M.Tech. / Among the materials being used for gas sensors, metal oxides are the most important materials because of their potential to detect many gases at low concentrations. Nevertheless, sensors made of metal oxide need to be operated at high temperatures (above 200°C) and have a weak sel ectivity. In order to overcome this difficulty, the materials are being investigated for gas sensing applications. Carbon nanotubes (CNTs) are promising materials with unique properties, such as high electrical conductivity, mechanical strength, nanometer–scale sizes, and high aspect ratio. Their adsorption ability and high surface area make them attractive as gas sensing materials, which have been intensively studied. CNTs can be used solely or combined with metals and oxides materials in order to constitute efficient gas sensors. In the present research, multi–walled CNTs (MWCNTs) were coated with tin dioxide (SnO2) and incorporated into two epoxy resins with widely different mechanical properties in order to study the effect of CNTs on the morphology, mechanical, electrical, and sensing properties of the composites. In the MWCNT/polymer composite study, Epon 828 was used as the polymer matrix and D–2000 (which gives rubbery composites) and T–403 (which gives glassy composites) as the hardeners. Composite were prepared with 0.1 wt.% MWCNTs in an epoxy matrix. Pristine MWCNTs (MWCNTs not treated with any acid and therefore used as received) and SnO2–MWCNTs were used for comparison and a two–step curing procedure was used with initial temperature set at 75°C for 3 hours, followed by additional 3 hours at 125°C. The sample s were characterized for morphology, mechanical, thermo–mechanical and electrical properties using scanning electron microscopy (SEM), an Instron tensile tester, dynamic mechanical analysis (DMA) and Cascade Microtech four–point probe, respectively. In both cases, strong covalent bonds were created as a bridge between the CNTs and matrix, but due to differences in viscosity, the nanotubes dispersion was much better in the rubbery epoxy resin than in the glassy epoxy resin. A 77% increase in tensile modulus was observed in the rubbery system using 0.1 wt.% SnO2–MWCNTs compared to the neat rubbery epoxy. As for the glassy epoxy based composite, only a 3% improvement in tensile modulus could be observed. In addition to the mechanical properties, the presence of CNTs has demonstrated a material with high vi electrical conductivity. But for the surface measurements during the gas sensing analysis, the conductivity was very low for the composites to be used for this application as envisioned. MWCNTs coated with SnO2 nanoparticles used in the present study, were synthesized by a microwave synthesis method. The composite samples were characterized by X–ray diffraction (XRD), Raman spectroscopy, high resolution transmission electron microscopy (HRTEM), scanning electron microscopy, Fourier transform infrared spectroscopy (FTIR) and Brunauer–Emmet–Teller (BET) surface area analysis. These techniques gave evidence for surface and chemical modifications of the synthesized composites. The results showed microwave synthesis to be a very efficient method in producing CNTs that are densely coated and well dispersed with SnO2 nanoparticles in a very short time (total reaction time of 10 minutes). Microwave synthesis is particularly interesting because of the energy used, the higher temperature homogeneity and the shorter reaction times led to nanoparticles with high crystallinity and a narrow particle size distribution. Controlling the morphology by varying synthesis conditions such as temperature, pressure and time is also possible.

