纳米结构钒氧化物和钒青铜的制备与表征

【作者】 费海龙；

【导师】 陈铁红；

【作者基本信息】 南开大学 ， 物理化学， 2009， 博士

【摘要】 钒的氧化物和钒青铜（Vanadium Bronze）在催化、传感器、光电开关、锂电池、超导、生物无机材料等诸多领域有着广泛的用途或潜在的应用前景。五氧化二钒（V₂O₅）、二氧化钒（VO₂）和含钠钒青铜是相对研究较多的材料,同其体相结构材料相比,纳米结构材料在能量的转化和存储等方面展现更优异的性能。到目前为止,已经发展多种方法制备V₂O₅、VO₂、含单一阳离子的钒酸盐和钒青铜材料的一维和二维纳米结构,相比之下,三维纳米结构的钒氧化物和钒青铜材料的研究报道不多。因此,探讨新的合成方法制备新晶相结构、新形貌的钒氧化物和钒青铜三维纳米结构材料具有重要的意义。本文主要研究以水热和溶剂热合成方法制备钒氧化物和钒青铜三维纳米结构,利用扫描电子显微镜（SEM）、透射电镜（TEM）、红外光谱（FT-IR）、X-射线衍射（XRD）、氮气吸附、紫外漫反射光谱、热重-差热分析（TG-DTA）和X-射线光电子能谱等表对所制备的材料进行表征,并对材料进行了紫外光照射降解若丹明B（RhB）和锂电池正极材料的充放电性能测试。主要内容有以下三部分:1)发展了一种新方法合成具有Paramontroseite矿物结构的VO₂,并以之为前驱体制备了不同表面形貌的V₂O₅空心球。合成体系以偏钒酸铵作为钒源,草酸作为还原剂,四氢呋喃作为溶剂通过溶剂热方法制备产物。通过控制溶剂热反应时间和反应原料配比控制产物形貌。反应6小时得到直径在3微米左右的核壳结构的Paramontroseite VO₂微球。而反应24小时得到直径在1～6微米间的由纳米片辐射组装的Paramontroseite VO₂微球。通过焙烧,分别得到不同表面形貌的V₂O₅空心球和微球。空心球的形成可能由于热解过程中释放内含物有机物而形成的。不同形貌的V₂O₅在紫外光照射下催化降解若丹明B染料（RhB）,发现光催化活性与空心球表面形貌有关,片混乱堆积的五氧化二钒空心球展现最高的活性,可能由于在混乱堆积的片间发生多重反射和散射增强了紫外光吸收。2)通过前驱体分解法原位制备V₂O₅纳米结构。在水热条件下,二甲基亚砜（DMSO）和偏钒酸铵反应生成玫瑰花状的NH₄V₃（OH）₆（SO₄）₂晶体,颗粒的平均尺寸大约在20微米。焙烧后,原位形成的单晶纳米颗粒作为构筑块,形成玫瑰花状的V₂O₅纳米结构。该纳米结构V₂O₅作为锂电池的正极材料展现较高的初始放电容量(449.5 mAhg^-1)。通过选择酸的种类,用乳酸和硝酸可分别形成球状的NH₄V₃（OH）₆（SO₄）₂)和玫瑰花状的VO₂,其原因可能由于酸的不同络合能力和硝酸根的强氧化性影响了对偏钒酸铵的还原。3)以水热方法制备了铵/钠双阳离子插层的钒青铜三维纳米结构。利用草酸作为还原剂,偏钒酸铵和硝酸钠为原料,通过简单的水热方法制备了单晶纳米片组成的三维花状钒青铜纳米结构。通过电平衡,Na⁺和NH₄⁺插层形成形成（NH₄）_0.83Na_0.43V₄O₁₀·0.26H₂O结构,延长水热处理时间,可转化为稳定的新晶相结构（NH₄）_0.26Na_0.14V₂O₅,形貌为单晶纳米片组成的花状纳米结构。双阳离子（钠离子和铵根离子）是诱导形成新结晶结构钒青铜的因素,而单一的钠离子和铵根离子存在的条件下,可分别得到VO₂和（NH₄）₂V₈O₂₀·3H₂O。合成中加入Li⁺能够形成同晶相结构的（NH₄）_0.44Li_0.01V₂O₅,加入K⁺可诱导形成类似晶相结构的（NH₄）_0.17K_0.47V₂O₅。分别以锂、钠、钾铵钒青铜（NH₄）_0.26Na_0.14V₂O₅,（NH₄）_0.83Na_0.43V₄O₁₀·0.26H₂O,（NH₄）_0.44Li_0.01V₂O₅和（NH₄）_0.17K_0.47V₂O_5.0作为锂电池的正极材料,进行充放电性能测试。（NH₄）_0.26Na_0.14V₂O₅在2.0～3.4V展现较高的放电比容量和良好的循环稳定性,初始放电容量为196 mAhg^-1。第30次的放电容量可达到200 mAhg^-1。（NH₄）_0.83Na_0.43V₄O₁₀·0.26H₂O也展现良好的循环稳定性。2.0～3.4 V条件下,初始放电容量达到165.5 mAhg^-1,循环49次后放电容量达到157.4 mAhg^-1,容量衰减4.9%。在1.5～3.4 V条件下,初始放电容量可达到225.5 mAhg^-1,循环50次后为220.8 mAhg^-1。这种双阳离子插层方法可拓展制备碱土金属钒青铜纳米结构。更多还原

【Abstract】 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.更多还原