<p>Graphene, first isolated in 2004 and the subject of the 2010 Nobel Prize in physics, has generated a tremendous amount of research interest in recent years due to its incredible mechanical and electrical properties. However, difficulties in large-scale production and low as-prepared surface area have hindered commercial applications. In this dissertation, a new material is described incorporating the superior electrical properties of graphene edge planes into the high surface area framework of carbon nanotube forests using a scalable and reproducible technology.</p><p>The objectives of this research were to investigate the growth parameters and mechanisms of a graphene-carbon nanotube hybrid nanomaterial termed “graphenated carbon nanotubes” (g-CNTs), examine the applicability of g-CNT materials for applications in electrochemical capacitors (supercapacitors) and cold-cathode field emission sources, and determine materials characteristics responsible for the superior performance of g-CNTs in these applications. The growth kinetics of multi-walled carbon nanotubes (MWNTs), grown by plasma-enhanced chemical vapor deposition (PECVD), was studied in order to understand the fundamental mechanisms governing the PECVD reaction process. Activation energies and diffusivities were determined for key reaction steps and a growth model was developed in response to these findings. Differences in the reaction kinetics between CNTs grown on single-crystal silicon and polysilicon were studied to aid in the incorporation of CNTs into microelectromechanical systems (MEMS) devices. To understand processing-property relationships for g-CNT materials, a Design of Experiments (DOE) analysis was performed for the purpose of determining the importance of various input parameters on the growth of g-CNTs, finding that varying temperature alone allows the resultant material to transition from CNTs to g-CNTs and finally carbon nanosheets (CNSs): vertically oriented sheets of few-layered graphene. In addition, a phenomenological model was developed for g-CNTs. By studying variations of graphene-CNT hybrid nanomaterials by Raman spectroscopy, a linear trend was discovered between their mean crystallite size and electrochemical capacitance. Finally, a new method for the calculation of nanomaterial surface area, more accurate than the standard BET technique, was created based on atomic layer deposition (ALD) of titanium oxide (TiO2).</p> / Dissertation

Single-walled carbon nanotubes (SWNTs) are one of the leading candidate materials to realize novel nanoscale photonic devices. In order to assess their performance characteristics as optoelectronic materials, it is crucial to examine their optical properties in highly non-equilibrium situations such as high magnetic fields, low temperatures, and under high photoexcitation. Therefore, we present our latest result on the magnetic susceptibility anisotropy of metallic carbon nanotubes due to the Aharonov-Bohm effect. Here, we performed magnetic linear dichroism on a metallic-enriched HiPco SWNT sample utilizing a 35 T Hybrid Magnet to measure absorption with light polarization both perpendicular and parallel to the magnetic field. By relating these values with the nematic order parameter for alignment, we found that the metallic carbon nanotubes do not follow a strict diameter dependence across the 7 chiralities present in our sample. In addition to the studying the absorption properties exhibited at high magnetic field, we performed temperature-dependent (300 K to 11 K) photoluminescence (PL) on HiPco SWNTs embedded in an ι -carrageenan matrix utilizing intense fs pulses from a wavelength-tunable optical parametric amplifier. We found that for each temperature the PL intensity saturates as a function of pump fluence and the saturation intensity increases from 300 K to a moderate temperature around 100-150 K. Within the framework of diffusion-limited exciton-exciton annihilation (EEA), we successfully estimated the density of 1D excitons in SWNTs as a function of temperature and chirality. These results coupled with our results of magnetic brightening, or an increase in PL intensity as a function of magnetic flux through each SWNT due to the Aharonov-Bohm effect, yield great promise that in the presence of a high magnetic field the density of excitons can be further increased.

