abstract: Flame retardants (FRs) are applied to variety of consumer products such as textiles and polymers for fire prevention and fire safety. Substantial research is ongoing to replace traditional FRs with alternative materials that are less toxic, present higher flame retardancy and result in lower overall exposure as there are potential health concerns in case of exposure to popular FRs. Carbonaceous nanomaterials (CNMs) such as carbon nanotubes (CNTs) and graphene oxide (GO) have been studied and applied to polymer composites and electronics extensively due to their remarkable properties. Hence CNMs are considered as potential alternative materials that present high flame retardancy. In this research, different kinds of CNMs coatings on polyester fabric are produced and evaluated for their use as flame retardants. To monitor the mass loading of CNMs coated on the fabric, a two-step analytical method for quantifying CNMs embedded in polymer composites was developed. This method consisted of polymer dissolution process using organic solvents followed by subsequent programmed thermal analysis (PTA). This quantification technique was applicable to CNTs with and without high metal impurities in a broad range of polymers. Various types of CNMs were coated on polyester fabric and the efficacy of coatings as flame retardant was evaluated. The oxygen content of CNMs emerged as a critical parameter impacting flame retardancy with higher oxygen content resulting in less FR efficacy. The most performant nanomaterials, multi-walled carbon nanotubes (MWCNTs) and amine functionalized multi-walled carbon nantoubes (NH2-MWCNT) showed similar FR properties to current flame retardants with low mass loading (0.18 g/m2) and hence are promising alternatives that warrant further investigation. Chemical/physical modification of MWCNTs was conducted to produce well-dispersed MWCNT solutions without involving oxygen for uniform FR coating. The MWCNTs coating was studied to evaluate the durability of the coating and the impact on the efficacy during use phase by conducting mechanical abrasion and washing test. Approximately 50% and 40% of MWCNTs were released from 1 set of mechanical abrasion and washing test respectively. The losses during simulated usage impacted the flame retardancy negatively. / Dissertation/Thesis / Doctoral Dissertation Materials Science and Engineering 2018

abstract: Nitrate is the most prevalent water pollutant limiting the use of groundwater as a potable water source. The overarching goal of this dissertation was to leverage advances in nanotechnology to improve nitrate photocatalysis and transition treatment to the full-scale. The research objectives were to (1) examine commercial and synthesized photocatalysts, (2) determine the effect of water quality parameters (e.g., pH), (3) conduct responsible engineering by ensuring detection methods were in place for novel materials, and (4) develop a conceptual framework for designing nitrate-specific photocatalysts. The key issues for implementing photocatalysis for nitrate drinking water treatment were efficient nitrate removal at neutral pH and by-product selectivity toward nitrogen gases, rather than by-products that pose a human health concern (e.g., nitrite). Photocatalytic nitrate reduction was found to follow a series of proton-coupled electron transfers. The nitrate reduction rate was limited by the electron-hole recombination rate, and the addition of an electron donor (e.g., formate) was necessary to reduce the recombination rate and achieve efficient nitrate removal. Nano-sized photocatalysts with high surface areas mitigated the negative effects of competing aqueous anions. The key water quality parameter impacting by-product selectivity was pH. For pH < 4, the by-product selectivity was mostly N-gas with some NH4+, but this shifted to NO2- above pH = 4, which suggests the need for proton localization to move beyond NO2-. Co-catalysts that form a Schottky barrier, allowing for localization of electrons, were best for nitrate reduction. Silver was optimal in heterogeneous systems because of its ability to improve nitrate reduction activity and N-gas by-product selectivity, and graphene was optimal in two-electrode systems because of its ability to shuttle electrons to the working electrode. "Environmentally responsible use of nanomaterials" is to ensure that detection methods are in place for the nanomaterials tested. While methods exist for the metals and metal oxides examined, there are currently none for carbon nanotubes (CNTs) and graphene. Acknowledging that risk assessment encompasses dose-response and exposure, new analytical methods were developed for extracting and detecting CNTs and graphene in complex organic environmental (e.g., urban air) and biological matrices (e.g. rat lungs). / Dissertation/Thesis / Ph.D. Civil and Environmental Engineering 2013

La croissance de nanotubes de carbone (NTC) sur particules micrometriques d'alumine (Al2O3) permet d'obtenir une dispersion uniforme des NTC dans des matrices sans enchevêtrement de NTC. Ce type de structure hybride NTC-Al2O3 fournit également une solution prometteuse au problème de sécurité de NTC car ils intègrent NTC avec des particules micrométriques, étendant la dimension des NTC à partir de nano-échelle au micro-échelle. Cependant, l'adhérence entre les NTC et les Al2O3 particules ne permet pas de fixer efficacement les NTC. Par ailleurs, une autre préoccupation essentielle de NTC est de savoir comment créer une forte adhésion interfaciale entre les NTC et les matrices polymères pour obtenir de bonnes propriétés mécaniques et de ne pas diminuer la conductivité électrique de NTC. Motivé par ces considérations, cette thèse vise à proposer plusieurs techniques concernant le dépôt d'une nano-couche conductrice sur la surface des structures hybrides NTC-Al2O3. De plus, les impacts de la nano-couche déposée sur la fixation des NTC à la surface d’Al2O3, sur la conductivité électrique des hybrides NTC-Al2O3, et sur l'adhésion interfaciale des systèmes NTC-Al2O3/epoxy composites sont étudiés en détail. / Growth of carbon nanotubes (CNTs) on micro-sized alumina (Al2O3) particles helps to achieve a uniform dispersion of CNTs in matrices without CNT entanglement. This kind of CNT-Al2O3 hybrids also provides a promising solution to the CNT safety problem since they integrate CNTs with micrometric particles, extending dimension of CNT fillers from nano-scale to micro-scale. However, the adhesion between the CNTs and the Al2O3 particles doesn’t sufficiently enable to fix the CNTs firmly and stably. Besides, another crucial concern of CNTs is how to create a strong interfacial adhesion between CNTs and polymer matrices for good mechanical properties and meanwhile not to degrade CNTs’ electrical conductivity. Motivated by these considerations, this PhD thesis aims to establishing several techniques for deposition of an electrically conductive nano-layer on the surface of CNT-Al2O3 hybrids. And the impacts of the deposited nano-layer on the fixing the CNTs on the Al2O3 surface, on bulk electrical conductivity of the CNT-Al2O3 hybrids, and on the interfacial adhesion of CNT-Al2O3/epoxy composite systems are investigated in detail.

