【作者】 祁琰媛；

【导师】 陈文；

【作者基本信息】 武汉理工大学 ， 材料物理与化学， 2007， 博士

【摘要】 一维纳米材料因其独特的电学、光学、磁学和力学特性引起了世界范围内科学家的研究兴趣。如何通过研究其生长机制，进而实现对其尺寸、维度、组成、晶体结构乃至物性的调控，对于深入研究结构与物性的关联、并最终实现按照人们的意愿设计合成功能材料具有重要的意义。MoO₃独特的层状结构使其在电池材料、催化剂、电致变色、敏感元件、光学材料等方面具有潜在而广泛的应用。本论文选择一维三氧化钼纳米材料为研究对象，采用现代测试手段对一维MoO₃纳米材料的合成、结构和性能进行了系统而深入研究，并对合成的MoO₃纳米带进行掺杂改性研究。主要内容和研究成果如下：1．分别以三种不同的方法（离子交换法、双氧水氧化法和双氧水分散法）制备了稳定的MoO₃溶胶，并以此三种溶胶为前驱体，采用水热合成方法在没有其它任何催化剂和有机模板剂的条件下，合成了形貌良好、尺寸均一的单晶α-MoO₃纳米带，宽度为150～400nm，平均厚度为70nm，长度可达十几微米；单根纳米带表面光滑完整，没有缺陷且结晶完整；纳米带相互聚集，形成整齐排列的“纳米带簇”结构。2．以MoO₃纳米带作为锂离子电池的正极材料时，随着放电的进行，由于正极表面锂离子富集层先逐渐增加随后减少的过程，使得整个电化学反应的电阻先增加后减小，同时锂离子既能嵌入到[MoO₆]八面体层间，也可进入其层内，但在层间的脱嵌是可逆的，而锂离子在层内的脱嵌会引起不可恢复的相变过程，从而导致不可逆容量的损失，与MoO₃体材料相比，纳米带具有较高的放电比容量（首次放电比容量为301 mAh／g）和较好的循环性能（循环5次容量保持率可达88％）；单根MoO₃纳米带的非线性Ⅰ-Ⅴ曲线表明其仍具有半导体特性，其电导率约为10^-4S／cm；与MoO₃体材料相比，纳米带分别在402nm和475nm出现了强紫光带和较弱的蓝光带，显示出良好的光致发光性能；MoO₃对甲基紫、孔雀石绿、藏红、罗丹明B四种染料溶液具有较好的光催化降解性能，山于纳米带尺寸小，比表面积很大，有效增强催化材料吸附有机物的能力，同时光生电子和空穴的氧化能力增强且复合几率减小，导致纳米带光催化活性的增加。3．通过考察水热反应温度和时间对产物结构和形貌的影响，结合材料热力学和动力学知识，探讨了纳米带的生长机理。离子交换法制备的溶胶在水热条件下首先转变为热力学亚稳相h-MoO₃六角柱，随着温度的升高和时间的延长，h-MoO₃按照溶解-重结晶过程转变为稳定相α-MoO₃纳米带；与前者不同，利用双氧水氧化法和分散法制备的溶胶（MoO₃·pH₂O·qH₂O）在较低的反应温度和较短的反应时间下，不稳定的过氧根首先发生裂解形成MoO₃水合物，进而多余的H₂O脱去形成最终产物α-MoO₃纳米带。上述三种方法制备的纳米带均沿着c轴方向生长。4．以合成的MoO₃纳米带为主体材料，成功将聚合物PEO和PANI嵌入到MoO₃中，分别得到（PEO）_0.1MoO₃、（PANI）_0.02MoO₃和（PANI）_0.05MoO₃纳米带，聚合物的存在使纳米带发生团聚，PEO和PANI均嵌入到MoO₃中的[MoO₆]八面体层间，引起层间距的增大，从而显著地改善了MoO₃纳米带的电化学性能；成功实现MoO₃纳米带的锂化改性，锂化后纳米带的结构与形貌基本保持不变，锂离子占据MoO₃层间使得层间距变大，锂化后纳米带的电学性能由原来的半导体特性变为金属特性，且电导率显著增大，同时其嵌锂性能也得到了改善；通过不同的金属阳离子(Cr⁶⁺、V⁵⁺和Ag⁺)对MoO₃进行了掺杂，其中与Mo⁶⁺具有相近离子半径的Cr⁶⁺和V⁵⁺取代了MoO₃中的Mo⁶⁺位置形成复合氧化物纳米带，Ag⁺离子能够稳定亚稳相MoO₃而形成六角微米柱复合氧化物。5．采用单晶硅为基板在水热条件下合成整齐、有序的MoO₃纳米带阵列，纳米带之间接触紧密，生长方向完全相同，由于彼此之间的约束，纳米带宽度明显变窄且分布均匀，由于结构的有序性，MoO₃纳米带阵列在电化学性能方面具有比一般随机分布纳米带高的放电比容量，在场发射性能方面具有较低的开启电压，且该阵列的场发射符合F-N理论；以聚碳酸酯（PC）膜为模板，结合溶胶凝胶法制备了非晶态氧化钼纳米棒阵列；390℃热处理1小时后转变为晶型良好的MoO₃·2H₂O纳米棒阵列，该阵列具有较好的电化学循环性能和场发射性能。更多还原

