Thesis (M.S.)--University of Texas at El Paso, 2009. / Title from title screen. Vita. CD-ROM. Includes bibliographical references. Also available online.

Made available in DSpace on 2014-06-11T19:23:29Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-01-08Bitstream added on 2014-06-13T18:09:38Z : No. of bitstreams: 1 silva_riv_me_bauru_prot.pdf: 20922417 bytes, checksum: 7a0be809afb7e675e99bba1b3539c247 (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / O presente trabalho teve como objetivo preparar o compósito de 1% (massa) de rutênio suportado sobre o condutor misto cerâmico (iônico e eletrônico), 'Ti IND. x'('Gd IND. 0,2''Ce IND. 0,8')'IND. (1-x)''O IND. (2-δ)', onde 0'< OU ='x'<OU='0,1, para utilizar como catalisador de reforma e ânodo (eletrodo tipo reforma interna) em Células a Combustível de Óxido Sólido (SOFC). O suporte cerâmico foi sintetizado pelo Método do Precursor Polimérico e calcinado a 400ºC, 700ºC, 1000ºC e 1150ºC em atmosfera estática de ar, sendo caracterizado por análise térmica simultânea (TG/DTA), Difração de Raio X (DRX) com refinamento estrutural pelo Método de Rietveld (REMR), análise textural por adsorção de 'N IND. 2' a 77K, Microscopia Eletrônica de Varredura (MEV) e Energia Dispersiva de Raio X (EDX). O Ru foi depositado (1% em massa) sobre o suporte cerâmico pelo Método do Ácido Fórmico. Em seguida foi calcinado a 300ºC em atmosfera de 'N. IND. 2' e tratado a 1000ºC em atmosfera de 'H IND. 2' (20% em 'H IND. 2' ). A deposição do Ru foi confirmada pela Espectrometria de Emissão Atômica com plasma acoplado indutivamente (ICP-AES). A caracterização do compósito foi feita mediante DRX, MEV com Fonte de Emissão Eletrostática (MEV-FEG) e Microscopia Eletrônica de Transmissão (MET). por último, o material compósito de Ru foi submetido a testes catalíticos para hidro-reforma de glicerol. A análise térmica do suporte cerâmico mostrou que os compostos orgânicos são eliminados até 700ºC. Os resultados de DRX e REMR mostraram a presença fase única de fluorita (g.e. Fm3m) em T=700ºC para 0'< OU ='x'<OU='0,1 e em T=1000ºC, para x<0,1. Em T=1000ºC e em T=1150ºC observou-se a presença da segunda fase, de titanato de gadolínio ('Gd IND. 2''Ti IND. 2''O IND. 7', g.e. Fd3m) para x'>OU='0,1 e x'>OU='0,025, respectivamente... / The current work aimed to prepare the composite of ruthenium supported on the ceramic mixed conductor (ionic and electronic), 'Ti IND. x'('Gd IND. 0,2''Ce IND. 0,8')'IND. (1-x)''O IND. (2-δ)',where 0'< OU ='x'<OU='0,1, to be used as a catalyst for the reforming and anode (internal reforming electrode) in Oxide Solid Fuel Cells (SOFC). The ceramic supports were synthesized by Polymeric Precursor Method and calcined at 400ºC, 700ºC, 1000ºC and 1150ºC in air. The characterization was carried out by simultaneous thermal analysis (TG/DTA), X-ray Diffraction (XRD) being the structure refined by Rietveld Method (SRRM), textural analysis by adsorption of 'N IND. 2' at 77K, Scanning Electronic Microscopy (SEM) and Energy Dispersive X-ray (EDX). The Ru was deposited on ceramic support by Formic Acid Method, calcined at 300ºC in 'N. IND. 2' and calcined at 1000ºC under 20vol% 'H IND. 2' flow. The deposition was confirmed by Inductively Coupled Plasma - Atomic Emission Spectrometry (ICP-AES). The characterization of the composite was performed by XRD, Field Emission Gun - Scanning Electronic Microscopy (FEG-SEM) and Transmission Electronic Microscopy (TEM). Finally, the catalytical activity of the composite material for glycerol steam reforming reaction was evaluated. The thermal analysis showed that most of organic compounds derived from the synthesis is eliminated up to 700ºC. The XRD and SRRM results showed that the samples crystallized as fluorite single phase (s.g.Fm3m) at T=700ºC for 0'< OU ='x'<OU='0,1and T=1000ºC,for x<0,1. The secondary phase of ('Gd IND. 2''Ti IND. 2''O IND. 7', g.e. Fd3m) was observed in the sample with x'>OU='0,1 when calcined at T=1000ºC and x'>OU='0.025 for the calcination temperature of 1150ºC. The textural analysis showed that the samples treated at 700ºC are mesoporous solids and, significant surface and porosity loss took place when treated at 1000ºC... (Complete abstract click electronic access below)