L'augmentation croissante de la demande en énergie et l'épuisement des combustibles fossiles exigent l'amélioration de l'efficacité de l'utilisation de l'énergie ainsi que la recherche de ressources durables et renouvelables. Les condensateurs sont des systèmes de stockage de l'énergie qui se sont imposés comme une des solutions aux problèmes énergétiques en raison de leurs avantages, tels que le respect de l'environnement, et la charge et la décharge d'énergie très rapides. Des besoins se sont créés pour un système de stockage capacitif à faible coût et à haut rendement, il est donc nécessaire de développer des matériaux avec une forte permittivité diélectrique. A ce propos, les composites diélectriques à matrice polymère suscitent une attention croissante en raison de leurs bonnes performances diélectriques. Des composites à matrice polymère chargée de particules céramiques ont par exemple été utilisés dans certains condensateurs pour le stockage d'énergie. Pourtant, en pratique, l'applicabilité de tels dispositifs est sérieusement entravée par la faible permittivité diélectrique des matériaux d'une part, et par la détérioration des propriétés mécaniques en raison de la forte teneur en particules céramiques rigides dans la matrice polymère flexible d'autre part. En remplaçant ces particules céramiques par des particules conductrices dans la matrice polymère, des composites percolatifs peuvent être réalisés avec une permittivité diélectrique nettement accrue au voisinage du seuil de percolation. Parmi les charges conductrices, les nanotubes de carbone (NTC) ont été les plus étudiés. En effet, du fait de leur facteur d'aspect et de leur conductivité élevée, ces derniers peuvent conduire à des niveaux de percolation dans les composites pour une très faible quantité de charges. Un des plus grands défis pour l'utilisation des NTC dans les matériaux composites est de séparer les NTC les uns des autres afin de réaliser une dispersion uniforme dans les polymères. Les travaux présentés dans cette thèse ont porté sur l'augmentation de la permittivité diélectrique de matériaux composites à matrice polymère à base de NTC en optimisant à la fois la dispersion des nanotubes ainsi que le contrôle de la microstructure des matériaux composites finaux. L'augmentation de la permittivité diélectrique dans les composites précédents provient de la formation de microcondensateurs au sein du matériau. Toutefois, les NTC ont toujours tendance à s'agglomérer dans le composite, ce qui n'est pas bénéfique à la formation de microcondensateurs. Pour surmonter ce problème, nous avons proposé une microarchitecture hybride SiC-NTC comme charge conductrice. Ces hybrides mulit-échelles ont été produits par dépôt chimique catalytique en phase vapeur assisté par aérosol. L'organisation des NTC sur les particules de SiC peut être efficacement contrôlée en ajustant les différents paramètres de synthèse. Les résultats ont montré que les propriétés de surface asymétriques des micro-particules de SiC étaient plutôt favorables à la croissance des NTC sur SiC selon "une direction unique", alors que certaines conditions expérimentales particulières peuvent aboutir à une croissance "multi-directionnelle". Les particules hybrides de SiC-NTC ainsi obtenues ont également été incorporées dans le PVDF pour préparer des composites percolatifs. Il a été constaté que les hybrides SiC-NTC permettent d'améliorer considérablement la permittivité diélectrique du composite avec un chargement extrêmement faible en NTC. Les NTC sont orientés le long d'un axe sur chaque microplaque de SiC et séparés par une couche mince de polymère, donnant lieu à un réseau de microcondensateurs. Par conséquent, de grandes permittivités diélectriques de plus de 8700 et 2100 à 100 Hz peuvent être obtenues pour un faible taux de chargement de NTC de l'ordre de 2,30% et 1,48% en volume pour les composites à renforts "multi-directionnel" et "unidirectionnel" respectivement. / Ever-increasing energy requirement and exhaustion of fossil fuels demands improving efficiency of energy usage as well as seeking sustainable and renewable resources. Energy storage capacitors are devices that could take this responsibility, and have been the focus of increasing attention due to their advantages such as environment friendliness and very fast energy uptake and delivery. As the requirements grow for a low-cost and high-efficiency capacitive storage system, there is great need for the development of materials with high dielectric permittivity. Polymer composite dielectrics are arousing increasing attention due to their large tunability in dielectric performances. Polymer composites filled with ceramic particles have been used in some energy storage capacitors. Still, their applicability for practical devices is severely hindered by the low dielectric permittivity and deteriorated mechanical and processing properties due to the high content of rigid ceramic particles in the flexible polymer matrix. By replacing ceramic particles with conductive particles in the polymer composites, the percolative polymer composites can be made with the dielectric permittivity dramatically increased in the vicinity of the percolation threshold. Among the conductive fillers, carbon nanotubes (CNTs) have been most intensively studied, as their large aspect