Numerous alternative energy sources are being researched for sustainable energy applications, but their overall benefit is still too costly for them to be considered viable. Commonly produced temperature gradients created by the environment, or are man-made, can be converted into useful energy by using thermoelectric materials. Inorganic semiconductors are the most commonly used thermoelectric materials, but have raised concerns due to toxicity issues, rarity of heavy elements used, and high fabrication temperatures. These concerns have led research efforts into electrically conductive polymer composites prepared in ambient conditions from aqueous solutions. By combining polymer latex with carbon nanotubes (CNT), electrical conductivity can resemble metals while thermal conductivity remains similar to polymers. Using different CNT stabilizers for these fully organic composites can tailor the thermoelectric properties and harvest thermal gradients from previously inconceivable places (e.g., body heat converted into a voltage). A semiconducting CNT stabilizer, meso-tetra(4-carboxyphenyl) porphine (TCPP), was used to investigate the influence stabilizers have on composite thermoelectric properties. As TCPP was compared to a similar system containing an insulating stabilizer, sodium deoxycholate (DOC), the multi-walled carbon nanotube (MWNT)-filled composites showed a 5x increase in the Seebeck coefficient (S). TCPP did not have a distinct effect on the electrical conductivity (σ), demonstrating the tailorability of S with this molecule. An intrinsically conductive polymer, poly(3,4-ethylenedioxythiophene) :poly(styrene sulfonate) (PEDOT:PSS), was used to stabilize highly conductive double-walled carbon nanotubes (DWNT) and demonstrate the promise of fully organic composites as thermoelectric materials. This combination of CNT and stabilizer produced metallic electrical conductivity (200,000 S m-1) and power factors (S2σ) within an order of magnitude of commonly used semiconductors (~400 μW m-1 K-2). Electrical conductivity was doubled by stabilizing single-walled carbon nanotubes (SWNT) with PEDOT:PSS in a thin film without the insulating polymer latex. To further demonstrate the tailorability of polymer composites, a dual stabilizer approach using semiconducting and intrinsically conductive stabilizers was used. This approach effectively provided the high electrical conductivity from PEDOT:PSS and the enhanced Seebeck coefficients of TCPP. By using multiple stabilizers for CNTs within the same composite, power factors among the highest reported for fully organic composites are achieved (~500 μW m-1 K-2). These water-based, flexible composites are becoming real competition as their conversion efficiencies, when normalized by density, are similar to commonly used semiconductors.

Multi-walled carbon nanotubes (MWCNTs) and other shaped carbon nanomaterials (SCNMs) were synthesized by the floating catalyst chemical vapour deposition (CVD) method, using either ferrocene [1] as the catalyst at 2.5 or 5 wt.%, or a synthesized heteroatom-containing ferrocene derivative, in toluene, in the range 750 to 950 °C. The derivatives used were ferrocenoyl imidazolide [3] (a source of N and O) at 2.5 and 5 wt.%, (N-phenylcarbamoyl)ferrocene [4] (a source of N and O) at 1.25 wt.% and S,S-bis(ferrocenylmethyl)dithiocarbonate [5] (a source of S and O) at 2.5 wt.%, which was synthesized from ferrocenylmethanol [2]. These were characterized by melting point, 1H- and 13C-NMR spectroscopy, IR spectroscopy and mass spectrometry (MS). The effects of variations in the CVD physicochemical reaction parameters, namely temperature, catalyst employed (and the effect of its heteroatoms, where applicable) and catalyst concentration, on the CVD products were investigated. These materials were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive Xray spectroscopy (EDX), Raman spectroscopy, thermogravimetric analysis (TGA) and some by the Brunauer, Emmett and Teller method (BET). The best temperature range, in terms of high yields of MWCNTs with relatively high thermal stabilities and surface areas, in general, was identified as being 800 to 900 °C, from results obtained with [1]. This temperature range was used for further experiments. Among other results, it was shown that [1] and [3], at 2.5 wt.%, and at 800 and 850 °C respectively, produced the best materials. Catalysts [4] and [5] produced primarily carbon spheres, however, in general, all experiments using N-containing catalysts produced bamboo-shaped MWCNTs. For [3], at 2.5 wt.%, smaller bamboo compartment lengths correlated with decreasing temperature and decreasing crystallinity, suggesting a larger incorporation of nitrogen with lowered temperature. Catalyst [3] at 2.5 wt.% also produced very “clean” MWCNTs and this was attributed to optimal levels of oxygen being able to convert amorphous carbons to gas. Certain MWCNT properties were shown to be dependent on the combined, or synergistic, effects of catalyst concentration and temperature. The best undoped MWCNTs that were synthesized and commercially produced MWCNTs were loaded with Pd nanoparticles using a metal organic CVD (MOCVD) method. Results revealed well dispersed metal nanoparticles of narrow size distribution. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2012.

