Dissertations / Theses on the topic 'Nanotubes – Synthesis'

This thesis focuses on two of the major challenges of carbon nanotube (CNT) research: understanding the growth mechanism of nanotubes by chemical vapour deposition (CVD) and the positioning of nanotubes on surfaces. The mechanism of growth of single–walled nanotubes (SWNTs) has been studied in two ways. Firstly, a novel iron nanoparticle catalyst for the production of single–walled nanotubes was developed. CVD conditions were established that produced high quality tubes. These optimised CVD conditions were then used as the basis of several comparative CVD experiments showing that the quality of nanotubes and the yield of carbon depended on the availability of carbon to react. The availability could be controlled by the varying concentration of methane in the gas phase or the residence time of the methane over the catalyst. Evidence is presented that the diameters of the tubes produced were affected by the availability of methane. A second mechanistic investigation was carried out to study the validity of the previously proposed ring addition mechanism for the growth of carbon nanotubes from camphor. In this mechanism, the formation of tubes is thought to occur through the addition of preformed carbon rings: so it would be expected that there would be a relationship between the molecular structure of the precursor and the resulting SWNTs. To explore this relationship, comparative CVDs were carried out to produce SWNTs with several different cyclic and acyclic compounds similar in structure to camphor. The vapour pressure and the chemical stability of the precursor were found to be important to the formation of nanotubes, while the compound’s structure was not related to the quality of tubes produced. The lack of a relationship between the structure of the precursor and the production of SWNTs suggests that preformed rings are not vital to the production of SWNTs. Differences in the growth of SWNT from benzene and methane were related to the stability of each compound. In particular, differences in the distributions of the diameters of the tubes formed from methane and benzene have been observed. These differences have been explained in terms of the relative kinetic stabilities of these molecules, and in terms of a competition between end–cap and sidewall growth. Positioning of nanotubes on surfaces has been explored using two approaches. In the first approach, commercially obtained SWNTs were functionalized by a sulfur plasma so that the products would form bonds with gold surfaces. The nanotubes were found to selectively deposit themselves onto gold surfaces from ethanolic dispersions of the functionalized samples. This selective deposition of the nanotubes allowed the production of prototype carbon nanotube field–effect transistors with higher device yields than were obtained with unfunctionalized tubes. In a second approach to positioning of carbon nanotubes, the growth of tubes on surfaces by CVD was explored. Iron nitrate and different magnesium compounds were dip–coated onto SiO2 surfaces so that MgO supported–Fe catalysts would be formed by calcination. SWNTs were grown on the surfaces by CVD. Surface area measurements of the equivalent powdered catalysts showed that a high surface area was vital to produce dense growth of high quality SWNTs. The morphology of the surface was also found to play a key role in the growth of the tubes. Patterned growth of carbon nanotubes was accomplished using soft lithography techniques to control the localization of catalyst deposition onto a surface. A long calcination step (10 h, 950 °C) before CVD, was found to improve the quality of nanotubes grown. Catalysts that had been calcined for 10 hours were also found to produce smaller diameter nanotubes than uncalcined samples. The formation of smaller diameter tubes was explained in terms of the formation of MgFe2O4 alloys, consistent with results reported previously in the literature. In addition, Raman spectroscopy of the calcined catalysts with 3% w/w loadings of Fe was used to confirm directly the presence of MgFe2O4.

The use of single-walled carbon nanotubes (SWNTs) as test tubes for the encapsulation of metallic nanoparticles (MNPs) and the formation of inorganic nanomaterials has been advanced. A methodology to encapsulate the group 10 and 11 metals inside SWNTs to investigate their properties has been optimised. Each metal interacts with carbon differently at the atomic level, as shown by aberration-corrected high resolution transmission electron microscopy (AC-HRTEM), leading to the promotion of a plethora of different processes stimulated by MNPs under the electron beam. Additionally, interactions between SWNTs and small clusters of the group 10 metals have been examined, revealing marked differences between metal-carbon bonding for each metal. This has allowed for a useful insight into metal-carbon interactions on the atomic level which could have profound implications on the future development of new catalysts or nanoscale devices. Following on from this, a series of chemical reactions with platinum compounds were carried out within SWNTs which have shown SWNTs to be both a very effective reaction vessel and template for the formation of low-dimensional PtX2 (X = I, S) nanocrystals, materials that are difficult to create by traditional synthetic methods. The stepwise synthesis within SWNTs has enabled the formation of the platinum compounds to be monitored at each reaction stage by AC-HRTEM, verifying the atomic structures of the products and intermediates, and also by an innovative combination of fluorescence-detected X-ray absorption spectroscopy (FD-XAS) and Raman spectroscopy, monitoring the oxidation states of the platinum guest compounds within the nanotube and the vibrational properties of the host SWNT respectively. The stepwise synthesis has appeared to offer only limited preparative potential because of the lack of stoichiometric control in the resultant inorganic nanomaterials. A new approach for nanoscale synthesis in nanotubes developed in this study utilises the versatile coordination chemistry of platinum which has enabled the insertion of the required chemical elements (e.g. metal, and halogens or chalcogens) into the nanoreactor in the correct proportions for the controlled formation of PtI¬2 and PtS2 with the exact stoichiometry and structure. FD-XAS has also been used to probe the transformations of Pt(acac)2@SWNT to Pt@SWNT, and Cu(acac)2@SWNT to Cu2Ox@SWNT (where x > 1). It was shown that the temperature of both transformations was significantly lower than required for the same reactions in the bulk, which demonstrates the ability of SWNTs to lower the activation energy by polarising encapsulated molecules. Finally, a variety of novel MNPs and MO¬x¬ (M = Pt, Pd, Ni) materials were encapsulated within hollow graphitised carbon nanofibres (GNFs) and evaluated for the sensing of glucose. MOx@GNFs were revealed to be more active sensors than their corresponding MNPs which can be attributed to the increase in Lewis acidity of the metal centres upon oxide formation. Furthermore, the effectiveness of each metal and their corresponding oxides for glucose detection was found to increase in the order Pt > Pd > Ni which can be attributed to both physical and chemical properties of the respective metals. Overall, this thesis demonstrates that nanotubes can be used effectively to not only investigate chemical transformations on the atomic level, but also act as nano-sized test tubes and templates for the formation of novel, low-dimensional inorganic materials with bespoke structure and composition.

Thesis (Ph. D.)--Mechanical Engineering, Georgia Institute of Technology, 2005.
Z.L. Wang, Committee Member ; Thomas Starr, Committee Member ; Mostafa Ghiaasiaan, Committee Member ; W. Jack Lackey, Committee Chair; Shreyes Melkote, Committee Member. Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of California, San Diego, 2009.
Title from first page of PDF file (viewed May 4, 2009). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 329-375).

Porphyrins, with their planar aromatic cores, are suitable and versatile building blocks to form functional nanostructures. This thesis describes the synthesis and properties of atomically precise porphyrin nanostructures with a specific focus on porphyrin nanotubes.

Carbon nanofibers (CNFs) and carbon nanotubes (CNTs) have attracted intense research efforts with the expectation that these materials may have many unique properties and potential applications. The most promising way for large-scale synthesis of CNFs and CNTs is chemical vapor deposition (CVD).

CNFs were synthesized on a series of hydrotalcite (HT) derived 77 wt.% Ni-Fe/Al₂O₃ catalysts in order to achieve the optimization of productivity and quality. It was found that only the Fe catalyst was active in CO disproportionation and only the Ni catalyst was active in ethylene decomposition, whereas all catalysts were active in ethylene decomposition when the reactants were a mixture of C₂H₄/CO. More control over the structure and diameter of the CNFs has been realized with the HT catalysts. At the same time, a high yield can be obtained. The synthesis process has been further studied as a function of various process parameters. It turned out that high hydrogen concentration, space velocity, and reaction temperature would enhance the production of CNFs. However, a slightly lower quality was associated with the higher productivity. The optimum CNF yield of 128 gCNF/gcat could be reached within 8 h on the HT catalyst with a Ni/Fe ratio of 6:1. Therefore, HT derived catalysts present a new promising route to large-scale controlled synthesis of CNFs.

CNTs has been synthesized from CO disproportionation on Ni-Fe/Al₂O₃ supported catalysts with metal loadings of 20 and 40 wt.%. A high space velocity resulted in a high production rate but a short lifetime and a low carbon capacity. Increasing the metal loading to 40 wt.% significantly increased the reaction rate and productivity, and produced similarly uniform CNTs. Furthermore, H₂ was found to be necessary for a high productivity, and the H₂ partial pressure could be changed to adjust the orientation angle of the graphite sheets.

The effects of catalyst particle size and catalyst support on the CNT growth rate during CO disproportionation were studied over SiO₂ and Al₂O₃ supported Fe catalysts with varying particle sizes. It was found that there was an optimum particle size at around 13-15 nm for the maximum growth rate, and the growth rate was influenced both by the particle size and the support but the particle size was the dominating factor. The trends have been demonstrated at two different synthesis temperatures of 600 and 650°C. The effect of gas precursors on the yield and structure of carbon growth has been systematically investigated over powder Fe and Fe/Al₂O₃ catalysts. CO/H₂, CO, CH₄, and C₂H₆/H₂ were the gas precursors studied. The carbon yield was higher on powder Fe from CO, but the yield was higher on Fe/Al₂O₃ from hydrocarbons. Completely different or similar carbon nanostructures were synthesized, depending on the gas precursors. It was suggested that the reactivity of gas precursors and the structures of carbon deposits are determined by the size and crystallographic faces of the catalyst particles, which are dictated by the interactions among metal particles, support, and the reactants. Controlled synthesis of CNT, platelet nanofiber, fishbone-tubular nanofiber, and onion-like carbon with high selectivity and yield was realized. A mechanism was proposed to illustrate the growth of different carbon nanostructures.