ratio coupled with high conductivity can lead to percolation levels in composites at much low loading. One of the greatest challenges for CNT usage in composites is to debundle pristine CNTs and realize uniform dispersion into polymers. This thesis focused on increasing the dielectric permittivity of CNT-based polymer composites by both carefully optimizing the dispersion of nanotubes as well as controlling the microstructure of the composites. The dielectric permittivity increment in the previous composite systems originated from the formation of microcapacitors. However, CNTs were always frizzy in the CNT/polymer composites, which was not beneficial in forming parallel pair electrodes of microcapacitors. To overcome this problem, we proposed a microarchitecture of hybrid SiC-CNT as conductive filler. Such micro/nano hybrids were produced by floating catalytic chemical vapor deposition. The organization mode of CNTs on SiC particles could be effectively tuned by adjusting synthesis conditions. The results showed that asymmetric surface properties of 6H-SiC were prone to led to “single-direction” growth of CNTs on SiC particles, while the competition between the substrate nature and the experimental conditions can resulted in a “multi-directions” hybrid structure. Resultant SiC-CNT hybrids were further incorporated into PVDF to prepare percolative composites. It was found that the SiC-CNT hybrid can significantly improve the dielectric permittivity of SiC-CNT/PVDF composite with an extremely low CNT loading. CNTs on each SiC microplate are oriented along an axis and separated by a thin polymer matrix, giving rise to a network of microcapacitors. As a result, a large dielectric permittivity of more than 8700 and 2100 at 100 Hz could be obtained at a low CNT loading of 2.30 vol% and 1.48 vol% in the “multi-directions” and “single-direction” composites respectively.

Dans le vaste domaine des nanosciences et nanotechnologies, les nanotubes de carbone (NTC) suscitent un intérêt particulier en raison de leur structure originale qui leur confère des propriétés exceptionnelles. Alors que le nombre d'applications ainsi que la quantité de NTC produite ne cessent d'augmenter chaque année, il est essentiel de comprendre les mécanismes régissant la formation de ces nanomatériaux afin de contrôler leur structure et leur organisation, optimiser les rendements, diminuer les risques sanitaires et environnementaux et améliorer les performances des matériaux et composants sous-jacents. Parmi les techniques de synthèse répertoriées, la CVD d'aérosol (Chemical Vapor Deposition) développée au laboratoire MSSMat, permet la croissance continue de NTC multi-feuillets de haute qualité sur divers substrats par l’injection simultanée de sources carbonées liquide (xylène) et gazeuse (acétylène) et de précurseur catalytique (ferrocène) dans un réacteur porté à une température comprise entre 400 et 1000°C. L'objectif de cette étude a consisté à examiner les différentes étapes de la formation des NTC dès l'injection des précurseurs jusqu'à la fin de la croissance. Grâce une nouvelle approche expérimentale faisant intervenir plusieurs diagnostics in situ couplés à des modèles numériques, nous avons pu suivre l'évolution des différents réactifs et produits lors de synthèses dans des conditions thermodynamiques (flux de gaz et températures) et chimiques (concentrations des différents précurseurs) variées. De fait, après avoir examiné l'évolution spatiale des gouttelettes formées lors de l'injection, la germination des nanoparticules en phase gazeuse a été étudiée par incandescence induite par laser (L2I) et spectroscopie de plasma induit par laser (LIPS). Une relation entre la taille de ces particules et celle des NTC a ainsi pu être mise en évidence. Les réactions chimiques pendant la synthèse ont ensuite été analysées par spectrométrie de masse et chromatographie en phase gazeuse. Différents mécanismes réactionnels ont ainsi pu être identifiés en fonction des sources de carbone utilisées, alors que l'effet de l'hydrogène sur la croissance, soit accélérateur ou soit inhibiteur selon les conditions, a été étudié. Les rôles du substrat ont par ailleurs été examinés en comparant la croissance et la morphologie des NTC obtenus sur différentes surfaces telles que des plaques de quartz, des fibres de carbone ou des micro-particules d'alumine, de carbure de silicium, de carbure de titane et de graphène de formes variées. L'effet catalytique de certains substrats ou mélanges de substrats sur la croissance des NTC a d'ailleurs été mis en évidence, de même que l'importance du rapport surface/volume des substrats sur les rendements massiques des NTC. La cinétique de croissance des NTC a finalement été étudiée et différents mécanismes à l'origine de la désactivation des catalyseurs ont été identifiés. Enfin, les différentes nanostructures hybrides issues de la croissance de NTC sur différents substrats ont servi à concevoir des matériaux composites multi-fonctionnels à hautes-performances dont les propriétés électriques, thermiques et mécaniques ont été analysées. / In the vast field of nanoscience and nanotechnology, carbon nanotubes (CNTs) are of particular interest because of their unique structure which provides them outstanding properties. While the number of CNT-based applications