Thesis advisor: Lawrence T. Scott / The distinctive molecular structure of carbon nanotubes makes them desirable for electronic and chemical materials; however, current production methods are limited with respect to purity and chirality. Geodesic polyarenes serve as superb templates for the bottom up synthesis of carbon nanotube end-caps, setting the chirality and dimensions of the carbon nanotubes. The work herein describes the synthetic efforts towards the rational synthesis of a [6,6] carbon nanotube end-cap. Chapter 1 describes the efforts towards the synthesis of a C60H12 end-cap, in which the synthesis of an advanced intermediate, peri-bis(dibenzo[a,g]corannulene) is complete; however, the insolubility of this material proved to be problematic in a subsequent cycloaddition reaction. This reaction is examined computationally in order to understand the failure of the addition of dienophile, maleic anhydride, to peri-bis(dibenzo[a,g]corannulene). In Chapters 2 and 3, the development of solubility-enhancing methods is described. The development of a solubility-enhancing dienophile is successfully employed to induce the solubility of a formerly insoluble diene, peri-bis(dibenzo[a,g]corannulene), through Diels-Alder addition. Another method, employs the incorporation of tert-butyl groups onto peri-bis(dibenzo[a,g]corannulene) to successfully induce solubility. The enhanced-solubility enables the successful Diels-Alder addition of simple maleimide dienophiles, installing all necessary carbon atoms for the desired end-cap. Pyrolysis of the bis-anhydride derived from the aromatized bis-maleimide adduct afforded the C60H12 end-cap, which is the second carbon nanotube end-cap ever synthesized and the first of these dimensions. Chapter 3 also explores a palladium catalyzed intramolecular arylation reaction to form a pivotal intermediate in the synthesis of the end-cap, dibenzo[a,g]corannulene. The mechanism for the formation of a problematic byproduct resulting from reductive dehalogenation is discussed. Utilizing a deuterium labeled solvent, it is found that deuterium is incorporated onto the hydrocarbon, indicating that the solvent (N,N-dimethylformamide-d7) is the source of hydrogen for the reductive dehalogenation. These conditions are further exploited in Chapter 4 for the convenient perdeuteration of a variety of polycyclic aromatic hydrocarbons. Chapter 5 describes the first synthesis of a nitrogen containing geodesic polyarene, dibenzo[g,m]azacorannulene. This synthesis is completed in seven steps from a commercially available source in a 28% overall yield. / Thesis (PhD) — Boston College, 2012. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

Thesis advisor: Lawrence T. Scott / Curved carbon-rich materials such as carbon nanotubes and carbon nanocones have unique mechanical strength, charge carrying ability and structure. Efficient syntheses to access these strained structures are required to obtain usable quantities of these materials in order to exploit their unique properties. This dissertation describes the recent efforts toward gaining access to these interesting structures using corannulene as the foundation for the curvature. Chapter 2 offers a microwave assisted tandem Suzuki-Heck-type coupling of <italic>peri</italic>-dichloroacenaphthene with various aryl boronic acids. This allows for the formation of strained unsaturated five-membered rings in a single transformation. The extension of this methodology to <italic>peri</italic>-chloroacenaphthylboronic acids and aryl halides was also investigated. Chapter 3 discusses efforts toward the total synthesis of a [10,10] carbon nanotube end-cap. The key step was optimized on bicorannulenyl and applied to 1,3,5,7,9-pentacorannulenylcorannulene. Preliminary Diels-Alder reactions have been successful with di-cyclopenta[<italic>def</italic>]phenanthro[3,3a,4,4a,5,6-<italic>cdefg</italic>;3',3a',4',4a',5',6'-<italic>nopqr</italic>]pentacene, suggesting that the C₁₂₀H₂₀ end-cap should also be reactive under similar conditions. Chapter 4 presents progress toward the total synthesis of a carbon nanocone with a single five-membered ring. The acid-catalyzed oxidative cyclization seems to effect a 1,2-aryl shift, preventing the desired six-membered ring cyclodehydrogenation. To render this rearrangement degenerate and thus irrelevant, 9-phenanthrylcorannulene was utilized to replace the problematic 1-naphthylcorannulene. Chapter 5 describes the collaboration between the Shenhar laboratory at The Hebrew University of Jerusalem and the Scott laboratory to form supramolecular polymers using corannulene derivatives. It had been shown that corannulene tetraanion can dimerize with lithium cations, so the limitations were probed with the following larger corannulene networks: <italic>p</italic>-dicorannulenylbenzene, 1,3,5-tricorannulenylbenzene and 1,3,5,7,9-pentacorannulenylcorannulene. / Thesis (PhD) — Boston College, 2011. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

This thesis deals with the analytical study of vibration of carbon nanotubes and graphene plates. First, a brief overview of the traditional Bresse-Timoshenko models for thick beams and Uflyand-Mindlin models for thick plates will be conducted. It has been shown in the literature that the conventionally utilized mechanical models overcorrect the shear effect and that of rotary inertia. To improve the situation, two alternative versions of theories of beams and plates are proposed. The first one is derived through the use of equilibrium equations and leads to a truncated governing differential equation in displacement. It is shown, by considering a power series expansion of the displacement, that this is asymptotically consistent at the second order. The second theory is based on slope inertia and results in the truncated equation with an additional sixth order derivative term. Then, these theories will be extended in order to take into account some scale effects such as interatomic interactions that cannot be neglected for nanomaterials. Thus, different approaches will be considered: phenomenological, asymptotic and continualized. The basic principle of continualized models is to build continuous equations starting from discrete equations and by using Taylor series expansions or Padé approximants. For each of the different models derived in this study, the natural frequencies will be determined, analytically when the closed-form solution is available, numerically when the solution is given through a characteristic equation. The objective of this work is to compare the models and to establish the eventual superiority of a model on others. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2018. / FAU Electronic Theses and Dissertations Collection

