Previous attempts to produce carbon nanotube (CNT) ceramic composites have resulted in poorly dispersed, unaligned and non-continuous CNTs in the composites with modest improvements in properties. The research presented in this thesis pertains to the production of dense aluminoborosilicate (ABS) glass matrix composites containing aligned and continuous multi- walled carbon nanotubes (MWCNT) of millimetre lengths. This was achieved by infiltrating CVD grown MWCNT preforms using a precursor sol and sintering which achieved 80 ± 2% dense composites. Focused ion beam milling together with image analysis showed that the composites contained 20 ± 2 vol.% MWCNTs, which are aligned and continuous within the glass matrix. Indentation studies showed greater damage tolerance in the composite compared to unreinforced ABS glass. Under compression, there is no significant change in the compressive strength between the composite and the unreinforced glass. The bend strength of microcantilever beams were 1.4 to 1.3 GPa for the composite and glass respectively. Elastic modulus of 84 GPa and fracture toughness (Kic of up to 2.4 MPa √m were obtained for the composite. The elastic modulus and fracture toughness results are an improvement of 30 % and 240 % over that of unreinforced ABS glass. Fracture surfaces showed apparent MWCNT pullout lengths of up to ~ 1 urn. Analysis indicates that crack bridging by intact MWCNTs provides the majority of the improvement in fracture toughness. Interlayer sliding of the MWCNTs and "sword in' sheath" failure mechanism of the MWCNTs prevented the maximum potential performance, with respect to elastic modulus and fracture toughness, from being achieved. Electrical conductivity in the alignment direction of the CNTs showed improvements by a factor of 106 compared to unreinforced ABS glass. Furthermore, improvement of a factor of ~ 10 in the thermal conductivity was obtained for the composite over that of ABS glass.

Thesis advisor: Goran Krilov / Solubilization and separation is an important step in utilizing both the unique mechanical and electrical properties of carbon nanotubes (CNTs). Due to different possible chiralities of CNTs, which can have drastically different electrochemical properties, it is also necessary to have a method of separation that will distinguish between these different species. Recent discovery of single-stranded DNA (ssDNA) absorption onto CNTs have shown high affinity towards forming soluble hybrids in polar solvents. The interactions between the ssDNA and CNTs as well as the geometry of the hybrid structure are not well understood. In order to study these phenomena we have implemented multiple all-atom replica exchange simulations. Simulations are carried out in an aqueous environment and vary in single-stranded decamer composition as well as nanotube chirality. The oligonucleotides readily adsorb onto the carbon nanotube surface and immediately following begin a slow structural rearrangement. Dependent upon both oligonucleotide composition and nanotube chirality, the ssDNA is found to form several unique backbone geometries as defined by both local and global order parameters. In contrast to the multiple geometries the backbone may form to, the nucleotide bases are found to organize themselves into either parallel or anti-parallel conformation with a high degree of orientational order. Binding appears to be mainly driven by π-stacking interactions between DNA bases onto the carbon nanotube surface, equilibrium of the structures is also controlled by a complex mixture of forces including DNA conformational strain and solvent interactions. The result of this is the free energy landscape is found to have multiple minima occupied at room temperature which are separated by high energy barriers. / Thesis (MS) — Boston College, 2010. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

Abstract Carbon nanotubes (CNTs) were grown catalytically by a chemical vapor deposition method and characterized by a range of techniques. Fe, Ru and Co catalysts supported on the carbon nanotubes were prepared and investigated for their performances in the Fischer-Tropsch synthesis. CNTs were synthesized in a quartz tubular reactor at atmospheric pressure and at temperatures of 700°C over iron supported on CaCO3 using C2H2 as carbon source. Prior to CNT synthesis, the iron catalyst was first reduced under the same conditions (700°C and atmospheric pressure) in a flow of 5% H2 balanced in Argon. The catalyst, for the preparation of the CNTs, was prepared by the incipient wetness impregnation. The purification of the CNTs was performed with 30 wt % HNO3. Characterization of the CNTs using TEM, SEM, HRTEM, BET and TPR revealed that the crude product contained solely CNTs, catalysts particles and support, while no amorphous carbon was observed. The purified product is comprised of an interwoven matrix of tubes that were shown to be multi-walled (MWCNTs). CNT supported FT based catalysts were also prepared by an incipient wetness impregnation method and tested in a plug flow reactor in Fischer-Tropsch synthesis. The TEM images of the different FT catalysts supported on CNTs revealed that the catalyst particles are well dispersed on the surface of the CNTs. The catalyst particles were very iii small, and some residual Fe catalyst material, not removed by the acid treatment, could clearly be seen on the surface of the CNTs. The reduction and metal dispersion properties of the catalysts were investigated through TPR and chemisorption techniques. A TPR study showed three reduction steps for Co catalysts, and addition of Ru to the catalyst decreased the reduction temperature of the catalysts. Gasification of the CNTs was noted to occur at temperatures higher than 600°C. The effect of metal catalyst loading and promoters on the activity and selectivity of CNT supported FT synthesis catalysts was studied under condition of 275°C, 8 bar, CO/H2 = 1/2 and different flow rates. The FT catalysts supported on carbon nanotubes displayed a high CO conversion and excellent stability with time on stream in the Fischer-Tropsch synthesis. Fe catalysts displayed the lowest methane selectivity compared to all other FT synthesis catalysts used in this study.

