京都大学 / 新制・課程博士 / 博士(工学) / 甲第23911号 / 工博第4998号 / 新制||工||1780(附属図書館) / 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 阿部 竜, 教授 陰山 洋, 教授 藤田 晃司 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Solar hydrogen has the potential to replace fossil fuels with a sustainable energy carrier that can be produced from sunlight and water via &quotewater splitting&quote. This study investigates the use of hematite (Fe&sub2O&sub3) as a photoelectrode for photoelectrochemical water splitting. Fe&sub2O&sub3 has a narrow indirect band-gap, which allows the utilization of a substantial fraction of the solar spectrum. However, the water splitting efficiencies for Fe&sub2O&sub3 are still low due to poor absorption characteristics, and large losses due to recombination in the bulk and at the surface. The thesis investigates the use of nanostructured composite electrodes, where thin films of Fe&sub2O&sub3 are deposited onto a nanostructured metal oxide substrate, in order to overcome some of the factors that limit the water splitting efficiency of Fe&sub2O&sub3. Doped (Si, Ti) and undoped Fe&sub2O&sub3 thin films were prepared using vacuum deposition techniques, and their photoelectrochemical, electrical, optical and structural properties were characterised. The doped Fe&sub2O&sub3 exhibited much higher photoelectrochemical activity than the undoped material, due to an improvement of the surface transfer coefficient and some grain boundary passivation. Schottky barrier modeling of Fe&sub2O&sub3 thin films showed that either the width of the depletion region or the diffusion length is the dominant parameter with a value around 30 nm, and confirmed that the surface charge transfer coefficient is small. An extensive review of the conduction mechanisms of Fe&sub2O&sub3 is presented. ZnO and SnO&sub2 nanostructures were investigated as substrates for the Fe&sub2O&sub3 thin films. Arrays of well-aligned high aspect ratio ZnO nanowires were optimised via the use of nucleation seeds and by restricting the lateral growth of the nanostructures. The geometry of the nanostructured composite electrodes was designed to maximise absorption and charge transfer processes. Composite nanostructured electrodes showed lower quantum efficiencies than equivalent thin films of Fe&sub2O&sub3, though a relative enhancement ofcollection of long wavelength charge carriers was observed, indicating that the nanostructured composite electrode concept is worthy of further investigation. The rate-limiting step for water splitting with Fe&sub2O&sub3 is not yet well understood and further investigations of the surface and bulk charge transfer properties are required in order to design electrodes to overcome specific shortcomings.

Thesis (Ph.D.)--Murdoch University, 2004. / Thesis submitted to the Division of Science and Engineering. Bibliography: leaves 172-182.

Anthropogenic climate change presents an unrivalled threat to environmental stability and the prosperity of future generations. Utilising abundant, renewable resources in energy generation and storage will be essential to halt climate change and its effects. Solar water splitting is an excellent tool in the renewable energy arsenal for countering climate change, as it utilises both sunlight and water, two of the most abundant resources available on earth. Furthermore, the direct formation of a chemical fuel, hydrogen, is thought to be more practical for storing in large quantities than electricity. Work in this thesis covers the investigation of a variety of materials, fabricated by aerosol assisted chemical vapour deposition (AACVD), for their ability to carry out photoelectrochemical water splitting. In one project, thin films of Bi2Ti2O7 (BTO), specifically of the pyrochlore crystal structure, are fabricated by AACVD and analysed for their photoelectrochemical properties. The resulting thin films are found to be phase pure with a band gap of 2.88 eV, which is 0.32 eV smaller than TiO2. Efforts to dope the BTO thin films are further investigated through the addition of iron. Significant modification to the band gap is observed, leading to a confirmed pyrochlore thin film exhibiting a band gap of 2.5 eV, a reduction of 0.38 eV from undoped BTO. The resulting thin film had a photocurrent 5 times higher than that of undoped BTO. Finally, efforts to fabricate Fe2Ti2O7 are