In this study, DLC thin films were electrodeposited at low DC potential using a mixture of acetic acid and DI water with different ratio. The parameters of DLC thin film deposition include the DC potential, deposition temperature, concentration of electrolyte solution, were correlated to the growth mechanism. The amount of nitrogen incorporated into DLC thin films were varied with the deposited temperature. The characteristics of DLC films by various measurements such as : the I-t curves of DLC film growth, SEM, AFM, FTIR, XPS, Raman and N&K spectroscopy, were investigated in detail. Experimental results showed that the surface roughness decreased, and sp3/sp2+sp3 value of DLC increased with the deposition temperature and deposition time. Optical properties showed that the refractive index, optical energy gap increased with the deposition temperature. For SEM cross-section measurement, it showed that the thickness of DLC films decreased due to the erosion process. However, the N-DLC films become graphitization. According to our study, we find that the surface morphology of the N-DLC films are homogeneous and compact. However, with the increase of the deposition temperature, the ratio of sp3-C-N bonds increase and the ratio of sp2-C-C bonds decrease, and these lead to the increase of refractive index and optical energy gap.

Nitrogen-doped TiO2 nanotubes with enhanced visible light photocatalytic activity have been synthesized using commercial titania P25 as raw material by a facile P25/urea co-hydrothermal method. Morphological and microstructual characteristics were conducted by transmission electron microscopy, powder X-ray diffraction, and nitrogen adsorption/desorption isotherms; chemical identifications were performed using X-ray photoelectron spectroscopy, and the interstitial nitrogen linkage to the TiO2 nanotubes is identified. The photocatalytic activity of all nitrogen-doped TiO2 nanotubes synthesized by different urea content, evaluated by the decomposition of rhodamine B dye solution under visible light using UV¡VVis absorption spectroscopy, is found to exhibit higher degradation rate than that of P25. Factors affecting the photocatalytic activity of RB were analyzed and a possible mechanism of photodegradation was also proposed. The high photocatalytic activity was attributed to the process of two different mechanisms, one was the direct degradation of the chromophoric system and the other was successive deethylation of the four ethyl groups.

This dissertation explores the electrochemical behavior of enzymes and their cofactors at carbon nanotube (CNT) and nitrogen-doped carbon nanotube (N-CNT) electrodes. Two common types of oxidoreductases are considered: flavin adenine dinucleotide (FAD)-dependent oxidases and nicotinamide adenine dinucleotide-dependent (NAD⁺)-dehydrogenases. Chapter 1 presents the oxygen reduction reaction (ORR) at N-CNT electrodes as a way to electrochemically measure enzymatic turnover at the electrode surface. The unique peroxide pathway at N-CNT electrodes, which catalytically disproportionates hydrogen peroxide (H₂O₂) back into oxygen, provides an increased ORR current directly proportional to the rate of enzymatic turnover for H₂O₂ producing enzymes, even in an oxygen saturated solution. Biosensing of L-lactate using the increased ORR current is demonstrated using L-lactate oxidase. Chapter 2 explores the surface bound electrochemical signal of FAD when FAD-dependent enzyme or free FAD is allowed to spontaneously adsorb onto the CNT/N-CNT surface. Specifically, the origin of the enzymatically generated FAD signal and the rate constant of the electron transfer are elucidated. Chapter 3 continues the discussion of the cofactor FAD by demonstrating its use as an informative surface specific redox probe for graphitic carbon surfaces. Primarily, FAD can be used to determine the electroactive surface area and the relative hydrophobicity/hydrophilicity of graphitic surfaces. Chapter 4 changes gears to NAD⁺-dependent dehydrogenases by investigating the electrocatalytic oxidation of NADH at N-CNTs in comparison with conventional carbon electrodes or nondoped CNTs. Biosensing of glucose through the oxidation of NADH is demonstrated using glucose dehydrogenase adsorbed onto the N-CNT surface. Chapter 5 continues the discussion of NAD⁺-dependent dehydrogenases by addressing the reaction kinetics of NADH oxidation at N-CNTs as a tool to measure the enzymatic reduction of NAD⁺.

No description available.

Carbon nanotubes (CNTs) are a relatively new allotrope of carbon that possess very unique and exciting physical characteristics. However, much is still unknown regarding their physical structure and chemical reactivity. The focus of this dissertation is to utilize the chemical modification of these filamentous carbon structures as a probe to investigate the structure and reactivity of carbon nanotubes. Also discussed is the ability of CNTs, once chemically modified, to interact with specific polymer matrices and how the addition of modified and unmodified CNTs affects the physical properties of these matrices.

