【作者】 杨植；

【导师】 陈小华；

【作者基本信息】 湖南大学 ， 材料物理与化学， 2009， 博士

【摘要】 由于碳纳米管在力学、电学、热学和光学等多方面的优异性能,从其被发现之日起,就已经引起了物理、化学及材料等学科的极大兴趣。目前,对于碳纳米管在应用方面的研究已取得了较大的进展,然而距人们的所期待值仍有很大的差距。从相关的研究进展来看,如何进一步开发实用、廉价的大量碳纳米管合成工艺以及如何实现碳纳米管的可控制备仍是当前最为重要的发展方向之一,与此同时,如何实现定向碳纳米管的低成本工业化生产也是当前急需解决的问题。本论文从CVD法制备碳纳米管入手,开发出了一种能高产率制备高质量多壁碳纳米管的高效催化剂,同时利用喷雾热解法系统地研究了定向碳纳米管的制备工艺,此外,针对碳纳米管在溶剂中难溶解以及在复合材料基体中难分散这一难题,还开展对多壁碳纳米管进行有机功能化修饰的研究。研究具有基础性和前瞻性,兼具重要的理论意义和应用前景。第一,采用溶胶-凝胶法制备出Ni/Mo/Mg三金属催化剂,并将其应用于CVD中试反应炉中,以乙炔为碳源,在750℃下,高效地制备出高质量、高纯度的多壁碳纳米管,在反应35min后,所得到碳纳米管的质量接近初始催化剂质量的10倍。SEM和TEM结果显示该样品中碳纳米管长度大约在50μm左右,管径在30~35nm之间。第二,以溶胶-凝胶法制备的Fe/Mg/Mo三金属作为催化剂,甲烷为碳源,在化学气相沉积反应炉中制备出了纯度较高单壁碳纳米管。此外,通过调节催化剂配比和改变其它工艺条件,由石墨层状结构组成的碳纳米带也被成功合成,电镜观察结果显示该纳米带的厚度约为10nm,宽度为几百纳米,长度在100μm的数量级。第三,采用喷雾热解法,以二甲苯为碳源,二茂铁为催化剂,通过调节各种实验工艺参数,得到了高质量定向碳纳米管的最佳生长环境,并对定向碳纳米管的生长机制做了较为系统、深入的探讨。与此同时,还制备了超长碳纳米管束(8.2mm)、“波浪式”碳纳米管阵列、碳微/纳米球和由这些碳球组成的碳球链。第四,通过选用戊烷、己烷、庚烷、辛烷、苯、甲苯、二甲苯和环己烷八种有机溶剂作为碳源来制备定向碳纳米管,可以发现,二甲苯、正庚烷和环己烷都是制备高质量定向碳纳米管的理想前驱体;此外,在对比分析由这些碳源所得产物的表面形貌和微观结构后,发现当选用直链烷烃制备碳纳米管时,其产物的表面形貌和微观结构主要是受其碳源先驱体热学性能(标准生成焓和吉布斯自由能)的影响;而当选用芳香烷烃制备碳纳米管时,其所得产物的形貌特征和微观结构主要取决于芳香烃自身的热分解机制,这些发现将为定向碳纳米管朝规模化、可控化方向制备提供重要的科学依据。第五,采用酸化法对CVD法制备的多壁碳纳米管进行化学纯化处理,并利用甲醛的亲电性能和多壁碳纳米管进行反应,成功在多壁碳纳米管的表面引入了羟甲基官能团,使多壁碳纳米管在水中的分散性明显改善,然后在此基础上通过酯化反应把马来酸酐和聚丙烯酸分别接枝在多壁碳纳米管的表面,提高了多壁碳纳米管在溶剂中的分散性能,为制备高性能的碳纳米管/聚合物复合材料打下了基础。第六,采用原位悬浮液聚合法,得到了聚酰亚胺非共价包覆的碳纳米管,此修饰后的碳纳米管的热稳定性能较修饰前有显著提高;另外,通过选用聚乙二醇-200做为分散剂,获得了一种单分散、高含量的碳纳米管/聚酰亚胺复合材料,碳纳米管的质量百分含量达到了43%,这对于制备其他碳纳米管/聚合物基复合材料有着十分重要的意义。更多还原