Multiwall carbon nanotubes filled with continuous single-crystals of the ferromagnetic phase -Fe were produced with two new synthesis methods: the boundary layer chemical vapour synthesis and the perturbed vapour chemical vapour deposition. In the first method, the nanotubes nucleate and grow radially from a central agglomeration of homogeneously nucleated spherical particles in a randomly fluctuating vapour created in the viscous boundary layer between a rough surface and a laminar pyrolyzed-ferrocene/Ar vapour flow. In the second method, the nanotubes nucleate and form in a flower-like arrangement departing from homogeneously nucleated particles. These particles are produced by the creation of a local perturbation in a vapour with a high density of Fe and C species obtained from the pyrolysis of ferrocene in a laminar Ar flow. Electron microscopy investigations revealed that the continuous single crystals obtained with both methods exhibit diameters much lower than the critical diameter for a single magnetic domain of -Fe (~ 66 nm). In the radial structures, the single-crystal diameter is in the range of ~ 17-37 nm, while in the flower-like structures the single crystals show mainly a diameter of ~ 30 nm and ~ 55 nm. The average single crystals length is 7-8 m in the case of the radial structures and 19-21 m in the case of the flower-like structures. DC magnetization measurements at 5 K show different magnetic behaviours. The flower-like structures present a very high saturation magnetization of 189.5 emu/g and a high coercivity of 580 Oe. The radial structures exhibit an exchange-coupled ferromagnetic/antiferromagnetic system despite only 2% of -Fe is present inside the nanotubes. The radial structures obtained at flow-rates of 3.5 ccm and 20 ccm, show saturation-magnetizations of 31emu/g and 13 emu/g, and coercivities of 790 Oe and 843 Oe respectively.

Biomedical research has shown that one-dimensional nanostructures present many potential advantages as delivery vehicles for drugs and biologics. These elongated structures have high aspect ratios that enable increased drug loading capacities and have been shown to have longer in vivo circulation times than other spherical nanoparticles. The increasing interest in these one-dimensional structures has necessitated the developments of fabrication methods for the precise control of the final morphology. A simple, cost effective means of producing nanotubes and nanorods is known as solution template wetting. While this technique has been used to fabricate many different types of elongated nanostructures, the parameters governing the final morphology remain ambiguous. The objectives of this research are to investigate these critical parameters, and furthermore to develop an understanding of the physical mechanism of nanostructure formation. The effects of the infiltration technique, dipping time, polymer molecular weight and template pore size on the morphology of the resulting nanostructure have been evaluated. Key results have established that the infiltration technique is a critical parameter that can enable the formation of stable nanotubes at very low polymer concentrations. Additionally, a tube to rod transition occurs as the infiltration time is increased over 18 hr. An investigation of the rheological properties of high and low molecular weight solutions also indicates that the capillary flow and infiltration of polymer occurs differently. Finally, the pore size was also shown to affect the ability to form hollow, stable structures, and that relatively large pore sizes are necessary for nanotube formation. The culmination of these results is an understanding of the physical layering mechanism of structure formation, and the tube to rod transition can thus be predicted by researchers investigating the use of elongated nanostructures for biomedical applications.