Orientador: Margarida Juri Saeki / Banca: Cristiane Barbieri Rodella / Banca: Luis Vicente de Andrade Scalvi / O Programa de Pós-Graduação em Ciência e Tecnologia de Materiais, PosMat, tem caráter institucional e integra as atividades de pesquisa em materiais de diversos campi da Unesp / Resumo: O presente trabalho teve como objetivo preparar o compósito de 1% (massa) de rutênio suportado sobre o condutor misto cerâmico (iônico e eletrônico), 'Ti IND. x'('Gd IND. 0,2''Ce IND. 0,8')'IND. (1-x)''O IND. (2-δ)', onde 0'< OU ='x'<OU='0,1, para utilizar como catalisador de reforma e ânodo (eletrodo tipo reforma interna) em Células a Combustível de Óxido Sólido (SOFC). O suporte cerâmico foi sintetizado pelo Método do Precursor Polimérico e calcinado a 400ºC, 700ºC, 1000ºC e 1150ºC em atmosfera estática de ar, sendo caracterizado por análise térmica simultânea (TG/DTA), Difração de Raio X (DRX) com refinamento estrutural pelo Método de Rietveld (REMR), análise textural por adsorção de 'N IND. 2' a 77K, Microscopia Eletrônica de Varredura (MEV) e Energia Dispersiva de Raio X (EDX). O Ru foi depositado (1% em massa) sobre o suporte cerâmico pelo Método do Ácido Fórmico. Em seguida foi calcinado a 300ºC em atmosfera de 'N. IND. 2' e tratado a 1000ºC em atmosfera de 'H IND. 2' (20% em 'H IND. 2' ). A deposição do Ru foi confirmada pela Espectrometria de Emissão Atômica com plasma acoplado indutivamente (ICP-AES). A caracterização do compósito foi feita mediante DRX, MEV com Fonte de Emissão Eletrostática (MEV-FEG) e Microscopia Eletrônica de Transmissão (MET). por último, o material compósito de Ru foi submetido a testes catalíticos para hidro-reforma de glicerol. A análise térmica do suporte cerâmico mostrou que os compostos orgânicos são eliminados até 700ºC. Os resultados de DRX e REMR mostraram a presença fase única de fluorita (g.e. Fm3m) em T=700ºC para 0'< OU ='x'<OU='0,1 e em T=1000ºC, para x<0,1. Em T=1000ºC e em T=1150ºC observou-se a presença da segunda fase, de titanato de gadolínio ('Gd IND. 2''Ti IND. 2''O IND. 7', g.e. Fd3m) para x'>OU='0,1 e x'>OU='0,025, respectivamente... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The current work aimed to prepare the composite of ruthenium supported on the ceramic mixed conductor (ionic and electronic), 'Ti IND. x'('Gd IND. 0,2''Ce IND. 0,8')'IND. (1-x)''O IND. (2-δ)',where 0'< OU ='x'<OU='0,1, to be used as a catalyst for the reforming and anode (internal reforming electrode) in Oxide Solid Fuel Cells (SOFC). The ceramic supports were synthesized by Polymeric Precursor Method and calcined at 400ºC, 700ºC, 1000ºC and 1150ºC in air. The characterization was carried out by simultaneous thermal analysis (TG/DTA), X-ray Diffraction (XRD) being the structure refined by Rietveld Method (SRRM), textural analysis by adsorption of 'N IND. 2' at 77K, Scanning Electronic Microscopy (SEM) and Energy Dispersive X-ray (EDX). The Ru was deposited on ceramic support by Formic Acid Method, calcined at 300ºC in 'N. IND. 2' and calcined at 1000ºC under 20vol% 'H IND. 2' flow. The deposition was confirmed by Inductively Coupled Plasma - Atomic Emission Spectrometry (ICP-AES). The characterization of the composite was performed by XRD, Field Emission Gun - Scanning Electronic Microscopy (FEG-SEM) and Transmission Electronic Microscopy (TEM). Finally, the catalytical activity of the composite material for glycerol steam reforming reaction was evaluated. The thermal analysis showed that most of organic compounds derived from the synthesis is eliminated up to 700ºC. The XRD and SRRM results showed that the samples crystallized as fluorite single phase (s.g.Fm3m) at T=700ºC for 0'< OU ='x'<OU='0,1and T=1000ºC,for x<0,1. The secondary phase of ('Gd IND. 2''Ti IND. 2''O IND. 7', g.e. Fd3m) was observed in the sample with x'>OU='0,1 when calcined at T=1000ºC and x'>OU='0.025 for the calcination temperature of 1150ºC. The textural analysis showed that the samples treated at 700ºC are mesoporous solids and, significant surface and porosity loss took place when treated at 1000ºC... (Complete abstract click electronic access below) / Mestre

