This dissertation discusses the influence of nitrogen doping (N-doping) on the electronic and catalytic properties of carbon nanotubes (CNTs). These properties have been studied using a variety of techniques, in order to both qualitatively and quantitatively analyze the relationship between the nitrogen concentration and observed properties. Chapter 1 provides a general overview of CNTs and N-doping and details some of the previous research from our group. Chapter 2 discusses the assembly and characterization of free-standing electrode mats, which are used in order to understand the intrinsic physicochemical properties of the material without relying on the secondary influence of another conductive support. Raman microscopy, X-Ray photoelectron spectroscopy, scanning and scanning-tunneling electron microscopy, as well as electrochemical methods were all used to demonstrate the viability of the mat electrodes for further experiments. Chapter 3 addresses the examination of a range of nitrogen concentrations in order to better understand the effects of nitrogen concentration on the electrochemical and electrical properties such as the differential capacitance, density of states at the Fermi level (D(E[subscript F])), bulk conductivity and work function. These properties were studied using a variety of techniques, including UV-photoelectron spectroscopy, electrochemical impedance spectroscopy and conductive four point probe. Chapter 4 investigates the inherent catalysis of the nitrogen doped CNTs (N-CNTs) with respect to O2 reduction, and a complex mechanism is proposed. Electrochemical methods such as cyclic and linear sweep voltammetries as well as thermo-gravimetric analysis and gasometric analysis were all employed to determine heterogeneous decomposition rates as well as to detect intermediates of the O₂ reduction reaction. Chapter 5 discusses the electrocatalytic degradation of free cyanide (CN⁻) at the N-CNT mat electrodes. These results both provide further support for the mechanism discussed in Chapter 4, and present the opportunity for a potential application of N-CNTs for environmental purposes. Specifically, spectroscopic and electrochemical methods, in conjunction with theoretical models show both that the presence of CN⁻ does not inhibit O2 reduction, and that it can be effectively converted to cyanate (OCN⁻) at the N-CNT electrodes. Future work involving the assembly and characterization of transparent N-CNT films is discussed in Chapter 6. / text

The heart is one of the most important organs of the human body and cardiovascular diseases remain the biggest cause of deaths worldwide. Today, due to the aging of the population and the growing demand for cardiovascular implants, improving the performance of artificial surfaces of vascular prostheses is highly desired. The common material for fabricating prostheses, such as stents used to remedy narrow and weak arteries, is Fluorocarbon polymers or expanded Polytetrafluoroethylene (ePTFE, Gore-tex). Although these polymers are well known for chemical inertness, thermal stability and low friction, they can cause early thrombosis (forming clot) and coagulation in blood vessels and require periodic replacement. Modifying the surface properties of Polytetrafluoroethylene (PTFE) by coating with carbon-based materials may improve its blood compatibility. Carbon-based coatings have properties similar to biomedical components, such as low friction, bioinertness, high wear resistance and exceptional hardness. Plasma processing methods are commonly used for coating thin films on various materials including carbon-based components. Plasma-based processes are also widely used in the aerospace, automotive, steel and biomedical industries. For example, extending the lifetime of surgically implanted hip joints and cutting tools are biomedical and industrial applications of plasma-based material processing respectively. Plasma-assisted deposition techniques are commonly used for carbon-based coating including nitrogen-doped amorphous carbon (a-C) films. In this thesis, PTFE samples with different thickness and roughness characteristics are used as substrates and diamond-like carbon (DLC) is deposited on them by simultaneous plasma-assisted sputtering and chemical vapour deposition (CVD). Hot filament plasma and ICP (Inductively coupling plasma) are used to coat DLC on PTFE and silicon (Si) substrates under various plasma conditions. The latter is the first report on the techniques to coat DLC by ICP plasma sputtering. This new technique (ICP-sputtering) is developed to improve low deposition rate and high temperature deposition of previous method (Hot filament plasma sputtering). Advantageous of this new developed method (ICP-sputtering) are discussed and compared with the previous method in this thesis. Various amount of nitrogen is introduced to the plasma chambers and the effect of nitrogen dopant is also studied using different characterization techniques for chemical, electronic and morphological properties of coated films. sp2 and sp3 contents were also estimated in amorphous carbon (a-C) and nitrogenated amorphous carbon (a-CN) films. Characterization techniques used for in this thesis are including SEM (scanning electron microscopy), AFM (atomic force microscopy), Raman spectroscopy, XAS (x-ray absorption spectroscopy), XES (x-ray emission spectroscopy), XPS (x-ray photoelectron spectroscopy) and XRD (x-ray diffraction).

