The solid solution Nb x Ti 1-x O 2+δ has been synthesized by a sol-gel method with 0.0 e x e 0.1. Structural and microstructural properties have been studied by XPS, XRD, Raman spectroscopy, and TEM as a function of the Nb/Ti atomic ratio and thermal treatment temperature (600-900 °C). XRD analyses showed that a percentage of the nominal added Nb was assimilated in substitutional Ti sites in the bulk of TiO 2 adopting a pentavalent state. On the other hand, XPS detected a high concentration of Nb at the surface. On the basis of the careful analysis of the XRD and XPS spectra it is reasonable to assume that the concentration of Nb at the surface of the nanoparticles is higher than that in the bulk, especially for rutile, giving a U-shaped Nb concentration profile. The niobium incorporation stabilizes the titania obstructing the diffusion of anatase-type surface atoms, which prevents grain coarsening and phase transformation. The solubility limit of niobium into titania is greater for the anatase phase (x > 0.1) than for the rutile phase (x ) 0.06). Once the solubility limit of Nb atoms is surpassed, a ternary phase ascribed to TiNb 2 O 7 has been detected. In addition, the crystallite sizes and the percentage of rutile phase were quite similar for Nb contents above the solubility limit. XRD and XPS measurements suggest that niobium mainly enters into titania phase with valence +5, while Ti maintains its higher oxidation state (4+), the extra charge being thus partially compensated by titanium vacancies. As derived from XPS analyses in the core levels and the valence band regions, the addition of Nb resulted in a displacement of the Fermi level toward the conduction band. In consequence, the Nbaltered samples presented a more marked n-type feature, as compared with that of the bare TiO 2 .

Carbon nanofibres (GANFG) decorated with metal nanoparticles were deposited over Kapton, a polymide flexible substrate, onto which an array of four interdigitated electrodes in one side and a common heater in the backside were printed using inkjet printing technique. The control over metal type and the decoration percentage have given us the possibility to improve the sensor sensitivity and also enhance the selectivity by taking advantages from the difference interaction behaviors of tested target gas molecules with different hybrid materials at room temperature.

No abstract

No abstract

No abstract