Superhydrophobic coatings attract significant attention regarding a variety of applications, such as in friction drag reduction, anti-contamination surfaces, and recently metals corrosion protection. Superhydrophobic surfaces are known to protect metals and their alloys from natural degradation by limiting water access and its surface interaction. Non-wetting properties of superhydrophobic surfaces are attributed to their low-surface energy, in combination with their surface microtexture. Several approaches based on tailoring a microtextured surface followed by surface modification with a low-surface-energy material have been employed for developing non-wetting metallic surfaces. However, developing a durable superhydrophobic coating, in terms of mechanical abrasion, thermal and chemical stability, which could serve in harsh environments, is still an outstanding challenge. In this research work two different approaches have been employed to create durable superhydrophobic aluminium alloy surfaces. In the first approach a practical and cost-effective method, which is based on direct surface acid/base etching is used to promote desired rough microstructure on aluminium alloy. Then, a facile surface modification with chlorosilanes as a low-surface-energy compound is utilized to generate surface superhydrophobicity. The superhydrophobic aluminium alloy has a water contact angle of about 165 ± 2˚ and rolling angle of less than 3 ± 0.2˚. The developed superhydrophobic aluminium alloy surfaces shows remarkable thermal stability up to 375 ˚C for 20 min. In the second approach, a controlled hydrothermal deposition process is utilized to develop cerium oxide based coatings with well-defined microtextured surface on aluminium alloy substrates. The superhydrophobicity of the cerium oxide coatings is acquired by further treatment with trichloro(octyl)silane surface. The impacts of various hydrothermal processing conditions on surface microstructure of coatings, wettability, and ultimate corrosion protection have been also investigated. The fabricated cerium oxide based coating exhibit high level of water repellency with a water contact angle of about 170 ± 2˚ and rolling angle of about 2.4 ± 0.2˚. The superhydrophobic coatings show outstanding wear-resistance by maintaining their non-wetting properties after abrasion by #800 abrasive paper for 1.0 m under applied pressures up to 4 kPa pressure. The coatings also show remarkable chemical stability under acidic and alkaline condition and during immersion in corrosive 3.5 wt % NaCl solution for more than 2 days. They also provide excellent corrosion protection for T6-6061 aluminium alloy substrate by decreasing its corrosion rate for about three orders of magnitude. / Graduate

Studies various nanostructured materials have gained considerable interest within the past several decades. This novel class of materials has opened up a new realm of possibilities, both for the fundamental comprehension of matter, but also for innovative applications. The size-dependent effect observed for these systems often lies in their interaction with the surrounding environment and understanding such interactions is the pivotal point for the investigations undertaken in this thesis. Three families of nanoparticles are analyzed: semiconductor quantum dots, metallic silver nanoparticles and rare-earth oxide nanomaterials. The radical scavenging ability of cerium oxide nanoparticles (CeO2) is quite controversial since they have been labeled as both oxidizing and antioxidant species for biological systems. Here, both aqueous and organic stabilized nanoparticles are examined in straightforward systems containing only one reactive oxygen species to ensure a controlled release. The apparent absence of their direct radical scavenging ability is demonstrated despite the ease at which CeO2 nanoparticles generate stable surface Ce3+ clusters, which is used to explain the redox activity of these nanomaterials. On the contrary, CeO2 nanoparticles are shown to have an indirect scavenging effect in Fenton reactions by annihilating the reactivity of Fe2+ salts. Cadmium selenide quantum dots (CdSe QD) constitute another highly appealing family of nanocolloids in part due to their tunable, size-dependent luminescence across the visible spectrum. The effect of elemental sulfur treatment is investigated to overcome one of the main drawbacks of CdSe QD: low fluorescence quantum yield. Herein, we report a constant and reproducible quantum yield of 15%. The effect of sulfur surface treatment is also assessed following the growth of a silica shell, as well as the response towards a solution quencher (4-amino-TEMPO). The sulfur treated QD is also tested for interaction with pyronin Y, a xanthene dye that offers potential energy and electron transfer applications with the QD. Interaction with the dye molecule is compared to results obtained with untreated quantum dots, as well as CdSe/ZnS core shell examples. In another chapter of this thesis, the catalytic potential of silver nanoparticles is addressed for the grafting of polyhydrosiloxane polymer chains with various alkoxy groups. A simple one-pot synthesis is presented with silver salts and the polymer. the latter serves as a mild reducing agent and a stabilizing ligand, once silver nanoparticles are formed in-situ. We evaluate the conversion of silane into silyl ethers groups with the addition of several alcohols, whether primary, secondary or tertiary, and report the yields of grafting under the mildest conditions: room temperature, under air and atmospheric pressure.