outlined. It is discovered that a stable phase of Fe2TiO5 is preferentially formed over the pyrochlore phase, even with dramatic modification to the deposition parameters and precursor stoichiometry. The high stability of this phase, coupled with the limiting features of the glass substrates, highlights the challenges with forming certain pyrochlore thin films. In a second project, the effect of depositing titanium nanoclusters onto the surface of bismuth vanadate is investigated. Nanoclusters are of huge interest because their properties lie between those of atoms and bulk materials. Additionally, nanoscale clusters can be fabricated with incredible precision, allowing one to select discrete diameter particles for deposition on surfaces. Ti nanoclusters over a range of sizes are deposited onto BiVO4 photoanodes. It is discovered that the deposition of ultralow loadings of Ti2000 clusters results in an 80 % enhancement in the photocurrent of the BiVO4 substrates. Further experimentation highlights that the photocurrent enhancement is linked to the size of the nanocluster and the density of the clusters on the surface. A mechanism is outlined, whereby the Ti nanoclusters partially reduce the surface of the BiVO4, leading to enhanced electron transport within the thin films due to the presence of oxygen vacancies. In a final project, polycrystalline InN, GaN and systematically controlled InxGa1-xN composite thin films are fabricated on FTO glass by a facile, low-cost and scalable aerosol assisted chemical vapor deposition technique. Variation of the indium content in the composite films leads to a dramatic shift in the optical absorbance properties, which correlates with the band edges shifting between those of GaN to InN. Moreover, the photoelectrochemical properties are shown to vary with indium content, with the 50 % indium composite having an external quantum efficiency of around 8 %. Whilst the overall photocurrent is found to be low, the photocurrent stability is shown to be excellent, with little degradation seen over 1 hour. Subsequent attempts to modify the morphology by conducting vertical-AACVD are also outlined. Thin films fabricated using vertical-AACVD are found to grow via a different mechanism, leading to undesired split phase growth, where two different compositions form on the same substrate.

abstract: Photocatalytic water splitting is a promising technique to produce H2 fuels from water using sustainable solar energy. To better design photocatalysts, the understanding of charge transfer at surfaces/interfaces and the corresponding structure change during the reaction is very important. Local structural and chemical information on nanoparticle surfaces or interfaces can be achieved through characterizations on transmission electron microscopy (TEM). Emphasis should be put on materials structure changes during the reactions in their “working conditions”. Environmental TEM with in situ light illumination system allows the photocatalysts to be studied under light irradiation when exposed to H2O vapor. A set of ex situ and in situ TEM characterizations are carried out on typical types of TiO2 based photocatalysts. The observed structure changes during the reaction are correlated with the H2 production rate for structure-property relationships. A surface disordering was observed in situ when well-defined anatase TiO2 rhombohedral nanoparticles were exposed to 1 Torr H2O vapor and 10suns light inside the environmental TEM. The disordering is believed to be related to high density of hydroxyl groups formed on surface oxygen vacancies during water splitting reactions. Pt co-catalyst on TiO2 is able to split pure water producing H2 and O2. The H2 production rate drops during the reaction. Particle size growth during reaction was discovered with Z-contrast images. The particle size growth is believed to be a photo-electro-chemical Ostwald ripening. Characterizations were also carried out on a more complicated photocatalyst system: Ni/NiO core/shell co-catalyst on TiO2. A decrease of the H2 production rate resulting from photo-corrosion was observed. The Ni is believed to be oxidized to Ni2+ by OH• radicals which are intermediate products of H2O oxidation. The mechanism that the OH• radicals leak into the cores through cracks on NiO shells is more supported by experiments. Overall this research has done a comprehensive ex situ and in situ TEM characterizations following some typical TiO2 based photocatalysts during reactions. This research has shown the technique availability to study photocatalyst inside TEM in photocatalytic conditions. It also demonstrates the importance to follow structure changes of materials during reactions in understanding deactivation mechanisms. / Dissertation/Thesis / Doctoral Dissertation Materials Science and Engineering 2015