Single walled carbon nanotubes (SWNTs) are considered potential biomedical materials because of their flexible structure, hollow interior for fluidic transport, propensity for functionalization of the exterior walls, and biocompatibility. Research into exploiting these properties has focused on SWNTs as building blocks for novel drug-delivery systems, dosage forms, and biomedical substrates. However, the use of the internal nanochannels as conduits for trans-membrane drug delivery has not been explored. This research was initially designed to explore the latter.<p> It is postulated that due to their mechanical strength and the presence of an internal conduit, SWNTs can be used for nanofluidic transport. Using a magnetic field, the magnetically responsive SWNT are driven into intact stratum corneum, creating nanochannels, for trans-membrane drug delivery. Initial studies showed however that a bottleneck is the aggregation of SWNTs on the surface of stratum corneum. To achieve trans-membrane nanofluidic delivery, the SWNTs have to be well dispersed in an appropriate pharmaceutical medium, and the SWNT have to be of high purity. Similarly, the presence of impurities in SWNTs, and the dispersion state of these materials in pharmaceutical solvents may give an insight into the discrepancies in toxicity that is reported.<p> The purity of five commercially available SWNTs (AP-SWNT and P2-SWNT, from Carbon Solutions Inc, HMS-SWNT from Helix Materials, and NA-SWNT from Nanostructured and Amorphous Materials Inc. and CT-SWNT from ChepTubes Inc.) were analyzed by raman and electron dispersive x-ray spectroscopy (EDS) spectroscopy. Secondly, the dispersion states of SWNTs in various pharmaceutical solvents were evaluated by ultraviolet (UV) spectroscopy, scanning electron microscopy (SEM), dynamic light scattering (DLS), zeta potential, and Raman spectroscopy to identify potential agents for exfoliation of SWNTs in selected pharmaceutical solution.<p> SWNTs were dispersed in various solvents (water, propylene glycol [PG], dimethylsulfoxide [DMSO], and ethanol) as well as in 0.1% w/v aqueous solutions of anionic, cationic and neutral surfactants at a SWNT concentration of 0.1 mg/mL. SWNT suspensions described as dispersed yielded an evenly coloured suspension with no visible precipitate. The most stable dispersions were obtained with the gemini surfactants, which were confirmed by SEM observation of exfoliated SWNTs. Zeta (î) potential measurements of the fully dispersed SWNTs showed typical values of greater than +30 mV, while non-dispersed samples were less than +20 mV. SEM images of the dispersed solution showed the presence of exfoliated SWNTs compared to the aggregated SWNT clusters observed in non-dispersed systems. Raman spectra of dispersed SWNTs showed G-band peak shifts (to higher wavelengths), confirming the presence of exfoliated SWNTs.<p> Even though the purity of SWNT did not correlate with amount of SWNT in dispersion, exfoliation of bundled SWNTs was accompanied by an increase in UV absorbance of the dispersion, with maximum exfoliation determined by a relatively stable UV absorbance.<p> As pharmaceutical excipients, we have demonstrated that gemini surfactants are suitable dispersing agents for SWNTs, and shown that the dispersion of SWNT for gemini surfactants (12-3-12) is achieved below the critical micelle concentration. The dispersion of SWNT bundles into individual strands is the first crucial step towards their use in biological systems as drug carriers.

Single walled carbon nanotubes (SWNTs) are considered potential biomedical materials because of their flexible structure, hollow interior for fluidic transport, propensity for functionalization of the exterior walls, and biocompatibility. Research into exploiting these properties has focused on SWNTs as building blocks for novel drug-delivery systems, dosage forms, and biomedical substrates. However, the use of the internal nanochannels as conduits for trans-membrane drug delivery has not been explored. This research was initially designed to explore the latter.<p> It is postulated that due to their mechanical strength and the presence of an internal conduit, SWNTs can be used for nanofluidic transport. Using a magnetic field, the magnetically responsive SWNT are driven into intact stratum corneum, creating nanochannels, for trans-membrane drug delivery. Initial studies showed however that a bottleneck is the aggregation of SWNTs on the surface of stratum corneum. To achieve trans-membrane nanofluidic delivery, the SWNTs have to be well dispersed in an appropriate pharmaceutical medium, and the SWNT have to be of high purity. Similarly, the presence of impurities in SWNTs, and the dispersion state of these materials in pharmaceutical solvents may give an insight into the discrepancies in toxicity that is reported.<p> The purity of five commercially available SWNTs (AP-SWNT and P2-SWNT, from Carbon Solutions Inc, HMS-SWNT from Helix Materials, and NA-SWNT from Nanostructured and Amorphous Materials Inc. and CT-SWNT from ChepTubes Inc.) were analyzed by raman and electron dispersive x-ray spectroscopy (EDS) spectroscopy. Secondly, the dispersion states of SWNTs in various pharmaceutical solvents were evaluated by ultraviolet (UV) spectroscopy, scanning electron microscopy (SEM), dynamic light scattering (DLS), zeta potential, and Raman spectroscopy to identify potential agents for exfoliation of SWNTs in selected pharmaceutical solution.<p> SWNTs were dispersed in various solvents (water, propylene glycol [PG], dimethylsulfoxide [DMSO], and ethanol) as well as in 0.1% w/v aqueous solutions of anionic, cationic and neutral surfactants at a SWNT concentration of 0.1 mg/mL. SWNT suspensions described as dispersed yielded an evenly coloured suspension with no visible precipitate. The most stable dispersions were obtained with the gemini surfactants, which were confirmed by SEM observation of exfoliated SWNTs. Zeta (î) potential measurements of the fully dispersed SWNTs showed typical values of greater than +30 mV, while non-dispersed samples were less than +20 mV. SEM images of the dispersed solution showed the presence of exfoliated SWNTs compared to the aggregated SWNT clusters observed in non-dispersed systems. Raman spectra of dispersed SWNTs showed G-band peak shifts (to higher wavelengths), confirming the presence of exfoliated SWNTs.<p> Even though the purity of SWNT did not correlate with amount of SWNT in dispersion, exfoliation of bundled SWNTs was accompanied by an increase in UV absorbance of the dispersion, with maximum exfoliation determined by a relatively stable UV absorbance.<p> As pharmaceutical excipients, we have demonstrated that gemini surfactants are suitable dispersing agents for SWNTs, and shown that the dispersion of SWNT for gemini surfactants (12-3-12) is achieved below the critical micelle concentration. The dispersion of SWNT bundles into individual strands is the first crucial step towards their use in biological systems as drug carriers.