【Abstract】 One-dimensional （1-D） nanomaterials including nanotubes, naorods, naowires and nanobelts, have been significantly attracted attentions due to their unique electrical, optical, magnetic and mechanical properties. It is important to control the geometry, dimension, composing, crystal structure and properties of the 1-D nanomaterias and investigate the relationship between structure and properties by studying their growth mechanism, which is useful to achieve the goal of synthesizing functional materials by our willing. Orthorhombic molybdenum trioxide have been widely applied in many fields, such as lithium ion secondary batteris, catalysts, sensors, electrochromic and optical materials because of their typical two-dimensional layered structure.In this dissertation, one-dimensional MoO₃ nanomaterials were chosen as the object of study. Modern testing methods were used to study the preparation, structure and properties of 1-D MoO₃ naomaterials, and MoO₃ nanobelts modified by some polymers and metal cations were also investigated. The obtained main results are as follows:（1） MoO₃ nanobelts were synthesized via the simple hydrothermal reaction with no template or catalyst by using stable MoO₃ sols, which were fabricated by three different methods. All of the as-synthesized samples consisted majority of orthorhombic MoO₃ nanobelts with width of 150～400 nm, average thickness of 70 nm, length of 4～15μm. The single nanobelt was structurely uniform single crystal without any dislocation and the surface of nanobelt was clean. The MoO₃ naobelts tended to grow together to form nanoblets bundle.（2） The electrochemical resistance firstly increased and then decreased with the discharge process because of the Li⁺ enrichment on the cathode surface. The Li⁺ ions were inserted not only into [MoO₆] interlayers space but also into intralayers along the b axis, and the Li⁺ ions could merely reversibly intercalte/deintercalate between the interlayer, however, the Li⁺ accommodated in the intralayers tended to trigger an uncoverable structural transformation of MoO₃, causing irreversible capacity loss. The first discharge capacity of the MoO₃ nanobelts was 301 mAh/g which was higher than that of bulk MoO₃ （249 mAh/g） and the nanobelts cell exhibited a capacity loss of only 12% after 5 cycles. The better electrochemical performance of MoO₃ nanobelts was attributed to their special structure. The single MoO₃ nanobelt showed nonlinear current/voltage （I/V） characteristics. The photoluminescence bands of the MoO₃ nanobelts were at 402 and 475 nm, and there was no obvious PL band in bulk MOO₃. MoO₃ could effectively decolorate four dyes. Contrasting with the bulk MOO₃, nanobelts had better photocatalytic activity because the specific surface area of MoO₃ nanobelts was larger, and the oxidation and reduction ability of the photo-generated electrons and holes of the nanobelts increased and the recombination rate of photo-generated electrons and holes decreased.（3） The growth mechanism of the MoO₃ nanbelts prepared via different process were investigated by studying the influence of hydrothermal temperature and reaction time on the structure and morphology of the products. The MoO₃ sols obtained by ion exchage method were firstly tansformed into metastable h-MoO₃ microrods, and subsequently stable orthorhombic MoO₃ nanobelts were formed with the reaction temperature increasing and time prolonging. With respect to the latter two MoO₃ sols, fabricated by peroxide oxidation and dispersion, the unstable O-O bonds in the MoO₃·pH₂O·qH₂O were broken up at the low hydrothermal temperature or for short reaction time to form the hydrated molybdenum trioxide particles and plates. When the temperature and time increasing, the H₂O molecule disappeared to form the orthorhombic MoO₃ nanobelts. The axis direction of the nanobelts was [001] direction.（4） PEO and PANI were introduced between the [MoO₆] interlayers in MoO₃ nanobelts, which led to the increasement of the interlayer distance, to form the （PEO）_0.1MoO₃, （PANI）_0.02MoO₃ and （PANI）_0.05MoO₃ nanobelts, respectively. Because of the existing of polymers, the nanobelts were easier to aggregate to form the flower-like morphology. The electrochemical properties of the nanobelts were improved with the intercalation of PEO and PANI into the MoO₃ nanobelts. The hydrothermally synthesizedα-MoO₃ nanobelts were lithiated by a sencondary reaction while preserving crystal structure and surface morphology. The single lithiated MoO₃ nanobelt showed linear current/voltage （I/V） characteristics and the electrical conductivity became higher due to the introduction of Li⁺ ions, and the electrochemical property was enchanted. In addition, MoO₃ nanobelts were doped by other metal ions, such as Cr⁶⁺, V⁵⁺ and Ag⁺, and different cations had different influence on the structure and morphology of the products.（5） Large-area ordered arrays of MoO₃ nanobelt were obtain on silicon substrate based on the hydrothermal process. The width range of nanobelts became smaller （width of 150～250 nm） because they grew tightly on the width direction. The improved electrochemical property was attributed to the alignment of the nanobelts. The field emission turn-on field (E_to) was 12.8 V/μm and the largest current density was 0.4 mA/cm², and the MoO₃ nanobelt arrays followed F-N theory. In addition, ordered amorphous molybdenum oxide nanorod arrays were synthesized in the pores of PC template by sol-gel method. MoO₃·2H₂O nanorods arrays were transformed after the heattreatment at 390℃for 1 hour. And their cycling property and field emission property were better.更多还原