Si nanoparticles are new prospective optoelectronic materials. Unlike bulk Si cry-stals, Si nanoparticles display intriguing room-temperature photoluminescence. A major challenge in the fabrication of Si nanoparticles is the control of their size distribution. The rare-earth element Er has unique photo emission properties, including low pumping power, and a temperature independent, sharp spectrum. The emission wavelength matches the transmission window of optical fibers used in the telecommunications industry. Therefore, the study of Er-doped Si nanoparticles may have practical significance. The goals of the research described in this dissertation are to investigate vapor phase pyrolysis methods and to characterize the microstructure and associated defects, particles size distributions and photoluminescence efficiencies of doped and undoped Si nanoparticles using analytical transmission electron microscopy, high resolution electron microscopy, and optical spectroscopy. Er-doped and undoped Si nanoparticles were synthesized via vapor-phase pyrolysis of disilane at Texas Christian University. To achieve monodisperse size distributions, a process with fast nucleation and slow growth was employed. Disilane was diluted to 0.48% with helium. A horizontal pyrolysis oven was maintained at a temperature of 1000 °C. The oven length was varied from 1.5 cm to 6.0 cm to investigate the influence of oven length on the properties of the nanoparticles. The Si nanoparticles were collected in ethylene-glycol. The doped and undoped Si nanoparticles have a Si diamond cubic crystal structure. Neither Er precipitation, Er oxides or Er silicides were detected in any of the samples. The Er dopant concentration was about 2 atom% for doped samples from the 3.0 and 6.0 cm ovens as determined by quantitative analysis using X-ray energy dispersive spectroscopy. The average Si nanoparticle size increases from 11.3 to 15.2 nm in the doped samples and from 11.1 to 15.7 nm in the undoped samples as the oven length increases from 1.5 to 6.0 cm. HREM data show that average Si nanocrystallite size varies from 6.4 to 3.3 to 5.9 nm in the doped samples, and from 7.5 to 12.2 nm in the undoped samples as the oven length increases. Room-temperature Er photoluminescence has been detected near 1.54 :m from all doped samples. Saturation of the Er photoluminescence intensity at large emission power and the monotonic decrease of the intensity as a function of the emission wavelength in the doped sample from the 3.0 cm oven suggest that a carrier-mediated energy transfer process occurs in the Er-doped Si nanoparticles. It is the first time to successfully fabricate and investigate Er-doped Si nanoparticles.

Chloride, bromide, pyridinium and quinolinium homologues of 4-(N- hexadecylpyridinium-4-ylmethylidene-amino)-2,6-dichlorophenolate have been investigated in solution, Langmuir and Langmuir-Blodgett films. Techniques including spectroscopy, surface potential measurement, quartz crystal microbalance, surface plasmon resonance, atomic force microscopy, reectometry and X-ray diffraction have been used to characterise these molecular systems. In solution, solvatochroism was observed and Benisi-Hildebrand analysis revealed dimeric aggregation. Langmuir monolayers were compressed at the air/water interface and chromophore rotation was observed by surface potential measurement. Langmuir- Blodgett monolayers showed lm-thickness dependence on the deposition-pressure. Monolayer thicknesses between 6-24Ä were measured using SPR and molecular areas between 40-l25Ä2 were measured using a quartz crystal microbalance. Both the molecular/s/area)and monolayer thicknesses were deposition-pressure dependent. The high tilt phases were visually distinguishable from the low tilt phases using atomic force microscopy, The compounds showed phase behaviour that was predominantly alike for the bromide and chloride homologues but different for the pyridinium and quinolinum homologues. Multilayer Y-type films of the merocyanine dyes were analysed using reectometry and deposition-pressure dependent thicknesses were found. Alternate layer structures of NLO-active hemicyanine amphiphiles were used to achieve homogeneous. orientation ordering using active and inactive spacer layers. Ordering was achieved but the optical efficiency was reduced by high proportions of inactive material and interlayer dipole formation. Double chained hemicyanine molecules were used to form Z-type structures and subsequent layers were found to significantly interdigitate. Different chain lengths were found to interdigitate by the length of the shortest chain. Gas detection experiments were undertaken on the quinolinium, dichloro merocyanine using three optical geometries. The absorption method showed slow switching and poor sensitivity. The Kretschmann SPR geometry showed high sensitivity and rapid switching. The grating SPR geometry showed rapid switching but was less sensitive than the ATR method. Protonation of the monolayers was investigated using hydrochloric acid gas, acetic acid vapour and stearic acid immobilised within the lm.