The aim of this research was to investigate the role of chemical functionalization on carbon nanotubes surfaces and its effect on FT catalysis. Multi walled carbon nanotubes (MWNT) were first treated with acid (HCl) to remove the residual metal particles and were then functionalized using H2O2 and HNO3 to introduce oxygen-containing groups to the MWNT surface. These treatments also add defects on MWNT surface. Morphological analyses were performed on the MWNT samples with TEM and it was found that the peroxide and acid treated MWNTs showed an increase oxygen functional groups and created additional surface defects on the MWNTs. Results of FT experiments showed enhanced CO conversion, FT activity and product selectivity towards liquid hydrocarbons due to functionalization. The liquid selectivity was found to be significantly high for H2O2 treated catalyst. HNO3 treated catalyst had highest activity although selectivity to methane and CO2 was found higher than the H2O2 treated catalyst. It was observed that the chemical treatments increase the carbon chain length of the produced hydrocarbons. While comparing hydrocarbon distribution of as-produced and H2O2 treated MWNT, it was found that carbon-chain length increases for peroxide treated catalyst. Along with as-produced and functionalized nanotube, FT experiments were also conducted using B-doped sponge, un-doped sponge and N-doped CNT catalyst. B-doped sponge showed enhanced CO conversion and FT activity as compared to un-doped sponge. Conversion and product selectivity were found to be affected by temperature when test was conducted with N-CNT. Operating conditions like temperature, syngas feed flow rate and syngas ratio were also to impact the FT performance.

Modern day engineering systems research presently lacks techniques to exploit the unique properties of many nanomaterials; coupled with this challenge exists the need to interface these nanomaterials with microscale and macroscale platforms. A nanomaterial of particular interest is the carbon nanotube (CNT), due to its enhanced physical properties. In addition to varied electrical properties, the CNT has demonstrated high thermal conductivity and tensile strength compared to conventional fiber materials. CNTs are beginning to see commercial applications in areas in which sufficient study has been dedicated. While a large part of the worldwide focus of CNT research has been in synthesis, an equally important area of research lies in CNT integration processes. The unique and useful properties of many nanostructured materials will never be realized in mainstream manufacturing processes and commercial applications without the proper exploration of integration methods such as those detailed in this thesis. The primary motivation for the research detailed in this thesis has been to develop CNT synthesis processing techniques that allow for novel interfacing methods between carbon nanotubes and eventual applications. In this study, an investigation was performed to look at several approaches to integrating CNTs into micro-electromechanical systems (MEMS). Synthesis of CNTs was studied in two different settings. Synthesis was first performed, directly on the microsystem, via a global scale chemical vapor deposition (CVD) process. Secondly, synthesis was performed directly onto a microsystem device via localized resistive heating. Following synthesis, the application of atomically layered, protective coatings was then investigated. Integration methods were then investigated to allow for CNT transfer to microsystem applications incapable of withstanding synthesis temperatures. The developed integration methods were evaluated by creating functional microscale electrical circuits in flexible substrates via hot emboss imprint lithography. Lastly, post synthesis processing methods were used to create micropatterned cell guidance substrates as well as neuronal stimulating substrates.

Since their discovery single-walled carbon nanotubes (SWNTs) have gained the interest of many scientists and engineers due to their prominent structural, mechanical and electronic properties which make them applicable in various areas including electronics, chemical and biological sensing and reinforced composite materials. Although SWNTs have many application areas their use can be limited since they are synthesised as a mixture of metallic and semiconducting species with different diameters and helicities and they have limited solubility in aqueous and non-aqueous solvents. Covalent modification of SWNTs is an important tool to introduce new functional groups onto the surface of nanotubes to improve their solubility and processability. It can also be used to separate metallic from semiconducting nanotubes. The work presented here has concentrated on the non-disruptive covalent modification of SWNTs using pyridine diazonium salt addition, 1,3-dipolar cycloaddition and reductive alkylation. The selectivitiy of the addition was probed by UV-vis-NIR and Raman spectroscopy where the metallic were found to be more selective than semiconducting SWNTs. The location and distribution of the functional groups was determined by AFM using electrostatic interactions with gold nanoparticles. Rheological data showed that the pyridine modified SWNTs were able to act as crosslinkers and hydrogen bond to poly(acrylic acid) to form SWNT hydrogels. The indolizine modified SWNTs, emitted blue light when excited ca. 330 nm, were capable of sensing 4-nitrophenol, 3-nitrophenol, 2-nitrophenol, 2-nitrosotoluene and 2,4-dinitrotoluene with a detection limit of ca. 10-8 M. The modified SWNTs were further characterised using FTIR, XPS, TGA-MS and optical microscopy.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2003.
Includes bibliographical references.
Carbon nanotubes are a remarkable material with many appealing properties. Despite the appeal of this material, there are few synthesis techniques capable of producing nanotubes in large quantities at low-cost. The broad objective of this study was to examine the potential of a premixed flame for the synthesis of carbon nanotubes with the view that flame synthesis may prove a means of continuous production at low-cost. The specific approach focused on the formation of metallic nanoparticles in flames; identification of nanotube formation zones, time scales, and transition conditions; characterization of material properties; and the development of a formation mechanism and associated flame-model. Carbon nanotube formation requires a source of carbon, a source of heat and the presence of metal particles. A fuel-rich flame is a high-temperature, carbon-rich environment and addition of metal is likely to give conditions suitable for nanotube growth. This study considered a premixed acetylene/oxygen/15 mol% argon flame doped with iron pentacarbonyl (Fe(CO)₅) vapor (typically 6100 ppm), operated at 50 Torr pressure and 30 cm/s cold gas feed velocity. The flame was investigated with regard to the growth of metal particles and subsequent formation and growth of carbon nanotubes. Thermophoretic samples were extracted from the flame at various heights above burner (HAB) and analyzed using transmission electron microscopy (TEM). HAB is representative of residence time in the flame. Size distribution and number density data were extracted from TEM images using a quantitative image analysis technique. The mean particle size for a precursor concentration of 6100 ppm was observed to increase from around 2 to 4 nm between 20 and 75 mm HAB.
(cont.) The particle number density results showed a decreasing number density with increasing HAB, giving a complementary picture of the particle dynamics in the flame. Single-walled carbon nanotubes (SWNT) were also observed to form in the premixed flame. Thermophoretic sampling and TEM analysis gave insight into nanotube formation dynamics. Nanotube structures were observed to form as early as 30 mm HAB (20 ms) with growth proceeding rapidly within the next 10 to 20 mm HAB. The growth-rate for the nanotubes in this interval is estimated to be between 10 and 100 ptm per second. The upper region of the flame (50 to 70 mm HAB; 35 to 53 ms) is dominated by tangled web structures formed via the coalescence of individual nanotubes formed earlier in the flame. The nanotube structures are exclusively single-walled with no multi-walled nanotubes observed in any of the flame samples. The effect of carbon availability on nanotube formation was tested by collecting samples over a range of fuel equivalence ratios at fixed HAB. The morphology of the collected material revealed a nanotube formation 'window' of 1.5 < < 1.9, with lower dominated by discrete particles and higher favoring soot-like structures. These results were also verified using Raman spectroscopy. A clear trend of improved nanotube quality (number and length of nanotubes) is observed at lower . More filaments were observed with increasing concentration, however the length (and quality) of the nanotubes appeared higher at lower concentrations ...
by Murray John Height.
Ph.D.

The aim of this research is to investigate the role of chemical functionalization on carbon nanotubes and its effect on the FT synthesis. Multi walled carbon nanotubes (MWNT) bought from the market were functionalized using HNO3 to introduce oxygen-containing groups to the MWNT surface. This treatment also adds defects on MWNT surface. Carboxyl functionalized multiwall carbon nanotubes (-COOH) and hydroxyl functionalized multiwall carbon nanotubes (-OH) were also bought from the market and used in the experiments, Results of FT experiments showed very high CO conversion. Fischer Tropsch activity and product selectivity were towards liquid hydrocarbons due to functionalization. Highly desired product distribution were obtained due to chemical functionalization of CNTs. The performance of all the functionalized Multi wall nanotubes was better than the pure Multi wall nanotubes. Operating conditions like temperature, syngas feed flow rate and syngas ratio were also to impact the FT performance.

Depuis la découverte des nanotubes de carbone (CNT) en 1991, beaucoup d'efforts ont été faits afin de connaître leurs propriétés intrinsèques et les applications possibles. Une des méthodes les plus efficaces, utilisée pour modifier ses propriétés physiques et chimiques, est le dopage de CNT à l'azote ou le bore. L’objectif de ce travail est de réaliser la synthèse de nanotubes de carbone dopés à l’azote (N-CNT) et d'étudier les performances catalytiques de ce matériau soit en tant que support de catalyseur soit directement comme catalyseur. L'influence des différents paramètres de synthèse sur les propriétés des N-CNT a été étudiée. Par la suite, les N-CNT ont été utilisés comme support de catalyseur pour l'hydrogénation du cinnamaldéhyde et leurs performances catalytiques ont été comparées à celles des CNT non-dopés. Il a été montré que les N-CNT synthétisés dans des conditions différentes présentent différentes performances catalytiques. Les N-CNT ont également été utilisés en tant que catalyseur pour l'oxydation sélective de l'H2S en soufre élémentaire et les résultats sont discutés dans cette thèse. Enfin, les études réalisées avec les nanotubes de carbone ont été transposées sur un matériau nouveau et prometteur qu’est le graphène et/ou graphène multi-couche. Nous avons dans un premier temps synthétisé ce matériau à partir de graphite expansé en utilisant les irradiations micro-ondes, puis une étude préliminaire a également été faite sur le dopage à l’azote de ce matériau par un traitement aux micro-ondes du graphite expansé dispersé dans de l'hydroxyde d'ammonium. Le FLG est utilisé dans ce travail comme support de catalyseur pour la réaction d'hydrogénation du cinnamaldéhyde et ses performances catalytiques sont comparées à d'autres catalyseurs supportés sur des supports tels que le graphite naturel, le graphite expansé et les nanotubes de carbone
Since the discovery of carbon nanotubes (CNT) in 1991, a lot of efforts have been done in order to find out their intrinsic properties and their possible applications. One of the most efficient methods used for tuning its physical and chemical properties is doping CNTs by nitrogen or boron. The aim of this work deals with the synthesis of nitrogen-doped carbon nanotubes (N-CNTs) and with the study of the catalytic performance of this material either as catalyst support or as a metal-free catalyst. The influence of the different synthesis parameters on the physical and chemical properties of the N-CNTs was investigated. Afterwards, the N-CNTs were used as catalyst support for the hydrogenation of cinnamaldehyde and its catalytic performance was compared to that obtained on the undoped CNTs. It was shown that N-CNTs synthesized in different conditions lead to different catalytic performances which was mainly linked with the nature of the incorporated nitrogen species. The N-CNTs were also employed as a metal-free catalyst for the selective oxidation of H2S into elemental sulfur and the results are discussed within this thesis. Recently 2D carbon material, namely graphene, has received a great interest due to its special physical properties. The previous investigations on the other graphitic material such as carbon nanotubes facilitate the understanding of the properties and behavior of this material. In this thesis we also worked on the synthesis of the few-layer graphene (FLG), using microwave irradiations. A preliminary study has also done on the nitrogen-doping of this material by microwave treatment on the expanded graphite dispersed in ammonium hydroxide. The FLGs were used as a catalyst support for the hydrogenation of cinnamaldehyde and its catalytic performance is compared to other graphitic materials such as natural graphite, expanded graphite and carbon nanotubes

Thesis (Ph.D. in Materials Engineering) -- University of Dayton.
Title from PDF t.p. (viewed 06/23/10). Advisor: Liming Dai. Includes bibliographical references (p. 136-162). Available online via the OhioLINK ETD Center.