Thesis (Ph.D.)--University of Delaware, 2008. / Principal faculty advisors: Dennis W. Prather, Dept. of Electrical & Computer Engineering; and Bingqing Wei, Dept. of Mechanical Engineering. Includes bibliographical references.

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2008. / Includes bibliographical references (leaves 113-120). Also available in electronic version.

Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2006. / Includes bibliographical references (leaves 160-175). Also available in electronic version.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Carbon nanotubes (CNTs) functionalized/embedded with ferromagnetic particles have several important advantages as materials for magnetic applications. The presence of ferromagnetic particles in a carbon matrix can substantially change the magnetic properties of CNT-based composites. For example, iron filled CNTs have been used as probes in magnetic force microscopy (MFM), and have potential in magnetic data storage applications. In addition, encapsulation in nanotubes provides iron nanoparticles with resistance to oxidation and mechanical damage. Chemical vapor deposition (CVD) is one of the most common single-step processes for the fabrication of high quality carbon nanotubes containing varying amounts of embedded ferromagnetic particles. This process results in the effective magnetic functionalization of CNTs and opens the door to numerous new applications. However, in order to optimize these materials for any application, their properties need to be understood. This study explores the ferromagnetic properties of carbon nanotubes containing nano-scaled iron particles which were derived from thermal decomposition of ferrocene. Both room temperature as well as low-temperature magnetic measurements will be presented and the results analyzed in the light of available theory.

Oxytetracycline (OTC) is a broad spectrum antibiotic used extensively in the agricultural and human-health sector, and is effective against various gram positive and –negative bacteria as well as large viruses and certain pathogenic Rickettsiae. This study addresses the lack of voltammetric knowledge regarding the electroanalytical characterisation of OTC and its analysis in complex matrices. Cyclic voltammetry (CV) revealed several irreversible anodic peaks for OTC at a bare glassy carbon electrode (GCE). These current responses were improved through the selection of a diluent for OTC stock preparation, electrolyte solution and electrolyte pH, stir time and applied preconditioning potential. Under enhanced adsorptive conditions and using square wave voltammetry (SWV), a detection limit of 24.3 nM was achieved. The electrode surface could be renewed in vitro for 10 successive scans. OTC oxidation was characterised as a one electron:one proton ECiE mechanisms. Next, investigating the viability of voltammetry in various complex microbiological growth media revealed that selected growth media contained interfering redox active components, which, while simultaneously coating the electrode surface, effectively reduced GCE performance and lowered the active electrode surface area, as ascertained through CV and electrochemical impedance spectroscopy (EIS) studies. This interference lowered OTC current response in the presence of growth media which was partially recovered by appropriate growth media selection and sample dilution. In testing the use of acid functionalised multi-walled carbon nanotubes (MWCNTs) to improve anodic OTC response, charge-based attraction was observed between the MWCNT dispersal agent Nafion® and OTC, while increased surface area associated with prolonged acid functionalisation time aided in improving OTC current response.

