Dissertations / Theses on the topic 'Metal oxide'
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1
Gillispie, Meagen Anne. "Metal oxide-based transparent conducting oxides." [Ames, Iowa : Iowa State University], 2006.
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Field, Marianne Alice Louise. "Transition metal oxides and oxide-halides." Thesis, University of Southampton, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.401833.
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Guo, Muyao, and 郭牧遥. "Metal oxide photocatalysis." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2013. http://hub.hku.hk/bib/B50434457.
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Photocatalysis has been attracting much research interest because of its wide applications in renewable energy and environmental remediation. Among the photocatalysts, metal oxide semiconductors are the best choice due to distinctive properties, durability and cost effectiveness. However, the mechanisms of photocatalysis are still not entirely clear and the photocatalytic activity of the metal oxide materials needs to be improved. Therefore, this thesis concentrates on the study of the photocatalytic mechanism and the factors affecting the photocatalytic activity.
The photocatalysis of different commercial metal oxide nanoparticles has been studied. Different photocatalytic experiments have been designed to find out the mechanisms of photocatalysis. It is found that the dominant mechanism of photocatalysis is direct charge transfer between metal oxide and organic compounds. Reactive oxygen species, such as hydroxyl radicals also play a minor role in the photocatalysis.
ZnO tetrapods were synthesized by evaporating Zn powder in the flow of Ar gas at high temperature in this study. They exhibit excellent photocatalytic activity. By the comparison between ZnO tetrapods and different ZnO nanoparticles, it is found that the photocatalytic activity of the metal oxide is strongly affected by the native defects, especially by the nonradiative defects.
1D TiO2 nanotubes and ZnO nanorods were synthesized by anodization and hydrothermal growth respectively. ZnO nanorods with alumina and titania shell were prepared by solution-based methods. These structures are interesting as supported catalysts, which is important for practical applications, since it enables simple removal of photocatalyst from treated water. The core shell structures are expected to improve the stability of ZnO. The results also imply that the photocatalytic avtivity of materials is affected by the native defects.
Two different solution based methods hydrothermal growth and electrodeposition to grow CuxO layer were used. The hydrothermal grown CuxO exhibit excellent photocatalytic activity and good photocorrosion resistance. It was also found that the photocatalytic activity of the CuxO prepared by hydrothermal methods can be recovered by simple immersion of the sample into the precursor solution.published_or_final_version
Physics
Master
Master of Philosophy
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Machin, Sophie Elizabeth. "Metal oxide nanowires." Thesis, University of Cambridge, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.648214.
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Zhang, Huichun. "Metal oxide-facilitated oxidation of antibacterial agents." Diss., Available online, Georgia Institute of Technology, 2004:, 2004. http://etd.gatech.edu/theses/available/etd-07072004-152317/unrestricted/zhang%5Fhuichun%5F200407%5Fphd.pdf.
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Thesis (Ph. D.)--School of Civil and Environmental Engineering, Georgia Institute of Technology, 2005. Directed by Ching-Hua Huang.Wine, Paul, Committee Member ; Pavlostathis, Spyros, Committee Member ; Mulholland, James, Committee Member ; Yiacoumi, Sotira, Committee Member ; Huang, Ching-Hua, Committee Chair. Includes bibliographical references.
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Dodd, Linzi Emma. "Fabrication optimisation of metal-oxide-metal diodes." Thesis, Durham University, 2014. http://etheses.dur.ac.uk/9474/.
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This thesis is based on the design, research and development of devices required to successfully recover waste heat and convert it into electrical power through the use of Microsystems Technology. This takes place using optical nano-antennas, in the same way a radio antenna picks up a radio station. The main aim of this project is the rectification of this signal into a useful DC voltage. Here we have used high frequency metal-oxide-metal (MOM) diodes, which involve the use of two dissimilar metals separated by a native oxide. In order to make successful MOM diodes, the following must be considered: maximise the work function difference between the metals for asymmetry in I-V characteristics, produce a uniform oxide layer that is sufficiently thin (a few nm) for electron tunnelling to occur and reduce the diode size to sub-micron dimensions to increase the cut-off frequency. Currently the diodes consist of titanium, titanium oxide and platinum, which provides a high enough work function difference that the I-V characteristics show significant asymmetry and figure of merit values are among the best published. It has been found, using ToFSIMS and TEM analysis of the oxide, that the thickness of the oxide can be controlled between 1 nm and 7 nm using RIE etching and subsequent oxygen plasma regrowth. Different oxides have been fabricated with different stoichiometries depending on the process used. Furnace oxidation grows a complex oxide in the range 6.9 to 7.6 nm thick. By contrast a more simple oxide can be produced using a controlled reactive ion etch and subsequent plasma oxidation, with thicknesses in the range 1 to 6 nm. The final significant issue involves the cross-sectional area of the diodes, which also determines their cut-off frequency. Extrapolation of existing diode results suggests that, if made sufficiently small, they would function at high enough frequencies for rectification of radiation in the terahertz regime. Furthermore, phase shift lithography has been used to demonstrate 200 to 400nm lines in diode features, with alternative possible high scale processes discussed for future fabrication.
