Resumo: O dióxido de carbono (CO2) é um importante gás de efeito estufa. No entanto, um aumento gradual ameaça substancialmente o clima. Um dos principais desafios do planejamento ambiental é identificar um modelo que vincule todos os fatores do ciclo de carbono, ou seja, oceano - ecossistema terrestre - emissão antropogênica - atmosfera. Princípios básicos de Termodinâmica podem ser aplicados em uma modelagem estatística com bases em séries históricas para obter concentrações de CO2 na atmosfera, possibilitando a construção de cenários para uma melhor tomada de decisões. Por este motivo, foi desenvolvido no trabalho um modelo que interliga todos os fatores do ciclo de carbono, focalizando em quatro zonas térmicas ou climáticas (Boreal, Temperada, Tropical, Polar), para cálculos de armazenamento de CO2 atmosférico. Os resultados mostram que no ano 2100 se atingirá uma concentração de CO2 quatro vezes maior do que antes do período pré-industrial. A zona temperada emite quase a metade de dióxido de carbono à atmosfera na atualidade; para o ano 2100, essa emissão aumentará a quinze vezes mais que a zona tropical. A China será responsável em uma proporção de vinte quatro a onze com relação aos Estados Unidos. A estabilização das concentrações de CO2 na atmosfera será obtida quando as emissões de dióxido de carbono antropogênico tiverem uma diminuição de mais do que trinta e quatro por cento para o ano 2100 na zona temperada. / Abstract: Carbon dioxide (CO2) is the most important greenhouse gas. A gradual increase on its atmospheric concentration threatens significantly the climate. One of the main challenges of environment planning is to identify a model that connects all factors that determine the carbon cycle, that is, ocean - terrestrial ecosystem - anthropogenic emissions - atmosphere. Basic thermodynamic principles can be applied in a statistical modeling with historic time series to obtain atmospheric CO2 concentration, creating the possibility of construction of scenarios that will help decision making. A model that links all carbon cycle factors was developed in this dissertation work, focusing in four thermal of climatic zones (Boreal, Temperate, Tropical, and Polar) for calculations of atmospheric CO2 storage. Results show that in 2100, the atmospheric CO2 concentration will reach a value four times higher than that of the pre-industrial period. The temperate zone already emits almost half of the carbon dioxide to the atmosphere; by 2100, this emission will increase 15 times more than that corresponding to the tropical zone. China will be responsible for emissions in a proportion of 24 to 11 in comparison to that of the United States. Stabilization of CO2 concentrations in the atmosphere will be obtained when the anthropogenic carbon dioxide emissions attain a decrease of at least 34% in 2100 in the temperate zone. / Orientador: João Andrade de Carvalho Junior / Coorientador: Luiz Fernando Costa Nascimento / Banca: José Antonio Perrella Balestieri / Banca: Maria Paulete Pereira Martins Jorge / Mestre

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No description available.

Carbon based materials such as CNTs and graphene have been widely studied over the last few years. The outstanding electrical and mechanical properties of these materials attracted researchers to find ways to grow and use them in nano-devices. Among the different techniques, PECVD is a relatively simple and low temperature process. It facilitates the growth of CNTs and graphene on particular sites of the substrate. The objective of this research project was to study the growth of CNTs and graphene using PECVD system and to employ them in renewable energy devices. Excimer laser processed materials were also the focus for flexible material for fuel cells and other applications to show the way to a one step manufacturing process that lends itself to large area and low cost processing using standard tools.In the growth of CNTs, the roll of a buffer layer and catalyst materials were studied in depth. Different metals were tested for best results in optimising nanotube growth for the selected applications. The role of the buffer layer in the formation of nanoparticles and their surface adhesion was studied. Different materials were used as a catalyst and analysed for best performance in the PECVD system. Growth parameters such as temperature, pressure, gas flow rate and plasma power were studied during the growth of CNTs in the PECVD system. The growth of graphene has been conducted in two ways: firstly, by the traditional mechanical exfoliation technique (with the help of Manchester University) and second by PECVD techniques.Polymer materials are promising flexible substrates for electronic and energy devices. An excimer laser was used to transform thin metallic films into nanoparticles which could play the role of the catalyst in proton exchange membrane fuel cells. In this study experiments have been conducted into a single step process to convert the poly ethylene naphthalate (PEN) surface to a robust mesoporous carbon material that conducts electrons, whilst depositing the catalyst. Such a technique has been developed for the first time in this work. Laser modification here produced a conical carbon structure and dense arrays of well defined catalysts.A prototype fuel cell was designed and crafted to employ the laser processed PEN as a proton exchange membrane. Some experiments were conducted regarding the transport of protons through laser processed PEN and the conventionally used fuel cell electrolyte, Nafion. It has been observed that the hydrophilic property of Nafion allowed proton transport across this material. It was also observed that PEN is not a good membrane for protonic transport. This material does not have free sites for vehicle transport. The catalytic activity of laser ablated Ni nanoparticles on PEN substrate was studied in temperature programme reaction (TPR) and it was observed that the metallic nanoparticles had some activity at higher temperature. Both Ni and Pt nanoparticles were tested as catalysts on the standard Nafion electrolyte. It was observed that Pt is active for the hydrogen combustion reaction and Ni has less activity for this purpose.It was not expected in this work that efficient hydrogen transport through the polymer would occur, but that future modification of the internal chemistry of PEN can be developed.

