【作者】 陶新永；

【导师】 张孝彬；

【作者基本信息】 浙江大学 ， 材料物理与化学， 2007， 博士

【摘要】 纳米碳管（CNTs）由于其独特的物理化学性质，其应用涉及到了纳米制造、电子材料和器件、生物医学、化学、物理、复合材料、储能材料、电子源等众多领域。CNTs合成方法已有数十种，热CVD法以其高效和低成本而备受关注。催化剂是热CVD法合成CNTs的关键因素。近年来热CVD法制备CNTs技术有了较大的发展，但仍然存在一些问题，例如常规催化剂的催化效率不高，CNTs的产率较低，因此需要开发一些高效率的催化剂。此外，除了传统的Fe、Co、Ni催化剂外，是否可以开发出新型催化剂以便合成结构不同于常规纳米碳材料的新型碳材料，目前国内外有关此方面的研究较少。本论文的工作中，我们制备出了Fe、Co、Ni掺杂的MgMoO₄催化剂，Li、Na、K氧化物掺杂的Cu／MgO催化剂和纳米SnO₂催化剂共三大类催化剂，利用这三类催化剂以热CVD法合成出了一系列以CNTs为主的新型碳纳米材料，并研究了它们的催化机理。基于所合成的各种碳纳米材料的结构特点，研究了其性能特征及功能化应用。利用溶胶凝胶燃烧法合成了活性组分含量可调的MgMoO₄催化剂，首次发现单相MgMoO₄催化剂可合成高产率多壁纳米碳管（MWNTs）束。在对MgMoO₄催化剂进行适当的Fe、Co、Ni掺杂后发现可以进一步提高催化剂的催化性能。利用掺杂后的MgMoO₄催化剂高温裂解甲烷气体，以氢气作为载气，反应1小时后，制备的MWNTs粗产物质量可超过原始催化剂的50倍；通过简单放大，1克催化剂的单炉产量在半小时内可超过40克，催化效率远超过现有的常规催化剂。利用透射电镜（T EM）分析MWNTs的生长机理，发现MWNTs束的形成中以底部生长机制为主，同时兼有顶部生长。我们还发现反应时间、碳源气氛、载气气氛对产物的形貌和结构均有影响。利用Co掺杂的MgMoO₄催化剂，以甲烷、氢气、氨气分别作为碳源气体、载气、掺杂气体，合成出了产率同样较高的氮掺杂MWNTs。氨气的引入影响了MWNTs的生长机制，因此不再以束状存在。此催化剂的催化效率仍然较高，反应1小时合成的产物质量超过原始催化剂的30倍。结果显示可以通过调节氨气流量使CNTs的氮含量控制在0.6 at.％到3.2 at.％之间。X射线光电子能谱（XPS）证明在氮掺杂MWNTs中有三种结构的氮原子，且以石墨结构氮为主。氮掺杂使CNTs中的缺陷和无序碳增加。首次利用碱金属（锂、钠或钾）氧化物掺杂的铜催化剂，以乙炔为碳源，氨气为氮源合成出了一系列新型碳纳米材料，包括纳米铜锥填充的纳米碳角、头部填充有纳米铜锥的CNTs、一端为纳米铜锥另一端为分叉纤维的CNTs、具有多孔分叉结构的纳米碳纤维、多分叉CNTs。碱金属氧化物掺杂含量和反应温度可调控产物的形貌，制备形态不同的碳纳米材料。碱金属掺杂在催化过程中起到了重要作用。我们认为碱金属氧化物的掺杂引起了铜电子结构的变化，从而改变了铜的催化性能。基于分叉纳米碳纤维的多孔结构，将其应用于双电层电容器中，结果证明此纤维是一种优异的电化学储能材料。基于头部填充有纳米铜锥的CNTs的独特结构，我们将其应用到了纳米焊接技术中，发现可以通过控制外电压来实现铜纳米锥的可控熔化和输运。利用铜的熔化和输运特性，我们成功实现了CNTs的自焊接。以纳米SnO₂为催化剂高温裂解乙炔气体制备出了单晶锡纳米线填充的CNTs（β-Sn／CNTs），即碳包覆锡纳米线。我们发现催化剂的活性组分为SnO₂而不是SnO或者金属Sn。反应温度对产物的形貌和微结构有明显的影响。将此类纳米碳管包覆的锡纳米线应用于锂离子电池负极中，发现此类新材料的电化学性能要优于纯金属锡电极。TEM观察发现单晶锡在电子束辐照下能够熔化，且熔化后的锡线能够随着电子束密度的变化而伸缩，我们对其熔化和伸缩机理进行了探讨。更多还原

