【作者】 邱汉迅；

【导师】 邱介山； 施祖进； 顾镇南；

【作者基本信息】 大连理工大学 ， 化学工程与工艺， 2007， 博士

【摘要】 碳纳米管一经发现便吸引了全世界科学家的广泛关注，已成为当前纳米科学研究领域最热门的材料之一。双壁碳纳米管（DWNTs）具有介于单壁碳纳米管与多壁碳纳米管之间的独特双层石墨层结构，因此兼具单壁碳纳米管与多壁碳纳米管的优点，对碳纳米管内部进行填充不但能改变碳纳米管本身的电学、力学等性能，而且还能调变被填充物质的性质。本论文的工作主要围绕双壁碳纳米管的可控合成、填充以及纳米空间内填充物质的结构与性质等展开，获得的主要结果如下：1．高产率合成了克量级、纯度达90wt％以上的双壁碳纳米管。采用FeS代替传统的Fe、Co、Ni、S等催化剂，并添加卤化物作为助催化剂，在有效改造传统电弧炉样品收集装置基础上，利用直流电弧法高选择性合成了DWNTs，其产率由文献报导的10wt％左右提高到50wt％以上，而且DWNTs的结构和质量都有很大改善。发展了一种有效的DWNTs纯化方法，经过空气选择性灼烧、过氧化氢氧化、盐酸溶液回流等简单纯化处理，获得了纯度大于90wt％的高质量DWNTs，为研究DWNTs本身的结构与性能及探索其应用途径提供了必要的物质前提与基础。2．发现了DWNTs的特殊形貌和新奇性质。在扫描电子显微实验中观测到丝状DWNTs原始烟炱在连续受到外力作用下表现出很强的机械力学性能，杂乱无章的碳纳米管逐渐变得取向有序；发现DWNTs管束的V型一维纳米结结构，每一个拐点处都存在一种特殊的纳米异质结，这种结构形态的纳米材料可能具有独特的电子输运特性。此工作为碳纳米管异质结的可控制备以及新型纳米电子器件的构建提供了新的思路。3．基于单壁和双壁碳纳米管材料，成功制备出富勒烯分子高效率填充的豆荚型新型碳纳米材料。通过高真空气相扩散的方法，成功地将富勒烯C₆₀分子填充到单壁碳纳米管和双壁碳纳米管的管腔内部，合成了C₆₀@SWNTs与C₆₀@DWNTs纳米豆荚新型材料。利用高分辨透射电子显微镜研究了被填充到碳纳米管内的C₆₀分子与体相材料的结构差异，发现C₆₀分子在DWNTs内随着DWNTs管径的不同具有不同的排列结构，并直接观测到一维直链型和双层排列型的C₆₀分子排列结构。这一结果很好地验证了前人的理论预测，为今后可控制备具有独特结构和性质的碳纳米材料提供了重要的实验依据。4．用拉曼光谱研究了C₆₀@DWNTs纳米豆荚的性质。发现在激光照射下填充到DWNTs内的C₆₀分子容易发生双分子聚合反应；DWNTs管壁与内部C₆₀分子之间具有弱的范得华力相互作用，并伴有电子转移发生。这一发现使得对碳纳米管进行电子给体或者电子受体搀杂以调控碳纳米管的能带结构成为可能，亦为制备具有特殊电学性质的电子器件奠定了物质基础。5．制备了二茂铁高效填充的双壁碳纳米管复合材料（Fc@DWNTs）。采用分子气相扩散的方法将有机小分子二茂铁填充入DWNTs纳米空腔内部，制得高比例填充的Fc@DWNTs纳米材料。红外光谱研究结果表明，填充到DWNTs孔腔内的二茂铁与DWNTs之间存在强的范得华力相互作用，且二茂铁容易将电子转移给DWNTs从而对其进行n型掺杂。研究了Fc@DWNTs的电化学性质，发现Fc@DWNTs表现出与Fc@SWNTs不同的循环伏安电化学性质，在低扫速情况下表现出薄层电化学行为，而在高扫速下表现为扩散电化学行为。电化学结果表明，DWNTs可以作为分子导线连接填充在其内部的二茂铁与外部电极，这将为新型电化学传感器的研制等提供有益的启示。6．利用热重—质谱联用仪研究了二茂铁在双壁纳米碳管空腔内，即在纳米限域空间内的热力学性质。发现二茂铁在DWNTs纳米空间内的热力学分解温度（540℃）比常规条件下（约500℃）有明显提高，表明二茂铁分子在纳米限域条件下变得的更加稳定，显现出与不同于常规条件下的物理化学性质。7．以双壁纳米碳管为限域性模板，成功实现了三壁碳纳米管的可控制备。以DWNTs为纳米反应模板，以填充入的二茂铁充当碳源与催化剂，发展了一种可控制备TWNTs的方法。用高分辨透射电子显微镜研究了内层碳纳米管的生长机理，证实内层碳纳米管的生长遵循根部生长（Root-growth）机制，这一工作为今后选控制备其它具有特定构型的碳纳米管材料提供了一种新的合成思路，亦对早期对有关碳纳米管生长机理的理论预测提供了新的直观而清晰的实验证据。更多还原