Nano-reinforced polymeric systems have demonstrated a great deal of interest within academia and industry, due to the intrinsic properties of the graphene nanofillers, having excellent mechanical, thermal and electrical properties. The reinforcement of multiwall carbon nanotubes (MWCNTs) and graphene nanoplatelets (GNPs) were introduced into a low cost, non-carcinogenic, high temperature PMR type polyimide resin. The effects of the interfacial interaction and dispersion quality resulted in improvement in the glass transition temperature (Tg), elastic modulus and thermal stability by, 31°C, 63% and 16°C, respectively. In fine, this study presents a simple but effective high temperature polyimide (HTPI) nanocomposites manufacturing procedure and established that nanoparticle reinforcement can be used to improve both thermal and mechanical properties. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2018. / FAU Electronic Theses and Dissertations Collection

Anodised titanium dioxide (titania, TiO2) nanotubes have been widely studied over the last few years, following the discovery in 1999 of nanoporous TiO2 films prepared via anodisation in aqueous solution containing small quantities of hydrofluoric acid. The synthesis of nanotubular titania by anodisation, a relatively simple and low cost technique, represents a motivation for scientists, considering the impact that such a material could have on a variety of applications, including gas-sensing, biomedical, photocatalysis, and photovoltaics. This research project has focused on the optimisation of the growth process of anodic titania nanotubes, both in an aqueous (NaF/Na2SO4) and an organic (Glycerol/NaF) electrolyte containing fluorine ions. Reproducibility and the ability to generate anodic films having a thickness of several micrometers are fundamental steps to be achieved before investigating any possible application of the nanotubes. To characterise the anodic specimens and build upon the general lack of information on the growth mechanism, a comprehensive study of the different stages of the process has been performed, using Scanning and Transmission Electronic Microscopy (SEM and TEM). Among the questions to be addressed in this thesis, is to establish whether the anodic film undergoes a transition from pores to tubes or develops a tubular morphology from the beginning of its growth. Additional characterisation of the anodisation process includes the study of current-time curves, and chemical composition analysis of the anodic layers using X-ray Photo-Electron Spectroscopy (XPS). The thermal stability of the nanotubes and structural/morphological changes as a result of heat treatment at different temperatures were also studied, again using SEM, TEM, XPS and Raman spectroscopy. The final part of the thesis is dedicated to preliminary work on the use of anodised TiO2 nanotubes in Dye Sensitized Solar Cells (DSSCs), along with suggestions for future works and general conclusions.