Carbon nanostructures have been extensively used in different applications; ranging from electronic and optoelectronic devices to energy conversion. The interest stems from the fact that covalently bonded carbon atoms can form a wide variety of structures with zero-, one- and two-dimensional configuration with different physical properties. For instance, while fullerene molecules (zero-dimensional carbon structures) realize semiconductor behavior, two-dimensional graphene shows metallic behavior with exceptional electron mobility. Moreover the possibility to even further tune these fascinating properties by means of doping, chemical modification and combining carbon based sub-classes into new hybrid structures make the carbon nanostructure even more interesting for practical application.  This thesis focuses on synthesizing SWCNT and different C60 one-dimensional structures as well as tuning their properties by means of different chemical and structural modification. The purpose of the study is to have better understanding of the synthesis and modification techniques, which opens for better control over the properties of the product for desired applications. In this thesis carbon nanotubes (CNTs) are grown by chemical vapor deposition (CVD) on iron/cobalt catalyst particles. The effect of catalyst particle size on the diameter of the grown CNTs is systematically studied and in the case of SWCNTs it is shown that the chirality distribution of the grown SWCNTs can be tuned by altering the catalyst particle composition. In further experiments, incorporation of the nitrogen atoms in SWCNTs structures is examined. A correlation between experimental characterization techniques and theoretical calculation enable for precise analysis of different types of nitrogen configuration in SWCNTs structure and in particular their effect on growth termination and electronic properties of SWCNTs are studied. C60 one-dimensional structures are grown through a solution based method known as Liquid-liquid interfacial precipitation (LLIP). By controlling the crystal seed formation at the early stage of the growth the morphology and size of the grown C60 one-dimensional structures where tuned from nanorods to large diameter rods and tubes. We further introduce a facile solution-based method to photo-polymerize the as-grown C60 nanorods, and show that such a method crates a polymeric C60 shell around the nanorods. The polymeric C60 shell exhibits high stability against common hydrophobic C60 solvents, which makes the photo-polymerized nanorods ideal for further solution-based processing. This is practically shown by decoration of both as grown and photo-polymerized nanorods by palladium nanoparticles and comparison between their electrochemical activities. The electrical properties of the C60 nanorods are also examined by utilizing a field effect transistor geometry comprising different C60 nanorods. In the last part of the study a variant of CNT is synthesized in which large diameter, few-walled CNTs spontaneously transform to a collapsed ribbon shape structure, the so called collapsed carbon nanotube (CCNT). By inserting C60 molecules into the duct edges of CCNT a new hybrid structure comprising C60 molecules and CCNT is synthesized and characterized. A further C60 insertion lead to reinflation of CCNTs, which eventually form few-walled CNT completely filled with C60 molecules.

Este trabalho apresenta o estudo do desempenho de catalisadores nanoestruturados de dióxido de titânio, TiO2, dopados com nitrogênio, visando melhorar sua atividade fotocatalítica sob radiação visível. Os nanotubos de TiO2 foram preparados pelo método hidrotérmico, onde partículas de TiO2 reagem com NaOH a temperatura e pressão elevadas. Em seguida o material é tratado, através de uma lavagem ácida e calcinação, de modo a apresentar as características desejáveis para a aplicação como fotocatalisador. Foram determinadas as melhores condições de obtenção dos nanotubos avaliando-se sua atividade fotocatalítica, variando-se o pH da solução de lavagem e temperatura de calcinação. Determinadas essas condições, buscou-se em três compostos nitrogenados o melhor desempenho para dopagem de nanotubos. Foram eles: amônia, uréia e tiouréia. A reação de degradação do corante rodamina B foi utilizada para avaliar a atividade fotocatalítica dos catalisadores. Os experimentos foram realizados em um reator batelada agitado, com o catalisador em suspensão e na presença de aeração, sob radiação UV e visível. Avaliaram-se inicialmente as condições de reação, como concentração de catalisador e de corante, com o catalisador comercial e precursor de Ti, P25 Degussa. Além da determinação da atividade fotocatalítica, foram feitas as seguintes análises para caracterização dos materiais: difração de raios X (DRX), espectroscopia de refletância difusa (ERD), microscopia eletrônica de transmissão (MET) e determinação da área específica e volume de poros. A partir dos ensaios fotocatalíticos observou-se que os tratamentos a que foram submetidos os materiais tiveram grande influência na sua atividade catalítica. Sob radiação UV nenhum catalisador foi mais ativo que o P 25. Sob radiação visível, as amostras dopadas com tiouréia (NTT-4-500/TiouréiaI) e amônia (NTT-7-600/NH3I) apresentaram os melhores resultados, com um aumento na fotodegradação de 16 e 30 % em relação às amostras não dopadas, respectivamente. / This work presents the study of the catalytic performance of nanostructured titanium oxide, TiO2, doped with nitrogen in order to improve its photocatalytic activity under visible light. TiO2 nanotubes were prepared by hydrothermal method, where TiO2 particles react with NaOH at high temperature and pressure. Then the material was handled through an acid wash and calcination, in order to produce desirable characteristics for the photocatalyst applications. The best conditions for titania nanotubes preparation were determined by varying the pH of the wash water and calcination temperature. Established these conditions, the research focused on obtaining among three nitrogen doping the one that provided best performance of nanotubes. They were: ammonium hydroxide, urea and thiourea. The degradation reaction of rhodamine B dye was used to evaluate the photocatalytic activity of catalyst. The experiments were performed in a stirred batch reactor, with the catalyst in suspension and in the presence of aeration, in the presence of UV and visible radiations. Initially the reaction conditions, such as catalyst and dye concentrations, were determined with the commercial catalyst and Ti precursor, P25 Degussa. In addition to determining the photocatalytic activity, the material characterization was made by X-ray diffraction (XRD), diffusive reflectance spectroscopy (DRS), transmission electron microscopy (TEM) and determination of specific area and pore volume by N2 absorption isotherms. The photocatalytic tests showed that the acid washed and calcination had a strong influence on its photocatalytic activity. No synthesized catalyst presented a larger photodegradation activity under UV light than P25. Under visible light, the samples doped with thiourea (NTT-4-500/TiouréiaI), and ammonia (NTT-7-600/NH3I) showed the best results with an increase in the photodegradation activity of 16 and 30% compared to the undoped samples, respectively.