Carbon forms the basis of a variety of compounds. The allotropic forms of carbon include graphene, fullerenes, graphite, carbon nanotubes and diamond. All these structures possess unique physical and chemical properties. This work focusses on the usage of carbon nanotubes (CNT), especially iron-filled CNT. An industrial application of CNT requires the understanding of the growth mechanism and the control of the synthesis process parameters. Regarding iron-filled CNT the shell formation as well as the filling process has to be understood in order to control the CNT morphology and distribution and dimension of the iron filling. The thesis involves two topics - synthesis of CNT and characterization of their mechanical properties. Chapter 2 of the present work deals with the synthesis of iron-filled CNT. In this thesis all experiments and the discussion about the growth process were conducted with respect to the demands of magnetic force microscopy probes. The experimental work was focused on the temperature profile of the furnace, the aluminum layer of the substrate, the precursor mass flow and their impact on the morphology of in-situ iron-filled CNT. By selecting appropriate process parameters for the temperature, sample position, gas flow and by controlling the precursor mass flow, CNT with a continuous filling of several microns in length were created. Existing growth models have been analyzed and controversially discussed in order to explain the formation of typical morphologies of in-situ filled CNT. In this work a modified growth model for the formation of in-situ filled CNT has been suggested. The combined-growth-mode model is capable to explain the experimental results. Experiments which were conducted with respect to the assumptions of this model, especially the role of the precursor mass flow, resulted in the formation of long and continuous iron nanowires encapsulated inside multi-walled CNT. The modified growth model and the synthesis results showed, that besides the complexity of the parameter interaction, a control of the morphology of in-situ iron-filled CNT is possible. In chapter 3 the measurements of mechanical properties of in-situ iron-filled CNT are presented. Two different experimental methods and setups were established, whereby one enabled a static bending measurement inside a TEM and another a dynamical excitation of flexural vibration of CNT inside SEM. For the first time mechanical properties and in particular the effective elastic modulus Eb of in-situ iron-filled CNT were determined based on the Euler-Bernoulli beam model (EBM). This continuum mechanic model can be applied to describe the mechanical properties of CNT and especially MWCNT in consideration of the restriction that CNT represent a macro molecular structure built of nested rolled-up graphene layers. For evaluation and determination of the elastic modulus the envelope of the resonant vibrating state was evaluated by fitting the EBM to the experimental data. The experiments also showed, that at the nanoscale the properties of sample attachment have to be taken into account. Thus, instead of a rigid boundary condition a torsion spring like behavior possessing a finite stiffness was used to model an one side clamped CNT. The extended data evaluation considering the elastic boundary conditions resulted in an average elastic modulus of Eb = 0.41 ± 0.11 TPa. The low standard deviation gives evidence for the homogeneity of the grown material. To some extend a correlation between the formation process, the morphology and the mechanical properties has been discussed. The obtained results prove the usability of this material as free standing tips for raster scanning microscopy and especially magnetic force microscopy. The developed methods provide the basis for further investigations of the CNT and the understanding of mechanical behavior in greater detail.

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.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2009.
MIT Barker Library copy printed in pages.
Includes bibliographical references (leaves 49-50).
The successful integration for carbon nanotubes in future electronic applications relies on advances in their synthesis. In this work optimization of growth parameters was conducted to obtain ultra long carbon nanotubes. Their morphology was analyzed by means of different techniques and evidence of the occurrence of nanotube bundles was found. The effect of varying several parameters on the morphology of the obtained nanotubes was investigated and successful growth of ultra long nanotubes was achieved. The settling process, i.e. the sinking of the nanotubes to the substrate, of those nanotubes was investigated by a newly developed in-situ rotation tool and statistical data for their behavior during growth was obtained.
by Mario Hofmann.
S.M.