Biofuel cells (BFCs) use either enzymes or bacteria to catalyse a fuel to generate power. Their advantages over conventional fuels is that they do not use precious metals and the high selectivity of biocatalysts mean that no separation membranes are required between the electrodes. However, the application of BFCs is limited by their low power output and poor enzyme lifetimes. This thesis addresses these limitations by investigating aligned carbon nanotubes (aCNTs) as potential electrode materials. These aCNT electrodes offer high surface areas to increase enzyme coverage and hence power output and their surface topology can stabilise the enzymes to ensure maximum lifetime and current density.A novel BFC half cell was developed using aCNTs and the fungal enzyme, Trametes versicolor laccase which catalyses the four-electron reduction of oxygen to water. Laccase was shown to communicate directly with the nanotubes enabling the oxidant reduction reaction to be monitored without the need for mediators. Initial investigations compared aCNTs with other commonly reported carbon electrodes and found that the current densities were ~30-fold higher on the aCNTs than at pyrolytic graphite edge electrodes. The high surface area of these electrodes contributed to greater electroactive coverage of enzyme and minimal loss of enzyme upon deposition. Cathodic currents increased linearly with geometric electrode area; however they did not scale with actual electrode surface area and the current density was limited to the order of μA cm-2 due to O2-transport limitations. It was also discovered that the porous contribution of these aCNT electrodes could lead to misleading interpretations on nanotube electrochemistry. This effect was observed when increments in electrode area resulted in apparently significantly faster kinetics. This improvement in catalytic behaviour was proposed to be due to a transition from mass diffusion limited to thin layer cell behaviour exhibited by porous materials. Thermal pretreatment of the aCNT electrodes in oxidative and reductive atmospheres were found to improve their performance. These treatments worked by changing the nanotube surface chemistry and purifying the nanotubes, as evidenced by various physical characterisation methods. Furthermore, laccase activity was enhanced significantly after electrodes had been treated under both atmospheres, where it was believed that the removal of contaminant material and higher defect densities increased electrochemical performance.Finally, mass transport limitations were addressed by developing micro-patterned aCNT electrodes which possessed channels in the arrays, allowing better oxygen diffusion. Fundamental studies showed higher current densities per surface area and thus represent a promising electrode for future BFC research.

The project has been concerned with structure/property relationships in a series of different carbon nanotube (CNT) composite fibres. Raman spectroscopy has been proved to be a powerful technique to characterise the CNT-containing fibres. Electrospinning has been used to prepare poly(vinyl alcohol) (PVA) nanofibres containing single-wall carbon nanotubes (SWNTs). The effect of the processing conditions including the polymer concentration, electric voltage, tip-to-collector distance, nanotube concentration and the collection method upon the morphology, diameter and the alignment of the fibres have been investigated.Raman spectroscopy of individual SWNTs dispersed in PVA electrospun fibres have been studied systematically in terms of the Raman band frequency, intensity and linewidth. The G'-band shift per unit strain during tensile deformation has been found to be dependent on the nanotube chirality. A detailed study has been undertaken of the efficiency of reinforcement in PVA/SWNT nanocomposites. The stress-induced Raman band shifts in the nanocomposites have been shown to be controlled by both geometric factors such as the angles between the nanotube axis, the stressing direction and the direction of laser polarisation, and by finite length effects and bundling. A theory has been developed that takes into account all of these factors and enables the behavior of the different forms of nanocomposite, both fibres and films, to be compared.The effects of dispersion and orientation of nanotubes and the interfacial adhesion on mechanical properties of poly(p-phenylene terephthalamide) (PPTA)/SWNTs composite fibres have been investigated. It has been shown the change of orientation of the polymer molecules upon incorporating nanotubes had direct effect on mechanical properties of the PPTA fibres. An in-situ Raman spectroscopy study during fibre deformation has revealed good stress transfer from the matrix to nanotubes in low strain range, and the interface failed when the strain exceeded 0.5%.Raman spectroscopy has also been employed to investigate the microstructure and micromechanical process of neat carbon nanotube (CNT) fibres. It has been found the fibres consisted of both SWNTs and MWNTs and varied in composition at different locations. High efficiency of stress transfer both within the fibre and in composites has been observed, suggesting the promising potential of CNT fibres in reinforcing polymers.