For the first time, new metallophthalocyanine (MPc) complexes: (i) nanostructured MPc (nanoMPc, where M = iron or cobalt); (ii) octabutylsulphonylphthalocyanine (MOBSPc, where M = iron or cobalt); and (iii) iron (II) tetrakis(diaquaplatinum)octacarboxyphthalocyanine (PtFeOCPc) were synthesized and characterized using advanced microscopic and spectroscopic techniques such as MS, AFM, HRTEM, FESEM, and EDX. Electrochemical techniques such as cyclic voltammetry, square wave voltammetry, chronoamperometry, rotating disk electrode, and electrochemical impedance spectroscopy, were used to explore the redox chemistry, heterogeneous electron transfer kinetics (HET), and electrocatalytic properties of these MPc complexes towards oxygen reduction reaction (ORR), oxidation of formic acid, thiocyanate and nitrite on a edge plane pyrolytic graphite electrode (EPPGE) platform pre-modified with or without acid functionalized multi-walled carbon nanotubes (MWCNTs). The MWCNT-MPc platforms exhibit enhanced electrochemical response in terms of (i) HET towards an outer-sphere redox probe ([Fe(CN)6]3-/[Fe(CN) 6]4-), and (ii) catalytic activities towards the investigated analytes. The MWCNTnanoMPc electrode exhibits faster HET constant (kapp ≈ 30 – 56 x 10-2 cms-1 compared to their bulk MPc counterparts (≈ 4 – 25 x 10-2 cms-1). The MWCNT-nanoMPc exhibited enhanced electrocatalytic properties (in terms of sensitivity and limit of detection, LoD) towards the detection of thiocyanate and nitrite in aqueous solutions. ORR was a 4- electron process with very low onset potential (-5 mV vs. Ag|AgCl saturated KCl). HET and ORR at MOBSPc complexes supported on MWCNTs showed that the MWCNT–MOBSPc exhibited larger Faradaic current responses than the electrodes without MWCNTs. The rate constant at the MWCNT-MOBSPc electrodes (kapp ≈ (22 – 37) x 10-2 cms-1) is about a magnitude higher than the electrodes without MWCNT (kapp ≈ (0.2 – 93) x 10-3 cms-1). The MWCNT–FeOBSPc electrode gave the best ORR activity involving a direct 4-electron mechanism with low onset potential (0.0 mV vs. Ag|AgCl saturated KCl). The onset potential is comparable and even much lower than recent reports. The HET and electrocatalytic properties of PtFeOCPc supported on a MWCNT platform (MWCNT-PtFeOCPc) gave enhanced electrochemical response in terms of (i) HET (kapp ≈ 78 x 10-2 cms-1), (ii) catalytic rate constant (kcat ≈ 41 cm3mol-1s-1) and (iii) tolerance towards CO poisoning during formic acid oxidation. The ORR activity is a direct 4-electron transfer process at a rate constant of 2.78 x 10-2 cms-1; with a very low onset potential approximately 0.0 mV vs. Ag|AgCl saturated KCl. The electrooxidation of formic acid at MWCNT-PtFeOCPc follows the preferred ‘direct pathway’. This work clearly proves that the MWCNT-MPcs hybrid exhibit enhanced electrochemical and electrocatalytic activities towards the selected analytes compared to the MPcs alone. Considering the ease of fabrication of these electrodes (drop-dry method), these nanocomposite materials are promising platform for potential application in sensing and cataly. / Thesis (PhD)--University of Pretoria, 2011. / Chemistry / unrestricted

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This dissertation describes the development of a processing route for fabricating conventional and doped multi-wall carbon nanotube (MWCNT)/polymer composite films for dielectric applications. Previous research has shown that such composites are promising dielectric materials, but their commercial development has been impeded by the nanotube agglomeration in the polymer matrix and the inefficiency in forming uniform films. Moreover, the harsh fabrication treatments often disrupt the structure of the nanotubes, hence damaging their inherent electrical properties. This work presents safer routes for forming non-aqueous, surfactant free dispersions of conventional and doped MWCNTs, which can be readily mixed with polymers and formed into films through aerosol spraying. Dispersibility behaviour of in-house synthesised conventional, nitrogen doped (N-MWCNTs), and boron doped (B-MWCNTs) MWCNTs was studied in 22 organic solvents. Based on thermodynamic theories it was suggested that doping, in particular nitrogen doping, significantly reduced the surface energy of the nanotubes. This aspect was crucial to understand the dispersibility of N-MWCNTs in low surface energy solvents and to achieve dispersions with high nanotube concentrations (0.82 mg/ml). Also, a "destruction reduced sonication protocol" involving mild sonication was suggested for forming MWCNT dispersions in organic solvents. Dispersions formed using this protocol were homogeneous and showed high stability of at least 2.5 years. Furthermore, the effect of ultrasonic probes on MWCNT lengths was studied and a decrease of 96–99% for MWCNTs and 85–95% for N-MWCNTs was observed. A numerical value for the nanotube length decrease during sonication has been reported for the first time. Preliminary studies to generate dielectric films of MWCNT/perfluoro alkoxy polymer were performed using aerosol spraying. An improvement in the dielectric constant (3.56) with a low dissipation factor (0.003) was observed in 0.3 wt.% B- MWCNT/PFA composite films. Consistency in the test results from various parts of the films confirmed the uniformity of the nanotube distribution within the composite. Future work should concentrate on the effects of B-MWCNTs and N-MWCNTs at the percolation threshold due to their inherent electric properties.

