【作者】 程继鹏；

【导师】 张孝彬；

【作者基本信息】 浙江大学 ， 材料物理与化学， 2005， 博士

【摘要】 碳纳米管的制备方法及其相关应用研究,是近十年来科学研究的热点。人们已开发出多种方法进行碳纳米管的制备,主要包括电弧放电法、激光蒸发法、化学气相沉积(CVD)等。相关的理论计算和实验测试表明,碳纳米管具有优良的导电、导热以及机械力学性能等,可以用于制作纳电子器件、场发射平板显示器、传感器、显微镜探针、高导热、导电性和优良机械性能的复合材料等。碳纳米管潜在的应用前景促使研究人员通过不同方法实现其可控大量制备,其中以CVD法最有可能制备出大量的满足商业应用和研究需求的碳纳米管。本论文简要概括了碳纳米管的形态、结构、物理性能及其制备方法,其中重点阐述了CVD法,同时讨论了催化剂载体对碳纳米管合成的影响。在此基础上,作者设计并采用特殊天然纳米矿物和纳米碳酸钙作为催化剂载体进行碳纳米管的制备。论文还评述了近几年来碳纳米管储氢的研究,文献报道的储氢结果很分散,为客观评估碳纳米管可能的储氢能力,作者在论文的最后一部分进行了碳纳米管及其相关材料的吸氢实验,并对实验结果进行了初步的分析。天然一维多孔海泡石族矿物,海泡石和坡缕石,在尺寸、形状和结构构造上都与人工合成的纳米材料(碳纳米管)十分相似。实验结果证实,它们都可以作为催化剂的载体,沉淀法承载金属催化剂,直接裂解乙炔,催化合成多壁碳纳米管。由于它们与金属催化剂之间的作用较强,可以避免高温下纳米金属催化剂颗粒的团聚,从其表面可以生长出直径均匀的碳纳米管。小粒径的催化剂金属催化活性良好,而较大颗粒的金属催化剂则被石墨层包覆,失去了催化活性。在上述情况下,天然纳米矿物材料仅仅充当了催化剂的载体,促使碳纳米管生长的是过渡族金属元素。坡缕石经过钛酸脂处理后,蕴含于其内部的金属铁元素在高温还原性气氛下可以改变其存在的状态,成为金属催化剂,裂解乙炔合成多壁碳纳米管。该催化剂的催化能力与温度紧密相关,因为高温下坡缕石将发生相变。在高温情况下,合成碳纳米管的内部嵌有一段或多段以其内孔为模板的Fe3C纳米线。进一步的实验证实,大洋锰结核矿物可以直接用作CVD法制备碳纳米管的催化剂。经过实验工艺的调整,还能够合成高产率的螺旋状多壁碳纳米管,在产物中还发现了形态、结构特殊的三重螺旋碳纳米结构。在实验观察的基础上,文中还提出了新的碳纳米管生长模式,即底部和顶部模式的叠加。 为了使CVD法合成的粗产物易于纯化,本文详细研究了纳米碳酸钙载体负载金属催化剂,分解乙炔合成碳纳米管的实验参数研究,包括金属催化剂的种类和含量、反应温度和时间等。实验结果表明,产物不仅易于纯化,而且提纯工艺不会影响到碳纳米管的结构特征,同时拓宽了纳米碳酸钙的应用领域。 在上述合成条件下,碳纳米管的产率明显地受到了催化剂和催化剂载体热稳定性的影响。高温条件通常有利于碳氢气体的裂解和金属催化剂活性的发挥,但是高温相变导致矿物多孔结构的坍塌,纳米碳酸钙载体的瓦解程度也随温度的升高而加剧,都会影响到金属催化剂的团聚和分布,并导致碳纳米管产率的降低。因此,为了保证碳纳米管的产率,一个适当的中等的反应温度是必须的。 室温中压下,作者制备的多壁碳纳米管及其相关材料的吸氢能力都<lwt%,氢气分子以物理吸附的方式与碳材料作用。机械球磨可以将碳纳米管剪切成短的纳米管,同时使其具有更多的结构缺陷,适当的球磨可以增加碳纳米管的吸氢能力,而过度的球磨则破坏了纳米管的结构,使其吸氮能力降低。定向碳纳米材料的间隙空间可以成为氢气吸附的位置,但是也不可能使其吸氢能力达到>lwt%。目前,室温中压条件下,碳纳米管的气态吸氢能力不可能达到应用的要求。关键词:碳纳米管,化学气相沉积,催化剂载体,天然纳米矿物,储氢更多还原