【Abstract】 Being a transition from single-walled carbon nanotubes (SWNTs) to multi-walled carbon nanotubes (MWNTs), double-walled carbon nanotubes (DWNTs) with unique structures and extraordinary properties are ideal and unique thinnest MWNTs, possessing the advantages of both SWNTs and MWNTs, and have been attracting considerable interests and broad attention of scientists all over the world. DWNTs have become one of the most prominent materials in nanoscience and are of great potential in nanoelectronics, nanobiology and other related fields. Filling foreign materials into the hollow cavities of carbon nanotubes may significantly modify their electronic and mechanical properties, as well as alter the properties of the filled materials. This thesis is mainly focused on the synthesis and filling of DWNTs, and the properties of substance filled in the nanospace, i.e. the central cavity of the DWNTs.1. Mass preparation of double-walled carbon nanotubes with perfect structural integrity has been achieved in high yiled by a modified DC arc discharge method. By adding trace amount of halide typically KC1 into the iron sulfide catalyst, the yield of DWNTs could be increased dramatically from about 10 wt% in related references to over 50 wt%. The quality of DWNTs can be greatly improved by using a newly developed purification method; DWNTs with a purity of over 90wt% have been obtained. It is believed that chlorine in halide plays an important role in the formation and growth of DWNTs. The successful synthesis of high quality DWNTs in large quantity made it possible for further studying the properties of DWNTs and for exploring their potential applications.2. Some novel properties of DWNTs are revealed for the first time. Raw soot consisting of thread-like DWNTs exhibits very high mechanical strength, and the DWNTs in random orientation would gradually become to be arranged in order under the effect of foreign force. Intramolecular nanotube junctions are found in the DWNTs bundles, which can be regarded as a kind of heterojunctions with unique electron transportation property, and may be of potential in the next generation electronic devices based on carbon nanotubes.3. Fullerene-filled SWNTs and DWNTs (so-called nanopeapods) with a purity of over 80% have been synthesized in high yield, in which the C60 molecules are introduced into the hollow cavities of nanotubes by a vapor phase diffusion method. HRTEM examination has revealed that C60 molecules are aligned with a distance of about 1.0 nm in the central cavity of SWNTs and DWNTs with a small diameter, the stacking phases of C60 inside DWNTs with a larger diameter are totally different. Depending on the inner diameter of DWNTs, the stacking phase of C60 varies, which can be the zigzag phase, double-helix phase, and phase of two molecule layers. This new observation provides direct solid experimental evidence to the previous theoretical prediction that the stacking phases would be sensitively dependent on the inner-tube diameters of the nanotubes.4. Raman measurements on DWNTs peapods have revealed for the first time that there are obvious differences between the spectrum of DWNTs peapods and SWNTs peapods in terms of the shifts, and the strengthened or weakened intensity of certain characteristic peaks. The difference is believed to be due to the special double-layer structure of DWNTs. C60 fullerenes would polymerize via a dipolymerization scheme under the laser irradiation, and C60 fullerenes would interact with the inner walls of DWNTs via weak force of van der Waals, during which charge transfers may take place between C60 molecules and carbon nanotubes.5. Ferrocene, a small metallorganic molecule with very good redox activity, has been successfully filled into the central cavity of DWNTs, resulting in a novel nanohybrid material Fc@DWNTs that is of potential as air-stable n-type transistors, building blocks and biosensors for various devices based on the redox activities of ferrocene and electronic properties of nanotubes. FT-IR study reveals that there exists a strong interaction between the ferrocene molecules inside the cavity of DWNTs and the nanotubes, and n-doped DWNTs are formed because of the electrons transfer from ferrocene molecules. The electrochemical properties of as-synthesized Fc@DWNTs have been evaluated using the cyclic voltammetry, showing the Fc@DWNTs are different from the Fc@SWNTs in terms of the electrochemical property. For the Fc@DWNTs materials, surface-confined thin-layer electrochemical behavior is observed at low scan rate, while a diffusion-confined electrochemical behavior would dominate at high scanning rate.6. The thermochemical behaviors of ferrocene molecules inside the confined nano-space of the DWNTs have been studied for the first time using the thermogravimetric analysis-mass spectrum (TG-MS) technique. The results show that the decomposion temperature of ferrocene molecules in the confined nano-space is 540℃, which is 40℃higher than the decomposion temperature of 500℃under normal conditions. The variation in thermochemical properties of ferrocene molecules is believed to be due to the confinement effect and protection of carbon layers. 7. Triple-walled carbon nanotubes (TWNTs) have been prepared for the first time by annealing of Fc@DWNTs nanohybrid materials at high temperature, in which the filled-ferrocene molecules decompose, resulting in a new carbon nanotube inside the central cavity of DWNTs that function as template at nanoscale. The detailed HRTEM examination confirms that the formation of the new nanotubes inside DWNTs follows a root-growth mechanism that has been predicted in previous theoretical studies but lacs solid evidence before the present work. This opens a new approach to the controllable synthesis of TWNTs, and may give a new impetus to the study of TWNTs.更多还原