Submitted by Luciana Sebin (lusebin@ufscar.br) on 2016-09-19T13:34:59Z No. of bitstreams: 1 TeseIAC.pdf: 3635782 bytes, checksum: af0cdbb8c8caf2d9a90377d533f6b0ca (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-09-20T18:14:48Z (GMT) No. of bitstreams: 1 TeseIAC.pdf: 3635782 bytes, checksum: af0cdbb8c8caf2d9a90377d533f6b0ca (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-09-20T18:14:55Z (GMT) No. of bitstreams: 1 TeseIAC.pdf: 3635782 bytes, checksum: af0cdbb8c8caf2d9a90377d533f6b0ca (MD5) / Made available in DSpace on 2016-09-20T18:15:04Z (GMT). No. of bitstreams: 1 TeseIAC.pdf: 3635782 bytes, checksum: af0cdbb8c8caf2d9a90377d533f6b0ca (MD5) Previous issue date: 2015-12-08 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / The use of semiconductors for environmental applications and solar photoconversion has been widely explored recently. Due the intensive researches on renewable energy such as the photoelectrochemical H2 evolution from water splitting reaction, the design of new catalysts has been investigated. In this context, tungsten oxide – WO3 – is a promising catalyst for such application, however its conduction band is located at a more positive potential than the potential of water reduction, as a result WO3 does not have the ability to reduce H+ to H2. In the first part, this work deal with the synthesis of WO3 by the oxidant peroxide method, as a promising catalyst for this reaction. Tuning of the band-edge levels for the different synthesized catalysts was verified from Mott Schottky plot, and it represents the effective photoelectrocatalytic water splitting.In the second part, the study of heterostructuring TiO2 with WO3was investigated because of the possibility to mitigate the recombination of electron–hole pairs and therefore obtain more active systems for photocatalytic applications. The synthesis of WO3/TiO2 heterostructures was evaluated by hydrothermal method using three different routes: (I) precursors used as peroxo-complexes; (II) tungsten peroxo-complex and TiO2 pre-formed oxide; (III) pre-formed oxides as building blocks. The results showed by electrochemical characterization demonstrated how the electronic parameters (band edge positions, Fermi level energy and charge migration) affect the photocatalytic activity of heterostructures obtained by the distinct synthetic routes. The as-synthesized materials was investigated toward the photodegradation of organic dye (Rhodamine-B) under visible and UV illumination. The growth mechanism was observed to play a significant role in governing surface and interfacial properties, which has a direct influence on xvi materials photoactivity. The band edge positions for the materials was determined from Mott Schottky plot and the experimentally determined energy diagram is consistent with the formation of a type II heterostructure for WO3/TiO2 and it is well correlated to recent reports in literature. As a result, the photogenerated electrons and holes can be spatially distributed in two different crystalline phases in contact and the charge recombination is inhibited, which is efficient for photocatalytic reactions.Additionally, regarding the energy diagram obtained for the heterostrucutres, it is possible from the thermodynamic aspect the use of those structures as promising candidates for the photoelectrocatalytic water splitting, since the band positions are sufficiently large to overcome the character of this reaction. / O uso de semicondutores para aplicações ambientais e na fotoconversão solar tem sido amplamente explorado recentemente. Devido a pesquisas intensivas sobre energias renováveis como a reação de produção fotoeletroquímica de H2 a partir da água, o desenvolvimento de novos catalisadores tem sido investigado. O óxido de tungstênio – WO3– é um material promissor para tais aplicações, entretanto, a posição da sua banda de