as well as the amount of CNTs produced are increasing year by year, it is essential to understand the mechanisms governing the formation of these nanomaterials to control their structure and organization, maximize the yields, reduce the health and environmental risks and improve the performance of the underlying materials and components. Among the listed synthesis techniques, the aerosol-assisted chemical vapor deposition (CVD) process developed in the laboratory MSSMat allows continuous growth of multi-walled CNTs (MWNTs) on various substrates by the simultaneous injection of carbon feedstock(s) (xylene and/or acetylene) and catalytic precursor (ferrocene) in a reactor heated up to a temperature ranging between 400 and 1000°C. The aim of this study was to analyse the different stages of the CNT formation from the first precursor injection until the growth termination. By the mean of a new experimental approach involving several in situ diagnostics coupled with numerical models, we were able to follow the evolution of the different products and reagents during the synthesis under various thermodynamic and chemical conditions. Hence, after investigating the spatial evolution of the droplets formed in the injection, the nanoparticle germination and nucleation in the gas phase has been studied by time resolved laser-induced incandescence (TRL2I) and laser-induced breakdown spectroscopy (LIBS). A relationship between the size of the particles and the CNTs has been highlighted. Moreover, the chemical reactions during the synthesis were analyzed by mass spectrometry (MS) and gas phase chromatography (GPC). Different reaction pathways have thus been identified depending on the carbon source(s) used, while the effect of hydrogen on the CNT growth, either accelerating or inhibiting based on the CVD conditions, was studied. The substrates' roles were then examined by comparing the growth and morphology of the CNTs obtained on various surfaces such as quartz plates, carbon fibers or micro-particles of alumina, silicon carbide, titanium carbide and graphene. The catalytic effect of some substrates or mixtures of substrates on the CNT growth has also been highlighted, as well as the importance of the substrate's surface/volume ratio on the CNT mass yields. Furthermore, the CNT growth kinetics have been studied and different mechanisms inducing catalyst deactivation and subsequently growth termination were identified. Finally, the different as-synthesized nanostructures originated from the hybridization of CNTs with other materials were used to prepare high-performance multi-functional composites. The electrical, thermal and mechanical properties of these materials have been examined.

Field emission is the emission of electrons from a solid under an intense electric field, of the order of 109 V/m. Emission occurs by the quantum mechanical tunneling of electrons through a potential barrier to vacuum. Field emission sources offer several attractive features such as instantaneous response to field variation, resistance to temperature fluctuation and radiation, a high degree of focusing ability in electron optics, good on/off ratio, ballistic transport, and a nonlinear current-voltage relationship. Carbon nanotubes (CNTs) are potential candidates as field emitters since they possess high aspect ratio and are chemically inert to poisoning, and physically inert to sputtering during field emission. They can carry a very high current density and do not suffer field-induced tip sharpening like metallic tips. In addition, the CNT field emitters have the advantage of charge transport through 1D channels and electron emission at the sharp tips due to large enhancement. But the injection of electrons from the back contact remains a technical challenge which requires binding of CNT emitters to metallic substrate. Also, detachment of the CNT from the substrate tends to occur with time. The electrically conducting mixtures of CNTs and polymer can provide an alternative route to address these issues in the field emission of CNTs. The composites can be casted on any substrate in desired shape and the polymer matrix provides necessary support. The research work reported in this thesis includes the preparation of high quality multiwall carbon nanotubes (MWCNTs), MWCNT-polystyrene (PS) composites, and experimental investigation on field emission properties of MWCNT¬PS composites in two different configurations. Electrical conductivity and percolation threshold of the MWCNT-PS composites are also investigated to ensure their high quality prior to the field emission studies. The study has been further extended to reduced graphene oxide (rGO) coated on polymer substrate. The main results obtained in present work are briefly summarized below. This thesis contains eight chapters. Chapter 1 provides an overview of basics of field emission, and the potential of CNT and CNT-polymer composites as field emitters. Chapter 2 deals with the concise introduction of various structural characterization tools and experimental techniques employed in this study. Chapter 3 describes the synthesis of MWCNTs and characterization by using electron microscopy and Raman spectroscopy. MWCNTs are synthesized by chemical vapor deposition (CVD) of toluene [(C6H5) CH3] and ferrocene [(C5H5)2 Fe] mixture