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第13834号 / 工博第2938号 / 新制||工||1434(附属図書館) / 26050 / UT51-2008-C750 / 京都大学大学院工学研究科物質エネルギー化学専攻 / (主査)教授 井上 正志, 教授 江口 浩一, 教授 田中 庸裕 / 学位規則第4条第1項該当

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Screen printed electrodes (SPEs), which are prepared by patterning conductive inks or pastes onto an insulating support (e.g., plastic film), are widely employed as sensing and biosensing platforms due to their ease of fabrication and relatively low cost. This is especially applicable to electrodes of this nature prepared with carbon-based inks (SPCEs). To date, the most successful and significant commercial application of SPEs has been as test strips for glucose meters. Despite the maturity of this technology, SPE research remains very active as improvements in sensitivity and selectivity, which often involve modifying the electrode surface, hold the key to advancing their utility in routine applications and extending their benefits to other target analytes. Recent studies in the Bishop research group have demonstrated that nitrogen-doped SPCEs (N-SPCEs) exhibit enhanced electrochemical response towards hydrogen peroxide (H2O2), a product of oxidase enzyme (e.g., glucose oxidase, lactate oxidase, etc.) reactions and a common target in biosensing strategies. The presence of nitrogen heteroatoms on the carbon surface facilitates breakage of oxygen-oxygen bonds, a key step in reduction of H2O2. Since previous studies showed only modest incorporation of nitrogen species on SPCEs prepared from commercial ink, these studies aim to investigate the possibility of enhancing N-doping by performing a simple pre-treatment strategy that reportedly increases surface oxygen content of SPCEs prior to N-doping. Since surface oxygen sites have been previously reported to be preferentially modified with nitrogen during N doping strategies, this seems like a promising technique for improving sensitivity of N-SPCEs for H2O2 reduction. To quantify the actuality of these claims, experimental groups were fabricated having undergone no enhancement, pretreatment enhancement only, nitrogen-doping enhancement only, and a combination of the pretreatment and nitrogen-doping enhancements. Here the electrochemical behaviors of pretreated SPCEs, N-SPCEs, and pretreated N-SPCEs for the detection of H2O2 by completing comparative cyclic voltammetry (CV) experiments with and without the presence of H2O2 and with it present in varying concentrations is compared. It is projected that, if successful, the fabricated electrodes that have undergone both the pretreatment protocol and the nitrogen-doping process will have an increased sensitivity and detection limit towards H2O2.

Screen printed electrodes (SPEs), which are prepared by patterning conductive inks or pastes onto an insulating support (e.g., plastic film), are widely employed as sensing and biosensing platforms due to their ease of fabrication and relatively low cost. This is especially applicable to electrodes of this nature prepared with carbon-based inks (SPCEs). To date, the most successful and significant commercial application of SPEs has been as test strips for glucose meters. Despite the maturity of this technology, SPE research remains very active as improvements in sensitivity and selectivity, which often involve modifying the electrode surface, hold the key to advancing their utility in routine applications and extending their benefits to other target analytes. Recent studies in the Bishop research group have demonstrated that nitrogen-doped SPCEs (N-SPCEs) exhibit enhanced electrochemical response towards hydrogen peroxide (H2O2), a product of oxidase enzyme (e.g., glucose oxidase, lactate oxidase, etc.) reactions and a common target in biosensing strategies. The presence of nitrogen heteroatoms on the carbon surface facilitates breakage of oxygen-oxygen bonds, a key step in reduction of H2O2. Since previous studies showed only modest incorporation of nitrogen species on SPCEs prepared from commercial ink, these studies aim to investigate the possibility of enhancing N-doping by performing a simple pre-treatment strategy that reportedly increases surface oxygen content of SPCEs prior to N-doping. Since surface oxygen sites have been previously reported to be preferentially modified with nitrogen during N-doping strategies, this seems like a promising technique for improving sensitivity of N-SPCEs for H2O2 reduction. To quantify the actuality of these claims, experimental groups were fabricated having undergone no enhancement, pretreatment enhancement only, nitrogen-doping enhancement only, and a combination of the pretreatment and nitrogen-doping enhancements. Here the electrochemical behaviors of pretreated SPCEs, N-SPCEs, and pretreated N-SPCEs for the detection of H2O2 by completing comparative cyclic voltammetry (CV) experiments with and with out the presence of H2O2 and with it present in varying concentrations is compared. It is projected that, if successful, the fabricated electrodes that have undergone both the pretreatment protocol and the nitrogen-doping process will have an increased sensitivity and detection limit towards H2O2.

