【作者】 罗勇锋；

【导师】 陈洪；

【作者基本信息】 中南大学 ， 材料科学与工程， 2012， 博士

【摘要】 随着纳米科技的发展,纳米材料已成为多学科交叉研究的基础,在化学、物理、能源、生物医学等诸多领域扮演越来越重要的角色。在各种纳米材料中,碳纳米管因为独特的结构和优异的化学物理性能,近二十年来吸引了科学界持久的兴趣。碳纳米管是由石墨层卷曲而成的中空纳米管体,根据石墨层数分成单壁和多壁两种,直径为0.4-100nm。碳纳米管具有优异的力学、电学、光学和热稳定性能。长期以来,碳纳米管主要作为各种纳米器件进行研究,但结构的可控性差严重限制其大规模应用,所以近年来更多的注意力转向碳纳米管宏观本体材料。然而,因为碳纳米管无规分布,获得的本体材料性能远低于单根碳纳米管,如何制备取向碳纳米管本体材料变得越来越迫切。本学位论文通过化学气相沉积法合成高质量取向碳纳米管阵列,在此基础上研究取向碳纳米管阵列的可纺性,并进一步研究取向碳纳米管材料在储能和光电转换两个能源领域中的应用。主要研究内容如下：1、首次通过无水辅助化学气相沉积法合成超长取向碳纳米管阵列。通过优化合成温度、合成时间,控制碳源、载气、还原气体的比例和流速,改进催化剂制备工艺,获取高质量取向碳纳米管阵列。在总流速保持不变的情况下,调节还原气体氢气和碳源乙烯的比例,成功合成超长取向碳纳米管阵列(高度达到4mm)。本方法具有较好的普适性,生长过程简单可控,制备效率高。2、比较系统地研究了碳纳米管阵列的可纺性。绝大部分报道的碳纳米管阵列是不可纺的,而文献报道的可纺阵列其高度往往小于0.9mm。另一方面,碳纳米管阵列以及纤维的物理性能与阵列高度紧密相关,一般阵列越高取向碳纳米管材料性能越好。本论文研究了催化剂制备过程的沉积速度和厚度、各种气体比例、流速、合成温度和时间等实验参数对碳纳米管阵列可纺性的影响,总结出一系列普适性的规律,获取了制备可纺碳纳米管阵列的最佳参数,在此基础上成功合成具有良好可纺性能碳纳米管阵列。以可纺阵列为初始材料,通过干法纺丝连续制备取向碳纳米管纤维,研究了碳纳米管纤维优异的力学和导电性能,发现其拉伸强度最高达到1GPa,室温导电率在102-103S/cm。3、研究直流辉光等离子对取向碳纳米管阵列刻蚀工艺以及功能化的取向碳纳米管阵列在储能方面的应用。利用直流辉光等离子体对碳纳米管阵列顶部进行刻蚀,在不破坏碳纳米管阵列整体形状的前提下打开碳纳米管端口,系统地比较氧气、氩气、氧-氩混合气体等离子体对刻蚀效率的影响,结果表明氧-氩混合气体等离子体刻蚀效果最好。采用刻蚀过的碳纳米管阵列作为超级电容器的电极材料,发现此电容器的容量大幅度提高。4、研究取向碳纳米管纤维在光电转换领域的应用。首次基于取向碳纳米管纤维优异的力学、电学性能和较高的比表面积制备出新型纤维状太阳能电池。N719染料分子通过溶液物理吸附到碳纳米管表面制备出碳纳米管/染料敏化分子复合纤维,以该复合纤维作为工作电极,以铂作为对电极组装电池,构建出新型染料敏化太阳能电池,并对其结构进行了初步优化。获得了光电转化效率为1.69%,并且具有较好的稳定性。更多还原