Les nanomatériaux représentent actuellement des systèmes très attractifs grâce à leurs propriétés physiques, chimiques et mécaniques particulières. La possibilité de manipuler ce type de structures est à la base d'une nouvelle science appelée nanotechnologie. En particulier, la recherche développée après la découverte de molécules tubulaires baptisées nanotubes de carbone représente une contribution fondamentale aux nanosciences. Les nanotubes de carbone (CNTs) sont constitués par des couches de graphite enroulées pour former des structures cylindriques. Deux catégories existent : les nanotubes de carbone à plusieurs parois concentriques (MWNTs ou Multi Walled carbon nanotubes) et les nanotubes à simple parois (SWNTs ou Single Walled carbon nanotubes). Leur diamètre est de l'ordre du milliardième de mètre ; pour les SWNTs il varie entre 0. 4 nm et 2 nm, et entre 1. 4 et 100 nm pour les MWNTs. La longueur est encore plus variable et est comprise dans les deux cas entre quelques centaine de nanomètres et quelques centaines de microns. Les CNTs sont considérés comme des matériaux uniques ayant des applications très prometteuses, spécialement en nanotechnologie, nanoélectronique, science des matériaux mais aussi en chimie médicinale. Les applications potentielles des nanotubes de carbone en chimie médicinale sont à l'heure actuelle très prometteuses étant donné leur capacité d'interagir avec des macromolécules comme les protéines, les polysaccharides et les oligonucleotides. Jusqu'à ce jour, les applications biologique des nanotubes ont été très peu explorées. La raison majeure est certainement l'absence de solubilité de ce matériau en solution aqueuse. La solubilisation des CNTs dans les solvants organiques est possible après le greffage de groupes solubilisants sur la structure tubulaires. Différentes techniques ont été explorées et des nombreuses réactions chimiques peuvent être utilisées pour cet objectif. Pour étendre les applications des CNTs en chimie médicinale il était absolument nécessaire de développer des méthodes permettant de les solubiliser dans des milieux aqueux. Nous avons ainsi développé une méthode de fonctionnalisation basée sur la réaction de cycloaddition 1,3-dipolaire d'ylure d'azométhine à la surface externe des nanotubes. Les nanotubes de carbone ont ainsi été fonctionnalisés par des groupements aminés solubles en solution aqueuse pouvant être facilement dérivatisés par des acides aminés. Ce travail a représenté la première étape vers la synthèse de premières conjugués peptides-nanotubes. La synthèse, la caractérisation et les éventuelles applications biologiques des nanotubes de carbone fonctionnalisés avec des acides aminés et des peptides n'ont pas été développées et exploitées de manière systématique. Cependant, nous avons immobilisé des peptides ayant une activité biologique sur les parois externes de ces nanotubes de carbone afin de trouver des applications médicales intéressantes. Le potentiel offert par ces nouvelles structures est de pouvoir être utilisé comme système d'intérêt thérapeutique dans des domaines aussi divers que la vectorisation des molécules bioactives (peptidiques ou non peptidiques), la vaccination, ainsi que la multiprésentation des molécules inhibitrices ou activatrices des récepteurs multimériques. Nous pouvons aussi les utiliser dans le domaine du diagnostique. Pour ce faire, différentes stratégies de synthèse ont été utilisées pour préparer des dérivés peptides-nanotubes de carbone qui ont été ensuite testés pour leur activité biologique. Une étude systématique a été conduit in vitro et in vivo afin de vérifier et d'évaluer l'influence de ces molécules à base de carbone sur l'activité biologique du peptide greffé. Nous avons choisi de lier aux nanotubes des peptides ayant des propriétés immuno-modulatrices pour des maladies comme la fièvre afteuse chez les animaux ou le Lupus Erythemateux Disséminé chez l'homme. Les propriétés antigéniques et la réactivité immunologique de ces nouvelles molécules conjuguées ont été vérifiées à l'aide de différentes techniques comme résonance plasmonique de surface (SPR), le test Elisa et par injection directe chez la souris. Nous avons mis en évidence que la présence des nanotubes augmente la réponse de la production d'anticorps in vivo par rapport à l'injection du peptide isolé et en plus, renforce la capacité de ces anticorps à tuer le virus. Les résultats obtenus à ce stade de notre recherche montrent l'énorme potentialité offerte par ces systèmes en ce qui concerne la biocompatibilité et leurs propriétés de délivrance et présentation. L'aspect lié à la toxicité a également été étudiée par cytométrie de flux. De même la capacité des nanotubes de carbone à pénétrer dans les cellules sans détruire les membranes ou les structures cellulaires à été étudié par microscopie à fluorescence. Nous avons montré qu'un nanotube de carbone fonctionnalisé avec une molécule fluorescente est capable de pénétrer dans des cellules bien qu'à l'heure actuelle nous ne connaissons pas encore en détail le mécanisme d'entrée à l'intérieur de la cellule. Apparemment le mécanisme de pénétration le plus probable semble être dû à des phénomènes d'endocitose aspécifiques passives plutôt que par des mécanismes actifs. Les interactions entre la membrane cellulaire et la structure polaire du nanotube fonctionnalisé constituent la force propulsif (driving force) pour l'internalisation du nanotube. Des expériences effectuées en condition d'absence d'énergie cellulaire ont montré la facilité d'internalisation d'un nanotube comme a été confirmé par l'analyse à l'aide de la microscopie électronique à transmission (TEM) des cellules traitées avec les MWNT. Sur la base de ces résultats, nous avons exploré la possibilité d'utiliser les nanotubes comme nouveaux vecteur thérapeutiques. En effet les nanotubes de carbone ont un gros potentiel dans le transport de molécules comme l'ADN ou autres petits médicaments ayant une faible biodisponibilité. Depuis des années les liposomes représentent les vecteurs normalement utilisés afin de véhiculer l'ADN pour des applications en thérapie génique. Après la synthèse d'un dérivé de CNT riche en groupes fonctionnels positivement chargés, il a été possible d'évaluer les interaction entre un nanotube et une molécule d'ADN plasmidique négativement chargée. L'idée était de comparer les deux systèmes de transport : les liposomes et les nanotubes de carbone. Différentes techniques ont été utilisées pour caractériser les complexes obtenus. La microscopie électronique à balayage, à transmission, les études de SPR, PCS et électrophorèse ont permis de montrer la formation du complexe CNT-ADN et de déterminer sa stabilité à différent rapport de charge négatif : positif. La condensation de matériel génétique à la surface de nanotubes fonctionalisés est donc réalisable et applicable pour le développement de nouveaux vecteurs pour la thérapie génique. L'étude de transfection in vitro a démontré l'efficacité du transport et de l'expression du plasmide véhiculé par les nanotubes à l'intérieur de la cellule. Suite à l'injection du complexe CNT-ADN à différentes doses et concentrations, nous avons ensuite évalué la réponse in vivo chez la souris. Le résultats d'expression des gènes ont montré une toutefois faible efficacité, en comparaison avec les liposomes-ADN. La longue optimisation qui a été nécessaire pour l'utilisation des liposomes comme vecteurs non virales dans la thérapie génique, nous donne fort espoir pour l'amélioration de notre système vecteur basé sur les nanotubes de carbone fonctionnalisés. En conclusion dans ce travail de thèse, nous avons réussi à développer et caractériser une nouvelle architecture chimique macromoléculaire fonctionnelle, utilisable comme nouveau outil pour la délivrance de molécules bioactives (médicaments, peptides antigéniques, acides nucléiques) et pour la reconnaissance supramoléculair. Le développement futur de la chimie des nanotubes de carbone et l'optimisation de leurs interactions avec les systèmes vivants constituent la continuation active de ce projet de recherche innovant
Carbon nanotubes (CNT) consist of graphene sheets rolled-up into a tubular form. Since their discovery, they appeared immediately as an interesting material for technological applications, including for instance the fabrication of nanoelectronic components. Recently, CNT have also attracted much attention for their potential in biological applications. The main difficulty to integrate this material into biological systems derives from its complete lack of solubility in organic solvents and aqueous solutions. The ability to solubilise and separate individual CNT is still a great challenge. A very general way to achieve this is by organic functionalisation, which is a rapidly expanding field. In this thesis, I focused my interests on the synthesis and use of the first water soluble side-wall functionalised carbon nanotubes. I employed the 1,3-dipolar cicloaddition of azomethine ylides to carbon nanotubes. I have demonstrated that it is possible to further derivatise them by coupling single N-protected amino acids. This was the first step towards the preparation of covalently linked peptide-carbon nanotube conjugates. In this context, I have developed a powerful strategy for linking bioactive peptides to carbon nanotubes for immunological applications. Immobilisation of peptides to the external walls of carbon nanotubes may find interesting applications in diagnostics, vaccine and drug delivery or multipresentation of bioactive molecules. For this aim, peptides with immunological properties were selected for their coupling to the external surface of the CNT. The immunological reactivity and the peptide recognition were assessed by a peptide specific antibody using surface plasmon resonance and ELISA test. These experiments showed that the peptide linked to CNT retain its conformational characteristics for antibody recognition. Furthermore, biological studies performed in vivo demonstrated that CNT-peptide conjugates elicited high antibody titers. Significant pathogen neutralising capacity was observed for the antibodies induced by CNT-peptide conjugates. This highlights: 1) the potential of carbon nanotubes for vaccine delivery, and 2) the importance of antigen presentation in vivo for the induction of antibodies with the right specificity. Functionalised carbon nanotubes have been showed able to cross the cell membrane and to accumulate in the cytoplasm or reach the nucleus without being toxic for the cell up to 10 µM concentration. These findings highlight the potential use of peptide-carbon nanotube conjugates for diagnostic purposes and pave the way for their application in vaccine and drug delivery. Although the elucidation of the mechanism of entry requires further investigations, I excluded active ATP dependent endocytosis. This is because inhibitors of endosome-mediated translocation and decrease of the incubation temperature did not prevent cellular uptake of the different functionalised CNT. In addition, TEM images revealed the tubes crossing the cell membrane as nano-needles without any perturbation or disruption of the membrane. Cell viability after treatment with functionalised nanotubes has also been largely investigated. Highly soluble functionalised CNT in aqueous biological media exhibited notably reduced cellular toxicity in vitro. Cell viability was studied using flow cytometry. Following the synthesis of positively charged carbon nanotubes I investigate their interaction with plasmid DNA. The cationic-anionic interaction between CNT and DNA has been characterised by different techniques both qualitatively and quantitatively. TEM, photocorrelation spectroscopy, SPR and electrophoresis allowed to describe the stability of the CNT-DNA complexes. The condensation of genetic material onto the carbon nanotubes was then confirmed and biological test were performed. The excellent ability of the ammonium functionalised carbon nanotubes to enter cells and potentially reach their nuclei was exploited for the delivery of plasmid DNA. In vitro experiments showed a high level of gene expression when mammalian cells were transfected with DNA-CNT complexes. The following success obtained in in vivo treatment of mice, highlighted the possibility to use this system for gene delivery in gene therapy. Preliminary comparative gene expression data between functionalised CNT:DNA and commercially available lipid:DNA delivery systems showed that our first generation CNT-based gene delivery system is less efficient for in vitro transfection than the lipid:DNA system. However, there is a lot of room for further improvement of the carbon nanotube system for gene delivery. In conclusion, in this Thesis it was possible to develop and characterise a new chemical macromolecular architecture exploitable as new tool for molecular delivery, and molecular recognition. The further development of carbon nanotube chemistry, the optimisation of their interaction with biomolecules and their use in biomedical applications represent the future perspectives of this research

Single-walled metal oxide nanotubes have emerged as an important class of 'building block' materials for molecular recognition-based applications in catalysis, separations, sensing, and molecular encapsulation due to their vast range of potentially accessible compositions and structures, and their unique properties such as well-defined wall structure and porosity, tunable dimensions, and chemically modifiable interior and exterior surfaces. However, their widespread application will depend on the development of synthesis processes that can yield structurally and compositionally well-controlled nanotubes. Moreover, such processes should be amenable to scale-up and preferably operate via benign chemistries under mild conditions. There is currently very little knowledge on the molecular-level 'design rules' underlying the engineering of such materials. The capability to engineer single-walled tubular materials would lead to a range of structures, with novel properties relevant to diverse applications. In this thesis, main objectives are to discover the first molecular-level mechanistic framework governing the formation and growth of single-walled metal-oxide nanotubes, apply this framework to demonstrate the engineering of nanotubular materials of controlled dimensions, and to progress towards a quantitative multiscale understanding of nanotube formation. The class of aluminosilicate (AlSiOH)/germanate (AlGeOH) nanotubes are of particular interest to us, and serve as the exemplar materials for single-walled metal oxide nanotubes. They can be synthesized in pure form from inexpensive and easily accessible reactants at low temperatures (95 ˚C) from aqueous solutions. The synthesis of nanotubes occurs on a time-scale of hours to days, making them an ideal model system to study the nanotube formation mechanism. In Chapter 2, the identification and elucidation of the mechanistic role of molecular precursors and nanoscale (1-3 nm) intermediates with intrinsic curvature, in the formation of single-walled aluminosilicate nanotubes is reported. The structural and compositional evolution of molecular and nanoscale species over a length scale of 0.1-100 nm, are characterized by electrospray ionization (ESI) mass spectrometry, and nuclear magnetic resonance (NMR) spectroscopy. DFT calculations revealed the intrinsic curvature of nanoscale intermediates with bonding environments similar to the structure of the final nanotube product. It is shown that curved nano-intermediates form in aqueous synthesis solutions immediately after initial hydrolysis of reactants at 25 ˚C, disappear from the solution upon heating to 95 ˚C due to condensation, and finally rearrange to form ordered single-walled aluminosilicate nanotubes. Integration of all results leads to the construction of the first molecular-level mechanism of single-walled metal oxide nanotube formation, incorporating the role of monomeric and polymeric aluminosilicate species as well as larger nanoparticles. Then, in Chapter 3, new molecular-level concepts for constructing nanoscopic metal oxide objects are demonstrated. The diameters of metal oxide nanotubes are shaped with Ångstrom-level precision by controlling the shape of nanometer-scale precursors. The subtle relationships between precursor shape and structure and final nanotube curvature are measured (at the molecular level). Anionic ligands (both organic and inorganic) are used to exert fine control over precursor shapes, allowing assembly into nanotubes whose diameters relate directly to the curvatures of shaped precursors. Having obtained considerable insight into aluminosilicate nanotube formation, in Chapter 4 the complex aqueous chemistry of nanotube-forming aluminogermanate solutions are examined. The aluminogermanate system is particularly interesting since it forms ultra-short nanotubes of lengths as small as ~20 nm. Insights into the underlying important mechanistic differences between aluminogermanate and aluminosilicate nanotube growth as well as structural differences in the final nanotube dimensions are provided. Furthermore, an experimental example of control over nanotube length is shown, using the understanding of the mechanistic differences, along with further suggestions for possible ways of controlling nanotube lengths. Ultimately, it is desired to produce the single-walled aluminosilicate nanotubes on a larger scale (e.g., kilogram or ton scales) for technological application. However, a quantitative multiscale understanding of nanotube growth via a detailed growth model, is critical to be able to predict and control key properties such as the length distribution and concentration of the nanotubes. Such a model can then be used to design liquid-phase reactors for scale-up of nanotube synthesis. In Chapter 5, a generalized kinetic model is formulated to describe the reactions leading to formation and growth of single-walled metal oxide nanotubes. This model is capable of explaining and predicting the evolution of nanotube populations as a function of kinetic parameters. It also allows considerable insight into meso/microscale nanotube growth processes. For example, it shows that two different mechanisms operate during nanotube growth: (1) growth by precursor addition, and (2) by oriented attachment of nanotubes to each other. In Chapter 6, a study of the structure of the nanotube walls is presented. It has usually been assumed in the literature that the nanotube wall is free of defects. A combination of 1H-29Si and 1H-27Al FSLG-HETCOR, 1H CRAMPS, and 1H-29Si CP/MAS NMR experiments were employed to evaluate the proton environments around Al and Si atoms during nanotube synthesis and in the final structure. The HETCOR experiments allowed to track the evolving Si and Al environments during the formation of the nanotubes from precursor species, and relate them to the Si and Al coordination environments found in the final nanotube structure. The 1H CRAMPS spectra of dehydrated aluminosilicate nanotubes revealed the proton environments in great detail. Integration of all the NMR results allows the structural assignment of all the chemical shifts and the identification of various types of defect structures in the aluminosilicate nanotube wall. In particular, five main types of defect structures are identified arising from specific atomic vacancies in the nanotube structure. It is estimated that ~16% of Si atoms in the nanotube inner wall are involved in a defect structure. The characterization of the detailed structure of the nanotube wall is expected to have significant implications for its chemical properties and applications. Chapter 7 contains concluding remarks, as well as suggestions for future directions in the engineering of single-walled nanotube materials.