Call number: LD2668 .T4 1957 T82 / Master of Science

Orientador: Márcia Justino Rossini Mutton / Resumo: A utilização de biomassa lignocelulósica para produzir biocombustíveis, como o etanol, pode fornecer uma alternativa sustentável aos combustíveis fósseis. Os bagaços de sorgo sacarino e sorgo biomassa são considerados matérias-primas lignocelulósicas potenciais para a produção de etanol por meio de pré-tratamento, hidrólise enzimática e fermentação. Um dos entraves do processo é a utilização de microrganismos capazes de metabolizar pentoses e fermentarem em altas temperaturas. Neste contexto, este trabalho teve como objetivo avaliar as condições de adaptação e o desempenho fermentativo das estirpes de leveduras (LJ04 e Pichia kudriavzevii LJ03), em temperaturas de 37Cº e 40ºC, para produção de etanol de segunda geração, a partir de hidrolisados de bagaço de sorgo sacarino (Malibu J53 e Malibu A1001) e sorgo biomassa (Palo Alto) pré-tratados com explosão à vapor catalisada com ácido. Os bagaços dos genótipos foram avaliados quanto a composição química e rendimentos dos açúcares recuperáveis. Testes fermentativos foram realizadas com as leveduras Pichia kudriavzevii LJ03 e LJ04, nas temperaturas de 37ºC e 40ºC para avaliar três meios de cultivo com diferentes teores de hidrolisado (Meio 1 – 0%; Meio 2 – 33%; Meio 3 - 50%) durante 120 horas de fermentação. A partir do melhor meio de cultivo, fermentações em bioerreatores foram realizadas com as condições estabelecidas, em 96 horas de fermentação. Os resultados evidenciaram a eficiência do pré-tratamento e da hidrólise enzimática... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Lignocellulosic biomass to produce biofuels such as ethanol may provide a sustainable alternative to fossil fuels. Sweet sorghum bagasse is considered a potential lignocellulosic raw material for the production of fuel ethanol by means of pretreatment, enzymatic hydrolysis and fermentation. One of the difficult to the process is the use of microrganisms capable of metabolizing pentoses and fermenting at high temperatures. In this context, this work aimed to evaluate the adaptation conditions and fermentative performance of two yeast strains (LJ04 and Pichia kudriavzevii LJ03), at temperatures of 37º and 40ºC, for production of second generation ethanol from hydrolysates of Sweet sorghum bagasse (Malibu J53 and Malibu A1001) and Sorghum biomass (Palo Alto) pretreated with acid catalyzed steam explosion. Bagasse from those genotypes was evaluated for chemical composition and recoverable sugar yields. Fermentation tests were performed with Pichia kudriavzevii LJ03 and LJ04 yeast strain at 37ºC and 40ºC to evaluate three culture media with different hydrolyzed liquor contents (Medium 1 - 0%; Medium 2 - 33%; Medium 3 - 50%) during 120 hours of fermentation. After that, the best culture medium was chosen, fermentation in bioreactors were performed under the established conditions, in 96 hours of fermentation. The results showed the efficiency of pretreatment and enzymatic hydrolysis and the recovery of sugars without the formation of inhibitors. Strain LJ04 was classified as Pichia... (Complete abstract click electronic access below) / Doutor

Thesis advisor: Dunwei Wang / When their electrodes are made of nanomaterials or materials with nanoscale features, devices for energy conversion and energy storage often exhibit new and improved properties. One of the main challenges in material science, however, is to synthesize these nanomaterials with designed functionality in a predictable way. This thesis presents our successes in synthesizing TiSi₂ nanostructures with various complexities using a chemical vapor deposition (CVD) method. Attention has been given to understanding the chemistry guiding the growth. The governing factor was found to be the surface energy differences between various crystal planes of orthorhombic TiSi₂ (C54 and C49). This understanding has allowed us to control the growth morphologies and to obtain one-dimensional (1D) nanowires, two-dimensional (2D) nanonets and three-dimensional (3D) complexes with rational designs by tuning the chemical reactions between precursors. Among all these morphologies, the 2D nanonet, which is micrometers wide and long but only approximately 15 nm thick, has attracted great interest because it is connected by simple nanostructures with single-crystalline junctions. It offers better mechanical strength and superior charge transport while preserving unique properties associated with the small-dimension nanostructure, which opens up the opportunity to use it for various energy related applications. In this thesis we focus on its applications in lithium ion batteries. With a unique heteronanostructure consisting of 2D TiSi₂ nanonets and active material coating, we demonstrate the performances of both anode and cathode of lithium ion batteries can be highly improved. For anode, Si nanoparticles are deposited as the coating and at a charge/discharge rate of 8400 mA/g, we measure specific capacities >1000 mAh/g with only an average of 0.1% decay per cycle over 100 cycles. For cathode, V₂O₅ is employed as an example. The TiSi₂/V₂O₅ nanostructures exhibit a specific capacityof 350 mAh/g, a power rate up to 14.5 kW/kg, and 78.7% capacity retention after 9800 cycles. In addition, TiSi₂ nanonet itself is found to be a good anode material due to the special layer-structure of C49 crystals. / Thesis (PhD) — Boston College, 2012. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