It has been known that a significant part of the thermal budget of an electronic package is occupied by the thermal interface material which is used to join different materials. Research in reducing this resistance through the use of vertically aligned multiwall carbon nanotube based thermal interface materials is presented. Transferred arrays anchored to substrates using thermal conductive adhesive and solder was analyzed through a steady-state infrared measurement technique. The thermal performance of the arrays as characterized through the measurement system is shown to be comparable and better than currently available interface material alternatives. Furthermore, a developed parametric model of the thermal conductive adhesive anchoring scheme demonstrates even greater potential for improved thermal resistances. Additionally, a developed transient infrared measurement system based on single point high speed temperature measurements and full temperature mappings is shown to give increased information into the thermophysical properties of a multilayer sample than other steady-state techniques.

A first principles atomistic calculation and analysis is used to conduct studies on the mechanical and electron transport properties of selected stretched single-wall carbon nanotube segments. The atomic forces, electron densities, current, voltage and total energies are calculated for these carbon nanotube segments using Atomistix's Virtual NanoLab (VNL) and ToolKit (ATK), a software package for electronic structure calculations and molecular dynamics simulations of different molecular systems. Plots of electronic energy spectra, densities of states, force versus length, and current-voltage data, are presented as output results. The mechanical properties of these carbon nanotube segments under a maximum strain of 1% are studied.A speculative atomistic-level stress-strain approach is tried for calculating Young's modulus for a single-wall carbon nanotube segment. The computed total energies are also used to extract the Young's modulus value. Based on the results, the approach is found to work and we were able to calculate the mechanical parameters for single-wall carbon nanotube segments. The electrical conductance is obtained from the current-voltage curves for strained single-wall metallic carbon nanotube segments placed between copper contacts. / Department of Physics and Astronomy

<p>The primary goals of this research were to investigate the electrochemical behavior of carbon nanostructures of varying morphology, identify morphological characteristics that improve electrochemical capacitance for applications in energy storage and neural stimulation, and engineer and characterize a boron-­doped diamond (BDD) electrode based electrochemical system for disinfection of human liquid waste. </p><p>Carbon nanostructures; ranging from vertically aligned multiwalled carbon nanotubes (MWCNTs), graphenated carbon nanotubes (g-­CNTs) to carbon nanosheets (CNS); were synthesized using a MPECVD system. The nanostructures were characterized by using scanning electron microscopy (SEM) and Raman spectroscopy. In addition to employing commonly used electrochemical techniques such as cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), a new technique was developed to evaluate the energy and power density of individual electrodes. This facilitated comparison of a variety of electrode materials without having to first develop complex device packaging schemes. It was found that smaller pore size and higher density of carbon foliates on a three-dimensional scaffold of carbon nanotubes increased specific capacitance. A design of experiments (DOE) study was conducted to explore the parametric space of the MWCNT system. A range of carbon nanostructures of varying morphology were obtained. It was observed that the capacitance was dependent on defect density. Capacitance increased with defect density.</p><p>A BDD electrode was characterized for use in a module designed to disinfect human liquid waste as a part of a new advanced energy neutral, water and additive-free toilet designed for treating waste at the point of source. The electrode was utilized in a batch process system that generated mixed oxidants from ions present in simulated urine and inactivated E. Coli bacteria. Among the mixed oxidants, the concentration of chlorine species was measured and was found to correlate to the reduction in E. Coli concentration. Finally, a new operating mode was developed that involved pulsing the voltage applied to the BDD anode led to 66% saving in energy required for disinfection and yet successfully reduced E. Coli concentration to less than the disinfection threshold.</p> / Dissertation

