Because of their remarkable structural, mechanical and electrical properties, carbon nanotubes, and especially single wall carbon nanotubes (SWNTs), represent one of the most widely investigated materials today in the emerging field of nanotechnology. The development of oriented growth of SWNTs critical for applications, novel approaches for the creation of functional SWNTs, and applications of both as-prepared and chemically functionalized SWNTs for electrochemically-induced hydrogen storage, in-situ formation of new polymer and ceramic nanocomposites with SWNTs, and the fabrication and study for the first time, to the best of our knowledge, of a SWNT-based biofuel cell and self-powered biosensor, are the thrusts of the research discussed in this thesis.
Introduction to the science and the potential applications of carbon nanotubes are presented in Chapters 1 to 2 of the thesis, and an overview of the methods used in this work is discussed in Chapter 3. Chapters 4 to 6 discuss the results of the work performed. Spin-coating deposition of a polymer-chelated catalyst precursor on conductive silicon wafers developed for the oriented growth of SWNTs, is discussed in Chapter 4. Oriented growth of SWNTs was obtained using chemical vapor deposition with alcohol as the carbon source. For application in biofuel cells and biosensors (discussed in the final segment), the oriented SWNTs on silicon were functionalized with selected redox enzymes to form the fuel cell and sensor electrodes. In initial tests, a substantial open circuit cell voltage of 200 mV, and analyte-sensitive direct electron transfer, were observed from the fabricated biofuel cell and biosensor devices, respectively.
Environmentally friendly, rapid and efficient microwave-induced chemical functionalization of SWNTs was achieved for the first time in the course of this work and is described in Chapter 5 of the thesis. The microwave radiation assisted technique has brought down the functionalization time from days using typical chemical methods, such as refluxing, to the order of minutes. Chemical functionalizations by the microwave method achieved include amidation, 1 ,3-dipolar cycloaddition and nitration, with the latter providing SWNTs that are very soluble in water and alcohol. Both microwave-induced and supercritical carbon dioxide approaches were also used to prepare and study the formation of ceramic (silicon carbide, SiC) and polymer (polymethyl methacrylate, PMMA) nanocomposites with SWNTs, respectively.
Electrochemically-induced functionalization of SWNTs by nitro groups and enzymes has been studied in some detail, whereas electrochemical hydrogen storage for fuel cell operation using pristine and functionalized SWNTs as the storage medium has also been studied in this work and discussed in Chapter 6 of this thesis. Strong evidence for electrochemically-induced hydrogen uptake approaching 3 wt % based on thermogravimetric measurements has been obtained on SWNT nanopaper membranes on which the nitrogen-containing conducting polymer, polyaniline, was deposited.
A summary of the work performed and suggestions for future work are provided in Chapter 7. The schematic molecular structures of the more complex molecules, polymers and enzymes used in this work (except those shown in the tables) are shown schematically in Appendix A.
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