Este trabalho apresenta o estudo do desempenho de catalisadores nanoestruturados de dióxido de titânio, TiO2, dopados com nitrogênio, visando melhorar sua atividade fotocatalítica sob radiação visível. Os nanotubos de TiO2 foram preparados pelo método hidrotérmico, onde partículas de TiO2 reagem com NaOH a temperatura e pressão elevadas. Em seguida o material é tratado, através de uma lavagem ácida e calcinação, de modo a apresentar as características desejáveis para a aplicação como fotocatalisador. Foram determinadas as melhores condições de obtenção dos nanotubos avaliando-se sua atividade fotocatalítica, variando-se o pH da solução de lavagem e temperatura de calcinação. Determinadas essas condições, buscou-se em três compostos nitrogenados o melhor desempenho para dopagem de nanotubos. Foram eles: amônia, uréia e tiouréia. A reação de degradação do corante rodamina B foi utilizada para avaliar a atividade fotocatalítica dos catalisadores. Os experimentos foram realizados em um reator batelada agitado, com o catalisador em suspensão e na presença de aeração, sob radiação UV e visível. Avaliaram-se inicialmente as condições de reação, como concentração de catalisador e de corante, com o catalisador comercial e precursor de Ti, P25 Degussa. Além da determinação da atividade fotocatalítica, foram feitas as seguintes análises para caracterização dos materiais: difração de raios X (DRX), espectroscopia de refletância difusa (ERD), microscopia eletrônica de transmissão (MET) e determinação da área específica e volume de poros. A partir dos ensaios fotocatalíticos observou-se que os tratamentos a que foram submetidos os materiais tiveram grande influência na sua atividade catalítica. Sob radiação UV nenhum catalisador foi mais ativo que o P 25. Sob radiação visível, as amostras dopadas com tiouréia (NTT-4-500/TiouréiaI) e amônia (NTT-7-600/NH3I) apresentaram os melhores resultados, com um aumento na fotodegradação de 16 e 30 % em relação às amostras não dopadas, respectivamente. / This work presents the study of the catalytic performance of nanostructured titanium oxide, TiO2, doped with nitrogen in order to improve its photocatalytic activity under visible light. TiO2 nanotubes were prepared by hydrothermal method, where TiO2 particles react with NaOH at high temperature and pressure. Then the material was handled through an acid wash and calcination, in order to produce desirable characteristics for the photocatalyst applications. The best conditions for titania nanotubes preparation were determined by varying the pH of the wash water and calcination temperature. Established these conditions, the research focused on obtaining among three nitrogen doping the one that provided best performance of nanotubes. They were: ammonium hydroxide, urea and thiourea. The degradation reaction of rhodamine B dye was used to evaluate the photocatalytic activity of catalyst. The experiments were performed in a stirred batch reactor, with the catalyst in suspension and in the presence of aeration, in the presence of UV and visible radiations. Initially the reaction conditions, such as catalyst and dye concentrations, were determined with the commercial catalyst and Ti precursor, P25 Degussa. In addition to determining the photocatalytic activity, the material characterization was made by X-ray diffraction (XRD), diffusive reflectance spectroscopy (DRS), transmission electron microscopy (TEM) and determination of specific area and pore volume by N2 absorption isotherms. The photocatalytic tests showed that the acid washed and calcination had a strong influence on its photocatalytic activity. No synthesized catalyst presented a larger photodegradation activity under UV light than P25. Under visible light, the samples doped with thiourea (NTT-4-500/TiouréiaI), and ammonia (NTT-7-600/NH3I) showed the best results with an increase in the photodegradation activity of 16 and 30% compared to the undoped samples, respectively.