Orientador: Italo Odone Mazali / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-26T22:22:44Z (GMT). No. of bitstreams: 1 Silva_IsaiasdeCastro_M.pdf: 4959698 bytes, checksum: 34689bf94c26337d3043ec67881ba30e (MD5) Previous issue date: 2015 / Resumo: Dado que o óxido de cério(IV) é um composto não-estequiométrico e que apresenta uma banda Raman sensível a mudanças na rede cristalina, utilizou-se a estratégia de oxidação e redução in situ empregando gases como agentes redutores e oxidantes para investigar as mudanças ocorridas no perfil da banda Raman do óxido de cério(IV), sintetizado em várias morfologias nanométricas com exposição específica de faces, em condições de controle da concentração de vacâncias de oxigênio não-estequiométricas. Foi observado um deslocamento para menores números de onda da freqüência do máximo da banda Raman quando a amostra se encontrava sob atmosfera redutora, e esse comportamento se mostrou reversível, de modo que a freqüência do máximo da banda deslocou-se para maiores números de onda quando em atmosfera oxidante. Esse deslocamento foi mais pronunciado na morfologia de nanobastões cominuídos, na qual predominam faces de índice {110}, que são favoráveis à formação de vacâncias de oxigênio não-estequiométricas. Ao correlacionar os resultados da espectroscopia Raman com outras técnicas sensíveis ao grau de não-estequiometria do composto, se observou aumento no parâmetro de rede na difratometria de raios X e perda de massa na determinação da capacidade de estoque de oxigênio, medida por termogravimetria, sob atmosfera redutora. As observações mostram que as responsáveis pelo deslocamento da frequência da banda Raman do óxido de cério(IV) são as vacâncias de oxigênio não-estequiométricas. Como certos espectros Raman apresentaram bandas assimétricas, a razão para tal poderia ser a ressonância de Fano, o que foi investigado variando-se a energia da radiação incidente. A razão para a assimetria não foi atribuída à ressonância de Fano, mas sim há outra banda relacionada a modos vibracionais de superfície. Por fim se comparou as atividades catalíticas dos cristais de diferentes morfologias de óxido de cério(IV) frente à oxidação de monóxido de carbono, sendo que a morfologia de nanobastões cominuídos apresentou melhor desempenho. Como o mecanismo de oxidação depende das vacâncias de oxigênio não-estequiométricas, a formação dessas é facilitada na morfologia de nanobastões cominuídos, e por isso o deslocamento da banda Raman é mais pronunciado nessa morfologia / Abstract: One remarking property of cerium(IV) oxide (CeO2) is its oxygen storage capacity (OSC). This property is related to the presence of oxygen vacancies, as CeO2 is a non-stoichiometric oxide. Once CeO2 presents only one Raman active mode, which is sensitive to changes in CeO2 lattice like the oxygen vacancies, it has been investigated the influence of oxygen vacancies over CeO2 Raman band. The crystals were synthesized in different nanometric morphologies, with exposure of specific facets. The samples were characterized by X-ray powder diffraction, transmission electron microscopy, OSC measurements by thermogravimetric equipment and Raman spectroscopy. Besides the microscopy, all other characterizations were performed with in situ control of temperature and atmosphere. The morphology with dominant {110} facets, favorable for oxygen vacancies generation, presents lattice parameter expansion, loss of mass and Raman band maximum red-shift after reduction with hydrogen-containing atmosphere, and sequent lattice parameter contraction, gain of mass and Raman band maximum blue-shift after oxidation with oxygen-containing atmosphere. These observations present reversible behavior as the atmospheres are alternated, consequence of generation or extinction of oxygen vacancies. Thereby, the correct morphology choice for a CeO2 crystal favors oxygen vacancies generation, and once generated they result in CeO2 Raman band maximum red-shift / Mestrado / Quimica Inorganica / Mestre em Química