The high balance-of-system costs of photovoltaic installations indicate that reductions in absorber cost alone are likely insufficient for photovoltaic electricity to reach grid parity unless energy conversion efficiency is also increased. Technologies which both yield high-efficiency cells (>25%) and maintain low costs are needed. GaAs and related III-V semiconductors are used in the highest-efficiency single- and multi-junction photovoltaics, but the technology is too expensive for non-concentrated terrestrial applications. This is due in part to the limited scalability of traditional syntheses, which rely on expensive reactors and employ toxic and pyrophoric gas-phase precursors such as arsine and trimethyl gallium. This work describes GaAs films made by close-spaced vapor transport, a potentially scalable technique which is carried out at atmospheric pressure and requires only bulk GaAs, water vapor, and a temperature gradient to deposit crystalline films with similar electronic properties to GaAs prepared using traditional syntheses. Although close-spaced vapor transport of GaAs was first developed in 1963, there were few examples of GaAs photovoltaic devices made using this method in the literature at the onset of this project. Furthermore, it was unclear whether close-spaced vapor transport could produce GaAs films appropriate for use in photovoltaics. The goal of this project was to create and study GaAs devices made using close-spaced vapor transport and determine whether the technique could be used for production of grid-connected GaAs photovoltaics. In Chapter I the design of the vapor transport reactor, the chemistry of crystal growth, and optoelectronic characterization techniques are discussed. Chapter II focuses on compositional measurements, doping, and improved electronic quality in CSVT GaAs. Chapter III describes several aspects of the interplay between structure and electronic properties of photoelectrochemical devices. Chapter IV addresses heteroepitaxial growth of GaAs on "virtual" Ge-on-Si substrates. This is a topic of importance for the broader III-V community as well as the photovoltaic community, as Si is the substrate of choice in many areas of industry. This dissertation includes unpublished and previously published co-authored material.

No presente trabalho foi estudado o efeito da adição de cálcio, bário e estrôncio (0%-5% em massa) em catalisadores Ni/Al2O3, contendo 5% de níquel em massa, frente à reação de reforma a vapor do etanol com o objetivo de inibir a reação de desidratação do etanol, precursor do carbono. Os catalisadores foram preparados por dois métodos: impregnação (I) e co-precipitação (C). Inicialmente todos os catalisadores obtidos foram submetidos a analise de espectroscopia dispersiva em emissão de raios X (EDX), para confirmação de suas composições químicas, em seguida foram aplicados na reação de reforma a vapor do etanol, dentre os catalisadores estudados os que apresentaram a menor formação de eteno foram, 5%Ca-5%Ni/Al (I) e 5%Ca-5%Ni/Al (C) dentre os que continham cálcio; 0,5%Ba-5%Ni/Al (I) e 5%Ba-5%Ni/Al (C) dentre os que continham bário e 5%Sr-5%Ni/Al (I) e 5%Sr-5%Ni/Al (C) dentre os que continham estrôncio, sendo então submetidos as etapas de caracterização, difração de raios X (DRX), redução a temperatura programada (RTP), área superficial específica pelo método BET e reação de decomposição do isopropanol. O desempenho destes catalisadores foi comparado com o obtido para os catalisadores sem aditivos 5Ni/Al(I) e 5Ni/Al(C). O método da impregnação demonstrou ser mais eficiente do que o método da co-precipitação para o alcance dos objetivos do trabalho e o catalisador 5Ca-5Ni/Al (I) foi o mais efetivo na redução da acidez da alumina e consequentemente mostrou menor deposição de carbono. / Catalysts of Ni/Al2O3 containing 5wt% of nickel and modified by calcium, barium and strontium addition (0wt% - 5wt%) were tested in the ethanol steam reforming with the goal of reduce the reaction of dehydratation of ethanol, a carbon precursor. The catalysts were prepared by two methods: impregnation (I) and co-precipitation (C). Initially, all catalysts were subjected to analysis by Energy-dispersive X-ray spectroscopy (EDX), to confirm their chemical compositions, then they were applied in the steam reforming of ethanol, Among the catalysts studied those with lower ethene production were: 5%Ca-5%Ni/Al (I), 5%Ca-5%Ni/Al (C) among those containing calcium; 0,5%Ba-5%Ni/Al (I), 5%Ba-5%Ni/Al (C) among those containing barium and 5%Sr-5%Ni/Al (I), 5%Sr-5%Ni/Al (C) among those containing strontium, being submitted to the characterization by X-ray diffraction (XRD), temperature programmed reduction (TPR), specific surface area by BET method and reaction of isopropanol decomposition. The performance of these catalysts was compared to with the catalysts without additives 5(wt%)Ni/Al(I) and 5(wt%)Ni/Al(C). The impregnation method was more effective than the method co-precipitation for achieving the objectives of this work and the catalyst 5Ni-5Ca/Al (I) was the more effective in the reduction of alumina acidity and also showed the lower carbon deposition.

