Growth Of Aligned Carbon Nanotubes At Low Pressure And Their Applications

Since the discovery of carbon nanotubes (CNTs) by Iijima in 1991, these novel materials have attracted great attention in the area of physics, chemistry and technical industry. Because of their extraordinary physical and mechanical properties such as nano-size, large surface area, good conductance and high mechanical strength, carbon nanotubes are attractive for a diverse range of applications in panel displays, quantum wires, sensors, super-capacitors and hydrogen storage. Carbon nanotubes can also be used as electrode marerials because of their metal or semiconductor properties. Moreover, the surface effect of carbon nanotubes such as high surface activity makes high electron transfer when used as electrode and has been well applied in electro-catalysis and electro-chemistry. For some applications, it is highly desirable to prepare aligned carbon nanotubes(ACNTs) so that the properties of individual nanotubes can be easily assessed and they can be incorporated effectively into devices.Recently, various fabrication techniques and methods have been devised to synthesize aligned carbon nanotubes such as pyrolysis of organometallic compounds or chemical vapor deposition (CVD) of hydrocarbons over prelocated catalysts on substrate. Aligned carbon nanotubes on quartz substrates can be prepared by templates or free-templates. The free-template method has been well employed because of its simpleness and effectiveness. However, it is crucial to control the length and diameter of ACNTs and get the products with high quality.Aligned carbon nanotubes have been prepared in this dissertation by the pyrolysis of iron(II) phthalocyanine, FeC₃₂N₈H₁₆, which contains both the metal catalyst and carbon source required for the nanotube growth. By adjusting the pressure of CVD system at low pressure, the raw material was effectively economized and the quality of ACNTs was developed, which was important for the potential applications. Moreover, a sensitive andselective ACNTs electrode has been fabricated in this dissertation to determine real samples successfully.The dissertation includes three parts:Chapter 1 The review of vertically aligned carbon nanotubesIn the beginning of this dissertation, the structure and character of carbon nanotubes are introduced, together with the unique properties of aligned carbon nanotubes. Then the preparation and the growth mechanism of aligned carbon nanotubes are introduced, especially chemical vapor deposition method. Finally, the applications of carbon nanotubes such as sensors, electrode materials and field emission displays are introduced.Chapter 2 Growth of Vertically Aligned Carbon Nanotubes by Pyrolysis of Iron Phthalocyanine at Low PressureLarge-scale of vertically aligned carbon nanotubes have been synthesized on quartz glass plates by pyrolysis of iron (II) phthalocyanine (FeC₃₂N₈H₁₆) at 750-1000°C at low pressure. The average length of ACNTs is about 20μm with a larger diameter ranging from 40 to 70 nm. The as-grown aligned carbon nanotubes have a cylindrical and bamboo-like structure and are multi-walled carbon nanotubus(MWNTs). The preparation parameters of ACNTs and different substrates are investigated and the growth mechanism of ACNTs is also discussed. The field emission properties of ACNTs were measured. The result shows a very powerful ability of electron emission with a turn-on voltage of 0.67 V·μm^-1(I=1μA) and a threshold voltage of 2.5 V·μm^-1.Chapter 3 Determination of nitrite with the electrocatalytic property to the oxidation of nitrite on thionine modified aligned carbon nanotubesA thionine modified aligned carbon nanotubes (ACNTs) electrode was fabricated and was used to electrochemically determine nitrite. The thionine modified ACNTs electrode exhibited enhanced electrocatalytic behavior to the oxidation of nitrite. The electrochemical mechanism of the thionine/ACNTs electrode towards the oxidation of nitrite was discussed. The thionine modified ACNTs electrode exhibited fast response towards nitrite with a detection limit of 1.12×10^-6 M and a linear range of 3.0×10^-6～5.0×10^-4 M. The proposed method was successfully applied in the detection of nitrite in real samples.