The rise of nanotechnology industries has led to the design and production of new nano-scaled materials such as quantum dots, nano-metals, carbon nanotubes, fullerenes and a myriad of functionalised derivatives. Extensive work concerning well characterised pathogenic fibres has led to the development of a fibre paradigm that suggests respirable fibres vary in their ability to cause disease based on length and pulmonary bio-persistence. Induction of oxidative stress is also a central plank of the mechanism used to explain inflammatory, fibrotic and carcinogenic effects of fibres. The toxicity of different particle types has consistently been shown to depend upon particle size and surface area, reactive surface molecular groups, metal content, organic content and the presence of endotoxins. A growing body of work has begun to examine the potential pathogenicity of carbon nanotubes to the pulmonary system as a consequence of superficial similarities to known pathogenic particle and fibres. The aim of this thesis was to investigate the potential toxicity of two commercially manufactured multi-walled carbon nanotubes (MWCNT) compared to a panel of low and high toxicity particles and fibres. The pro-inflammatory nature of MWCNT was examined in vitro and in vivo to determine the effects they may exert in the pulmonary system. In aqueous solutions of phosphate buffered saline, saline and cell culture medium (with or without foetal calf serum supplementation) MWCNT were found to exist as tight aggregates even after sonication. Analysis of metal content of MWCNT by ICP-AES revealed the presence of a low percentage of non extractable residual iron. From analysis of MWCNT by electron spin resonance (ESR) the CNT were found to be ready producers of a free radical species, despite this MWCNT were not able to cleave plasmid DNA. Upon incubation with the alveolar epithelial cell line A549 MWCNTs did not cause noticeable toxicity but did dose dependently deplete total glutathione levels. No increase in production of the pro-inflammatory cytokine IL-8 could be detected at the level of protein or at the level of mRNA. Analysis of the levels (protein and mRNA) of the pro-fibrotic mediator TGF-β did not indicate induction of a fibrotic response to MWCNT. Neither were MWCNTs found to consistently activate the pro-inflammatory associated transcription factor nuclear factor kappa B (NF-κB). Upon instillation into the peritoneal cavity of mice MWCNT failed to induce a pro-inflammatory response in contrast to long amosite asbestos that induced an extensive inflammatory reaction. Analysis of the diaphragms of exposed animals revealed the induction by MWCNT of an apparent foreign body type reaction. Overall with limited processing and dispersion MWCNT were morphologically more akin to particles than fibres. Although apparently able to spontaneously generate ROS in aqueous solution this did not translate into a capacity to cause toxicity or a capacity to induce inflammation either in vitro or in vivo.