The major objective of this thesis is to systematically investigate the effect of hexagonal BN (h-BN) islands on electronic and vibrational properties of single wall carbon Nanotubes. All our investigation are based on first principle Density Functional Theory (DFT) calculations. Our study is motivated by interesting metal-semiconductor transition recently found in periodically patterned graphene with h-BN islands. After reproducing the electronic band structure for pristine single wall zigzag carbon nanotubes (which shows metallic or semiconducting properties depending on their chirality), we investigated their electronic band structure in the presence of h-BN islands. The band structure depends not only on the defect concentration, but also on the pattern of the defect atoms. Our results also suggest that, if we start with a metallic /semiconducting mixture of ZSWCNTs, upon h-BN addition, the sample converts to fully semiconducting. This is a promising result for applications of CNTs in molecular electronics. Fundamental understanding of vibrational properties of nano electronics component is equally important in their applications especially in thermal management and thermoelectric applications. Defect engineering is one of the potential approach for tuning nanoelectronic devices for optimal thermal management and thermoelectric devices. In this work, I present a systematic investigation on how the group velocity and frequency of different phonon modes depend on various h-BN defect concentrations and defect patterns in ZSWCNTs. The study was extended to investigate the effect of hexagonal-C defects on the electronic and vibrational properties of zigzag single wall Boron Nitride nanotubes (ZSWBNNTs).

Orientadores: Gisela de Aragão Umbuzeiro, Vitor Rafael Coluci / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Tecnologia / Made available in DSpace on 2018-08-20T12:15:06Z (GMT). No. of bitstreams: 1 Honorio_JaquelineGoncalves_M.pdf: 1809951 bytes, checksum: 7885a8cfa050d72f934edad04cce0f92 (MD5) Previous issue date: 2012 / Resumo: Nanomateriais, tais como nanotubos de carbono de paredes múltiplas (MWCNT) têm apresentado potencial para remediação de águas e solos poluídos por compostos orgânicos devido a sua área superficial elevada, que pode melhorar a capacidade dos NTC em adsorver compostos orgânicos. Embora o tratamento de MWCNT com ácido nítrico possa aumentar a capacidade de dispersão do material em água através da introdução de grupos oxigenados sobre a superfície dos NTC, como ácidos carboxílicos, a diminuição da capacidade de MWCNT de interagir com moléculas orgânicas pode ocorrer como consequência não intencional. Para investigar esta possibilidade, foi avaliada a capacidade de MWCNT tratados com ácido de adsorver um poluente ambiental comum, 1-Nitropireno (1-NP), que é um nitro-hidrocarboneto policíclico aromático altamente mutagênico e carcinogênico. Diferentes doses de MWCNTs caracterizados foram testadas com diferentes doses de 1-NP, e a detecção do 1-NP não adsorvido foi avaliada pelo ensaio de mutagenicidade Salmonella/microssoma, usando a linhagem TA98 que é altamente sensível a 1-NP. Assim, apenas 1-NP não adsorvido aos MWCNT são absorvidos pelas bactérias e causam mutagenicidade. Encontramos uma relação inversa entre a oxidação por tratamento ácido dos MWCNT e a mutagenicidade da mistura. Os dados obtidos sugerem que o tratamento ácido de MWCNT pode, de fato, reduzir a capacidade de poluentes orgânicos se ligarem a MWCNT, reduzindo a eficácia na remediação / Abstract: Nanomaterials, such as multi-wall carbon nanotubes (MWCNT) have been shown potential to remediate soil or water polluted with organic compounds because of their high specific-surface area, which can enhance the ability of the CNT to adsorb organics. Although treatment of MWCNT with nitric acid can increase the water solubility of MWCNT by introducing oxygenated groups such as carboxylic acids onto the surface, it may have the unintended consequence of decreasing the ability of MWCNT to interact with organic molecules. To investigate this possibility, we evaluated the ability of acid-treated MWCNT to absorb a common environmental pollutant, 1- nitropyrene (1-NP), which is a highly mutagenic and carcinogenic nitro-polycyclic aromatic hydrocarbon. Different doses of well-characterized MWCNTs were tested with different doses of 1-NP, and the detection of the non-adsorbed 1-NP was assessed by the Salmonella mutagenicity assay in strain TA98, which is highly sensitive to 1-NP. Thus, only free 1-NP not bound to the MWCNT was able to enter the bacteria and induce mutagenesis. We found an inverse association between the amount of oxidation by nitric-acid treatment of the MWCNT and the amount of mutagenicity of the reaction mixture. Our data suggest that acid treatment of MWCNT may, in fact, reduce the ability of MWCNT to bind organic pollutants, reducing their effectiveness for remediation / Mestrado / Tecnologia e Inovação / Mestre em Tecnologia