Hu, Zhuofeng. / Thesis Ph.D. Chinese University of Hong Kong 2014. / Includes bibliographical references. / Abstracts also in Chinese. / Title from PDF title page (viewed on 24, October, 2016).

The subject to be discussed in this thesis is an experimental problem in heat transfer across a carbon-liquid helium I interface. The interest in this particular problem arose from experimental work first presented by Luce (1) concerning a similar heat transfer problem from a heated bismuth surface immersed in liquid helium. This study produced some interesting results which it was hoped could be duplicated with carbon. The choice of carbon as an alternative material was based on reasons which will be discussed later. Before beginning a detailed discussion of the problem a history of its development and the results which were obtained using bismuth single crystals will first be presented.

This dissertation describes research on the synthesis and characterization of extended heptazine–based, graphite–like carbon nitride materials (CNx), as well as molecular heptazine (C6N7) derivatives. Spurred on by recent triazine to heptazine conversion studies, a structural examination was performed on an amorphous nitrogen–rich carbon nitride material formed via the rapid and exothermic self-propagating decomposition of a triazine (C3N3) precursor, trichloromelamine (TCM). The thermally stable and insoluble CNxHy product was determined to be composed of heptazine repeat units. This conclusion was supported by 13C solid state NMR and isolation of molecular heptazine anions after base hydrolysis (structural deconstruction) of the CNxHy material. Modifications to the decomposition of TCM were explored. Introduction of a solid template (NaCl or silica) led to morphological changes in the TCM–CNx product, observed by scanning electron microscopy. It was found that the sodium salts, NaBr and NaN3, led to chloride exchange with TCM. The use of mixtures of NH4Cl and NaN3 also showed changes in the morphology of the material, while leading to slight changes in the IR spectra. A series of reactions between NaBH4 and TCM yield novel thermally stable boron carbon nitride (BCN) materials. Reactions between TCM and Li2C2 or aromatic organic solids led to CNx materials with increased carbon contents. Crystalline metal–heptazine precipitates were generated by cation exchange reaction with the base hydrolysis product of TCM–CNx, potassium cyamelurate. A structure solution was attempted for the crystalline copper cyamelurate salt, KCu[C6N7O3]·4H2O. Neutral molecular heptazines were also synthesized; these species included 2,5,8–tribromo–s–heptazine (TBH), 2,5,8–triphenyl–s–heptazine (TPH), 2,5,8–tris(diisopropylamino)–s–heptazine (TAmH), and 2–bis(trimethylsilyl)amido–5,8–dichloroheptazine (DCAH). These materials were sublimable and showed interesting optical absorption and emission properties. A polymeric heptazine material was synthesized by thermal decomposition of DCAH. Several attempts were made to synthesize polymeric materials from heptazine precursors. Extended solids with C6N8 and C9N7 stoichiometry were made through solid state metathesis reactions between trichloroheptazine and either lithium nitride or lithium carbide. Powder X–ray diffraction indicated that salt formation was occurring during these reactions and products had the desired stoichiometry by elemental analysis. It was generally observed that CNx materials containing excess carbon displayed increased thermal stability when compared to pure CNx.

Includes bibliographical references.