Nitrogen oxides (NOx) are atmospheric pollutants that pose a serious threat to both the environment and human health. Although catalytic deNOx technologies for engines working under stoichiometric air-to-fuel ratios (i.e., most gasoline engines) are already available, their performance is unsatisfactory under excess air conditions like those under which diesel engines operate. The selective catalytic reduction of NOx with hydrocarbon reductants (HC-SCR) is a potential deNOxsolution for diesel engines, whose operating temperatures are 150-500 ºC. Given that is unlikely for a single catalyst to show acceptable activity throughout this entire temperature span, the use of two catalysts is proposed in this dissertation. Whereas several catalysts active at high temperatures (>300 ºC) are already available, a catalyst showing an acceptable performance at low temperatures (<300 ºC) is yet to be found. Platinum group metals (PGMs) supported on activated carbon have been identified as promising low temperature HC-SCR catalysts. However, these materials show three main drawbacks: 1) the propensity of the carbon support to undergo combustion in an oxidizing environment, 2) a narrow temperature window of operation; and 3) a high selectivity towards N2O (as opposed to N2). To address the first limitation, the use of multi-walled carbon nanotubes (MWCNTs) as the support has been investigated and found to yield catalysts displaying a higher resistance to oxidation. Further, the acid activation of MWCNTs prior to their use as catalyst support has been explored, following reports than link carrier acidity with improved catalyst performance. In turn, the use of PGM alloys as the active phase has been examined as a means to improve catalyst activity and selectivity. Additionally, kinetic, spectroscopic and mechanistic studies have been performed in an attempt to probe structure-activity relationships in the MWCNTs-based formulations showing the best deNOx performance. The fundamental insights gained through these studies may inform further improvements to HC-SCR catalysts. Finally, the synthesis of the most promising formulations has been scaled-up using commercial metal monoliths as the catalyst substrate and the resulting monolithic catalysts have been tested in a diesel engine for activity in the HC-SCR reaction.

Carbon nanotubes (CNTs) are of special interest to industry and they have been increasingly utilised as advanced nanovectors in drug/gene delivery systems. They possess significant advantages including high surface area, welldefined morphologies, unique optical property, superior mechanical strength and thermal conductivity. However, despite their unique and advanced physicochemical properties, the low compatibility of some of those materials [e.g. multiwalled CNTs (MWCNTs)] in most biological and chemical environments has also generated some serious health and environment concerns. Chemical functionalization broadens CNT applications, conferring new functions, and at the same time was found potentially altering toxicity. Although considerable experimental data related to functionalised CNT toxicity, at the molecular and cellular levels, have been reported, there is very limited information available for the corresponding mechanism involved (e.g. cell apoptosis, genotoxicity. The toxicity of carbon nanotubes has been confirmed on many cell lines including A549 (lung cancer cell line) and MRC-5 (lung fibroblasts). However, the sensitivity of each cell line in terms of cellular morphology, apoptosis and DNA damage are still unknown. In this report the different levels of cellular response to oxidative stress and phagocytosis have been investigated in A549, MCF-7 and MRC-5 cell lines to better understand the mechanisms of the toxicity pathway. siRNA as an ideal personalized therapeutics can specifically regulate gene expression, but efficient delivery of siRNA is difficult while it has been shown that MWCNTs protect siRNA, facilitate entry into cells. In this study, we comprehensively evaluated the in vitro cytotoxicity of pristine and functionalized (-OH, -COOH) multi-wall carbon nanotubes (MWCNTs), via cell viability test, reactive oxygen species (ROS) generation test, cell apoptosis and DNA mutation detection, to investigate the non-toxic dose and influence of functional group in A549, MCF-7 and MRC-5 cells exposed to 1-1000 μg/mL MWCNTs from 6 to 72 hours. In addition, 84 toxicity related genes have been detected to investigate the change of RNA regulation after treatment with MWCNTs. The research findings suggest that functionalized MWCNTs are more genotoxic compared to their pristine form, and the level of both dose and dispersion in the matrix used should be taken into consideration before applying further clinical applications of MWCNTs. Among all three cell lines, MCF-7 was the most sensitive to cell death and DNA damage induced by pristine carbon nanotubes. The majority of MCF-7 cell death was in necrotic. In A549 cells, apoptosis played a notable role in cytotoxicity. MRC-5 didn’t show significant cell loss or membrane damage, which might be explained by its low cell growth rate, notably however, a great reduction of the F-actin and attachment points was observed after treatment which indicates that MRC-5 cells are under very unhealthy condition and less attached to the bottom of flasks. Despite their toxicity, which is still being researched, carbon nanotubes have a great potential in clinical medicine. Thus, understanding the sensitivity of different cell lines could offer a more individualized approach for future treatment regimes. In regards to gene delivery, MWCNTs were found to be less toxic than chemical agents (positive control) without weakening the delivery efficiency, which proves that MWCNTs have a good potential in medicine area.