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Sayle, D. C. "Computer simulation of heteroepitaxial oxide/oxide and metal/oxide interfaces." Thesis, University of Bath, 1992. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317429.
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Nguyen, Thanh Dinh. "Metal oxide, Mixed oxide, and hybrid metal@oxide nanocrystals: size-and shape-controlled synthesis and catalytic applications." Thesis, Université Laval, 2011. http://www.theses.ulaval.ca/2011/28408/28408.pdf.
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Le contrôle de la taille et de la morphologie de nanocristaux d’oxydes métalliques simples, d’oxydes mixtes et d’oxydes métalliques hybrides est un sujet de grand intérêt. La dépendance de leur propriétés physio-chimiques avec leurs taille et morphologies, génèrent une variété de leur applications dans plusieurs domaines. Cependant, le dévellopement des nanocristaux en controllant la taille, la forme, l’assemblage et l’homogénéité de la composition chimique pour l’optimisation de propriété spécifiques demandent la combinaison de nombreux parametres de synthèse.
Les trois différentes approches ont été développées dans le cadre de la thèse pour la synthèse d’une variété de nouveaux nanomatériaux d’oxydes simples, d’oxydes mixtes et d’oxydes métalliques hybrides dont la taille et la forme ont été bien controllées. Ces méthodes ont été nommées comme des méthodes solvo-hydrothermiques assistées par des molécules structurantes à l’état monophasique (eau ou eau/éthanol) et à l’état biphasique (eau-toluène). Nos approches de synthèse ont permi de préparer des nanocristaux des oxydes de métaux de transition (V, Cr, Mn, Co, Ni, In), et des terres rares (Sm, Ce, La, Gd, Er, Ti, Y, Zr), ainsi que des oxydes métalliques mixtes (tungstate, orthovanadate, molybdate). Ces nanomatériaux sont sous forme colloïdale mono-dispersée qui présente une cristallinité élevée. La taille et la forme de tels nanocristaux peuvent facilement être contrôlées par une simple variation des paramètres de synthèse telle que la concentration de précurseurs, la nature de la molécule structurante, la température et le temps de réaction. A large variété de techniques a été utilisée pour la caracterisation de ces nanomatériaux telles que TEM/HRTEM, SEM, SAED, EDS, XRD, XPS, FTIR, TGA-DTA, UV-vis, photoluminescence, BET. Les propriétés catalytiques de ces matériaux ont aussi été étudiées.