Metal nanoparticles have been a primary focus in areas of catalysis and electrocatalysis applications as a result of their large surface area-to-volume ratios. While there is an increased interest in understanding the properties and behaviors of metal nanoparticles, they can become expensive over time. Recent research has incorporated the idea of using heteroatom-doped materials as a cheaper catalytic alternative to metal nanoparticles. In this study nitrogen-doping and phosphorous-doping techniques were applied to chemical vapor-deposited carbon ultramicroelectrodes in order to study the electrocatalytic properties toward the oxygen reduction reaction and the enhanced affinity for the deposition of gold nanoparticles onto the electrodes.

Nitrogen-doped carbon materials have garnered much interest due to their abilities to behave as electrocatalysts for reactions important in energy production (oxygen reduction) and biosensing (hydrogen peroxide reduction). Here, we demonstrate fabrication methods and determine electrocatalytic properties of nitrogen-doped screen-printed carbon (N-SPCE) electrodes. Nitrogen doping of graphite was achieved through a simple soft-nitriding technique which was then used in lab-formulated screen-printing inks to prepare N-SPCEs. N-SPCEs displayed good electrocatalytic activity, reproducibility and long term stability towards the electrochemical reduction of hydrogen peroxide. N-SPCEs exhibited a wide linear range (20 µM to 5.3 mM), reasonable limit of detection of 2.5 µM, with an applied potential of -0.4 V (vs. Ag/AgCl). We also demonstrate that nitrided-graphite can similarly be used as a platform for the deposition of electrocatalytic platinum nanoparticles, resulting in Pt-N-SPCEs with a lower limit of detection (0.4 µM) and better sensitivity (0.52 µA cm-2 µM-1) towards H2O2 reduction.

Supercapacitor is the best potential candidate of the energy storage system due to the superior charge or discharge efficiency, high power density (>10 kW kg-1), and long cycling life. Porous carbon materials as the promising electrode material have been widely used in supercapacitor. In fact, conventional porous carbon supercapacitor electrodes cannot fulfil the growing demand of high energy and power densities of supercapacitor. A large number of studies show that nitrogen doping can change the surface electronic structure of carbon materials, thus significantly improving the electrochemical properties. In addition to, the pore structure and morphology of carbon materials have great influence on the electrochemical performance. In this work, we firstly fabricated nitrogen-doped porous carbon nanotubes by using a simple mixed salts (NaCl/ZnCl2) activation strategy. The as-obtained porous carbon nanotubes exhibited excellent electrochemical performance in supercapacitor. Furthermore, two- dimension nitrogen-doping porous nanosheets were prepared by a salt template-assisted monomer deposition method. In this study, by optimizing the synthesis conditions, the as-obtained carbon nanosheets showed a high specific capacitance of 277 F g-1 at 1 A g-1 and excellent cycle stability retained 91 % after 10,000 cycles. / College of Engineering, Science and Technology / M. Tech.( Civil and Chemical Engineering