The aim of this project was to investigate methods for purification and modification of Single Wall and Multi Wall Carbon Nanotubes. Covalent and noncovalent approaches to functionalization were studied. The dispersibility, structure and electronic properties of modified tubes were characterized by Raman, UV-vis-NIR and XPS. Fluorescence, NMR and TEM were further employed to characterize the interaction between nanotubes and non-covalent modifiers. The effects of five different purification methods on the dispersibility, and degree of carboxylic acid functionality of SWCNTs, along with the level of defects on the tube side walls, and the resulting electronic properties of SWCNTs have been investigated. It was found that all oxidation treatments successfully removed metallic oxides and amorphous carbon impurities, while different oxidation treatments introduced different levels of oxidized sites on the SWCNTs. Heat treatment after oxidation eliminated some of the carboxylic groups introduced by oxidation. SWCNTs covalently functionalized by aromatic diazonium salts containing nitro, carboxylate and fluoro groups on the aromatic ring were prepared. Heating of these tubes in vacuum at 350_C for 5 h partially reversed the effects of functionalization. However, due to the low degree of functionalization achieved in the preliminary studies, the dispersibility/solubility of functionalized tubes did not greatly improve. The interaction in stable suspensions of CNTs with positively or negatively charged pyrene derivatives via noncovalent functionalization, was extensively studied. 1-pyrene methylamine hydrochloride gave most stable dispersions. 1H and 2H NMR spectroscopy of MWCNTs/1-pyrene methylamine hydrochloride dispersion in DMF-d7 showed that the broadened signals are associated with weakly or unbound pyrene, while strongly bound pyrene is not observable in solution-state NMR. The strong pyrene attachment on MWCNTs by π-π stacking can be reversed by dialysis and/or extensive washing. Biological molecules such as polypeptides and amino acids also dispersed MWCNTs into solvents by noncovalent modification. It is found that polytryptophan demonstrated the greatest ability to disperse MWCNTs. Digestion with chymotrypsin enabled polytryptophan binding to be reversed. A combination of tube cutting and non-covalent functionalization by pyrenes or peptides enables tubes to be suspended/dissolved in solvents such as DMF and ethanol, and significantly allows tubes to be manipulated for practical device applications.

The work presented in this thesis is concerned with electrodes modified with carbon nanotubes. Carbon nanotubes have been characterised with special emphasis on the oxygenated species generated from cutting in acid mixtures. Several different techniques have been used for the analysis, especially infrared spectroscopy (IR) in combination with X-ray spectroscopy (XPS) analysis and transmission electron microscopy (TEM) in combination with atomic force microscopy (AFM). TEM analyses were used to reveal the morphological differences between various nanotube cutting times. The lengths of the nanotube were found to decrease with increasing cutting time. Electrochemical measurements were performed on carbon nanotube modified electrodes using nanotubes of different cutting time. The peak separation of ferricyanide redox reaction was found to depend strongly on the length of nanotube and also on the orientation of nanotube at the interface. Whilst at the randomly dispersed, the peak separation showed a decrease with decreasing nanotube length, vertically aligned nanotubes showed no dependence of the peak separation on the nanotube length. Electrochemical results together with spectroscopy measurements show that the highly electroactive edge planes were located on the carbon nanotubes and the oxygenated species in the ends of the nanotubes from cutting in acid mixtures were responsible for the good electrochemical properties. Bamboo-shaped carbon nanotube is a morphological variation of multi-walled carbon nanotubes where the graphite planes are formed at an angle to the axis of the tube. Glassy carbon electrodes modified with bambootype carbon nanotubes showed greater electrochemical signal compared with electrodes modified with singlewalled carbon nanotubes due to the edge planes of graphite located at regular intervals along the walls of the bamboo-shaped carbon nanotube, thus confirming the importance of the ends of nanotube in controlling the kinetics of electron transfer events. Effect of nanotube orientation was studied using ferrocenemethylamine attached to randomly dispersed and vertically aligned nanotubes. The electron transfer kinetics was found to depend strongly on the orientation of the nanotube with the electron transfer at the randomly dispersed slower than vertically aligned. Results were addressed using the analogy that the ends of the nanotubes are like the ends of the tubes can be described as edge-plane-like whilst the tube walls are basal-plane-like. Difference in electron transfer kinetics suggested that the electron transfer in nanotubes could occur via two different pathways: through the edge plane-like opening of the nanotube or by hopping across the walls of the nanotube. Triton X-100 was used to dialyse the acid cut nanotubes. XPS analysis of dialysed nanotubes was compared with non-dialysed nanotubes. A reduced concentration of sulfate ions was found in the dialysesd sample. Nitrate ion (407 eV) was removed after dialysis. Amino groups (400 ev) and protonated amino-group (402 eV) both seemed to be removed slowly by dialysis. Theses ions could be ascribed to residual ions trapped inside nanotubes from cutting in acid mixtures. The electrochemical response of ferrocenemethylamine was also studied. The electron transfer rate constants were rate constants were higher at dialysed nanotube assembly than non-dialysed, which was attributed to doping effect incurred from cutting. Electron transfer between nanotube and gold electrode surface was studied by attaching nanotubes to linker length of 6, 8, and 11 carbons. The results were exploited to rationalise the role of the chemical structure of the nanotubes in facilitating electron transfer from the redox species to the electrode surface that was otherwise suppressed without the presence of nanotubes. The observed redox activity was a consequence of resonant electron transfer from the LUMO of the acceptor to the HOMO of the donor under the influence of an applied voltage, assuming the nanotube modified electrode behaves similarly to the metal-molecule-metal junction mode.