condução possui valores mais positivos que o potencial de redução da água, e desta forma este material não tem a habilidade de reduzir diretamente o H+ para H2. Na primeira parte, este trabalho aborda a síntese de WO3 pelo método dos peróxidos oxidantes (OPM), como um catalisador promissor para esta reação. Foi observado deslocamento nas bandas de energia para o filme de WO3 obtido pela rota OPM em relação ao óxido obtido pela rota convencional, determinado pela da relação de Mott Schottky e estes resultados caracterizam a efetiva reação water splitting. Na segunda parte, foi investigado a formação de heteroestruturas de TiO2 com WO3, no acoplamento entre as estruturas eletronicas dos óxidos semicondutores para obtenção de sistemas mais ativos em processos fotocatalíticos. A síntese de heteroestruturas WO3/TiO2 foi avaliada pelo método hidrotérmico utilizando três rotas distintas: (I) precursores na forma de peroxo-complexos estáveis; (II) peroxo-complexo de tungstênio e óxido pré-formado de TiO2 e (III) óxidos pré-formados como “blocos de construção”. De acordo com os resultados obtidos por caracterização eletroquímica, os parâmetros eletrônicos (posições de banda de energia, nível de Fermi e migração de cargas) influenciaram na atividade fotocatalítica de heteroestruturas obtidas por rotas sintéticas distintas. Os materiais foram investigados na reação defotodegradação do corante orgânico (Rodamina-B) sob xiv iluminação visível e UV. Observou-se que o mecanismo de crescimento das estruturas desempenha um papel significativo nas propriedades finais dos catalisadores produzidos, e uma influência direta sobre a fotoatividade destes. As posições do nível de Fermi para os materiais foi determinada a partir da caracterização eletroquímica pela relação de Mott Schottky e o diagrama de energia determinado experimentalmente é consistente com a formação de uma heteroestrutura tipo II para WO3/TiO2 e está de acordo com relatos recentes na literatura. Como consequência, os elétrons e buracos fotogerados podem estar espacialmente distribuídos nas fases cristalinas em contato e a taxa de recombinação é inibida, o que é eficaz para reações catalíticas. Além disso, em relação ao diagrama de energia obtida para as heteroestruturas, é possível do ponto de vista termodinâmico, a utilização como candidatos promissores para a reação fotoeletrocatalítica de water splitting, uma vez que os potenciais são energeticamente favoráveis para esta reação. / FAPESP: 2011/07484-8 / CAPES: 8218-13-7

Orientador: Armando Lopes Moreno Junior / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenhaira Civil, Arquitetura e Urbanismo / Made available in DSpace on 2018-08-05T00:18:16Z (GMT). No. of bitstreams: 1 Tramontin_AndrePenteado_M.pdf: 3029877 bytes, checksum: d1ddf2e0086571a9cb41c8abef993f75 (MD5) Previous issue date: 2005 / Resumo: As fissuras na interface alvenaria-estrutura são comuns e pouco se conhece a respeito da sua ocorrência, embora sejam freqüentes, especialmente as que aparecem na ligação alvenaria-pilar de concreto. O objetivo deste trabalho foi estudar a melhor técnica de ancoragem entre alvenaria-estrutura, avaliando sua eficiência no combate a esse tipo de fissura. Foram utilizados para a elaboração dos ensaios, além dos materiais usados na alvenaria de vedação (bloco cerâmico, argamassa etc), diferentes materiais de ancoragem (tela metálica eletrosoldada e barras de aço) e dispositivos de ligação (adesivo epóxi, pinos, arruelas e cantoneira), analisando-se assim o melhor conjunto do ponto de vista técnico. Foram feitos ensaios de caracterização dos materiais e de arrancamento à tração direta, até a ocorrência da primeira fissura visível a olho nu. Concluiu-se finalmente que a tela metálica eletrosoldada galvanizada malha 15 x 15 mm e diâmetro do fio 1,65 mm, sem cantoneira e com tratamento de chapisco com adesivo acrílico no pilarete foi a melhor técnica de ancoragem para a prevenção do aparecimento de fissuras na interface alvenaria de vedação e pilar de concreto / Abstract: The splitting of the fair-faced masonry-structure are very usual but it is not wellknown the reason of its occurrence, although they are frequent, specially the ones that appear in the linking of the masonry-concrete column. The purpouse of this work was to study the best anchorage technique between masonrystructure, being evaluated