【Abstract】 Great attentions have been paid in the studies of synthesis and applications of carbon nanotubes （CNTs） since the last decade. Several methods have been developed to synthesize nanotubes, including arc-discharge, laser ablation of graphite and chemical vapor deposition （CVD）. The experimental results and theoretical calculations have proved that CNTs are of excellent properties in electronic and thermal conducting, as well as mechanics, which enable them to be used in nano-electronic devices, flat panel display, sensors, probes of tunneling microscopes and composites with good electronic, thermal conducting and mechanical reinforcements. All these potential application fields promote researchers to synthesize of CNTs in a high yield. The CVD method, because of its simplicity and low cost, will probably become the method of choice to produce the large quantities of CNTs necessary for fundamental as well as nano-technological purposes.In the thesis, the morphologies, structures, physical properties and preparation methods of CNTs were briefly reviewed. The syntheses of CNTs by CVD method were discussed in details, especially the effects of catalyst carriers （support） on the CNTs syntheses. Thereafter, the ideas of special natural nano-mineral materials and nanocrystalline CaCO₃ as catalyst carriers came into consideration. The previous reports on hydrogen storage in CNTs were also reviewed. The obviously dispersed data reported in literatures stimulated the author to perform the experimental measurements of H₂ absorption abilities in CNTs and related materials in order to evaluate its capacity of H₂ storage.The naturally formed minerals of hormites in the earth, such as sepiolite and palygorskite, are very similar to those of artificial nanomaterials （CNT） in size, morphology and structure. Experimental results proved that both of them could support metallic catalyst by precipitation, and directly decompose acetylene to prepare multiwalled CNTs. The intensive interaction between the supports and catalytic metal kept the formed catalyst nanoparticles from agglomeration at high temperature and gave rise to the uniform diameters of CNTs grown over the supports. The catalytic metal nanoparticles with a smaller size could nucleate CNTs, while nanoparticles with a larger size tended to be covered by graphene sheets and deactivated its catalysis property.At previous cases, the nano-minerals only played a role of catalyst carrier. What nucleated CNTs and was responsible for their growth were transition metallic nanoparticles. Titanate modified palygorskite could change the conditions of ferric components in the mineral under reductive atmosphere at elevated temperature. They could transform into iron nanoparticles and catalyze CNTs growth. The catalytic activity of the modified mineral was strongly correlated with temperature, for the mineral phase would be changed at higher temperature. Judging from TEM observations, the central cores of the CNTs were usually filled with single-crystalline nanowires which were formed using CNT as template at high temperature,>800. Marine manganese nodules powders could decompose acetylene to synthesize CNTs without any prior modification, which was proved by further experimental performance. A large fraction of helically coiled CNT product could be obtained by facilely changing the experimental conditions. In the product, a unique category of carbon nanostructure with harmoniously triple helices was firstly observed. A typically dual growth mode of CNT was developed in the thesis based on the TEM observations, i.e., a combination of based growth and tip growth.In order to easily remove catalyst impurities, nanocrystalline CaCO3 was also used as catalyst carrier. Some important parameters were investigated in the paper, such as category and content of metallic catalyst, reaction temperature and time, et al. The purification of the raw product could be achieved in one step, possessing little structural destructivity. All these results might broaden the application fields of nanocrystalline更多还原