Synthesis and chemical modification of single -walled carbon nanotubes and inorganic nanowires

This dissertation describes the study of single-walled carbon nanotubes (SWNTs), inorganic nanowires, and carbon aerogels. A novel catalyst of iron/molybdenum nanoparticles supported on alumina aerogel was developed for CVD synthesis of SWNTs. Using this catalyst, the yield of SWNTs was enhanced by at least three times compared to previously reported best results. The highest yield of SWNTs was achieved when the reaction temperature was between 850°C and 900°C with CO (∼1000 sccm) as feeding gas.;A combination of acid wash and mild oxidation processes was used to purify tire raw SWNT product. Transmission electron microscopy (TEM) and thermogravimetric analysis (TGA) indicated that the majority (>90%) of the purified product was SWNTs.;The purified SWNTs were fluorinated by diluted fluorine gas at 250°C. It was found that F-SWNTs could be recovered at an annealing temperature as low as 100°C. The thermal recovery behaviors of metallic and semiconducting SWNTs were very similar at annealing temperature ≥150°C, as suggested by 2D UV-Vis-NIR correlation spectroscopy. F-SWNTs were also added into poly(ethylene oxide) (PEO) to form a PEO/F-SWNT composite. Mechanical properties measurements showed that the F-SWNTs significantly increased the strength of the resulting composite.;A highly efficient method of SWNT synthesis on surfaces was also developed. It was found that the combination of carbon monoxide and hydrogen as a feeding gas greatly enhanced the surface growth of SWNTs. This method showed a large window of optimal HZ concentration (20%--80%) and synthesis temperature (800--900°C), so the result was very reproducible.;In the second project, two novel methods of preparing silicon oxide and tungsten oxide nanowires, respectively, were developed. By using a millimeter-sized liquid gallium ball as a metal solvent at 920--940°C, bulk quantities of ultralong, uniform and well-aligned silicon oxide nanowires were synthesized. XPS and EDX indicated that the atomic ratio of Si to O in the nanowires was 1:1.5. On the other hand, isolated tungsten oxide nanowires were directly grown on tungsten tips and plates by a simple oxidation procedure at elevated temperature. These nanowire preparation techniques are simple, fast and economical.;The third project focused on the fabrication of carbon aerogel. Resorcinol and furfural were polymerized in isopropanol using HCl as a catalyst and an organic gel was formed. This gel was dried under the supercritical condition of isopropanol, followed by carbonization at 900°C. Morphology study, surface area and resistance measurements indicated that the obtained carbon aerogel had similar properties to the one prepared under the supercritical condition of carbon oxide, which is a much longer process and requires much more energy.