Preparation And Characterization Of Nanostructured Vanadium Oxides And Vanadium Bronze

Vanadium oxides and bronzes have wide application or potential in catalysis, superconductor,lithium batteries,actuators,sensors,catalysis,switch and bio-inorganic materials.V₂O₅,VO₂ and sodium vanadium bronze were widely investigated.Compared to their bulk counterpart,nano-structured vanadium oxides have significantly improved their performances in devices for energy storage and sensing.Until now,many methods have been developed to prepare low dimensional nano-structures of VO₂,V₂O₅,vanadate and vanadium bronzes(containing single type of cations),while little attention was paid to the preparation of tri-dimensional vanadium oxides and vanadium bronzes nano-architectures.Therefore,it is necessary and significant to explore new method to prepare crystalline vanadium oxides with novel morphology and tri-dimensional vanadium bronzes nano-architectures.In this dissertation,3D vanadium oxides and vanadium bronzes nano-architectures have been prepared by simple hydrothermal or solvothermal method.Various methods,including Scanning Electron Microscope(SEM), Transmission Electron Microscope(TEM),Fourier Transform Infrared spectroscopy (FT-IR),X-Ray Powder Diffraction(XRD),N₂ adsorption-desorption,UV-Vis diffuse reflection spectroscopy,Thermo Gravimetric-Differential Thermal Analysis (TG-DTA) and X-ray Photoelectron Spectroscopy(XPS),were used to characterize the prepared materials.The as-synthesized V₂O₅ was tested as photocatalyst to degrade Rhodamine B(RhB) under the irradiation of UV light.The discharge-charge properties of the vanadium bronzes as cathode materials in lithium batteries were tested.The main content of the thesis is composed of the following three parts:1) A new method was developed to synthesize Paramontroseite VO₂.The synthesis was performed by a solvo-thermal route with NH₄VO₃ as vanadium source, oxalic acid as reducing agent and THF as solvent.The morphologies of the products can be adjusted via variation of the solvothermal time,as well as the proportion of the reactants.Core/shell structured Paramontroseite VO₂ microspheres were obtained after 6 h of reaction.While Paramontroseite VO₂ microspheres consisted of radially oriented platelets were obtained after 24 h of reaction.With the Paramontroseite VO₂ microspheres as precursors,after calcinations,hollow V₂O₅ microspheres were obtained with different morphologies,respectively.The formation of hollow spheres maybe due to release of organic inclusion in the process of calcinations.V₂O₅ spheres with different morphologies were used to degrade Rhodamine B under the radialization of UV light.The results showed that the photocatalytic activity was related to the surface morphology of V₂O₅ microspheres.Hollow V₂O₅ microspheres consisting of randomly packed platelets exhibited the highest photocatalytic activity, and it might be attributed to enhanced UV light absorbance via multiple reflection and diffraction due to the randomly packed platelets on the surface of the V₂O₅ microspheres.2) A method was proposed to prepare V₂O₅ nano-structure via in situ decomposition of the precursors.Under the hydrothermal condition,rose-like crystalline particles of NH₄V₃(OH)₆(SO₄)₂ with the average size of 20μm were synthesized via the reaction between dimethyl sulfoxide(DMSO) and NH₄VO₃.After calcination,rose-like V₂O₅ micro-architectures were formed by the in situ generated single-crystalline V₂O₅ nanoparticles as building blocks.When used as the cathode material in lithium battery,the rose-like V₂O₅ nano-architecture exhibited high initial discharge capacity of 449.5 mAhg^-1.Sphere-like NH₄V₃(OH)₆(SO₄)₂ and rose-like VO₂ could be prepared via addition of lactic and nitric acid,respectively.The main difference may be attributed to different complex ability and strong oxidation of NO₃^-under acidic conditions,which affected the reducing of ammonium vanadate.3) Tri-dimensional ammonium/sodium dual-cation intercalated vanadium bronze nano-architectures were prepared by hydrothermal method.Tri-dimensional flower-like vanadium bronze nano-architectures consisted of single crystalline nano-platelet was prepared with the reducing agent oxalic acid,NH₄V₄O₁₀ and NaNO₃ via hydrothermal reaction.Na⁺ and NH₄⁺ was intercalated via electrical balance,resulting in the formation of metastable(NH₄)_0.83Na_0.43V₄O₁₀·xH₂O.It was converted to stable new crystalline structured(NH₄)_0.26Na_0.14V₂O₅ after prolonging the reaction time.The morphologies were flower-like nano-architectures consisted of single crystalline nano-platelets.The presence of two kinds of different cations is proposed to give rise to the novel crystalline vanadium bronze,as VO₂ and (NH₄)₂V₈O₂₀·3H₂O was obtained in the presence of single NH₄⁺ or Na⁺,respectively. The introduction of Li⁺ could result in the formation of same crystalline (NH₄)_0.44Li_0.01V₂O₅.The introduction of K⁺ could induce to form similar crystalline (NH₄)_0.17K_0.47V₂O₅.The lithium,sodium and potassium ammonium vanadium bronzes,such as (NH₄)_0.26Na_0.14V₂O₅,(NH₄)_0.83Na_0.43V₄O₁₀·0.26H₂O,(NH₄)_0.44Li_0.01V₂O₅ and (NH₄)_0.17K_0.47V₂O_5.0 were tested in lithium battery as cathode materials. (NH₄)_0.26Na_0.14V₂O₅ exhibited high capacity and excellent cycle stability between 2.0～3.4 V.The initial discharge capacity was 196 mAhg^-1,while the 30^th discharge capacity was as high as 202 mAhg^-1.(NH₄)_0.83Na_0.43V₄O₁₀·0.26H₂O also exhibited good cycle stability.The initial discharge capacity was 165.5 mAhg^-1 in the range of 2.0～3.4V.The discharge capacity was 157.4 mAhg^-1 after 49^th cycle,corresponding to 95.1%of the electrode capacity of initial cycle.The initial and final(50^th) discharge capacity for(NH₄)_0.83Na_0.43V₄O₁₀·0.26H₂O was 225.5 and 220.8 mAhg^-1, corresponding to about 95.1%of the initial electrode capacity.This facile bi-cation intercalation method can be extended to prepare alkaline earth vanadium bronzes nano-architectures.