【Abstract】 Since their discovery in 1991, carbon nanotubes (CNTs) have attracted much attention in various disciplines such as physics, chemistry, biology, and material science due to their unique structural, mechanical, electronic and thermal properties. So far, plenty of progress on CNTs related studies has been achieved. However, many challenges for large-scale applications of CNTs still exist. On the basis of the present research advancement, the high-yield and controllable production of high-quality CNTs at low cost is still an important developing aim. In addition, it is also a very intractable problem to achieve the industrial production of aligned CNTs. In this dissertation, we firstly develop a new kind of catalyst with great efficiency for the mass production of CNTs by CVD. The synthetic route of the aligned CNTs has been systemically investigated by spray pyrolysis method. Moreover, the organic functionalization of CNTs is developed to improve the dispersibility of CNTs and to enhance the chemical compatibility between CNTs and matrix material. The research is fundamental and pioneering, and is of great significance on the theory and application potential.Firstly, the Ni/Mo/Mg catalysts with high activity and efficiency were synthesized by sol-gel method. CNTs with high quality were obtained on the catalyst at 750℃by decomposition of acetylene. After reaction of 30min, the yield of synthesized CNTs is closed to 10 times of the pristine catalyst. The results of SEM and TEM show that the CNTs with hollow and multi-walled structure possess a relatively uniform diameter of about 30～35nm, and their length is about 50μm.Secondly, single-walled carbon nanotubes(SWNTs) were prepared by decomposition of CH4 at 900℃on Fe/Mg/Mo catalyst in a CVD reaction furnace. Moreover, carbon nanobelts made of graphite layers were successfully synthesized by adjusting the experimental parameters. The SEM and TEM results reveal that the nanobelts have the thickness of approximate 10nm, the width of several hundreds nanometer, and the length of several hundreds micron.Thirdly, the aligned CNTs with high quality were synthesized by spray pyrolysis of ferrocene/xylene solutions and their growth mechanism was also discussed based on the experimental phenomena and results. Furthermore, ultralong aligned CNT bundles (8.2mm), wave-like CNT arrays, carbon spheres and chains were also obtained in the spray pyrolysis method.Fourthly, by selecting some homologous series, including three aromatic hydrocarbons, four straight-chained alkanes, and a cyclane, as carbon sources, we systemically and comparatively investigated the relationship between properties of precursory carbon source and quality of aligned CNTs in a similar growth condition. It is found that the thermodynamic properties of precursory carbon sources such as Gibbs free energy and formation enthalpy play decisive roles in the morphology and structure of the nanotube samples in four straight-chained alkanes, while for three aromatic hydrocarbons, the decomposition mechanism rather than the thermodynamic property strongly influences the quality of the products. The results of SEM, HRTEM and Raman reveal that the aligned CNTs obtained from them have different nanotube parameters such as diameter and degree of graphitization. We find also that xylene, n-heptane and cyclohexane are favored for the growth of aligned CNTs with high quality and yield. These will be very helpful for the controllable preparation of aligned CNTs at relatively low cost in the spray pyrolysis method.Fifthly, by using eletrophilicity of formaldehyde, multi -walled carbon nanotubes (MWNTs) were methylolated and then grafted by maleic anhydride. The IR spectra showed that there were many hydroxyl and methylene groups on the surface of the methylolated MWCNTs(MWNTs-OH). Some ester and methylene groups appeared on the MWNTs grafted by maleic anhydride(MWNTs-MAH). The dispersion of MWNTs-OH in water was improved significantly and the dispersion of the MWNTs-MAH in xylene was enhanced remarkably. Moreover, the graft functionalization with poly (acrylic acid) (PAA) was also carried out for the MWCNTs-OH and MWNTs-PAA composites have been formed. The IR and TEM results show presence of covalent band and so-called“core-shell”structures for MWNTs-PAA. The MWNTs-PAA exhibits excellent solubility in water, which is significant to explore the potential application of carbon nanotube in biological and medical systems.Finally, MWNTs were functionalized with polyimide (PI) via an in-situ polymerization. The TEM and SEM images show that the functionalized MWNTs were wrapped by PI. The TGA and DSC results indicate that the thermal stability of the functionalized MWNTs with PI was improved. In addition, using polyethylene glycol-200 as processing aids, we successfully prepared CNTs-reinforced polyimide composite with well-dispersed and high-loading of CNTs. The content of CNTs in composite can arrive at 43 wt %. The preparation process will give birth to a promising strategy for the production of CNTs/polymer composite materials.更多还原