M.Sc. / Radionuclides exist in the environment because of natural and human activities that are an essential part of our lives. Nuclear processing, medicinal applications (using isotopes) and electric power production by nuclear stations are few examples of human activities that result in production of radioactive waste (RAW). The nuclear power stations in our world have to store their waste in such a manner that the present and future generations are protected from harmful radiations and this is a challenge. Exposure to RAW can result in severe, diverse and irreversible consequences such as damage of the ecosystem, pollution, cancers, birth mutations, to mention just a few. Solvent extraction (SE) technique is currently used to purify large volumes of secondary liquid waste before they are released to the environment or stored. However, even after the SE purification, highly radioactive liquid waste is given off. This highly radioactive liquid waste is solidified in a glass matrix (vitrification). In an attempt to reduce the disposal of large volumes of secondary RAW generated during the purification technology, this study was initiated to investigate the possibility of using multiwalled carbon nanotubes (MWCNTs) as part of the SE technique. As the main nuclear liquid extraction processes involve tributyl phosphate (TBP), the MWCNTs were linked to TBP, polymerised to give a MWCNTs-TBP polymer that was tested in the nuclear environment. This polymer should possess good chelating properties due to the inclusion of the phosphate and should be a good absorbent as MWCNTs are promising absorbent carbon materials. To test the hypothesis of the study MWCNTs-TBP polymer was tested for uranium extraction. The MWCNTs-TBP polymer gave a zero Kd value which indicates that the adsorption capacity of the polymer to remove radionuclides from waste streams was not successful. The MWCNTs were then tested for iodine-131 extraction whereby they were compared with single walled carbon nanotubes (SWCNTs) and double walled carbon nanotubes (DWCNTs). In this test SWCNTs gave a Kd value of 81694 mL/g which proved that they can be used in nuclear waste applications.

M.Sc. / Water is often contaminated with organic and inorganic compounds by natural means and through human activities. Once contaminated, water of this nature has little or no use. However, water that is free from toxic chemicals is essential to both human health and the environment. Current water treatment techniques such as separation by membranes (reverse osmosis), adsorption (activated carbon) and ion exchange are not always very efficient at removing contaminants which may be present in parts per billion (ppb) levels. Techniques need to be developed that are reasonably inexpensive and easy to use, and yet effective at removing both organic and inorganic pollutants to acceptable levels. Adsorption is a technique that has the potential to meet these criteria. In our laboratories, insoluble beta cyclodextrin (β-CD) polymers have been used to remove pollutants from water at concentrations as low as ppb levels. However, they exhibited some disadvantages, such as poor structural integrity and difficulty in recovery. This project sought to deal with these limitations by incorporating functionalized multi-walled nanotubes (f-MWNTs) into the polymer, and then embedding polymer particles in an alginate matrix as small beads for ease of use. The polymer composites, 1% f-MWNTs with β-CD polyurethane, were synthesised and embedded in alginates to form alginate composite beads. Composite beads were tested against a model organic and heavy metal pollutants, namely p-nitrophenol and Pb2+, respectively. The composites were characterized using Fourier Transform Infra Red spectroscopy (FT-IR), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDXS), among other techniques. The absorption capacity of f-MWNTs, β-CD, and alginates combined proved to be effective and stable adsorbents. They showed an adsorption efficiency of at least 95% for p-nitrophenol at a concentration of 10 mg/L and 98% for Pb2+ at a concentration of 50 mg/L. vii The novel adsorbents show a good thermal stability and maintain their structural integrity after repeated (thirty times) use in recycling experiments. The recycled beads maintained a high average adsorption efficiency of 96%, indicating the potential cost benefit of these materials. As a comparison, the plain calcium alginate (CaAG) beads and plain β-CD polyurethane beads showed an average adsorption of 55% and 74%, respectively, but their structural integrity was significantly compromised during similar recycling. Brunauer Emmett Teller (BET) surface area analysis showed that incorporation of f-MWNTs (1% loading) increased the surface area of the composite beads, and adsorption isotherms showed a good fit with both Langmuir and Freundlich models. This project has demonstrated the use of f-MWNTs as copolymer which improves the structural stability of the polymers, and that the combination of these polymers and alginates provide a potentially useful material for water treatment applications.

Magister Scientiae - MSc / In this study we report on the effect of the deposition parameters on the morphology and structural properties of CNTs, synthesized by means of the hot-wire chemical vapour deposition technique. SEM, Raman and XRD results show that the optimum deposition conditions for the HWCVD synthesis of aligned MWCNTs, with diameters between 50 and 150 nm and lengths in the micrometer range are: Furnace temperature of 500 ºC, deposition pressure between 150 and 200 Torr, methane/hydrogen dilution of 0.67 and a substrateto- filament distance of 10 cm. / South Africa