Aquesta Tesi descriu la preparació de varis híbrids formats per nanotubs de carboni i material inorgànic per a diferents aplicacions, que van des de l’electrònica fins a la biomedicina. El propòsit d’aquesta recerca ha estat treballar en la funcionalització de nanotubs de carboni mitjançant la decoració externa i l’emplenat amb materials inorgànics per obtenir híbrids amb propietats funcionals. Com a pas previ a la funcionalització, els nanotubs de carboni s’han de purificar per a eliminar les impureses no desitjades. En aquesta Tesi, hem proposat un mètode de purificació per a nanotubs de carboni multicapa consistent en l’ús servir vapor d’aigua, que és un agent oxidant lleu. Hem investigat l’efecte del temps de tractament amb vapor d’aigua en el grau de purificació i escurçament dels nanotubs de carboni. Hem vist que la purificació amb vapor d’aigua genera mostres de nanotubs de carboni d’alta qualitat i amb les puntes obertes. A més, hem apreciat que la seva llargada pot ser modulada fàcilment. Un cop purificats els nanotubs de carboni, hem preparat diferents tipus d’híbrids mitjançant la incorporació del material a les seves parets. Hem procedit a la decoració externa dels nanotubs de carboni amb nanopartícules d’òxid de ferro superparamagnètiques a través d’un mètode dut a terme in situ. S’ha aconseguit obtenir un agent de contrast dual tant per ressonància magnètica com per imatge nuclear a través del etiquetat de les nanopartícules amb 99mTc. A més, s’ha mostrat que l’ús de nanotubs de carboni més curts milloren les propietats magnètiques de l’híbrid, obtenint així valors de relaxivitat més elevats. D’altra banda, hem incorporat de manera covalent clústers de metalacarborans a les parets de nanotubs de carboni monocapa, formant un híbrid amb alt contingut de 10B, que serà apropiat per la teràpia per captura neutrònica de bor. Diferents rutes sintètiques han estat investigades. La dispersabilitat de l’híbrid resultant ha estat més alta que en el cas dels nanotubs de carboni monocapa oxidats i, per tant, l’híbrid és un candidat potencial per a aplicacions biomèdiques. Finalment, hem investigat l’emplenat de nanotubs de carboni multicapa amb un sòlid van der Waals per capil·laritat del material en la seva fase fosa. Hem reportat per primer cop la formació de nanotubs monocapa inorgànics dins dels nanotubs de carboni. Així mateix, hem investigat la transformació dinàmica dels nanomaterials encapsulats sota la irradiació amb un feix d’electrons. També hem demostrat, utilitzant la teoria de la funció de densitat, que els nanotubs monocapa inorgànics són estables. Els resultats presentats en el marc d’aquesta Tesi expandeixen la capacitat dels híbrids formats per nanotubs de carboni i material inorgànic.
Esta Tesis describe la preparación de varios híbridos formados por nanotubos de carbono y material inorgánico para diferentes aplicaciones, que van desde la electrónica hasta la biomedicina. El propósito de esta investigación ha sido trabajar en la funcionalización de nanotubos de carbono mediante la decoración externa y el llenado con nanotubos inorgánicos para obtener híbridos con propiedades funcionales. Como paso previo a la funcionalización, los nanotubos de carbono se tienen que purificar para eliminar las impurezas no deseadas. En esta Tesis, hemos propuesto un método de purificación para nanotubos de carbono multicapa consistente en el uso vapor de agua, que es un oxidante leve. Hemos investigado el efecto del tiempo de tratamiento con vapor de agua en el grado de purificación y acortamiento de los nanotubos de carbono. Hemos visto que la purificación con vapor de agua genera muestras de nanotubos de carbono de alta calidad y con puntas abiertas. Además, hemos apreciado que su longitud puede ser modulada fácilmente. Una vez que se han purificado los nanotubos de carbono, hemos preparado diferentes tipos de híbridos mediante la incorporación del material en sus paredes. Hemos procedido a la decoración externa de los nanotubos de carbono con nanopartículas de óxido de hierro superparamagnéticas a través de un método in situ. Se ha conseguido obtener un agente de contraste dual tanto para resonancia magnética como para imagen nuclear a través del etiquetado de las nanopartículas con 99mTc. Además, se ha mostrado que el uso de nanotubos de carbono más cortos mejoran las propiedades magnéticas del híbrido, obteniendo así valores de relajatividad más elevados. Por otro lado, hemos incorporado de manera covalente clústers de metalacarboranos en las paredes de nanotubos de carbono monocapa, formando un híbrido de alto contenido de 10B, que será apropiado para la terapia por captura neutrónica de boro. Diferentes rutas sintéticas han sido investigadas. La dispersabilidad del híbrido resultante ha sido más alta que en el caso de nanotubos de carbono monocapa oxidados y, por lo tanto, el híbrido es un candidato potencial para aplicaciones biomédicas. Finalmente, hemos investigado el llenado de nanotubos de carbono multicapa con un sólido van der Waals por capilaridad del material en su fase fundida. Hemos reportado por primera vez la formación de nanotubos inorgánicos monocapa dentro de los nanotubos de carbono. Asimismo, hemos investigado la transformación dinámica de los nanomateriales encapsulados bajo la radiación de un haz de electrones. También hemos demostrado, usando la teoría de la función de densidad, que los nanotubos monocapa inorgánicos son estables. Los resultados presentados en el marco de esta Tesis expanden la capacidad de los híbridos formados por nanotubos de carbono y material inorgánico.
This Thesis reports on the preparation of various carbon nanotube‒inorganic hybrids for different applications, ranging from electronics to biomedicine. The purpose of the investigation has been to work on the functionalization of carbon nanotubes by both external decoration and endohedral filling with inorganic materials to obtain hybrids with functional properties. Prior to the functionalization, a purification step must be conducted to remove undesired side products from the synthesis of CNTs. In this Thesis, a purification method using steam, a mild oxidizing agent, is proposed for multi-walled carbon nanotubes. We have investigated the effect of the steam treatment time on the degree of purification and shortening of the carbon nanotubes. Steam purification results in samples open-ended, high-quality nanotubes, which length can be easily modulated. Once carbon nanotubes have been purified, we have prepared different types of hybrids by incorporating the material on the walls of the carbon nanotubes. We have externally decorated carbon nanotubes with superparamagnetic iron oxide nanoparticles by an in situ method. A dual imaging in vivo agent for both magnetic resonance and nuclear imaging has been achieved after labelling the nanoparticles with 99mTc. Moreover, it has been revealed that shorter carbon nanotubes enhance the magnetic properties of the hybrid, obtaining higher relaxivity values. On the other hand, we have covalently attached metallacarborane clusters on the walls of single walled carbon nanotubes to form a hybrid with high 10B content that will be appropriate for boron neutron capture therapy. Different synthetic routes have been studied. The dispersibility of the resulting hybrid was higher than that of oxidized single-walled carbon nanotubes, and therefore the hybrid is a potential candidate for biomedical applications. Finally, we have investigated the filling of multi-walled carbon nanotubes with a van der Waals solid by molten phase capillary wetting. We have reported on the formation of single-layered inorganic nanotubes inside carbon nanotubes for the first time. We have also investigated the dynamic transformation of the encaged nanomaterials under electron beam irradiation. Moreover the intrinsic stability of the single-layered inorganic nanotube has been demonstrated using density function theory. The results presented within this Thesis further expand the capabilities of carbon nanotube‒inorganic hybrids.