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Carbon based materials such as CNTs and graphene have been widely studied over the last few years. The outstanding electrical and mechanical properties of these materials attracted researchers to find ways to grow and use them in nano-devices. Among the different techniques, PECVD is a relatively simple and low temperature process. It facilitates the growth of CNTs and graphene on particular sites of the substrate. The objective of this research project was to study the growth of CNTs and graphene using PECVD system and to employ them in renewable energy devices. Excimer laser processed materials were also the focus for flexible material for fuel cells and other applications to show the way to a one step manufacturing process that lends itself to large area and low cost processing using standard tools.In the growth of CNTs, the roll of a buffer layer and catalyst materials were studied in depth. Different metals were tested for best results in optimising nanotube growth for the selected applications. The role of the buffer layer in the formation of nanoparticles and their surface adhesion was studied. Different materials were used as a catalyst and analysed for best performance in the PECVD system. Growth parameters such as temperature, pressure, gas flow rate and plasma power were studied during the growth of CNTs in the PECVD system. The growth of graphene has been conducted in two ways: firstly, by the traditional mechanical exfoliation technique (with the help of Manchester University) and second by PECVD techniques.Polymer materials are promising flexible substrates for electronic and energy devices. An excimer laser was used to transform thin metallic films into nanoparticles which could play the role of the catalyst in proton exchange membrane fuel cells. In this study experiments have been conducted into a single step process to convert the poly ethylene naphthalate (PEN) surface to a robust mesoporous carbon material that conducts electrons, whilst depositing the catalyst. Such a technique has been developed for the first time in this work. Laser modification here produced a conical carbon structure and dense arrays of well defined catalysts.A prototype fuel cell was designed and crafted to employ the laser processed PEN as a proton exchange membrane. Some experiments were conducted regarding the transport of protons through laser processed PEN and the conventionally used fuel cell electrolyte, Nafion. It has been observed that the hydrophilic property of Nafion allowed proton transport across this material. It was also observed that PEN is not a good membrane for protonic transport. This material does not have free sites for vehicle transport. The catalytic activity of laser ablated Ni nanoparticles on PEN substrate was studied in temperature programme reaction (TPR) and it was observed that the metallic nanoparticles had some activity at higher temperature. Both Ni and Pt nanoparticles were tested as catalysts on the standard Nafion electrolyte. It was observed that Pt is active for the hydrogen combustion reaction and Ni has less activity for this purpose.It was not expected in this work that efficient hydrogen transport through the polymer would occur, but that future modification of the internal chemistry of PEN can be developed.

The aim of this project was to investigate methods for purification and modification of Single Wall and Multi Wall Carbon Nanotubes. Covalent and noncovalent approaches to functionalization were studied. The dispersibility, structure and electronic properties of modified tubes were characterized by Raman, UV-vis-NIR and XPS. Fluorescence, NMR and TEM were further employed to characterize the interaction between nanotubes and non-covalent modifiers. The effects of five different purification methods on the dispersibility, and degree of carboxylic acid functionality of SWCNTs, along with the level of defects on the tube side walls, and the resulting electronic properties of SWCNTs have been investigated. It was found that all oxidation treatments successfully removed metallic oxides and amorphous carbon impurities, while different oxidation treatments introduced different levels of oxidized sites on the SWCNTs. Heat treatment after oxidation eliminated some of the carboxylic groups introduced by oxidation. SWCNTs covalently functionalized by aromatic diazonium salts containing nitro, carboxylate and fluoro groups on the aromatic ring were prepared. Heating of these tubes in vacuum at 350_C for 5 h partially reversed the effects of functionalization. However, due to the low degree of functionalization achieved in the preliminary studies, the dispersibility/solubility of functionalized tubes did not greatly improve. The interaction in stable suspensions of CNTs with positively or negatively charged pyrene derivatives via noncovalent functionalization, was extensively studied. 1-pyrene methylamine hydrochloride gave most stable dispersions. 1H and 2H NMR spectroscopy of MWCNTs/1-pyrene methylamine hydrochloride dispersion in DMF-d7 showed that the broadened signals are associated with weakly or unbound pyrene, while strongly bound pyrene is not observable in solution-state NMR. The strong pyrene attachment on MWCNTs by π-π stacking can be reversed by dialysis and/or extensive washing. Biological molecules such as polypeptides and amino acids also dispersed MWCNTs into solvents by noncovalent modification. It is found that polytryptophan demonstrated the greatest ability to disperse MWCNTs. Digestion with chymotrypsin enabled polytryptophan binding to be reversed. A combination of tube cutting and non-covalent functionalization by pyrenes or peptides enables tubes to be suspended/dissolved in solvents such as DMF and ethanol, and significantly allows tubes to be manipulated for practical device applications.