Thesis (M.Sc. (Chemistry)) -- University of Limpopo, 2022 / Heart and Stroke Foundation South Africa (HSFSA) reports that about 17.3% of deaths in the country are associated with heart-related diseases and this rate is expected to increase to 41% by the year 2030. This severe increase in death cases is related to diseases caused by consumption of meat (i.e., pork, fish, red meat, and poultry) with high levels of hypoxanthine. Therefore, this raises the need to investigate and detect hypoxanthine levels in the meat. This study aimed at developing a highly stable and sensitive biosensor for the detection of hypoxanthine in fish meat using the glassy carbon electrode (GCE) modified with carbon nanocomposites materials (consisting of metal oxides doped multi-walled carbon nanotubes (MO-MWCNTs) that are treated with amine groups) and an enzyme, xanthine oxidase (XOD) as a catalyst. The sol gel method was used to prepare the metal oxides including zinc oxide (ZnO), zirconium dioxide (ZrO2), manganese (MnO2), cobalt oxide (Co3O4), and titanium dioxide (TiO2). The in-situ method of functionalisation of MWCNTs was employed to increase their current outputs/sensitivity using selected amines, namely, methylenediamine, hydrazine, ethylenediamine (EDA), and triethylenetetramine (TETA). The electrochemical properties of the metal oxides and amine functionalised MWCNTs were studied using both cyclic and differential pulse voltammetry. Fourier transform infrared spectroscopy (FTIR) confirmed the presence of carboxyl (COOH), hydroxyl (OH), and amino (NH2) groups on the surface of the modified MWCNTs; as well as formation of stretching vibrations which appear at lower wavelengths due to the metallic species within the nanocomposite. Thermal gravimetric analyser (TGA) was employed to determine the thermal stability of the nanocomposite. Scanning electron microscopy (SEM) was used to confirm the composite structure and correct deposition of the metal oxides on the walls of MWCNTs. XRD was used to confirm correct structure formation, the crystallinity, and the purity of the nanocomposite. Optimum conditions of the developed biosensor were determined, and the application of the developed biosensor was undertaken on fish meat bought at the local supermarket using the Cyclic and Differential pulse voltammetric techniques. vi Two highly electrochemical metal oxides among others were TiO2 and Co3O4. The modified MWCNTs containing TETA possess good electrochemical properties with improved sensitivity and selectivity towards hypoxanthine. The presence of metal oxides on MWCNTs and their treatments with amines as confirmed by techniques such as TGA, SEM, XRD, and FTIR have provided a suitable matrix for the immobilisation of the enzyme, namely, xanthine oxidase at 0.5 unit (U). TGA results showed that the unmodified MWCNTs decompose at around 600 0C, but when they are modified with acids and amine decomposition starts at 230 0C, proving that functionalisation of MWCNTs tempers with their thermal stability. Based on the SEM morphological results, attachment of the amines and metal oxides on MWCNTs was seen at x60 000 magnification. Morphology of acid treated MWCNTs appeared thinner, revealing that acids tends to deteriorate the MWCNTs, while the amino treated MWCNTs appeared well modified with less damage on the MWCNTs. XRD confirmed the successful purification of MWCNTs with the intense diffraction peak at 260 that can be assigned to the (002) reflection of graphite. The strong diffraction peak at 250o and a broad peak at 450 indicate that the titania nanoparticles are pure and in the anatase phase. They also show successful deposition of the titanium dioxide onto the surface of the MWCNTs. However, on the formation of cobalt oxide two phases were observed which were CoO, and Co3O4, and on bimetallic nanocomposite (cobalt titanium oxide) also two phases were observed which were CoTiO3, and Co2TiO4. It was found that the sensor performs better at 25 oC at a pH of 7.5 in a phosphate buffer at concentration of 5 mM. The limit of detection of the biosensor was found to be 0.16 nM. The highly electroconductive electrode was XOD/3%Co2TiO4-MWCNTs-TETA/GCE, which was selected for analysis of fish meat. The biosensor has shown low interfering values with high stability, good reusability retaining 73.4% of its initial performance after 50 days of continuous study. The excellent results were obtained on fish meat analysis using cyclic and differential pulse voltammetry revealed that even meat which is deep frozen can also deteriorate as time passes by. Altogether, the findings from this study suggest that the developed biosensor is a reliable analytical tool for the determination of freshness of fish meat using hypoxanthine levels as a marker. / NRF Sasol Inzalo Foundation