Dans ce travail, le contrôle de la cinétique de croissance des nucléides ainsi que le mécanisme gouvernant la forme qui conduit à la taille et la morphologie finale du nanocrystal ont été proposé. L’effet de la taille et de la forme des nanoparticules d’oxyde métallique hybrides sur les propriétés catalytiques pour la réaction d’oxydation du CO et la photo-dégradation du bleue de méthylène a été aussi étudié. Car les catalyseurs existant actuellement à base de métaux nobles sont très couteux et en plus très sensibles à l’empoisonnement par le gas H2S ou les émissions polluantes de SOx. L’activité catalytique des nanocristaux d’oxydes métallique hybrides Cu@CeO2 de formes cubiques dans l’oxydation de CO et de Ag@TiO2 de formes de ceinture dans la photo dégradation du bleue de méthylène ont montré la dépendance de la taille et la forme des nanocristaux avec leur propriétés catalytiques.The ability to finely control the size and shape of metal oxide, mixed metal oxide, hybrid metal/oxide nanocrystals has become an area of great interest, as many of their physical and chemical properties are highly dependent on morphology, and the more technological applications will be possible for their use. Large-scale synthesis of such high-quality nanocrystals is the first and key step to this area of science. A tremendous effort has recently been spent in attempt to control these novel properties through manipulation of size, shape, structure, and composition. Flexibly nanocrystal size/shape control for both monodisperse single and multiple-oxide nanomaterial systems, however, remains largely empirical and still presents a great challenge. In this dissertation, new synthetic approaches have been developed and described for the synthetic design of a series of colloidal monodisperse metal oxide, mixed metal oxide, hybrid metal-oxide nanocrystals with controlled size and shape. These materials were generally characterized using TEM/HRTEM, SEM, SAED, EDS, XRD, XPS, FTIR, TGA-DTA, UV-vis, photoluminescence, BET techniques. Effect of the size and shape of these obtained hybrid metal-oxide nanocrystals on the catalytic properties is illustrated. We have developed three different new surfactant-assistant pathways for the large-scale synthesis of three types of nanomaterials including metal oxide, mixed metal oxide, hybrid noble-metal-oxide colloidal monodisperse nanocrystals. Namely, the solvo-hydrothermal surfactant-assisted methods in one-phase (water or water/ethanol) and two-phase (water-toluene) systems were used for the synthesis of metal oxide (transition metal-V, Cr, Mn, Co, Ni, In and rare earth-Sm, Ce, La, Gd, Er, Ti, Y, Zr) and mixed metal oxide (tungstate, orthovanadate, molybdate). The seed-media growth with the assistant of bifunctional surfactant was used for the synthesis of hybrid noble metal@oxide (Ag@TiO2, (Cu or Ag)@CeO2, Au/tungstate, Ag/molybdate, etc.) nanocrystals. A significant feature of our synthetic approaches was pointed out that most resulting nanocrystal products are monodisperse, high crystallinity, uniform shape, and narrow distribution. The size and shape of such nanocrystals can be controlled easily by simple tuning the reaction parameters such as the concentration of precursors and surfactants, the nature of surfactant, the temperature and time of synthetic reaction. The prepared nanocrystals with the functional surface were used as the building blocks for the self-assembly into hierarchical mesocrystal microspheres. The effective ways how to control the growth kinetics of the nuclei and the shape-guiding mechanisms leading to the manipulation of morphology of final products were proposed. Our current approaches have several conveniences including used nontoxic and inexpensive reagents (most using inorganic metal salts as starting precursors instead of expensive and toxic metallic alkoxides or organometallics), relatively mild conditions, high-yield, and large-scale production; in some causes, water or ethanol was used as environmentally benign reaction solvent. Catalytic activity and selectivity are governed by the nature of the catalyst surface, making shaped nanocrystals ideal substrates for understanding the influence of surface structure on heterogeneous catalysis at the nanoscale. Finally, this work was concentrated on demonstration of heterogeneous catalytic activity of hybrid metal-oxide nanomaterials (Cu@CeO2, Ag@TiO2) as a typical example. We synthesized the high-crystalline titanium oxide and cerium oxide nanocrystals with control over their shape and surface chemistry in high yield via the aqueous surfactant-assist method. The novel hybrid metal-oxide nanocrystals were produced by the depositing noble metal ion (Cu, Ag, Au) precursors on the pre-synthesized oxide seeds via seed-mediated growth. The catalytic activity of these metal-oxide nanohybrids of Cu@CeO2 nanocubes for CO oxidation conversion and Ag@TiO2 nanobelts for Methylene Blue photodegradation with size/shape-dependent properties were verified.
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Nguyen, Thanh-Dinh. "Metal oxide, Mixed oxide, and hybrid metal@oxide nanocrystals : size-and shape-controlled synthesis and catalytic applications." Doctoral thesis, Université Laval, 2011. http://hdl.handle.net/20.500.11794/22994.