This work is studying the layers of cerium oxide (doped with platinum) prepa- red by magnetron sputtering on different types of substrates. Attention is focused mainly on modes of growth and morfology of (Pt−)CeO2 layers. The study was carried out by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The specimens (lamellas) were created by using focused ion beam (FIB) with respect to transparency for electron beam and material contrast. The emphasis was on elimination of redeposition and minimize the amorphous layer of lamella. Representation of elements was determined by energy-dispersive spectroscopy (EDX) and electron-energy loss spectroscopy (EELS). 1

>Magister Scientiae - MSc / The industrial safety requirements and environmental pollution have created a high demand to develop gas sensors to monitor combustible and toxic gases. As per specifications of World Health Organization (WHO) and Occupational Safety and Health Administration (OSHA), lengthy exposure to these gases lead to death which can be avoided with early detection. Semiconductor metal oxide (SMO) has been utilized as sensor for several decades. In recent years, there have been extensive investigations of nanoscale semiconductor gas sensor.

Cerium oxide nanoparticles (nanoceria) have recently been shown to protect cells against oxidative stress in both cell culture and animal models. Nanoceria has been shown to exhibit superoxide dismutase (SOD) activity using a ferricytochrome C assay, and this mimetic activity that has been postulated to be responsible for cellular protection by nanoceria. The nature of nanoceria's antioxidant properties, specifically what physical characteristics make nanoceria effective at scavenging superoxide anion, is poorly understood. In this study electron paramagnetic resonance (EPR) analysis confirms the reactivity of nanoceria as an SOD mimetic. X-ray photoelectron spectroscopy (XPS) and UV-visible analyses of nanoceria treated with hydrogen peroxide demonstrate that a decrease in the Ce 3+/4+ ratio correlates directly with a loss of SOD mimetic activity. These results strongly suggest that the surface oxidation state of nanoceria plays an integral role in the SOD mimetic activity of nanoceria and that ability of nanoceria to scavenge superoxide is directly related to cerium(III) concentrations at the surface of the particle.

Cerium oxide nanoparticles are established scavengers of reactive oxygen and nitrogen species. They have many potential biomedical applications that depend on their physicochemical properties and mode of preparation. Recent studies have found these nanoparticles possess phosphatase mimetic activity. Studying such catalytic activities will qualify their biomedical applications and render information on their bioavailability and potential toxicity. Two oxidation states of cerium exist in these nanoparticles (3+ or 4+). It is hypothesized that the oxidation state of cerium in the nanoparticles determines the amount of adsorbed water on the crystal lattices. This in turn governs their activity as phosphatases. Nanoparticles with higher levels of cerium in the 4+ state exhibit phosphatase activity while those with higher levels of cerium in the 3+ state do not. This phosphatase activity may be controlled with the addition of inhibitory anions. It is hypothesized that anions with structures similar to phosphate can inhibit phosphatase activity by leading to the production of complexes on the surface of cerium oxide nanoparticles. Substrates that were used to test this activity include para-nitrophenyl phosphate (pNPP), 4-methylumbelliferyl phosphate (MUP) and adenosine triphosphate (ATP). To highlight the role of adsorbed water, we also performed experiments on pNPP with methanol as a solvent. The activity was measured by absorbance (pNPP and ATP) or fluorescence (MUP) and reported as nmol of phosphate/min. In some cases this rate was calculated through coupled reactions or by measuring the rate of formation of other colored products formed along with the release of phosphate such as pNP (para-nitrophenol). The phosphatase activity increased as the amount of adsorbed water increased implying that the abundance of adsorbed water makes the surface of 4+ ceria nanoparticles more active. Phosphatase activity for all the substrates exhibited Michaelis-Menten kinetics. Although the phosphatase activity of these nanoparticles is slow (turnover rate) as compared to real biological phosphatases, it can be used as a model catalytic activity to follow other catalytic activities that are associated with nanoparticles that have an abundance of cerium in the 4+ state, such as catalase activity. These results also provide information on the nature of the active sites involved in the catalytic activities associated with these nanoparticles. We identified three inhibitors, tungstate, molybdate and arsenate, which decreased the phosphatase activity of these nanoparticles in a dose dependent manner. Vmax, Km and Ki values were determined by varying substrate concentrations in the presence and absence of inhibitors. A partial mixed inhibition model was fit for each of these inhibitors. Summary: Phosphatase activity of cerium oxide nanoparticles with higher levels of cerium in the 4+ oxidation state was used as a model catalytic activity to study the nature of the active sites involved in catalysis. The study of inhibitors can reveal more information as to the surface binding of substrates in catalysis.