Catalisadores de Ni suportado em La2O3, SiO2 e La2O3-SiO2 (com teores mássicos de La2O30 de 10%, 30% e 50%) tiveram seu desempenho avaliado frente a reação de reforma a vapor de glicerol. O efeito do suporte sobre a atividade, estabilidade e seletividade do catalisador foi avaliado, assim como diferentes métodos de preparo, teores de Ni e temperaturas de reação. Os catalisadores foram preparados pelos métodos da impregnação úmida seqüencial, impregnação úmida simultânea, impregnação sobre o suporte precipitado e co-precipitação, utilizando teores mássicos de 5%, 10% e 15% de Ni. Foram utilizadas as seguintes técnicas de caracterização: espectroscopia de energia dispersiva de raios X, fisissorção de nitrogênio, difratometria de raios X, redução a temperatura programada e difração de raios X in situ. Os catalisadores foram testados por um período de 5h, a fim de verificar a atividade e seletividade para a reação de reforma a vapor de glicerol a 500°C, 600°C e 700°C, e as propriedades dos catalisadores foram correlacionadas com os resultados obtidos dos ensaios catalíticos. Após as reações, os catalisadores foram submetidos as seguintes análises: análise elementar, difratometria de raios X e microscopia eletrônica de varredura. Foi observado que o Ni interage de forma variada com os diferentes suportes, que o método de preparação utilizado influencia propriedades dos catalisadores e que, dependendo do teor mássico de Ni suportado, o catalisador pode ser mais ou menos ativo para a reação de reforma a vapor de glicerol. Observou-se também que a temperatura influencia no desempenho da reação, sendo que os melhores resultados foram obtidos a 600°C com o catalisador 15Ni30LaSi preparado por impregnação úmida simultânea, que foi testado também por 20h para que fosse analisada sua estabilidade em um maior intervalo de tempo. / Ni catalysts supported on La2O3, SiO2 and La2O3-SiO2 (with 10%, 30% and 50%wt.La2O3) were evaluated in the glycerol steam reforming reaction. The effect of the supports was analyzed on the catalysts activity; stability and selectivity as well as different methods of preparation, Ni contents and reaction temperatures. Catalysts were prepared by the sequential wet impregnation, simultaneous wet impregnation, impregnation of Ni on support precipitate and co-precipitation methods using 5%, 10% and 15%wt.Ni. The catalysts were characterized by energy dispersive X-ray spectroscopy, nitrogen physisorption, X-ray diffraction, temperature programmed reduction and X-ray diffraction in situ. The catalytic tests were performed during 5 hours in order to verify the activity and selectivity for the glycerol steam reforming at 500°C, 600°C and 700°C, and identify the relationship between the catalysts properties and the results obtained with the catalytic tests. After the reactions, the catalysts were characterized by elemental analysis, X-ray diffraction and scanning electron microscopy. It was observed that the Ni interacted variously with different supports; the preparation method used influenced on the catalysts properties and, depending on the Ni content, the catalyst was more or less active for the glycerol steam reforming. It was also observed that the temperature of reaction influenced on the reaction performance, and the best results were obtained at 600°C with the 15Ni30LaSi catalyst, prepared by simultaneous wet impregnation, which was also tested for 20 hours to analyze its stability in a longer period.