Full textAbstract:
Le contrôle de la taille et de la morphologie de nanocristaux d’oxydes métalliques simples, d’oxydes mixtes et d’oxydes métalliques hybrides est un sujet de grand intérêt. La dépendance de leur propriétés physio-chimiques avec leurs taille et morphologies, génèrent une variété de leur applications dans plusieurs domaines. Cependant, le dévellopement des nanocristaux en controllant la taille, la forme, l’assemblage et l’homogénéité de la composition chimique pour l’optimisation de propriété spécifiques demandent la combinaison de nombreux parametres de synthèse. Les trois différentes approches ont été développées dans le cadre de la thèse pour la synthèse d’une variété de nouveaux nanomatériaux d’oxydes simples, d’oxydes mixtes et d’oxydes métalliques hybrides dont la taille et la forme ont été bien controllées. Ces méthodes ont été nommées comme des méthodes solvo-hydrothermiques assistées par des molécules structurantes à l’état monophasique (eau ou eau/éthanol) et à l’état biphasique (eau-toluène). Nos approches de synthèse ont permi de préparer des nanocristaux des oxydes de métaux de transition (V, Cr, Mn, Co, Ni, In), et des terres rares (Sm, Ce, La, Gd, Er, Ti, Y, Zr), ainsi que des oxydes métalliques mixtes (tungstate, orthovanadate, molybdate). Ces nanomatériaux sont sous forme colloïdale mono-dispersée qui présente une cristallinité élevée. La taille et la forme de tels nanocristaux peuvent facilement être contrôlées par une simple variation des paramètres de synthèse telle que la concentration de précurseurs, la nature de la molécule structurante, la température et le temps de réaction. A large variété de techniques a été utilisée pour la caracterisation de ces nanomatériaux telles que TEM/HRTEM, SEM, SAED, EDS, XRD, XPS, FTIR, TGA-DTA, UV-vis, photoluminescence, BET. Les propriétés catalytiques de ces matériaux ont aussi été étudiées. Dans ce travail, le contrôle de la cinétique de croissance des nucléides ainsi que le mécanisme gouvernant la forme qui conduit à la taille et la morphologie finale du nanocrystal ont été proposé. L’effet de la taille et de la forme des nanoparticules d’oxyde métallique hybrides sur les propriétés catalytiques pour la réaction d’oxydation du CO et la photo-dégradation du bleue de méthylène a été aussi étudié. Car les catalyseurs existant actuellement à base de métaux nobles sont très couteux et en plus très sensibles à l’empoisonnement par le gas H2S ou les émissions polluantes de SOx. L’activité catalytique des nanocristaux d’oxydes métallique hybrides Cu@CeO2 de formes cubiques dans l’oxydation de CO et de Ag@TiO2 de formes de ceinture dans la photo dégradation du bleue de méthylène ont montré la dépendance de la taille et la forme des nanocristaux avec leur propriétés catalytiques.The ability to finely control the size and shape of metal oxide, mixed metal oxide, hybrid metal/oxide nanocrystals has become an area of great interest, as many of their physical and chemical properties are highly dependent on morphology, and the more technological applications will be possible for their use. Large-scale synthesis of such high-quality nanocrystals is the first and key step to this area of science. A tremendous effort has recently been spent in attempt to control these novel properties through manipulation of size, shape, structure, and composition. Flexibly nanocrystal size/shape control for both monodisperse single and multiple-oxide nanomaterial systems, however, remains largely empirical and still presents a great challenge. In this dissertation, new synthetic approaches have been developed and described for the synthetic design of a series of colloidal monodisperse metal oxide, mixed metal oxide, hybrid metal-oxide nanocrystals with controlled size and shape. These materials were generally characterized using TEM/HRTEM, SEM, SAED, EDS, XRD, XPS, FTIR, TGA-DTA, UV-vis, photoluminescence, BET techniques. Effect of the size and shape of these obtained hybrid metal-oxide nanocrystals on the catalytic properties is illustrated. We have developed three different new surfactant-assistant pathways for the large-scale synthesis of three types of nanomaterials including metal oxide, mixed metal oxide, hybrid noble-metal-oxide colloidal monodisperse nanocrystals. Namely, the solvo-hydrothermal surfactant-assisted methods in one-phase (water or water/ethanol) and two-phase (water-toluene) systems were used for the synthesis of metal oxide (transition metal-V, Cr, Mn, Co, Ni, In and rare earth-Sm, Ce, La, Gd, Er, Ti, Y, Zr) and mixed metal oxide (tungstate, orthovanadate, molybdate). The seed-media growth with the assistant of bifunctional surfactant was used for the synthesis of hybrid noble metal@oxide (Ag@TiO2, (Cu or Ag)@CeO2, Au/tungstate, Ag/molybdate, etc.) nanocrystals. A significant feature of our synthetic approaches was