at 980 °C. Here toluene acts as carbon source material and ferrocene provides catalytic iron (Fe) particles. The MWCNT formation is based on the thermal decomposition of the precursor mixture. Scanning electron microscopy (SEM) characterization shows that the MWCNTs are closely packed and quite aligned in one direction. The average length of MWCNTs is about 200 μm and outer diameter lies in the range of 50-80 nm. The high quality of as-prepared MWCNT sample is confirmed by Raman spectroscopy. The as-grown MWCNTs are encapsulated with catalytic Fe nanoparticles, revealed by transmission electron microscopy. The Fe nanoparticles trapped within the MWCNT serve as fantastic system for studying the magnetic properties. Three types of MWCNT samples filled with Fe nanoparticles of different aspect ratio (~10, 5 and 2) are synthesized by varying the amount of ferrocene in the precursor material, and their magnetic properties are investigated. Enhanced values of coercivity (Hc) are observed for all samples, Hc being maximum (~2.6 kOe) at 10 K. The enhancement in Hc values is attributed to the strong shape anisotropy of Fe nanoparticles and significant dipolar interactions between Fe nanoparticles. Chapter 4 deals with the field emission studies of MWCNT-PS composites in the parallel configuration. By incorporating as-prepared MWCNTs in PS matrix in a specific ratio, composites with varying loading from 0.01-0.45 weight (wt.) fraction are prepared using solution mixing and casting. High degree of dispersion of MWCNTs in PS matrix without employing any surfactant is achieved by ultrasonication. Low percolation threshold (~0.0025 wt. fraction) in the MWCNT-PS composites ensures the good connectivity of filler in the fabricated samples. Field emission of MWCNT¬PS composites is studied in two different configurations: along the top surface of the film (parallel configuration) and along the cross section of the sample (perpendicular configuration). In this chapter field emission results of the MWCNT-PS composites in parallel configuration are presented. The effect of charge transport in limiting the field emission of MWCNT-PS composite is discussed. Field emission results of MWCNT-PS composites in parallel configuration indicate that the emission performance can be maximized at moderate wt. fraction of MWCNT (0.15). The obtained current densities are ~10 µA/cm2 in the parallel configuration. Chapter 5 presents the study of field emission characteristics of MWCNT¬PS composites of various wt. fractions in the perpendicular configuration. Till date most studies using nanotube composites tend to have the nanotubes lying in two dimensional plane, perpendicular to the applied electric field. In the perpendicular configuration, the nanotubes are nearly aligned parallel to the direction of the applied electric field which results in high field enhancement, and electron emission at lower applied fields. SEM micrographs in cross-sectional view reveal that MWCNTs are homogeneously distributed across the thickness and the density of protruding tubes can be scaled with wt. fraction of the composite film. Field emission from composites has been observed to vary considerably with density of MWCNTs in the polymer matrix. High emission current density of 100 mA/cm2 is achieved at a field of 2.2 V/µm for 0.15 wt. fraction. The field emission is observed to follow the Fowler– Nordheim tunneling mechanism, however, electrostatic screening plays a role in limiting the current density at higher wt. fractions. Chapter 6 highlights the field emission response of rGO coated on a flexible PS film. Field emission of rGO coated PS film along the cross section of the sample is studied in addition to the top film surface of the film. The effect of geometry on the improved field emission efficiency of rGO coated polymer film is demonstrated. The emission characteristics are analyzed by Fowler–Nordheim tunneling for field emission. Low turn-on field (~0.6 V/µm) and high emission current (~200 mA/cm2) in the perpendicular configuration ensure that rGO can be a potential field emitter. Furthermore, stability and repeatability of the field emission characteristics are also presented. Chapter 7 deals with the synthesis, characterization, and field emission of two different kinds of hybrid materials: (1) MWCNT coated with zinc oxide (ZnO) nanoparticles (2) ZnO/graphitic carbon (g-C) core-shell nanowires. The field emission from the bucky paper is improved by anchoring ZnO nanoparticles on the surface of MWCNT. A shift in turn on field from 3.5 V/µm (bucky paper) to 1.0 V/µm is observed by increasing the ZnO nanoparticle loading on the surface of MWCNT with an increase in enhancement factor from 1921 to 4894. Field emission properties of a new type of field emitter ZnO/g-C core-shell nanowires are also presented in this chapter. ZnO/g-C core/shell nanowires are synthesized by CVD of zinc acetate at 1300 °C. Overcoming the problems of ZnO nanowire field emitters, which in general possess high turn on fields and low current densities, the core-shell nanowires exhibit excellent field emission performance with low turn on field of 2.75 V/µm and high current density of 1 mA/cm2. Chapter 8 presents a brief summary of the important results and future perspectives of the work reported in the thesis.

