Novel Synthesis of One Dimensional Tubular Carbon Materials from Reactive Template Na@AAO

• Main Authors: Lung-Shen Wang, 王隆昇
• Other Authors: Hsin-Tien Chiu
• Format: Others
• Language: en_US
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/70988190251386823602

博士 === 國立交通大學 === 應用化學系所 === 94 === In this thesis, I present several methods to synthesize the one dimensional materials by employing bottom-up concept relied on the chemical reduction of the reagents. In Chapter 2, we have demonstrated a novel synthesis methodology for nanostructured materials. The reactive template strategy is exemplified by the preparation of Na@AAO and the use of it to generate high-density ordered arrays of carbon nanotube (CNT). Applications of the template structure and the halide source are discussed in the content. In Chapter 3, we conclude that amorphous carbon tubes were prepared via a template-assisted synthesis route. First, using AAO as the substrate, short a-CNT arrays are grown from SiCl3CCl3 at 1073 K by low pressure chemical vapor deposition. Elongation of the tubes into bundles joined at one end is achieved by filling the AAO channels with Na to generate the reactive template, followed by the reaction with C6Cl6. The fabrication of heterojunctions structure of CNT arrays is discussed. In Chapter 4, we conclude that the double-shelled amorphous SiO2/C nanotubes were prepared via the designed synthesis route. First, using AAO as the substrate, Na nanotubes are grown by decomposing NaH at 623 K to form the Na@AAO reactive template. For the formation of the outer amorphous carbon shell, hexachlorobenzene (C6Cl6) is used as the C source to react with Na@AAO. Following the above Wurtz type reaction, we employed an analogous route which deposits the Si layer in the pre-grown a-CNT by reacting chlorosilanes with Na@a-C/AAO at 623 K. After the removal of AAO by HCl, we generated well-aligned coaxial double-shelled SiO2/C nanotubes successfully. These noble fabrications of the coaxial multi-shelled nanotubes in a controlled manner may facilitate probable building of a variety of nanodevices. In Chapter 5, graphitization of the a-CNT and the porous CNT generated both tubular and fibrous products but with different yields. A possible explanation for the phenomenon is routed in the original structure of the tubes. Apparently, the CNT with a porous structure is structurally stronger and more resistant to the collapsing of the tube walls than the CNT with a hollow tubular structure. The later does not have the internal support and probably collapse more easily to form CF at high temperature. The study shows the importance of the micromorphology to the structural transformation in a high temperature process. In Chapter 6, we have synthesized highly-ordered CNT arrays over a large area on AAO from acetylene by CVD. The growth property of carbon tubes were closely related to the structure of the deposition temperature and time. We found that the pyrolysis temperature of acetylene to deposit carbon atom starts above 773 K. Increasing the temperature of deposition to 1073 K, CNT with more ordered graphite structure can be obtained. The study provides a simple low cost, low temperature, and controllable technique to grow CNT. The highly-oriented and isolated CNT array membranes could be very useful in a variety of applications. In Chapter 7, by using Na@AAO as a catalytic template, we developed a novel process to deposit a-CNT from C2H2 in the channels of AAO. Employing sodium metal into the process lowers the energy barrier of acetylene decomposition, probably by forming stable intermediates sodium hydride and sodium acetylides. At elevated temperatures, these intermediates decompose to deposit tubular shaped a-C, to release H2 gas, and to regenerate the Na catalyst. The catalytic template Na@AAO not only assisted the growth of a-C but also guided the tubular shape development.