pointed out that most resulting nanocrystal products are monodisperse, high crystallinity, uniform shape, and narrow distribution. The size and shape of such nanocrystals can be controlled easily by simple tuning the reaction parameters such as the concentration of precursors and surfactants, the nature of surfactant, the temperature and time of synthetic reaction. The prepared nanocrystals with the functional surface were used as the building blocks for the self-assembly into hierarchical mesocrystal microspheres. The effective ways how to control the growth kinetics of the nuclei and the shape-guiding mechanisms leading to the manipulation of morphology of final products were proposed. Our current approaches have several conveniences including used nontoxic and inexpensive reagents (most using inorganic metal salts as starting precursors instead of expensive and toxic metallic alkoxides or organometallics), relatively mild conditions, high-yield, and large-scale production; in some causes, water or ethanol was used as environmentally benign reaction solvent. Catalytic activity and selectivity are governed by the nature of the catalyst surface, making shaped nanocrystals ideal substrates for understanding the influence of surface structure on heterogeneous catalysis at the nanoscale. Finally, this work was concentrated on demonstration of heterogeneous catalytic activity of hybrid metal-oxide nanomaterials (Cu@CeO2, Ag@TiO2) as a typical example. We synthesized the high-crystalline titanium oxide and cerium oxide nanocrystals with control over their shape and surface chemistry in high yield via the aqueous surfactant-assist method. The novel hybrid metal-oxide nanocrystals were produced by the depositing noble metal ion (Cu, Ag, Au) precursors on the pre-synthesized oxide seeds via seed-mediated growth. The catalytic activity of these metal-oxide nanohybrids of Cu@CeO2 nanocubes for CO oxidation conversion and Ag@TiO2 nanobelts for Methylene Blue photodegradation with size/shape-dependent properties were verified.
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Eskhult, Jonas. "Electrochemical Deposition of Nanostructured Metal/Metal-Oxide Coatings." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-8186.
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Gu, Yanjuan, and 谷艳娟. "Nanostructure of transition metal and metal oxide forelectrocatalysis." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2006. http://hub.hku.hk/bib/B37774396.
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Ramanathan, S. "Electrochemical studies on metal-metal oxide pH sensors." Thesis, University of Salford, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376871.
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Bharde, A. "Microbial synthesis of metal oxide and metal nanoparticles." Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 2007. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/2553.
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Al-Ahmadi, Ahmad Aziz. "Complementary orthogonal stacked metal oxide semiconductor a novel nanoscale complementary metal oxide semiconductor architecture /." Ohio : Ohio University, 2006. http://www.ohiolink.edu/etd/view.cgi?ohiou1147134449.
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Al-Ahmadi, Ahmad Aziz. "COMPLEMENTARY ORTHOGONAL STACKED METAL OXIDE SEMICONDUCTOR: A NOVEL NANOSCALE COMPLEMENTRAY METAL OXIDE SEMICONDUCTOR ARCHTECTURE." Ohio University / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1147134449.
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Xu, Chunbao. "Continuous and batch hydrothermal synthesis of metal oxide nanoparticles and metal oxide-activated carbon nanocomposites." Diss., Available online, Georgia Institute of Technology, 2006, 2006. http://etd.gatech.edu/theses/available/etd-07302006-231517/.
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Thesis (Ph. D.)--Chemical and Biomolecular Engineering, Georgia Institute of Technology, 2007.Teja, Amyn, Committee Chair ; Kohl, Paul, Committee Member ; Liu, Meilin, Committee Member ; Nair,Sankar, Committee Member ; Rousseau, Ronald, Committee Member.
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Messi, C. "Nanostructured catalytic metal oxides supported over oxide supports of various nature : the iron oxide system." Doctoral thesis, Università degli Studi di Milano, 2008. http://hdl.handle.net/2434/57081.
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Getton, Frederick P. "Design of metal oxide catalysts." Thesis, Brunel University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314049.
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Jin, Jidong. "Metal-oxide-based electronic devices." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/metaloxidebased-electronic-devices(2ccabdd1-398b-4787-9455-e034f9001867).html.