To answer the growing energy needs around the globe, novel materials and structures are being investigated to fabricate photovoltaic (PV) cells. Different types of nanostructures are being incorporated in PV cells to increase their performance since these structures can be tailored to answer specific needs related for example to larger light absorption wavelength range or very high electrical conductivity. However, complex fabrication processes hinder the development of this technology. In this work we propose the use of a 3-D carbon nanotube (CNT) network grown directly from a metallic substrate and decorated with CdSe nanoparticles (NPs) acting as the photoactive electrode for a PV cell. Simple fabrication methods that require no wet chemistry have been chosen to diminish waste and avoid the difficulties inherent to dispersing nanomaterials in liquids. More specifically, in a vacuum chamber, a CdSe target is irradiated using a high energy nanosecond pulsed Nd:YAG laser to form an expanding vapor plume that subsequently condenses into NPs which are deposited on the desired substrate. CdSe NPs between 2 and 6 nm in diameter were produced, in the two common crystalline phases for CdSe, hexagonal (wurtzite) and cubic (sphalerite). The composition of the NPs was 54% atomic Cd and 46% atomic Se. It was observed that the size of the NPs increases with increasing pressure from 0.1 to 4620 Pa, but the laser fluence, from 0.48 to 2.36 J/cm^2, had no impact on the size of the NPs. Light absorption spectroscopy suggested that the NPs produced had a large size distribution. Coating the CNTs with CdSe for different amounts of time, from 100 s to 90 min, produced CNTs with a CdSe coating only a few nanometers thick up to two micrometers. Photoelectrochemical measurements using this heterogeneous nanostructure as the working electrode revealed that the CdSe coating was slightly photoactive. However, due to insufficient photocurrent generated, no power could be drawn from this cell. The first problem found was an interaction between the CNTs and the solution which caused variability in the cell. The second problem was a very large dark current which may be attributed to leaking of electrons from the CdSe to the solution due to a large resistance for transport of electrons to the outer electrial circuit.
Afin de répondre à nos besoins énergétiques grandissants, de nouveaux matériaux et de nouvelles structures sont en développement dans le but de fabriquer des cellules photovoltaïques (PV). Plusieurs nanostructures sont intégrées dans ces cellules PV pour augmenter leur performance. Ces nanostructures peuvent répondre à des besoins spécifiques tels qu'un spectre d'absorption de la lumière plus large ou une plus grande conductivité électrique. Par contre, des processus de fabrication complexes empêchent le développement de cette technologie. Dans ce projet, nous proposons l'utilisation d'une structure 3D de nanotubes de carbone (NTCs), synthétisés directement sur un substrat métallique, et décorés par des nanoparticules de CdSe. Des méthodes simples de fabrication qui ne font pas appel à la chimie en solution ont été choisies afin de diminuer les déchets chimiques et éviter les difficultes inhérentes à la dispersion de nanomatériaux en solution. Dans une chambre à vide, une cible faite en CdSe est irradiée par un laser pulsé Nd:YAG haute énergie menant à la formation d'une plume en expansion contenant du Cd et du Se. Les atomes à l'intérieur de la plume se condensent pour former des nanoparticules qui se déposent par la suite sur le substrat désiré. Les nanoparticules de CdSe obtenues ont un diamètre entre 2 et 6 nm et se retrouvent dans les deux phases crystallines typiques au CdSe soit hexagonale (wurtzite) et cubique (sphalerite). La composition des NPs est de 54% atomique pour le Cd et 46% atomique pour le Se. Il a été observé que les NPs augmentent de taille lorsque la pression durant l'ablation de la cible est augmentée entre 0.1 et 4620 Pa. Cependant, cette taille n'est pas influencée par des changements dans la fluence de l'impulsion entre 0.48 et 2.36 J/cm^2. Les spectres d'absorption de la lumière des NPs indiquent une large distribution de tailles des NPs produits. En recouvrant les NTCs avec des NPs de CdSe pendant différentes périodes de temps allant de 100 s à 90 min, des NTCs recouverts d'une monocouche de NPs de CdSe jusqu'à une couche micrométrique sur les NTCs ont été fabriqués. Cette nanostructure a été testée dans une cellule photoélectrochimique (PEC). Ces mesures ont révélé que la couche de CdSe sur les NTCs est photoactive mais dû à certains problèmes dans la cellule, une quantité insuffisante de courant a été produit par ce système pour qu'il puisse être utilisé en tant que cellule photovoltaïque. Premièrement, une interaction entre les NTCs et la solution ont causé des instabilités dans la cellule ne permettant pas la reproductiblité dans les mesures effectuées. Deuxièmement, le courant obtenu sans illumination de la cellule était très élevé. Ce courant pourrait provenir d'une fuite indésirée d'électrons de la couche de CdSe vers la solution due à une résistance électrique trop élevée des électrons vers le circuit électrique de la cellule PEC.

Thesis (Ph.D.)--University of Delaware, 2008.
Principal faculty advisors: Dennis W. Prather, Dept. of Electrical & Computer Engineering; and Bingqing Wei, Dept. of Mechanical Engineering. Includes bibliographical references.

In the past two decades, an appreciation of the extraordinary properties of nanotubular materials has led to the discovery and investigation of many different nanotubes. A wide variety of nanotubes can be synthesised using scalable hydrothermal techniques, but understanding of the synthesis mechanisms is often limited. This research is concerned with manipulating the synthesis conditions of metal oxide and silicate nanotubes in order to improve understanding of the underlying synthesis mechanism, and investigating the properties of the nanotubes as hydrogen storage materials. This thesis presents experimental results for the syntheses of aluminium silicate, nickel silicate and vanadium oxide multiwalled nanotubes under controlled hydrothermal conditions. A novel synthesis method at 220ºC, pH2 was developed for Al2Si2O5(OH)4 nanotubes through substitution of a mole fraction of SiO2 with GeO2 in the precursor SiO2 + Al(OH)3 suspension. An ideal Ni/Si molar ratio of 1.5 was demonstrated in the synthesis of Ni3Si2O5(OH)4 nanotubes at 195ºC. It was shown that increasing the concentration of NaOH widens the length distribution and increases the average length of the nanotubes. Variable temperature experiments with vanadium oxide nanostructures revealed a low temperature route for the synthesis of flexible elongated VOx nanosheets under reflux (90ºC) in an ethylenediamine-water mixture. The hydrothermal experiments revealed important details about the nanotube formation mechanisms, including the scrolling mode of nanosheets into nanotubes, which occurs in a specific crystallographic direction relative to the nanosheet growth axis. Subsequent investigations into the room temperature stability of Al2Si2O5(OH)4 nanotubes under aqueous acidic and alkaline conditions revealed significant dissolution within 10 days in 1 mol dm-3 NaOH, H2SO4 and HCl solutions, initiated at the inner surface. The effect of acid or alkali concentration on the initial dissolution rate was measured, and the dissolution mechanism discussed. Acid treatment was shown to be an effective method for increasing nanotube surface area. Investigations into the hydrogen adsorption properties of metal oxide nanotubes revealed weak adsorption of hydrogen at 77–298 K up to 150 bars (15MPa) pressure. Temperature-corrected adsorption isotherms for adsorbing H2TinO2n+1 (titanate), Ge-Al2GeO3(OH)4 and Ni3Si2O5(OH)4 nanotubes were compared with M3[Fe(CN)6]2 Prussian-blue analogues, and dimensions of the adsorbed hydrogen layer were derived using the Langmuir-Freundlich model.

Portland cement (PC) is one of the most consumed products of the world. Its derivates (concrete, mortar, paste) have good compressive characteristics, but on the other hand have poor tensile behavior. Carbon nanotubes have exceptionally high tensile strength and are therefore candidates for structural reinforcement of cement materials. Many tentative have been reported to develop composites with the physical mixture of high quality nanotubes and cement. These processes today are still unviable for large scale production of construction material. The problems are linked to the scale and costs of production and the dispersion and bond of the nanotubes to the cement matrix. In order to solve these problems in present work an in-situ synthesis process was developed to produce nanotubes and nanofibers on clinker and silica fume particles. Steelmaking by-products, such as steel mill scale and converter dust were also added to improve product characteristics. The synthesis products were characterized by scanning electron microscopy, thermogravimetric analysis and loss on ignition. The products showed highly heterogeneous morphology. An in-situ functionalization process was also developed based on ammonia. The nano-structured materials were added to Brazilian CP-III and CP-V type cements in 0.3 % concentration to perform common physical and chemical cement analysis. Setting time of CP-V suffered a slight delay, but other characteristics were not altered significantly after the addition of nano-structured clinker. Mortars were prepared in order to determine compressive and flexural or splitting tensile strength of the composites. Gains in the compressive and tensile strengths were observed of mortars incorporating 0.3 % nanotubes prepared with a combined polycarboxylate and polynaphtalene and a lignosulfonate based plasticizer. Positive results were also observed with the use of hydrogen peroxide as functionalizing agent. The addition of nano-structured silica fume also resulted in increase of the mechanical strength of the composites. BET and helium pycnometry analysis of the mortars showed an increase in specific surface area and reduction of mean pore diameter of the composites.
O cimento Portland (PC) é um dos produtos mais consumidos no mundo. Seus derivados (concreto, argamassa, pasta) apresentam características satisfatórias quanto à compressão, entretanto o mesmo não ocorre com relação à tração. Os nanotubos de carbono (NTCs) possuem elevada resistência à tração, sendo deste modo candidatos para reforçar estruturalmente materiais cimentícicos. Várias tentativas foram realizadas no mundo para desenvolver processos envolvendo a produção de compósitos a partir da mistura física de cimento e de nanotubos de alta qualidade. Atualmente estes processos são ainda inviáveis para produzir material de construção em grande escala. Os problemas a isto associados estão relacionados à escala e custo de produção, além da dispersão e ligação dos nanotubos na matriz de cimento. Para tentar resolver estes problemas, neste trabalho foi desenvolvido um processo de síntese in-situ de nanotubos e nanofibras de carbono em clínquer e sílica ativa. Além disso, resíduos da siderurgia como carepa de laminação de aço e pó de aciaria foram utilizados para melhorara as características dos produtos. Os produtos da síntese foram caracterizados por microscopia eletrônica de varredura, por análise termogravimétrica e por resíduo por queima. Estes produtos apresentaram grande heterogeneidade em morfologia. Foi desenvolvido também um processo de funcionalização in-situ dos nanotubos via amônia. Os materiais nano-estruturados foram adicionados aos cimentos CP-III e CP-V em uma concentração de 0,3 % para realização de análises físico-químicas convencionais de cimento. O tempo de pega apresentou um leve aumento no cimento CP-V, mas os demais parâmetros não sofreram alterações significativas pela adição de clínquer nano-estruturado. Argamassas foram preparadas para testar as resistências à compressão e à tração dos compósitos, este último por flexão ou por compressão diametral. Aumentos nas resistências à compressão e à tração foram observados em argamassas preparados com 0,3 % de nanotubos em relação ao peso do cimento, e com aditivos plastificantes a base de policarboxilato e polinaftaleno além de lignosulfonato. Resultados promissores também foram obtidos com o uso de peróxido de hidrogênio como agente de funcionalização. A adição de sílica ativa nano-estruturada também provocou aumento de resistência mecânica dos compósitos. Análises por BET e por picnometria a hélio mostraram aumento da área superficial específica e redução dos diâmetros dos poros dos compósitos.