This study reports on the synthesis of N-doped carbon spheres (N-CSs) by a simple synthetic procedure. A horizontal CVD type reactor was used to synthesize N-CSs from pyridine. Depending on the dilution of the pyridine with toluene, a nitrogen content of 0.13-5 mol % was obtained. The use of a vertical CVD reactor gave N-CSs with a N-content of 0.19-3 mol % when an ammonium solution and acetylene were used as reactants. The diameters of carbon spheres were found to be in the range of 40 nm to 1000 nm for both CVD reactors. The diameter can be controlled by varying the flow rate, temperature, time, concentration and the reactor type. The samples were characterized by TEM, HRTEM, elemental analysis, Raman spectroscopy, TGA, PXRD and ESR. We have demonstrated that unsubstituted thiophene can be polymerized by Fe3+-catalyzed oxidative polymerization. The average particle size was about 50 nm, within a narrow particlesize distribution. The undoped carbon spheres (CSs) were reacted with thiophene to give polymer/carbon composites containing polythiophene and carbon nanospheres via chemical oxidative polymerization reaction. Polythiophene molecules were either chemically bonded or physically adsorbed to the surface of carbon spheres. The microstructure and properties of the two types of composites were compared. The thermogravimetric analysis data confirmed that the presence of CSs in the polymer\carbon composites is responsible for the higher thermal stability of the composite material in comparison with pristine polythiophene. The FTIR analysis showed that covalent functionalized nanocomposites exhibit a high intensity of a C-S bond This study reports on the synthesis of N-doped carbon spheres (N-CSs) by a simple synthetic procedure. A horizontal CVD type reactor was used to synthesize N-CSs from pyridine. Depending on the dilution of the pyridine with toluene, a nitrogen content of 0.13-5 mol % was obtained. The use of a vertical CVD reactor gave N-CSs with a N-content of 0.19-3 mol % when an ammonium solution and acetylene were used as reactants. The diameters of carbon spheres were found to be in the range of 40 nm to 1000 nm for both CVD reactors. The diameter can be controlled by varying the flow rate, temperature, time, concentration and the reactor type. The samples were characterized by TEM, HRTEM, elemental analysis, Raman spectroscopy, TGA, PXRD and ESR. We have demonstrated that unsubstituted thiophene can be polymerized by Fe3+-catalyzed oxidative polymerization. The average particle size was about 50 nm, within a narrow particlesize distribution. The undoped carbon spheres (CSs) were reacted with thiophene to give polymer/carbon composites containing polythiophene and carbon nanospheres via chemical oxidative polymerization reaction. Polythiophene molecules were either chemically bonded or physically adsorbed to the surface of carbon spheres. The microstructure and properties of the two types of composites were compared. The thermogravimetric analysis data confirmed that the presence of CSs in the polymer\carbon composites is responsible for the higher thermal stability of the composite material in comparison with pristine polythiophene. The FTIR analysis showed that covalent functionalized nanocomposites exhibit a high intensity of a C-S bondThis study reports on the synthesis of N-doped carbon spheres (N-CSs) by a simple synthetic procedure. A horizontal CVD type reactor was used to synthesize N-CSs from pyridine. Depending on the dilution of the pyridine with toluene, a nitrogen content of 0.13-5 mol % was obtained. The use of a vertical CVD reactor gave N-CSs with a N-content of 0.19-3 mol % when an ammonium solution and acetylene were used as reactants. The diameters of carbon spheres were found to be in the range of 40 nm to 1000 nm for both CVD reactors. The diameter can be controlled by varying the flow rate, temperature, time, concentration and the reactor type. The samples were characterized by TEM, HRTEM, elemental analysis, Raman spectroscopy, TGA, PXRD and ESR. We have demonstrated that unsubstituted thiophene can be polymerized by Fe3+-catalyzed oxidative polymerization. The average particle size was about 50 nm, within a narrow particlesize distribution. The undoped carbon spheres (CSs) were reacted with thiophene to give polymer/carbon composites containing polythiophene and carbon nanospheres via chemical oxidative polymerization reaction. Polythiophene molecules were either chemically bonded or physically adsorbed to the surface of carbon spheres. The microstructure and properties of the two types of composites were compared. The thermogravimetric analysis data confirmed that the presence of CSs in the polymer\carbon composites is responsible for the higher thermal stability of the composite material in comparison with pristine polythiophene. The FTIR analysis showed that covalent functionalized nanocomposites exhibit a high intensity of a C-S bond at 695 cm-1 , which is not observed in the noncovalent functionalized nanocomposites