Este trabalho apresenta o estudo do desempenho de catalisadores nanoestruturados de dióxido de titânio, TiO2, dopados com nitrogênio, visando melhorar sua atividade fotocatalítica sob radiação visível. Os nanotubos de TiO2 foram preparados pelo método hidrotérmico, onde partículas de TiO2 reagem com NaOH a temperatura e pressão elevadas. Em seguida o material é tratado, através de uma lavagem ácida e calcinação, de modo a apresentar as características desejáveis para a aplicação como fotocatalisador. Foram determinadas as melhores condições de obtenção dos nanotubos avaliando-se sua atividade fotocatalítica, variando-se o pH da solução de lavagem e temperatura de calcinação. Determinadas essas condições, buscou-se em três compostos nitrogenados o melhor desempenho para dopagem de nanotubos. Foram eles: amônia, uréia e tiouréia. A reação de degradação do corante rodamina B foi utilizada para avaliar a atividade fotocatalítica dos catalisadores. Os experimentos foram realizados em um reator batelada agitado, com o catalisador em suspensão e na presença de aeração, sob radiação UV e visível. Avaliaram-se inicialmente as condições de reação, como concentração de catalisador e de corante, com o catalisador comercial e precursor de Ti, P25 Degussa. Além da determinação da atividade fotocatalítica, foram feitas as seguintes análises para caracterização dos materiais: difração de raios X (DRX), espectroscopia de refletância difusa (ERD), microscopia eletrônica de transmissão (MET) e determinação da área específica e volume de poros. A partir dos ensaios fotocatalíticos observou-se que os tratamentos a que foram submetidos os materiais tiveram grande influência na sua atividade catalítica. Sob radiação UV nenhum catalisador foi mais ativo que o P 25. Sob radiação visível, as amostras dopadas com tiouréia (NTT-4-500/TiouréiaI) e amônia (NTT-7-600/NH3I) apresentaram os melhores resultados, com um aumento na fotodegradação de 16 e 30 % em relação às amostras não dopadas, respectivamente. / This work presents the study of the catalytic performance of nanostructured titanium oxide, TiO2, doped with nitrogen in order to improve its photocatalytic activity under visible light. TiO2 nanotubes were prepared by hydrothermal method, where TiO2 particles react with NaOH at high temperature and pressure. Then the material was handled through an acid wash and calcination, in order to produce desirable characteristics for the photocatalyst applications. The best conditions for titania nanotubes preparation were determined by varying the pH of the wash water and calcination temperature. Established these conditions, the research focused on obtaining among three nitrogen doping the one that provided best performance of nanotubes. They were: ammonium hydroxide, urea and thiourea. The degradation reaction of rhodamine B dye was used to evaluate the photocatalytic activity of catalyst. The experiments were performed in a stirred batch reactor, with the catalyst in suspension and in the presence of aeration, in the presence of UV and visible radiations. Initially the reaction conditions, such as catalyst and dye concentrations, were determined with the commercial catalyst and Ti precursor, P25 Degussa. In addition to determining the photocatalytic activity, the material characterization was made by X-ray diffraction (XRD), diffusive reflectance spectroscopy (DRS), transmission electron microscopy (TEM) and determination of specific area and pore volume by N2 absorption isotherms. The photocatalytic tests showed that the acid washed and calcination had a strong influence on its photocatalytic activity. No synthesized catalyst presented a larger photodegradation activity under UV light than P25. Under visible light, the samples doped with thiourea (NTT-4-500/TiouréiaI), and ammonia (NTT-7-600/NH3I) showed the best results with an increase in the photodegradation activity of 16 and 30% compared to the undoped samples, respectively.