The present research work aims to develop a new heat transfer fluid by combining multiwalled carbon nanotubes (MWCNT) and microencapsulated phase change materials (MPCMs). Stable nanofluids have been prepared using different sizes of multiwalled carbon nanotubes and their properties like thermal conductivity and viscosity have been measured. Microencapsulated phase change material slurries containing microcapsules of octadecane have been purchased from Thies Technology Inc. Tests have been conducted to determine the durability and viscosity of the MPCM slurries. Heat transfer experiments have been conducted to determine the heat transfer coefficients and pressure drop of the MWCNT nanofluids and MPCM slurries under turbulent flow and constant heat flux conditions. The MPCM slurry and the MWCNT nanofluid have been combined to form a new heat transfer fluid. Heat transfer tests have been conducted to determine the heat transfer coefficient and the pressure drop of the new fluid under turbulent flow and constant heat flux conditions. The potential use of this fluid in convective heat transfer applications has also been discussed. The heat transfer results of the MPCM slurry containing octadecane microcapsules was in good agreement with the published literature. The thermal conductivity enhancement obtained for MWCNTs with diameter (60-100 nm) and length (0.5-40?m) was 8.11%. The maximum percentage enhancement (compared to water) obtained in the heat transfer coefficient of the MWCNT nanofluid was in the range of 20-25%. The blend of MPCMs and MWCNTs was highly viscous and displayed a shear thinning behavior. Due to its high viscosity, the flow became laminar and the heat transfer performance was lowered. It was interesting to observe that the value of the maximum local heat transfer coefficient achieved in the case of the blend (laminar flow), was comparable to that obtained in the case of the MPCM slurry (turbulent flow). The pressure drop of the blend was lower than that of the MWCNT nanofluid.

Polyamide 6 (PA6) was melt-blended with an intumescent flame retardant (FR) and nanoparticles (multi-wall carbon nanotubes [MWNTs] and nanoclays) to produce multi-component FR-PA6 nanocomposites. Thermal, flammability properties, char residue morphology, and mechanical properties of FR-PA6 nanocomposites were characterized. The flame retardant properties were enhanced according to UL 94 and microscale combustion calorimeter (MCC) measurements, whereas the thermal stability was decreased. Mechanical properties of the bulk material, especially elongation at break, were severely reduced, with the exception of tensile modulus which increased significantly. FR-PA6 nanofibers were processed via electrospinning. Electrospinnability, morphology of the nanofibers, combustion, and thermal properties were also analyzed. As for the bulk-form nanocomposite, improved combustion properties of these nanofibers were successfully achieved though thermal stability was compromised. With proper FR additive, the synergism between MWNTs and nanoclays was observed in PA6 resin. / text

Multi walled carbon nanotubes (MWCNT) grown in highly ordered porous alumina templates were incorporated into a resistive gas sensor design and were evaluated for their sensitivities. The material characteristics and electrical properties of the nanotubes were analyzed. A study was undertaken to elucidate the effect of UV light on desorption characteristics and the dependence of sensitivity on (i) thickness of amorphous carbon layers and (ii) flow rates of analyte gases. These sensors were highly responsive to both oxidizing and reducing gases with steady state sensitivities of 5% and 10% for 100ppm of NH3 and NO2 respectively, at room temperature. As part of a comparative study, thick films of MWCNTs grown on Si/SiO2 substrates were integrated into various nano-composite based sensors and were evaluated for their response. Steady state sensitivities as high as 10% and 11% were achieved for 100ppm of NH3 and NO2 respectively, at room temperature. MWCNTs were characterized for their electrical properties by I–V measurements at room temperatures. A typical I-V curve with an ohmic behavior was observed for a device with high work function metals (example: Au, Pt); Schottky behavior was observed for devices with metal contacts having low work functions (example: Al, Cu).

Electrically conductive adhesives (ECA) are discussed and studied with everincreasing interest as an environmentally friendly alternative to solder interconnection in microelectronics circuit packaging. They are used to attach surface mount devices (SMD), Integrated Circuits (IC) and Flip chips in electronic assembly. The use of ECAs brings some benefits like flexibility, mild processing conditions and process simplicity. Multi walled carbon nanotubes (MWCNT) are used instead of metal fillers because of their novel properties such as light weight, high aspect ratio, corrosion resistant, reduced processing temperature, lead free, good electrical conduction and mechanical strength. The purpose of the present work is to investigate the aging behavior of MWCNT filled adhesives based on anhydride cured epoxy systems and their dependence on loading. Composites with different loadings of MWNT in epoxy and epoxy: heloxy are prepared and then stencil printed onto different surface finished boards like gold, silver and tin to prepare contact resistance samples and onto aluminum oxide boards to prepare volume resistivity samples. These samples are kept at room temperature for about 90 days and then placed in a temperature chamber to observe the behavior of these samples after accelerated aging. The readings are taken for as prepared samples, after 45 days, after 90 days and after accelerated aging. The results are summarized and different trends are observed for different loadings of MWNT, different combinations of epoxy: heloxy and for different surface finished boards.