Preparation And Characterization Of Vanadium Oxide Nanotubes And Thin Films

As an important kind of functional materials,vanadium oxide can be used to prepare gas sensors,electric/optic switchs,electrochromic films,and so on.In this thesis,vanadium oxide nanotubes were prepared by hydrothermal method,vanadium oxide sols were prepared by quenching method,vanadium oxide gel films were prepared by sol-gel method,and V₂O₅/Pd composite films were prepared by magnetron sputtering method.The vanadium oxide nanotubes and thin films were characterised with SEM,TEM,XRD,etc.The sensitivity of vanadium gel films and V₂O₅/Pd composite films to humidity and hydrogen gas was studied through an optical fiber sensing system,and the sensitive mechanisms were discussed.In this thesis,the main contents and experimental results are as follows:(1) Vanadium oxide nanotubes were prepared by hydrothermal method using 1-hexadecylamine as template and the sol precursor achieved by the mixture of V₂O₅ powder and H₂O₂.The SEM images show that the length of the nanotubes are about 1～5μm;the TEM images show that the diameter of the nanotubes is about 30～80 nm; the XRD curves indicate that the tube walls are lamellar;the FT-IR spectrum suggests that 1-hexadecylamine is inserted into the walls of the vanadium oxide nanotubes. The formation of the nanotubes may be related to lamella-peeling and rolling process;(2) Stable V₂O₅ sols were prepared through water quenching method using V₂O₅ powder as vanadium source.Vanadium oxide gel films were prepared through pulling method or spincoating method.The XRD curves shows that the dry V₂O₅ gels are basically noncrystalline and that the main crystalline phases in annealed films are V₂O₅ and a small quantity of V₃O₅;the vibration modes of V-O bonds in the films were analysesed through the Raman spectra;the optical absorption behaviors of the sols and the films were analysesed with a UV-vis spectrophotometer;(3) The sensitive properties of the vanadium oxide gel films were tested on an optic fiber experimental setup.The testing results show that the dry gel films are sensitive to humidity with a short response time,about 1～2 s.However,the sensitivity decrease significantly after the dry gel films were heat treated.The humidity sensitive may result from the the adsorption of water molecules by the dry gel films.The adsored water molecules change the refractive index of the dry gel films and result in the change of reflective optical power.The heat-treated films is sensitive to hydrogen,but the response time is too long and the repeatability is no good;(4) V₂O₅/Pd composite films were prepared by magnetron sputtering method and their sensitive preperty were tested.The results show that V₂O₅/Pd composite films are sensitive to hydrogen.For 4%hydrogen/nitrogen,the response time is about 60 s, the change amplitude of reflective optical power is about 25%and the repeatability is very good.The testing results show that V₂O₅/Pd composite films are almost not sensitive to humidity.