Synthesis of nanostructured solid-state phases of V₇O₁₆ and V₂O₅ compounds for ppb-level detection of ammonia

Solid state phase of V₇O₁₆ with separate V₂O₅ phase were fabricated by pulsed laser deposition. The crystal structure and symmetry of the deposited films were studied with X-ray diffraction and Raman spectroscopy, respectively. Rietveld analysis was performed to the X-ray diffraction measurement results. The surface potentials and morphologies of the films were studied with atomic force microscopy, and microstructure of the thin films was analysed by transmission electron microscopy. Raman spectroscopy and Rietveld refinement results confirmed that the thin-film crystal structures varied between orthorombic V₂O₅ phase and another phase, triclinic V₇O₁₆, previously found only in the walls of vanadium oxide nanotubes (VO_x-NT), bound together with organic amine. We have earlier presented the first results of stable and pure metal-oxide solid-state phase of V₇O₁₆ manufactured from ceramic V₂O₅ target. Here we show more detailed study of these structures. The microstructure studies showed a variation on the porosity of the films according to crystal structures and also some fibre-like nanostructures were found in the films. The surface morphology depended strongly on the crystal structure and the surface potential studies showed ∼50 meV difference in the work function values between the phases. Compounds were found to be extremely sensitive towards ammonia, NH₃, down to ∼40 ppb concentrations, and have shown to have the stability and selectivity to control the Selective Catalytic Reduction process, where nitrogen oxides are reduced by ammonia in, e.g. diesel exhausts. - Highlights: • The triclinic V₇O₁₆ phase is proven to exist in solid state thin-film form. • The existence of V₇O₁₆ in thin-film form is proven by several methods. • The structure of mixed V₇O₁₆ and V₂O₅ is proven to be sensitive to NH₃ at ppb-level.