【Abstract】 Many potential applications have been proposed for carbon nanotubes （CNTs）, including nanofabrication, electronical materials and devices, biomedicine, chemistry, physics, composites, energy storage, electron resource and so on, based on their unique physical and chemical properties. Among tens of synthesis methods for CNTs, the thermal chemical vapor deposition （CVD） method attracts more attentions because of its low cost and high efficiency. The catalyst plays a key role in the synthesis procedure. Although the CVD synthesis of CNTs has been developed in recent years, there are many barriers to overcome. The conventional catalyst is not yet sufficiently effective and limited to transition metals such as Fe, Co, Ni and their alloys. Particularly, it is interesting to see the possibility of exploring some new catalysts to synthesize unconventional carbon nanomaterials.In the thesis, we successfully prepared three kinds of catalysts, i.e., transition metals （Fe, Co and Ni） doped MgMoO₄, alkali metal （Li, Na and K） oxide doped Cu/MgO catalyst and nanosized SnO₂ catalyst. Using these catalysts, a series of novel carbon nanomaterials, mainly CNTs, can be synthesized via CVD method. Some properties and applications were studied, based on their special structures.Single phase MgMoO₄ catalyst was prepared by a sol-gel combustion method. We found that the multi-walled carbon nanotube （MWNT） bundles can be produced using this MgMoO₄ catalyst for the first time. The experiments revealed that the transition metals such as Fe, Co and Ni doped MgMoO₄ catalyst have much higer activity and efficiency than the pure MgMoO₄. After reaction for 1 h, the maximum yield of synthesized MWNTs bundles is over 50 times of the pristine doped MgMoO₄ catalyst. With a simple enlarged process, a single furnace can produce over 40 g CNTs from 1 g doped MgMoO₄ catalyst in 30 min. The efficiency of these transition metals doped MgMoO₄ is higher than the conventional catalyst. The transmission electron microscopy （TEM） results proved that most of the MWNTs grow in the base-growth mechanism. It was also found that the reactive activity of the catalyst depends on the reaction time, carbon source and carrier gas. The nitrogen doped MWNTs can also be produced on the transition metals doped MgMoO₄ catalyst using CH₄, H₂ and NH₃ as carbon source, carrier gas and nitrogen source, respectively. After reacted for 1 h, the maximum yield ofsynthesized nitrogen doped MWNTs is over 30 times of the pristine Co doped MgMoO₄ catalyst. By controlling the flow-rate of NH₃, the nitrogen concentration of 0.6 at.% to 3.2 at.% was obtained. X-ray photoelectron spectroscopy （XPS） revealed that three different structures of the nitrogen atoms were involved in the nitrogen-doped MWCNTs, among which graphite-like structure was dominant in these MWCNTs. More defects and disorders are introduced into MWCNTs due to the nitrogen doping.It was found that several categories of novel carbon nanomaterials can be synthesized using alkali metal （Li, Na and K） oxide doped Cu/MgO catalyst via thermal CVD method using C₂H₂ and NH₃ as carbon source and nitrogen source, respectively. By controlling the reaction temperature and the content of alkali metals, various products such as Cu nanocone filled single crystalline carbon nanohorns, carbon nanotubes filled with Cu nanocones at the tips （Cu-CNTs）, Cu-CNTs with carbon nanofiber, multi-branched carbon nanotubes and multi-brandched carbon nanofibers with porous structure can be produced. It is proposed that the alkali metal oxide doping changes the electronic structure of the copper catalyst. The carbon nanofiber shows fascinating potential in the electrochemical double-layed capacitors due to its porous structure. Spot welding using Cu-CNTs was investigated experimentally using nanorobotic manipulation inside a TEM. Controlled melting and flowing of copper inside nanotube shells were realized by changing the bias voltage. The self welding of the CNTs was realized based on the melting and flowing property of Cu.Carbon nanotubes filled with single crystalline β-Sn nanowires （β-Sn/CNTs） have been synthesized on the nanosized SnO catalyst by thermal CVD method using C₂H₂ as carbon source. It was found that the SnO₂ is the active component for the deposition of carbon. The products are affected by the growth temperature. The prepared β-Sn/CNTs were used as the anode of lithium ion battery. Upon the electrochemical testing, the β-Sn/CNTs electrodes show better electrochemical prperties than the pure Sn. Upon TEM observasions, it was also found that the Sn can be molten under the irradiation of electron beam and elongation/contraction alone the CNTs with the density change of electron beam. The mechanism of melting and elongation/contraction of the Sn nanowires were discussed.更多还原