L'objectif de ce travail est la synthèse et l'étude des propriétés acido-basiques de nanotubes de carbone (CNT) dopés à l’azote pour les utiliser comme catalyseurs ou supports de catalyseurs. Pour ce faire, trois types de nanotubes de carbone dopés à l'azote ont été synthétisés, caractérisés et testés dans la conversion de l'alcool isopropylique. Les nanotubes de carbone dopés diffèrent par le taux d’azote et la présence ou non d'une section non dopée dans leur structure. Pour les matériaux à faible teneur en azote, la réaction conduit à la formation d'acétone indiquant la présence de sites basiques. À plus forte teneur en azote, les catalyseurs dopés conduisent à la formation d'acétone et de propène, mettant en évidence la présence de sites basiques et acides. La caractérisation par XPS nous a permis de proposer que les sites basiques sont constitués de groupes de surface pyridiniques et les sites acides sont des groupements sulfoniques formés au cours de la purification de ces matériaux avec de l'acide sulfurique. Des catalyseurs au ruthénium et au palladium supportés (2%) sur des nanotubes de carbone non dopés et dopés à l'azote (N-CNT), ont été préparés et évalués dans la réaction de décomposition de l'alcool isopropylique comme réaction test. La présence de fonctionnalités azotées (azote pyridinique, pyrrolique et quaternaire) sur le support dopé à l'azote induit une plus grande dispersion du métal. En ce qui concerne les catalyseurs supportés, ceux de palladium étaient plus actifs et plus sélectifs que ceux au ruthénium. De plus, les catalyseurs au Pd sont sélectifs en acétone, tandis que les catalyseurs au Ru conduisent à la déshydratation et la déshydrogénation. Le dopage des nanotubes de carbone par l’azote conduit aussi à l'apparition de propriétés d'oxydo-réduction. Enfin, nous avons montré que des nanotubes de carbone, constitués de deux sections différentes : une partie non dopée hydrophobe reliée à un segment hydrophile, sont amphiphiles. Nous les avons utilisés comme supports tensioactif de catalyseur au palladium. Ces nouveaux catalyseurs à base de Pd supporté ont été testés dans la réaction d'oxydation de plusieurs alcools en utilisant l'oxygène moléculaire en phase liquide. L'oxydation du 2- heptanol produit sélectivement la cétone correspondante, alors que l'oxydation de l'alcool benzylique est très sélective vis-à-vis de l'aldéhyde. Par ailleurs, l'oxydation de l'éthanol produit de l'acide acétique de manière sélective. / The objective of this work is the synthesis and the investigation of the acid and basicproperties of nitrogen doped carbon nanotubes (CNTs) able to be used as catalysts or catalystsupports. For this, three types of purified nitrogen doped CNTs were synthesized,characterized and tested for isopropyl alcohol conversion under nitrogen or air atmosphere,and compared to undoped CNTs. The N-doped CNTs differ from their nitrogen content andfrom the presence or not of undoped section in their structure. The reaction lead to theformation of acetone as the sole product on catalysts presenting no nitrogen or low nitrogencontent (< 2.8% w/w), pointing to the presence of basic sites. At higher nitrogen content, Ndopedcatalysts lead to the formation of acetone and propene, highlighting the presence ofboth basic and acids sites on such material. XPS characterization allow us to propose that thebasic sites consist in pyridinic surface groups and the acidic sites in sulfonic surface groupsformed during the purification of these material with sulfuric acid. Ruthenium and palladiumsupported catalysts (2% w/w) were prepared on nitrogen-doped and non-doped carbonnanotubes (N-CNT), and evaluated for the reaction of decomposition of isopropyl alcohol asprobe reaction. The presence of nitrogen functionalities (pyridinic, pyrrolic and quaternarynitrogen) on the nitrogen doped support induces a higher metal dispersion: 1.8 nm (Pd/NCNT)< 4.9 nm (Pd/CNT), and 2.4 nm (Ru/N-CNT) < 3.0 nm (Ru/CNT). As far as thesupported catalysts are concerned, the palladium ones were more active and more selectivethan the ruthenium ones. The Pd catalysts were selective towards acetone, whereas Rucatalysts lead to dehydration and dehydrogenation products. The nitrogen doping induces theappearance of redox properties, which appear when oxygen is present in the reaction mixture.Finally, we have shown that unique amphiphilic magnetic hybrid carbon nanotubes thatcontain on the same nanotube two different sections: a hydrophobic undoped part connectedto a hydrophilic N-doped segment are synthesized and used as tensioactive supports forpalladium catalysts. These new Pd-supported catalysts have been used in the alcoholoxidation reaction using molecular oxygen in the liquid phase. The oxidation of 2-heptanolproduces selectively the ketone, the oxidation of benzyl alcohol is very selective towards thealdehyde, and ethanol oxidation produces selectively acetic acid.