【Abstract】 With the development of nanotechnology, nanomaterials have become the basis of multidisciplinary research. They play an increasingly important role in chemistry, physics, energy, biomedicine, and many other fields. Because of the unique structure and excellent chemical and physical properties, carbon nanotubes have been continuously attracting increasing interest in the scientific community in the past two decades. Intuitively, carbon nanotubes are hollow nano-tubes, their diameters are in0.4-100nm. According to the graphite layers, carbon nanotubes are divided into two kinds of single-walled and multi-walled. Carbon nanotubes have excellent mechanical, electrical and optical properties and thermal stability. Carbon nanotubes are mainly studied as a variety of nano-scale devices, but the complexity and controllability of the structure severely limit their large-scale application, so more and more attention is turned to carbon nanotubes macroscopic bulk materials in recent years. However, because of random distribution,the carbon nanotube bulk material properties are much lower than the single carbon nanotube. How to fabricate aligned carbon nanotube bulk materials has become more urgent.Chemical vapor deposition synthesis of high-quality aligned carbon nanotube array was studied in this dissertation. And then we further fabricated aligned carbon nanotube fibers on this basis. We focused on two aspects research of the aligned carbon nanotubes in energy field. Firstly, we etched carbon nanotube arrays by using DC glow plasma technology to synthesize end-functionalized carbon nanotube arrays, to improve the comprehensive performance of their application in supercapacitors. Secondly, the novel dye-sensitized solar cells based on carbon nanotube fibers as working electrode have high photoelectric conversion efficiency. The main content was detailed in the following.Firstly, long aligned carbon nanotube array by chemical vapor deposition synthesis without water-assisted was firstly fabricated in this thesis. By optimizing growth temperature, time, controlling the carbon source, carrier gas, reducing gas ratios and flow rates, improving the catalyst preparation process, we prepared high-quality aligned carbon nanotube array. In the case of the total flow rate remaining unchanged, by adjusting the ratio of reducing gas of hydrogen and carbon source of ethylene, we prepared super-long aligned carbon nanotube arrays (up to4mm in height). This method has good universality, and the growth process is simple and controllable for high preparation efficiency.Secondly, spinnability of carbon nanotube arrays was systematically studied. The majority of reported carbon nanotube arrays were not spinnable. The height of spinnable array was often less than0.9mm in the reported literature. On the other hand, the physical properties of carbon nanotube array and fiber are closely related to height of the array. Higher qulity of aligned carbon nanotubes array material, better the performance. In this thesis, the deposition rate and thickness of catalyst, the proportion of various gases, the reaction temperature and time can impact spinnability of the carbon nanotube arrays, and we summed up a series of universal law, gained best synthesis parameters of spinnable carbon nanotube arrays. With spinnable array as initial material, aligned carbon nanotube fibers were continuously fabricated by dry spinning. We mainly study the excellent mechanical and electrical properties of carbon nanotube fibers, tensile strength was up to1GPa, and conductivity was up to102-103S/cm at room temperature.And then, aligned carbon nanotube arrays were studied in the application of energy storage. DC glow discharge plasma was used to etch the end cap of carbon nanotube array. Without destroying the overall shape of carbon nanotube arrays, we can open carbon nanotube ends by using plasma etching. Comparison of oxygen, argon, oxygen-argon mixture plasma etching efficiency, which showed that oxygen-argon mixture plasma etching was best. Carbon nanotube arrays were etched as electrode materials to build a super-capacitor, and we found that capacity of the capacitor was greatly improved. Finally, aligned carbon nanotube fibers were studied in the application of the photoelectric conversion. With excellent mechanical and electrical properties and high specific surface area, aligned carbon nanotube fibers were used as the working electrode to build a novel dye-sensitized solar cell. The typical build process included three parts: adsorption of N719dye molecules through the solution process to form the carbon nanotube composite fiber; carbon nanotube composite fiber was closely adhered to the fluorine-doped indium tin oxide conductive glass, and platinum was used as counter electrode of the cell; and finally they were packaged after injection of electrolyte. Photoelectric conversion efficiency of the novel fiber solar cells was up to1.69%, and it has very good stability.更多还原