"Electrochemistry, based on the study of an electrochemical reaction at the interface between an electrode and an electrolyte, is having a profound effect on the development of different fields of science and engineering including battery, fuel cell, electrochemical sensor, electrochromic display, electrodeposition, electroplating, electrophoresis, corrosion, and so on. The performance of the electrochemical reaction depends strongly on the nature of the employed electrode such as structure, chemical composition, and surface morphology. Nanomaterials, notable for their extremely small feature size (normally in the range of 1-100 nm), exhibit new properties which are different from those of bulk materials due to their small size effect. In past decade, nanomaterials have been widely used to develop new strategies for designing electrode and its surface morphology for electrocatalysis and electrochemical sensing applications. My work is aimed at exploring the application of low dimensional nanomaterials (nanotubes and nanoparticles) in electrocatalysis and electrochemical biosensors. Electrocatalysis plays an important role in energy and industrial applications. As one of the most attractive support materials for electrocatalyst, carbon nanotubes have been extensively reported to enhance the performance of various electrochemical catalytic reactions. In recent years, carbon nanotubes with a bamboo-like structure due to nitrogen doping have become a hot topic of increased interest in the field of electrocatalysis because of the unique bamboo shaped structure associated properties. In this work, bamboo shaped carbon nanotubes, synthesized by chemical vapor deposition method, were investigated for ethanol/methanol electro-oxidation, respectively. Small sized platinum nanoparticles (Pt NPs) were dispersed onto BCNT surface through an impregnation method. The role of nitrogen doping in the formation of bamboo shaped structure and its effect in the electrochemical performance of CNTs were discussed. The electrochemical studies showed that the as-prepared Pt/BCNTs electrocatalysts indeed exhibited a remarkable enhancement in catalytic activity for methanol/ethanol oxidation compared to that of the Pt/commercial CNT electrocatalysts. In order to further investigate the potential of using BCNTs as bioelectrocatalyst support materials, a hybrid organic-inorganic nanocomposite film of BCNTs/ploymer was constructed to immobilize an enzyme horseradish peroxidase (HRP) to examine the direct electrochemical behavior of the enzyme towards electrocatalysis process of H2O2. The results indicated that the immobilized HRP onto the film retains its good bioelectrocatalytic activity to H2O2. The defective sites on the BCNTs surface induced by nitrogen doping could help to promote the direct electron transfer between enzyme and the electrode. The BCNT/polymer film structure provides a vast array of new opportunities to use BCNTs as building units for bioelectrochemical and biomedical applications. Compared to carbon nanotubes, TiO2 nanotubes have much better biocompatibility and show greater potential as implant materials. The advantages of TiO2 nanotube array include high biocompatibility, good corrosion resistance in biological environments and highly ordered one dimensional nanotubular geometry. Herein, a well performing non-enzymatic electrochemical glucose biosensor by using CuO nanoparticle decorated TiO2 nanotube array electrode was developed. Well-aligned TiO2 nanotube arrays were successfully synthesized by electrochemical anodization. Highly uniform CuO nanoparticles were electrodeposited onto TiO2 nanotube arrays through a two-step method and used to electrocatalyze the glucose oxidation. The proposed electrode produced a high sensitivity of 239.9 ìA mM-1 cm-2 and a low detection limit of 0.78 ìM with good stability, reproducibility, selectivity and fast response time, suggesting its potential to be developed as a low-cost nano-biosensor for glucose measurements in human fluids. The final work of this thesis presents a simple sandwich-type electrochemical impedance immunosensor with antitoxin heavy-chain-only VH (VHH) antibodies labeled gold nanoparticles as the amplifying probe for detecting Clostridium difficile toxins. Gold nanoparticles (Au NPs) with diameter of ~13-15 nm were synthesized and characterized by transmission electron microscopy and UV-vis spectra. The electron transfer resistance of the working electrode surface was used as parameter in the measurement of the biosensor. With the increase of the concentration of toxins from 1pg/mL to 100 pg/mL, a linear relationship was observed between the relative electron transfer resistance and toxin concentration. In addition, the detection signal was enhanced due to the amplification effect. This proposed method achieved a limit of detection for TcdA and TcdB as 0.61 pg/mL and 0.60 pg/mL, respectively. The pilot study with spiked clinical stool samples showed promising results, indicating the designed biosensor has a great potential in clinical applications."

The aim of this work is to produce a manufacturing strategy for high current (>10 mA) field emission (FE) devices for military (microwave generation) and civilian (particle accelerator electron beam) applications using carbon nanotubes (CNT) as base material. With a particular focus on the relationship of the laser time pulse duration used for cutting CNTs and how this affects the field emission performance. Material selection for this work was narrowed to CNT as they possess unique characteristics such as: high aspect ratio; high thermal conductivity; high chemical stability and high current carrying capacities up to a theoretical limit of 1,200 MA∙cm-1 making them an ideal material for FE. The CNT material studied in this work is produced in two distinct forms, fibres (∅~7-10 μm) and films (h~30 μm), using a floating catalyst chemical vapour deposition process which produces high quantities of CNT material with mixed mechanical and electrical properties. The material is difficult to handle because of its dimensions and is susceptible to environmental changes i.e. electrostatic forces. In order to reduce the variability in electrical properties, a laser purification process was developed. The process consists of locally irradiating an infra-red (IR) laser several microseconds directly at the material. A percentage is vaporised (mainly non-conductive or defective material) and the remaining CNT material shows very high crystallinity with an increase of up to ten times (G/D ratio > 100) compared to the original material and electron mean free path is increased by an order of magnitude. The production strategy is based on directly coating the CNT material with copper using an electroplating process. This allowed for CNT fibre and film to be easily handled and improved the overall electrical contact. Emitter geometry was customised by a laser cutting process to achieve increased enhancement factor geometries, in this case, triangles with 29 tips whilst reducing FE variability. FE performance was quantified by testing the devices in a continuous DC mode with a sweep up to 1,000 V until the material suffered catastrophic failure. The gap distance between the tip of the triangles and the anode was varied to increase the electric field until failure. FE results using the production strategy improved more than 400% compared to untreated material. Applications for these devices are intended to be in the creation of high energy electron beam lines and generation of high powered directed microwaves.

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