M.Sc. / The statistical proof that most forms of cancer metastasize to bone has redirected the focus of secondary bone cancer to probe into the most efficient forms of treatment. Due to the fact that secondary bone cancer delocalizes to bone, chemotherapy has been established as an efficient form of treatment. Bisphosphonates is one chemotherapeutic agent that has shown a great potency in treating bone related sicknesses. Bisphosphonates are analogues of pyrophosphates that are characterized by the presence of two P-C bonds. They have a very high affinity for bone undergoing renewal and are thus able to inhibit tumour induced resorption. Bisphosphonates’ efficiency is however reduced due to that they have a low molecular weight hence are excreted before reaching targeted sites. In this study, an attempt to improve the efficiency was done by providing carbon nanotubes (which were synthesized in our laboratories) as delivery systems. By conjugating bisphosphonates onto carbon nanotubes the molecular weight was increased. Bisphosphonates conjugated carbon nanotubes have been radiolabelled to increase their anticancer activity. By exploiting the Enhanced Permeability Retention (EPR) effect and the high energy electrons from the radioisotope (³²P), it is anticipated that bone metastasis will be successfully treated by the ³²P labelled bisphosphonates carbon nanotube conjugates. Successful synthesis of bisphosphonates conjugated carbon nanotubes was confirmed by several characterization techniques namely: the Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), Raman spectroscopy, Thermal Gravimetric Analysis (TGA), Electron Dispersive X-ray (EDX), and the Fourier Transmission Infrared spectroscopy (FT-IR). Oxidation and bisphosphonates conjugation onto carbon nanotubes were further confirmed by the Raman, TGA, FT-IR, EDX and the SXPS (Scanning X-ray photoelectron spectroscopy) Successful radiolabelling was determined by a liquid scintillation counter (LSC).

M.Tech. (Chemistry) / Please refer to full text to view abstract

The thesis describes novel glass micropipette thermal sensor fabricated in cost-effective manner and thermal conductivity measurement of carbon nanotubes (CNT) thin film using the developed sensor. Various micrometer-sized sensors, which range from 2 µm to 30 µm, were produced and tested. The capability of the sensor in measuring thermal fluctuation at micro level with an estimated resolution of ±0.002oC is demonstrated. The sensitivity of sensors was recorded from 3.34 to 8.86 µV/oC, which is independent of tip size and dependent on the coating of Nickel. The detailed experimental setup for thermal conductivity measurement of CNT film is discussed and 73.418 W/moC was determined as the thermal conductivity of the CNT film at room temperature.

Single wall carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs) were dispersed in mineral oil and epoxy resin. The magnetorheological properties of these dispersions were studied using a parallel plate rheometer. Strain sweeps, frequency sweeps, magneto sweeps and steady shear tests were conducted in various magnetic fields. G', G", h* and ty increased with increasing magnetic field, which was partially attributed to the increasing degree of the alignment of nanotubes in a stronger magnetic field. The SWNT/mo dispersions exhibited more pronounced magnetic field dependence than SWNT/ep and MWNT/mo counterparts due to their much lower viscosity. The alignment of SWNTs in mineral oil increased with rising nanotube concentration up to 2.5vol% but were significantly restricted at 6.41vol% due to nanotube flocculation.

This work investigates the material properties and production parameters of carbon infiltrated carbon nanotube structures (CI-CNT's). The impact of non homogeneous infiltration and the porosity of cross section regions, coupled with changes in designed geometry, in this case beam width, on the density and modulus of elasticity are compared. Three potential geometric models of beam cross section are proposed and evaluated. 3-point bending, SEM images, and numerical optimization are used to assess the validity of each model and the implications they have for future CI-CNT material applications. Carbon capping near exterior beam surfaces is observed and determined to be a contributing factor to variations in material properties correlated with changes in designed geometry and infiltration parameters (temperature, time, and hydrogen flow rate). Unexpected relationships between beam width and elastic modulus are partially explained by modeling the carbon-capped beams as C-shaped structural members consisting of a graphitic carbon shell of varying porosity and thickness and uninfiltrated carbon nanotube internal regions with a near negligible stiffness. Findings of previous works on the effects of infiltration parameters and carbon capping on materials properties are confirmed and expanded. Flange and web thickness and porosity of the graphitic carbon shell are identified as potential design parameters for pursuing tunable material properties in high precision geometry MEMS and compliant mechanism applications.

Single molecule biosensing techniques offer unique advantages and opportunities for basic biological studies and medical diagnostic applications. However, their signal levels are intrinsically very weak and can be easily masked by the noise from the sensor itself or the measurement electronics. Thus, the biosensing systems and devices must be carefully characterized and optimized to reduce noise. This thesis first presents optimizations that enable high bandwidth, single channel recordings of the calcium-induced calcium release channel ryanodine receptor 1. By directly integrating a suspended bilayer with a complementary metal oxide semiconductor transimpedance amplifier, the total input capacitance and, therefore, high frequency noise are lowered, enabling gating events to be recorded at an order of magnitude higher bandwidth than the previous state of the art. Next, low frequency noise optimizations for carbon nanotube transistors are explored using hexagonal boron nitride substrates. These devices have improved 1/f noise performance compared to equivalent devices on silicon oxide and demonstrate evidence of contact limited noise. Finally, a basic characterization of 1/f noise in carbon nanotubes is developed using correlated transport and noise measurements in crossed carbon nanotube homojunction devices. These methods of optimizing and characterizing noise can aid in the development of single molecule biosensors with improved temporal resolution and error rates.

Placement of single walled carbon nanotubes is demonstrated through massively parallel indirect dielectrophoresis (MPID). MPID is shown to be able to control the placement of carbon tubes as well as the number of tubes placed. Lumped element analysis for AC circuits is used to model MPID. This model allows for predictions of the number of tubes that will be captured in a trap. This model has been consistent with experimental data of numbers of nanotube placed in a junction. Carbon nanotubes placed with MPID are shown to be electrically active.