nm. 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