The further developments in nanotechnology in last few years provide usage of nanoscale particles for many applications in various areas such as electronics, pharmaceutical, and biomedical due to their strengthened mechanical, thermal and electrical properties. Boron nitride nanotubes are a good example of nanoparticles. In this study, boron nitride nanotubes were successfully synthesized from the reaction of ammonia gas with mixture of boron and iron oxide. Physical and structural properties of the synthesized materials were determined by X-Ray Diffraction, Energy Dispersive X-Ray Spectroscopy, nitrogen sorption, X-Ray Photoelectron Spectroscopy, Fourier Transform Infrared Spectroscopy, and Scanning Electron Microscopy. Experiments were conducted in a tubular furnace at different temperatures and also at different weight ratios of boron to iron oxide. Qualitative chemical analysis of the reactor effluent stream was carried out using a mass spectrometer. The mass spectrometer analysis of the reaction products proved formation of nitrogen in addition to hydrogen and water during the reaction of ammonia gas with the mixture of boron and iron oxide. XRD results showed that hexagonal and rhombohedral boron nitrides and cubic iron were the solid phases formed in the product. FTIR and XPS results also indicated the presence of boron nitride and the atomic ratio of boron to nitrogen was compatible with the chemical stoichiometric relation between boron and nitrogen. It was observed that the crystanility of the product increased with an increase in temperature. The diameter of the produced nanotubes varied from 64 nm to 136 nm. The synthesized nanotubes exhibited Type II isotherms. The surface areas of the produced boron nitride nanotubes decreased with a decrease in both temperature and the weight ratio of boron to iron oxide. The best temperature and weight ratio of boron to iron oxide to produce boron nitride nanotubes were found to be 1300°
C and 20, respectively.

Nanotechnology has reached the status of the 21st century's leading science and technology based on fundamental and applied research during the last two decades. An important feature of nanotechnology is to bridge the crucial dimensional gap between the atomic and molecular fundamental sciences and microstructural scale of engineering. Accordingly, it is very important to have an in-depth understanding of the synthesis of nanomaterials for the use of state-of-the-art high technological devices with enhanced properties. Recently, the 'bottom-up' approach for the fabrication of nanomaterials has received a great deal of attention for its simplicity and cost effectiveness. Tailoring the various parameters during synthesis of selected nanoparticles can be used to fabricate technologically important components. During the last decade, carbon nanotubes (CNTs) have been envisioned for a host of different new applications. Although carbon nanotubes can be synthesized using a variety of techniques, large-scale synthesis is still a great challenge to the researchers. Three methods are commonly used for commercial and bulk productions of carbon nanotubes: arc-discharge, chemical vapor deposition and laser ablation. However, low-cost, large-scale production of high-quality carbon nanotubes is yet to be reported. One of the objectives of the present research is to develop a simplified synthesis method for the production of large-scale, low-cost carbon nanotubes with functionality. Herein, a unique, simple, inexpensive and one-step synthesis route of CNTs and CNTs decorated with nanoparticles is reported. The method is simple arc-discharge in solution (ADS). For this new method, a full-fledged optoelectronically controlled instrumen is reported here to achieve high efficiency and continuous bulk production of CNTs. In this system, a constant gap between the two electrodes is maintained using a photosensor which allows a continuous synthesis of the carbon nanostructures. The system operates in a feedback loop consisting of an electrode-gap detector and an analogue electronic unit, as controller. This computerized feed system was also used in single process step to produce in situ-decorated CNTs with a variety of industrially important nanoparticles. To name a few, we have successfully synthesized CNTs decorated with 3-4 nm ceria, silica and palladium nanoparticles for many industrially relevant applications. This process can be extended to synthesize decorated CNTs with other oxide and metallic nanoparticles. Sixty experimental runs were carried out for parametric analysis varying process parameters including voltage, current and precursors. The amount of yield with time, rate of erosion of the anode, and rate of deposition of carbonaceous materials on the cathode electrode were investigated. Normalized kinetic parameters were evaluated for different amperes from the sets of runs. The production rate of pristine CNT at 75 A is as high as 5.89 ± 0.28 g.min-1. In this study, major emphasis was given on the characterizations of CNTs with and without nanoparticles using various techniques for surface and bulk analysis of the nanostructures. The nanostructures were characterized using transmission electron microscopy, high resolution transmission electron microscopy, scanning transmission electron microscopy, energy dispersive spectroscopy and scanning electron microscopy, x-ray photo electron spectroscopy, x-ray diffraction studies, and surface area analysis. Electron microscopy investigations show that the CNTs, collected from the water and solutions, are highly pure except the presence of some amorphous carbon. Thermogravimetric analysis and chemical oxidation data of CNTs show the good agreement with electron microscopy analysis. The surface area analysis depicts very high surface area. For pristine multi-walled carbon nanotubes, the BET surface area is approximately 80 m2.g-1. X-ray diffraction studies on carbon nanotubes shows that the products are clean. Nano-sized palladium decorated carbon nanotubes are supposed to be very efficient for hydrogen storage. The synthesis for in-situ decoration of palladium nanoparticles on carbon nanotubes using the arc discharge in solution process has been extensively carried out for possible hydrogen storage applications and electronic device fabrication. Palladium nanoparticles were found to form during the reduction of palladium tetra-chloro-square planar complex. The formation of such a complex was investigated using ultraviolet-visible spectroscopic method. Pd-nanoparticles were simultaneously decorated on carbon nanotubes during the rolling of graphene sheets in the arc-discharge process. Zero-loss energy filtered transmission electron microscopy and scanning transmission electron microscopy confirm the presence of 3 nm palladium nanoparticles. The deconvoluted X-ray photoelectron spectroscopy envelope shows the presence of palladium. Surface area measurements using BET method show a surface area of 28 m2.g-1. The discrepancy with pristine CNTs can be explained considering the density of palladium (12023 kg.m-3). Energy dispersive spectroscopy suggests no functionalization of chlorine to the sidewall of carbon nanotubes. The presence of dislodged graphene sheets with wavy morphology as observed with high-resolution transmission electron microscopy supports the formation of CNTs through the 'scroll mechanism'.
Ph.D.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Materials Science and Engineering

Block copolymers containing pendant pyrene, terpyridine and poly(3- hexylthiophene) moieties with different block ratios and chain lengths were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. The block copolymers obtained had narrow molecular weight distribution. The applications of these polymers for non-covalent functionalization of carbon nanotubes and in photovoltaic devices were studied. The molecular weight distribution and block sizes of the block copolymers could be controlled quite well. The polydispersities measured were below 1.25. The block copolymers could be functionalized on the surface of CNTs. The functionalized CNTs had an improved dispersing ability and a maximum dispersing ability of 0.30 mgmL-1 in DMF was achieved. The photosensitizing properties of an individual functionalized CNT were studied by conductive atomic force microscopy. In the presence of the photosensitizing unit, the photocurrent was measured to be 6.4 nAμW-1 at 580 nm. This suggests the role of metal complexes in the photosensitizing process in the block copolymer. Poly(3-hexylthiophene)-block-pendant pyrene copolymers were synthesized by Grignard metathesis and RAFT polymerization. Different loadings of the block copolymers functionalized CNT were employed as the electron accepting materials in bulk heterojunction photovoltaic devices. A maximum power conversion efficiency of 0.77 × 10-3 % was achieved for the poly(3- hexylthiophene): 0.5% polymer functionalized CNT devices. The poor efficiency was attributed to the low CNT loadings that limited the electron transport in the devices. The poly(3-hexylthiophene)-block-pendant pyrene copolymer were employed as compatibilizer for poly(3-hexylthiophene): [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) bulk heterojunction photovoltaic devices. With the addition of 20 % of the block copolymer, a maximum power conversion efficiency of 1.62 % could be achieved. The long term stability of the encapsulated photovoltaic devices was studied. There was more than 30 % reduction in the degradation of performance after 30 days when the block copolymer was added as compatibilizer. These results suggested the role of the block copolymer compatibilizers in improving both the photovoltaic performances and stability of the devices. Differential scanning calorimetry results suggested that the improved photovoltaic performances may be attributed to the enhanced compatibility between poly(3- hexylthiophene) and PCBM.
published_or_final_version
Chemistry
Doctoral
Doctor of Philosophy

碩士
國立中正大學
化學工程所
95
This research was studied on growth of branched CNTs by thermal chemical vapor deposition. The process was mainly including three steps: First, FeNi powder was dispersed on Si wafer by spinning coater, and producing carbon nanotubes on Si wafer that there was FeNi on by thermal chemical vapor deposition . Second , Ni catalysts was loaded on the first carbon nanotubes by sputter, Ni-coated carbon nanotubes were formed. Third , branched carbon nanotubes were produced by thermal chemical vapor deposition , and Ni coated CNTs were catalytic roles. By the instruments, ex: SEM,TEM,HR-TEM analysis, we can gain much information. How was the effect by the different parameters, such temperature , the catalytic thickness , the time of the carbon sources. Three conclusion: 1. temperature: the higher temperature, the lower density of branched CNTs 2. the catalytic thickness : the more catalytic thickness , the larger diameters of branched CNTs. 3. the time of carbon sources : the longer time of carbon sources , the higher density of branched CNTs and the longer branched-CNTs . Otherwise , were there branched CNTs with no new carbon source? Yes, there were. And we were also studying the mechanism about it. Furthermore , discussing the hydrophobic of branched CNTs. The results is that the hydrophobic effect is better with branched carbon nanotubes.

碩士
國立中正大學
化學工程所
98
This research was mainly including two parts:First,we used FeNi catalyst to synthesize primary CNTs which the size of diameter is larger by the 1st-CVD process. And we deposited the Ni particles both on the homemade CNTs and the commercial CNTs which the size of diameter is smaller by impregnation and calcination,then we obtained the branched CNTs by the 2nd-CVD process. Secondary, two types of the above branched CNTs was preparation to the suspension,and finally we fabricate branched carbon nanotube paper by vacuum filtration. In the experiment results of part 1,to prepare the branched CNTs which the diameter is in the range of 150nm~400nm,we need to use the Nickel nitrate/Ethanol solutions as the precursor, and reaction at the temperature of 560oC for 2 hours.and if we want to obtain the branched CNTs which the diameter is in the range of 40nm~60nm,we need to use the Nickel acetate/Methanol solutions as the precursor, and reaction at the temperature of 560 oC~600oC for 1 hours. In the experiment results of part 2,when we compare the branched CNT paper to the original CNT paper from the FESEM analysis,we can see that many branched CNTs were grown on the primary CNTs,and because the branched CNTs which the diameter is in the of 150nm~400nm has the higher yield of branched CNTs in the product,so the phenomenon was more obvious. Because the effect of branched CNTs, the conductivity of branched CNT paper was increased, and when we prepared the PVA/branched CNT composite paper, we can find the mechanical properties also increased.