its efficiency to prevent this type of splitting. Beyond the materials that are usually used for masonry (ceramic block, mortar etc), changeable materials of anchorage (stell welded tie and steel wire) and apparatus of linking (adhesive epoxy, bolts, washers and angle-steel) were used, analyzing the best combination for the technical view. Tests of characterization of the materials and the pullout test were made, until the occurrence of the first splitting visible by naked eye. Finally, it was concluded that the metallic wall tie, 15 x 15 mm and the diameter of wire 1,65 mm, without angle-steel and with mortar with acrylic adhesive in the concrete column was the best anchorage technique for to prevent occurrence of splitting in the fair-faced masonry-concrete structure / Mestrado / Edificações / Mestre em Engenharia Civil

Em mamíferos, a temperatura corporal (Tc) varia ao longo do dia, de forma rítmica, bem como a atividade locomotora. Essa ritmicidade diária é gerada endogenamente, por osciladores circadianos. Em geral, os valores mais elevados de Tc concentram-se nos mesmos horários em que há atividade locomotora. No entanto, variações diárias de Tc são observadas mesmo em indivíduos imóveis, evidenciando que o ritmo de Tc não é uma mera consequência dos efeitos agudos da atividade locomotora. Este trabalho teve o objetivo de estudar o ritmo circadiano de Tc no roedor Ctenomys aff. knighti (tuco-tuco) e sua relação temporal com o ritmo de atividade locomotora. A caracterização do ritmo de Tc nesse animal é particularmente interessante, pois ele habita o ambiente subterrâneo, que impõe desafios tanto à expressão rítmica (pois os ciclos ambientais são ausentes ou têm baixa amplitude) quanto à termorregulação (devido à características como alta umidade e atmosfera hipóxica e estagnada). Medimos a Tc e a atividade locomotora dos tuco-tucos em condições controladas de laboratório. Na caracterização inicial, constatamos que o ritmo de Tc dos tuco-tucos persiste mesmo em escuridão e temperatura constantes. Quando houve exposição a um ciclo diário de claro/escuro, o ritmo de Tc foi sincronizado, e os valores mais altos ocorreram na fase de escuro. Os ritmos de Tc e de atividade locomotora mostraram-se fortemente associados no tempo. Investigamos, então, se a corrida na roda de atividade modificaria a amplitude do ritmo de Tc, por envolver atividade muscular intensa. Observamos, no entanto, que a amplitude é pouco alterada com a retirada da roda e que na sua ausência os animais substituem a corrida por outras atividades que também causam efeitos agudos na Tc. Em seguida, estudamos a variação da sensibilidade da Tc aos efeitos agudos da atividade ao longo do dia. Através de um método estatístico, que também foi utilizado para filtrar os dados de Tc, verificamos que há maior correlação entre variações de Tc e de atividade no início da noite. Por fim, investigamos se o controle do ritmo de Tc é exercido pelos núcleos supraquiasmáticos, os quais são os osciladores circadianos do ritmo de atividade locomotora. Nossa abordagem utilizou animais neurologicamente intactos, comparando os padrões do ritmo de Tc e de atividade locomotora durante a ocorrência do fenômeno de \"partição do ritmo\". Constatamos que na maioria dos casos os padrões de partição, tanto da Tc como da atividade locomotora são idênticos, sugerindo um controle temporal comum. No entanto, em um dos animais observamos diferenças entre os dois ritmos, sugerindo que esse controle circadiano pode ser ainda mais complexo. / In mammals, body temperature (Tb), as well as locomotor activity, changes during the day, exhibiting a rhythmic pattern. This daily rhythmicity is generated endogenously by circadian oscillators. Usually, the highest Tb values occur simultaneously to locomotor activity. Nevertheless, daily Tb changes are observed even in immobile individuals. This fact is evidence that the Tb rhythm is not a mere consequence of the acute effects of locomotor activity. The present work,which os performed in the research center CRILAR, in Argentina, had the objective of studying the circadian rhythm of Tb. in the rodent Ctenomys aff. knighti (tuco-tuco) and its temporal relationship with the locomotor activity rhythm. The characterization of the Tb rhythm in this animal is especially interesting because it inhabits the subterranean