Neste trabalho foram realizadas simulações computacionais para investigar as propriedades eletrônicas de nanossistemas baseados em nanotubos de carbono e grafeno por meio de cálculos de primeiros princípios. Um dos nanossistemas investigados é formado por um nanotubo de carbono acoplado a eletrodos de nanofios de paládio encapsulados. Foi mostrado que estados provenientes dos eletrodos interagem fortemente com os estados do nanotubo de carbono. Cálculos de transporte eletrônico foram realizados para investigar a potencialidade desse nanossistema em aplicações como transistor de efeito de campo. Foi mostrado que a intensidade da corrente elétrica desse nanossistema pode ser variada com o campo elétrico de gate. Outro trabalho desenvolvido no presente trabalho tem como base um nanossistema formado pelo grafeno depositado nos substratos SiO2 amorfo e h-BN. Foi determinada a energia de adsorção e a quantidade de carga transferida para investigar a influênicas desses substratos na adsorção da molécula de H2 pelo grafeno. Foi mostrado que a energia de adsorção da molécula de H2 adsorivda na interface grafeno/SiO2 amorfo é menor em comparação com o grafeno suspenso ou disposto sobre o substrato h-BN. Além disso, a adsorção do H2 nessa região resulta em uma transferência de carga de uma ordem de grandeza maior em comparação com a adsorção no grafeno suspenso, sendo observado um deslocamento do Cone de Dirac em relação ao nível de Fermi. Esse estudo poderá contribuir para a construção de futuros sensores de H2 à base de grafeno. / In this work, ab initio calculations were performed within DFT framework to analyse electronic properties of Carbon nanotubes and grapheme nano systems. In this work, computer simulations were performed to investigate the electronic properties of nanosystems based on carbon nanotubes and graphene within DFT framework. One of these systems studied is a Carbon nanotube semiconductor coupled to encapsulated leads of Pd nanowires. It has been shown that leads states interact strongly with the carbon nanotube states. Electronic transport calculations were performed to unfold new applications of this system, such as the field effect transistor. We noticed that charge current intensity can be tuned by electrical field. We also described the influence of amorphous SiO2 and h-BN, in H2 energy adsorption and charge transfer, where both materials are used as graphene substrates. It was shown that the latter adsorption energy in the graphene/Si02 is smaller than graphene/h-Bn and the graphene suspended itself. In fact this adsorption results in a charge transference one order greater than in the suspended graphene, which can be seen as a vertical shift of the Dirac Cone. This study may improve the construction of future H2 sensors based on graphene.

Orientador: Ana Flavia Nogueira / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-10T16:04:48Z (GMT). No. of bitstreams: 1 Lomba_BrunoStelutti_M.pdf: 2789085 bytes, checksum: c5cf56c110af4564ce46cde2fd239d4f (MD5) Previous issue date: 2007 / Resumo: Nanotubos de carbono de paredes simples (SWNT) têm atraído grande interesse devido a sua aplicação em diversas áreas de pesquisa, incluindo novos materiais e dispositivos optoeletrônicos. Entretanto uma boa dispersão destes materiais é um fator necessário na obtenção de filmes homogêneos, com menor grau de agregação para se obter dispositivos com maior desempenho. Neste trabalho, foi realizada uma modificação química das extremidades e defeitos dos SWNT com grupos tiofenos com a finalidade de melhorar a interação do nanotubo de carbono com a matriz polimérica de poli(3-octiltiofeno) (POT). De fato, células solares com melhor desempenho foram obtidas. O SWNT modificado e seu compósito com POT foram caracterizados por espectroscopia Raman, espectroscopia no infravermelho, espectroscopia UV-VIS e voltametria cíclica. A melhor célula solar de heterojunção dispersa foi obtida usando 5 % m m de SWNT modificado (SWNT-TIOF), e apresentou potencial de circuito aberto (Voc), fotocorrente (Isc) e eficiência (h) de 0,75 V, 9,5 mA cm e 0,184 %, respectivamente. O uso de um derivado de indenofluoreno (DPIF) como camada transportadora de buraco no lugar do polietilenodioxitiofeno dopado com sulfato de poliestireno (PEDOT:PPS) também foi investigado. Os resultados iniciais indicam que o uso dessa camada pode ser uma tentativa interessante para melhorar o Voc de células solares orgânicas / Abstract: Single-wall carbon nanotubes (SWNT) have attracted great interst for applications in a variety of research areas, including electronics and functional materials. However, a good dispersion of these materials is a demanding factor in order to obtain more homogeneous and less bundled films for constructing devices. In this report we describe how a covalent modification with thiophene groups at the edges and defects of SWNT can improve interaction with a polymer matrix, resulting in solar cells with improved performance. The modified SWNT and its composite with poly(3-octylthiophene) were characterized by Raman, Infrared and UV-VIS spectroscopies and cyclic voltammetry. The best bulk heterojunction solar cell was obtained using 5 wt % of the modified carbon nanotube (SWNT-THIOP) and shows open circuit voltage (Voc), photocurrent (Isc) and efficiency (h) of 0.75 V, 9.5 mA cm e 0,184 %, respectively. The use of an idenofluorene derivative as a hole transport layer in replacement of the PEDOT:PPS was also investigated. The primary results indicate that the use of this layer can be an interesting approach to improve the open-circuit voltage in polymer/nanotube solar cells / Mestrado / Quimica Inorganica / Mestre em Química

Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2017-03-29T12:58:51Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertação OK Priscila Mendonça.pdf: 4293178 bytes, checksum: abd6cd49376b8e172e0ce8adf3135b8d (MD5) / Made available in DSpace on 2017-03-29T12:58:51Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertação OK Priscila Mendonça.pdf: 4293178 bytes, checksum: abd6cd49376b8e172e0ce8adf3135b8d (MD5) Previous issue date: 2016-06-10 / CAPES / CNPQ / A dengue é uma doença viral considerada um dos maiores problemas de saúde pública nas regiões tropicais e sub-tropicais do mundo, sendo endemicamente prevalente em cerca de 112 países. Anualmente, afeta cerca de 50 a 100 milhões de pessoas, resultando em taxas de mortalidade entre 0,03% a 1,4%. É uma doença auto-limitante, caracterizada por febre, dor de cabeça, mialgia, entre outros sintomas. Na sua forma severa (síndrome do choque por dengue e febre hemorrágica), a doença pode levar ao óbito, principalmente em crianças. A proteína não estrutural 1 (NS1) do vírus dengue circula abundantemente no sangue durante toda a viremia, estando em níveis maiores na fase aguda; assim esta pode ser utilizada como marcador do estado agudo. Para o controle da infecção estão disponíveis testes diagnósticos baseados em ensaios sorológicos, testes imunocromatográficos e moleculares, entretanto estes apresentam limitações. O desenvolvimento de alternativas mais práticas, quantitativas e econômicas tem resultado na crescente busca por testes baseados em biossensores. Neste trabalho foi desenvolvido um imunossensor para detecção de NS1 baseado em uma plataforma nanoestruturada, constituída de nano-híbrido formado por nanotubos de carbono e filme polimérico de polietilenoimina montado sobre sistema eletroquímico constituído por microeletrodo de ouro. Os anticorpos monoclonais anti-NS1 foram imobilizados sobre a superfície eletródica por ligações covalentes com os nanotubos de carbono, permitindo um alta estabilidade durante as medidas. Todas as etapas de modificações da superfície eletródica foram caracterizadas eletroquimicamente, estrutural e morfologicamente através das técnicas de voltametria cíclica, espectroscopia de infravermelho por transformada de Fourier (FT-IR) e microscopia eletrônica de varredura, respectivamente. A espessura do filme nanoestruturado foi determinada por medidas piezoelétricas, em um sistema de microbalança de cristal de quartzo de acordo com a equação de Sauerbrey. A resposta analítica do imunossensor frente a proteína NS1 foi obtida por amperometria aplicando-se a técnica de voltametria de onda quadrada (VOC). O imunossensor apresentou resposta linear entre 0,1 a 0,6 µg.mL-1 de NS1. Os dados ajustados para a equação de regressão linear exibiu coeficiente de correlação de 0,996 (p << 0,01, n = 7) e um baixo erro relativo (aproximadamente 1%). O imunossensor apresentou limite de detecção de 0,038 µg.mL-1 e limite de quantificação de 0,1 µg.mL-1 de NS1, sendo similar aos obtidos na literatura, porém com a vantagem de não requerer antígenos ou anticorpos marcados (label-free) e utilizar técnica analítica mais simples (VOC). Os resultados indicam que o imunossensor apresenta sensibilidade compatível para detecção de NS1 em níveis sorológicos, permitindo ser uma ferramenta prática, rápida e econômica para o diagnóstico da dengue, sobretudo para detecção precoce da fase aguda. / Dengue is a viral disease considered as a major public health problems in tropical and sub-tropical world, endemically being prevalent in about 112 countries. Annually, it affects 50 to 100 million people, resulting in mortality rates of 0.03% to 1.4%. It is a self-limiting disease characterized by fever, headache, myalgia, among other symptoms. In its severe form (shock syndrome and dengue haemorrhagic fever), the disease can lead to death, especially in children. The nonstructural protein 1 (NS1) of the dengue virus circulates in blood abundantly throughout viremia, with higher levels in the acute phase; thus it can be used as a marker of the acute stage. For control of infection are available diagnostic testings based on serological assays, immunochromatographic and molecular assyas, however these have limitations. The development of more practical, quantitative and economic alternatives has resulted in growing demand for tests based on biosensors. In this work, it was developed an immunosensor for NS1 detection based on a nanostructured platform consisting of nanohybrid comprising carbon nanotubes and polymeric film polyethyleneimine mounted on electrochemical system consisting of gold microelectrode. The anti-NS1 monoclonal antibodies were immobilized on the electrode surface by covalent bonds with carbon nanotubes, allowing for a high stability during the measurements. All steps of electrode modifications were characterized by electrochemical, structural and morphologically techniques through cyclic voltammetry, infrared spectroscopy by Fourier transform (FT-IR) and scanning electron microscopy, respectively. The thickness of the nanostructured film was determined by piezoelectric system using a quartz crystal microbalance, according to the Sauerbrey equation. The analytical response of the immunosensor against NS1 protein was obtained by applying amperometry by square wave voltammetry (SWV). The immunosensor showed a linear response between 0.1 to 0.6 μg.mL-1 NS1. The data set into the linear regression equation showed a correlation coefficient of 0.996 (p << 0.01, n = 7) and a low relative error (about 1%). The immunosensor presented detection limit of 0.038 μg.mL-1 and a limit of quantification of 0.1 μg.mL-1 NS1, being similar to those obtained in literature, but with advantage of not requiring labeled antigen or antibody (label- free) and to require a more simple analytical technique (VOC). The results indicate that the achieved sensitivity was similar NS1 immunosensors, allowing it to be convenient, fast and economical tool for dengue diagnosis, particularly for early detection of acute phase.