碩士
國立臺灣科技大學
工程技術研究所材料科技學程
90
The purpose of this research is to investigate the growth mechanisms of carbon nanotubes (CNT ) by pyrolyzing polycarbosilane ( PCS ), and synthesis of carbon nanotubes by polymer procedure . Preparation of carbon nanotubes from polycarbosilane has been successfully performed in our laboratory, but the growth mechanisms has not been realized. Hence we designed several experiments to understand the growth mechanisms of carbon nanotubes. As a result, the growth mechanisms of carbon nanotubes by polycarbosilane is dominated by gas-solid reaction. On the other hand, carbon nanotubes were synthesized from polypropylene ( PP ) and polystyrene ( PS ). The method has been developed to produce carbon nanotubes by the catalytic decomposition of the polymers at a temperature about 700℃. While iron chloride ( FeCl3 ) was used as the catalysts, the diameters of carbon nanotubes become as small as 15nm. So this experiment can offer a simple way to from carbon nanotubes.

碩士
國立中正大學
化學工程研究所
93
The purpose of this study is to use novel flame-conbustion method, i.e, diffusion-flame method, to synthesize high purity carbon nanomaterials including carbon nanotubes and carbon nanocapsules. We used two kinds of flame apparatus, a alcohol burner and a acetylene-oxygen flame, in the experiment. Reaction parameters, such as reaction time, reaction position, types of catalyst, catalytic concentration, solvents, etc, also were discussed for the formation of carbon nanomaterials. The well-aligned carbon nanotubes with a diameter of 20-30nm and a length of 2-3μm can be synthesized on the stainless steel substrate with Co catalyst using the alcohol burner as a heating source. Preparation of carbon nanoparticles used acetylene-oxygen flame to react with the stainless steel substrate for 10 minutes. The diameter of carbon nanoparticles is about 20-30 nm in diameter and with graphitic structure (about 25-35 layers). FESEM、HRTEM、Raman Spectrum and EDS will be employed to characterize carbon nanomaterials. Identify the composition, structure, shape, purity and properties of carbon nanomaterials fabricated by the flame method. It is very important for us to understand the growth mechanism of the carbon nanomaterials.

碩士
國立東華大學
材料科學與工程學系
92
The objective of this research project is to investigate several important parameters for quantitative production of carbon nanotube and nanocapsule by using an arc-discharge technique. These carbon products were evaluated by TEM, SEM, XRD and Raman spectroscopy. Attempt has also been made to determine the feasibility of carbon nanotubes and nanocapsules for hydrogen storage. Experimental results indicate that the chamber temperature decreased from ambient temperature (~25℃) to 5℃ by controlling cooling water temperature, carbon nanotubes and nanocapsules increased from 0.76 to 1.13 gm. Pure iron powder was used as catalysis for synthesizing carbon nanotubes and nanocapsules. The ratio of Fe:C from 1:1 up to 4:1 was evaluated, it was found that the ratio of nanotube and nanocapsule decreases with increasing Fe to C ratio. Purification of nanotubes and nanocapsules was performed in concentrated acid at 140℃ as a function of cooking time. TEM and XRD examinations were made and revealed that purified carbon nanotubes and nanocapsules can be obtained at about 3 hours cooking time, when the soot residuals, such as graphitic particles and amorphous carbon, were removed sufficiently. As the cooking time was greater than 3 hours, the amount of purified carbon nanotubes and nanocapsules tended to decrease. All the carbon products would be dissolved completely after 5 hours. An attempt was also made on the adsorption experiment of hydrogen by carbon nanotubes and nanocapsules using TPD facility. The preliminary result showed that approximately 0.3133% wt of hydrogen had been adsorbed by the carbon nanotubes. Carbon nanotubes appears to be feasible for future fuel cell application.

M.Sc.
Carbon nanotubes are among the most exciting new materials being investigated and synthesized, owing to their outstanding mechanical, electronic and optical properties. For more than a decade, the translation of these properties into realistic applications has been hindered by solubility and processing difficulties. Recently the development of efficient methodologies for covalent chemical modification has raised hope for the use of these materials in various fields of application such as biosensors, vaccine and drug delivery systems, medical imaging, biomaterials, water purification, etc... Phosphorylation of functionalized and unfunctionalized multiwalled carbon nanotubes (MWCNTs) is reported in this dissertation. This was achieved by the incorporation of phosphorus moieties on the end and side walls of the MWCNTs. Pristine MWCNTs were functionalized through oxidation by sodium hypochlorite and with a mixture of sulphuric and nitric acids, a diazonium coupling method and by reduction of amide functions on the surface of MWCNTs. Then condensation reactions with alkyl or aryl chlorophosphates were undertaken to obtain compounds 7 to 12. Phosphorylation of pristine MWCNTs was achieved by a 1, 3 dipolar cyclo addition of diphenyl phosphoryl azide. Characterization of the phosphorylated multiwalled carbon nanotubes has been performed by Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Energy X-Ray Dispersive Spectroscopy (EXDS), Thermal Gravimetric Analysis (TGA), Fourier Transform Infrared (FTIR) and Raman Spectroscopy. These techniques together gave evidence for surface, structure and chemical modifications of the synthesized material.

Carbon nanotubes (CNTs) are advanced materials that have numerous novel and useful properties. Controlling the synthesis and properties of CNTs is the major challenge toward their future applications. This thesis addresses this challenge with several contributions. This thesis begins with the brief introduction of CNTs, including the history of their discovery, their geometric structure, unique properties and potential applications. Then focus is laid on the subsequent three sections: characterization, synthesis, and manipulation of CNTs. Chapter 2 describes three characterization tools: AFM, SEM and Raman, which are commonly used to analyze CNTs and other nanomaterials. They offer both qualitative and quantitative information on many physical properties including size, morphology, surface texture and roughness. Also, they can be used to determine the structure of CNTS. Chapter 3 addresses the synthesis of CNTS, because synthesis is an important and indispensible process to study CNTs experimentally. Specifically, two controllable synthesis techniques are realized, which are capable to produce iron catalyst nanoparticles for single-walled carbon nanotube (SWNT) growth. Iron nanoparicles of different sizes obtained from both wet chemistry and electrodeposition can be used for diameter-controlled synthesis of SWNTs. Following synthesis, two manipulation methods of CNTs are discussed in Chapter 4. Firstly, effort of electrical breakdown of CNTs is introduced. Both SWNTs and MWNTs (Multi-walled carbon nanotubes) are cut using this method. Moreover, SWNT kink is shown using AFM tip manipulation. These two manipulation methods provide us a possibility to fabricate large cavity from a MWNT for our purposes. In the end of this thesis, conclusions on my master work in research field of CNTs are drawn and future research directions are proposed.

The chemistry and applications of carbon nanotubes are critically dependent on nanotube chirality. To date, no one has demonstrated chirality-selective synthesis of single-walled carbon nanotubes from pre-synthesized catalyst nanoparticles. A proposed chemical approach to the mass production of chirality-selective SWNTs is their "cloning" by chemical cutting, decoration with catalyst nanoparticles, and continued growth. The progress of this process will be reviewed. Purified HiPco nanotubes were sidewall functionalized to allow suspension in water and organic solvents. Methods were developed to end-functionalize suspended nanotubes with linkers used to attach preformed catalyst particles. SWNT-catalyst complexes (SWNTcats) were deposited on a surface and exposed to hydrogen to show the feasibility of controlled etching of a single nanotube resulting in removal of the functional linker. To orient the nanotubes for growth, SWNTcats were assembled into open structures on a carbon fiber grid. Vertically oriented carbon nanotube carpets grown by catalytic CVD have received enormous attention because of their suitability in a growing number of important technological applications. An area of concern is the sudden termination of growth that occurs after micron heights are attained. A previously unexplored factor in this termination is the coarsening of the catalyst particles used for growth by Ostwald ripening. The coarsening behavior of Fe catalyst films supported on alumina deposited by atomic layer deposition as a function of thermal annealing in H2 and H2/H2O is demonstrated. The results reveal that the addition of water in water assisted growth of single-walled carbon nanotube carpets may be a means of inhibiting Ostwald ripening through the ability of oxygen and hydroxyl species to reduce diffusion rates of catalyst atoms and thus delay the termination of growth.

碩士
國立臺北科技大學
製造科技研究所
89
This thesis is mainly focused on the synthesis and field emission property applications of carbon nanotubes (CNTs). A two-step process was employed to synthesize CNTs in that ion beam sputtering deposition (IBSD) was used to deposit iron or nickel catalyst thin films on silicon and Corning glass 7059 followed by hydrogen plasma pretreatment to form nano-size Fe or Ni particles and the CNTs growth by microwave plasma-enhanced chemical vapor deposition (MPECVD) at the second step. Well-aligned, uniform carbon nanotubes (CNTs) have been obtained in large area at low temperature of 500 °C using the present technique. The thickness of the catalyst thin film was found to be the most important factor in the low temperature growth process. Systematic control of the length, diameter, and alignment of the CNTs has been achieved by changing the deposition parameters such as microwave power, pressure, temperature, N2 flow rate and thickness of catalyst film. High resolution SEM and TEM were used to characterize the morphology and structure of the nanotubes. Raman spectroscopy was employed to analyze the bonding state of CNTs. For the property of the carbon nanotubes, field emission measurement showed a low turn on field (6.2 V/μm) and high emission current density (0.1 mA/cm2) for the films grown at a low temperature of 500 °C. However, a much lower turn on field (2.8 V/μm) and higher emission current density (35 mA/cm2) can be achieved for the films grown at a higher temperature of 1000 °C.