environment, which poses challenges to both rhythmic expression (because environmental cycles are either absent or have low amplitude) and thermoregulation (due to high relative humidity, hypoxic atmosphere and limited ventilation). We measured Tb and locomotor activity of tuco-tucos under controlled laboratory conditions. An initial characterization showed that the tuco-tuco\'s Tb rhythm persisted even in constant darkness and constant temperature. This rhythm synchronized to a daily light/dark cycle, with highest values occurring during the dark phase. Tb and locomotor activity rhythm were robustly associated in time. Then, we investigated whether the wheel running would modify the Tb rhythm amplitude, because this behavior involves intense muscular activity. However, we observed that the amplitude is only slightly altered upon running-wheel removal and that in the absence of the wheel tuco-tucos substitute running with other behaviors which also have acute effects on Tb. Applying a statistical method, which was also used to filter Tb data, we verified that there is a stronger correlation between Tb changes and activity in the beginning of the night. Finally, we investigated whether the Tb rhythm is also under control of the suprachiasmatic nuclei, which are knowingly the circadian oscillators for the locomotor activity rhythm. We used an approach which involved neurally intact animals, by comparing the rhythmic patterns of Tb and locomotor activity rhythms during the occurrence of a phenomenon called \"splitting\". In most cases, splitting patterns of both Tb and locomotor activity rhythms were identical, indicating a common temporal control of these two variables. Nevertheless, we observed, in one animal, differences between the two rhythms, which suggest that the circadian control might be even more complex.

In this work, the technique of designing and optimizing broadband volume transmission holograms using dichromate gelatin (DCG) is summarized for solar spectrum-splitting application. Spectrum splitting photovoltaic system uses a series of single bandgap PV cells that have different spectral conversion efficiency properties to more fully utilize the solar spectrum. In such a system, one or more high performance optical filters are usually required to split the solar spectrum and efficiently send them to the corresponding PV cells. An ideal spectral filter should have a rectangular shape with sharp transition wavelengths. DCG is a near ideal holographic material for solar applications as it can achieve high refractive index modulation, low absorption and scattering properties and long-term stability to solar exposure after sealing. In this research, a methodology of designing and modeling a transmission DCG hologram using coupled wave analysis for different PV bandgap combinations is described. To achieve a broad diffraction bandwidth and sharp cut-off wavelength, a cascaded structure of multiple thick holograms is described. A search algorithm is also developed to optimize both single and two-layer cascaded holographic spectrum splitters for the best bandgap combinations of two- and three-junction SSPV systems illuminated under the AM1.5 solar spectrum. The power conversion efficiencies of the optimized systems under the AM1.5 solar spectrum are then calculated using the detailed balance method, and shows an improvement compared with tandem structure.

A tear in the subducting Nazca slab is located between the end of the Pampean flat slab and normally subducting oceanic lithosphere. Tomographic studies suggest mantle material flows through this opening. The best way to probe this hypothesis is through observations of seismic anisotropy, such as shear wave splitting. We examine patterns of shear wave splitting using data from two seismic deployments in Argentina that lay updip of the slab tear. We observe a simple pattern of plate-motion-parallel fast splitting directions, indicative of plate-motion-parallel mantle flow, beneath the majority of the stations. Our observed splitting contrasts previous observations to the north and south of the flat slab region. Since plate-motion-parallel splitting occurs only coincidentally with the slab tear, we propose mantle material flows through the opening resulting in Nazca plate-motion-parallel flow in both the subslab mantle and mantle wedge.