Made available in DSpace on 2018-06-27T18:56:39Z (GMT). No. of bitstreams: 3 Ivi Lara.pdf: 2225740 bytes, checksum: 7987b7b16ad759ad1c13cf82cc2ba0ae (MD5) Ivi Lara.pdf.txt: 179428 bytes, checksum: 7367389b56d0393e07698631b3f3e926 (MD5) Ivi Lara.pdf.jpg: 3328 bytes, checksum: adc571d951701abcdea7d0b3762d108a (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This dissertation studied the interaction of carboxyl groups -COOH with (8,0) and (16,0) single wall carbon nanotubes, both semiconductors, by ab initio calculation based on the formalism of the Density Functional Theory using the SIESTA code, in which were adopted localized bases to the electronic wave functions description and Troullier- Martins pseudopotentials for describing the interaction between valence electrons and core electrons. As the -COOH group is taken as default when the purpose of the carbon nanotubes functionalization is to make them hydrophilic, this interaction was studied by different positions of the carboxyl on the nanotubes walls with different concentrations of those seeking to verify the influence of these parameters in the electronic character of the carbon nanotubes. By analyzing the energetic, structural and electronic properties of all patterns, it is observed that the carboxyl groups interact with the nanotubes through covalent bonds (binding energies between &#8722;3.39 and &#8722;0.73 eV , with the smallest for the case of carboxyl confined within the nanotube), nanotubes (16,0) are more flexible than the (8,0) (when connected to the same number of carboxyl groups), and a behavior, very interesting, is presented when the concentration of carboxylation is varied: the character of the system can be modulated from a semiconductor to semiconductor with a halffilled level over the Fermi level (methalic character tendency). It is still studied in this work, the dynamics of water molecules around pure and carboxylated carbon nanotubes, obtained from ab initio calculations, through classic molecular dynamics simulations, using empirical parameters with the GROMACS program. The structural analysis of water around the tubes indicated the already expected hydrophobic character of the pure nanotubes and the hydrophilic character of the carboxylated nanotubes with which the water molecules interactions are greater with its walls, a fact confirmed by energy analysis, which shows a higher interaction energy in this system. This work has, in addition to contributing to the understanding and analysis of related experimental results, pointing out also the possibility to modulate the electronic behavior of these systems at the nanoscale. / Nesta dissertação é estudada a interação de grupos carboxila (-COOH) com nanotubos de carbono de paredes simples dos tipos (8,0) e (16,0), ambos semicondutores, através de cálculos ab initio baseados no formalismo da Teoria do Funcional da Densidade. Foi utilizado o programa SIESTA, no qual foram adotadas bases localizadas para a descrição das funções de onda eletrônicas, bem como pseudopotenciais de Troullier-Martins para a descrição da interação entre os elétrons de valência e o caroço atômico. Como o grupo -COOH é usado como grupo padrão quando o objetivo da funcionalização ao dos NTCs é torná-los hidrofílicos, esta interação foi estudada através de diferentes posições das carboxilas nas paredes dos nanotubos, com diferentes concentrações destas, buscando verificar a influência destes parâmetros no caráter eletrônico dos NTCs. Analisando as propriedades energéticas, estruturais e eletrônicas de todas as configurações estudadas, observa-se que as carboxilas interagem com os nanotubos através de ligações covalentes (energias de ligação entre &#8722;3, 39 e &#8722;0, 73 eV , sendo a menor para o caso da carboxila confinada no interior do nanotubo), os nanotubos (16,0) se mostram mais flexíveis que os (8,0) (quando ligados ao mesmo número de carboxilas) e, um comportamento, bastante interessante, se apresenta quando a concentração da carboxilação é variada: o caráter do sistema pode ser modulado de semicondutor para semicondutor com gap semipreenchido (tendência a caráter metálico). É, estudada ainda, neste trabalho, a dinâmica das moléculas de água em torno de nanotubos puros e carboxilados, obtidos a partir dos calculos ab initio, através de simulações de dinâmica molecular clássica, utilizando parâmetros empíricos com o programa GROMACS. A análise estrutural da água em torno dos nanotubos indicou o já esperado caráter hidrofóbico dos NTCs puros, bem como o caráter hidrofílico do nanotubo carboxilado, com o qual as moléculas de água passam a ter uma maior interação com suas paredes, fato este confirmado através da análise energética, que mostra uma maior energia de interação nesse sistema. Este trabalho vem, além de contribuir na compreensão e análise dos referentes resultados experimentais, apontar, ainda, a possibilidade de modular o comportamento eletrônico desses sistemas na nanoescala.