No description available.

Submitted by Caroline Xavier (caroline.xavier@pucrs.br) on 2017-06-29T14:22:10Z No. of bitstreams: 1 DIS_VINICIUS_PEREIRA_PIRES_COMPLETO.pdf: 3149553 bytes, checksum: ed2310b8c811ad36bd1d5507d95e83c4 (MD5) / Made available in DSpace on 2017-06-29T14:22:10Z (GMT). No. of bitstreams: 1 DIS_VINICIUS_PEREIRA_PIRES_COMPLETO.pdf: 3149553 bytes, checksum: ed2310b8c811ad36bd1d5507d95e83c4 (MD5) Previous issue date: 2017-03-27 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior - CAPES / The essential oils are of great economic importance for several sectors of the world industry due to the varied range of properties and for being an alternative to the synthetic substances existing in the market. One way of obtaining these essential oils is through the technique of steam distillation, process widely used due to simplicity and low cost. The goals of this work were to obtain the essential oil of the species Achyrocline satureioides by steam distillation in different operating conditions, heading to model this process mathematically, to obtain the volatile compounds present in the essential oil by solid phase microextraction (SPME) technique, to analyze the oil and the volatile compounds accomplished by chromatographic/olfatomatric methods and to carry out a theoretical study of the separation of the major compounds of the essential oil by the fractional batch distillation technique. The achieved results demonstrated that the mathematical model, based on the one-dimensional mass balance in the fluid and solid phases to represent the extraction of essential oils in a pilot scale steam distillation unit, fitted well to the experimental data. The major compounds obtained by gas chromatography/mass spectrometry (GC/MS) were E-Caryophyllene, ?-Pinene, ?-Copaene and ?-Humulene. In addition, it can be observed by gas chromatography/olfactometry (GC/O) that the major compounds, of higher concentrations, do not present the highest aromatic intensities, except for the ?-Pineno compound that presented high concentration and aromatic intensity. The methodology applied to fractional distillation of the A.satureioides oil showed potential in the development of essential oil fractioning processes, since a high purity (99.10%) was obtained in the ?-Pinene fraction. / Os ?leos essenciais apresentam grande import?ncia econ?mica para diversos setores da ind?stria mundial em fun??o da variada gama de propriedades e por serem uma alternativa frente ?s subst?ncias sint?ticas existentes no mercado. Uma forma de obten??o desses ?leos essenciais ? atrav?s da t?cnica de extra??o por arraste a vapor; processo amplamente utilizado devido ? simplicidade e baixo custo. Os objetivos deste trabalho foram obter o ?leo essencial da esp?cie Achyrocline satureioides por extra??o por arraste a vapor em diferentes condi??es de opera??o, visando modelar matematicamente esse processo, obter os compostos vol?teis presentes no ?leo essencial pela t?cnica de microextra??o em fase s?lida (SPME), analisar o ?leo e os compostos vol?teis obtidos por m?todos cromatogr?ficos/olfatom?tricos e realizar um estudo te?rico de separa??o dos compostos majorit?rios do ?leo essencial pela t?cnica de destila??o fracionada em batelada. Os resultados obtidos demostraram que o modelo matem?tico, baseado no balan?o de massa unidimensional nas fases fluido e s?lido para representar a extra??o de ?leos essenciais em uma unidade de arraste a vapor em escala piloto, ajustou-se bem aos dados experimentais. Os compostos majorit?rios obtidos por cromatografia gasosa/espectrometria de massa (CG/EM) foram E-Cariofileno, ?-Pineno, ?-Copaeno e ?-Humuleno. Al?m disso, pode-se notar pela cromatografia gasosa/olfatometria (CG/O) que os compostos majorit?rios, de maiores concentra??es, n?o apresentam as maiores intensidades arom?ticas, com exce??o do composto ?-Pineno que apresentou alta concentra??o e intensidade arom?tica. A metodologia aplicada ? destila??o fracionada do ?leo de A.satureioides demonstrou potencial no desenvolvimento de processos de fracionamento de ?leos essenciais, j? que foi obtida uma alta pureza (99,10%) na fra??o de ?-Pineno.