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Metal oxides exhibit a wide range of chemical and electronic properties, making them an extremely interesting subject for numerous applications in modern electronics. The primary goal of this research is to develop metal-oxide-based electronic devices, including thin-film transistors (TFTs), resistance random-access memory (RRAM) and planar nano-devices. This research requires different processing techniques, novel device design concepts and optimisation of materials and devices. The first experiments were carried out to optimise the properties of zinc oxide (ZnO) semiconductors, in particular the carrier concentration, which determines the threshold voltage of the TFTs. Thermal annealing is one common method to affect carrier concentration and most work in the literature reports performing this process in a single-gas environment. In this work, however, annealing was carried out in a combination of air and nitrogen, and it was found that the threshold voltage could be tuned over a wide range of pre-determined values.Further experiments were undertaken to enhance the carrier mobility of ZnO TFTs, which is the most important material quality parameter. By optimising deposition conditions and incorporating a high-k gate dielectric layer, the devices showed saturation mobility values over 50 cm2/Vs at a low operating voltage of 4 V. This is, to our knowledge, one of the highest field-effect mobility values achieved in ZnO-based TFTs by room temperature sputtering. As an important type of metal-oxide-based novel memory devices, which have been studied intensively in the last few years, RRAM devices were also explored. New materials, such as tin oxide (SnOx), were tested, exhibiting bipolar-switching operations and a relatively large resistance ratio. As a novel process variation, anodisation was performed, which yielded less impressive results than SnOx, but with a potential for ultra-low-cost manufacturing. Finally, novel planar nano-devices were explored, which have much simpler structures than conventional multi-layered transistors and diodes. Three types of ZnO-based nano-devices (a side-gated transistor, a self-switching diode and a planar inverter) were fabricated using both e-beam lithography and chemical wet etching. After optimisation of the challenging wet etching procedure at nanometre scale, ZnO nano-devices with good reproducibility and reliability have been demonstrated.
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Ahmed, Mahmoud Hashim Mohammed. "Metal oxide surfaces : beyond UHV." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/metal-oxide-surfaces-beyond-uhv(84394071-1773-4cd7-95d6-4d709524e08b).html.
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In this thesis, three experimental studies of metal oxide surfaces beyond UHV conditions are presented, in an attempt to bridge the so-called ‘pressure’ gap. In the first of these studies, surface X-ray diffraction has been employed to elucidate the surface structure of #-Cr2O3(0001) as a function of water partial pressure at room temperature. In ultra high vacuum, subsequent to exposure to ~ 2000 Langmuir of H2O, the surface is determined to be terminated by a partially occupied double layer of chromium atoms. No evidence of adsorbed OH/H2O is found under this regime. At a water partial pressure of ~ 30 mbar, a surface termination involving a single OH/H2O species bound atop to each surface Cr atom is obtained. Surface X-ray diffraction has also been employed to elucidate the geometry of the TiO2(011)/H2O interface at room temperature. In ultra high vacuum, a surface structure in quantitative agreement with previously published studies is found. Most notably at a water partial pressure of ~ 30 mbar, the interface geometry is determined to be consistent with the predicted structure emerging from ab initio calculations in which the surface undergoes transformation from a (2×1) reconstruction to a (1×1) unit cell. In the final investigation a procedure for non-UHV wet-chemical preparation of TiO2 single crystal substrates is detailed. The potential of this recipe is demonstrated through application to rutile-TiO2(110) and rutile-TiO2(011) substrates. Characterisation with scanning probe microscopy, low energy electron diffraction and auger electron spectroscopy, indicate that flat, well-ordered, carbon-free surfaces can be generated. Notably, in contrast to the (2×1) surface unit cell found for TiO2(011) prepared in ultra high vacuum, wet-chemical preparation results in a (4×1) termination; wet-chemically prepared TiO2(110) displays an unreconstructed (1x1) surface.
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Sundqvist, Jonas. "Employing Metal Iodides and Oxygen in ALD and CVD of Functional Metal Oxides." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-3450.
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Price, Robert. "Metal/metal oxide co-impregnated lanthanum strontium calcium titanate anodes for solid oxide fuel cells." Thesis, University of St Andrews, 2018. http://hdl.handle.net/10023/16018.
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Solid Oxide Fuel Cells (SOFC) are electrochemical energy conversion devices which allow fuel gases, e.g. hydrogen or natural gas, to be converted to electricity and heat at much high efficiencies than combustion-based energy conversion technologies. SOFC are particularly suited to employment in stationary energy conversion applications, e.g. micro-combined heat and power (μ-CHP) and base load, which are certain to play a large role in worldwide decentralisation of power distribution and supply over the coming decades. Use of high-temperature SOFC technology within these systems is also a vital requirement in order to utilise fuel gases which are readily available in different areas of the world. Unfortunately, the limiting factor to the long-term commercialisation of SOFC systems is the redox instability, coking intolerance and sulphur poisoning of the state-of-the-art Ni-based cermet composite anode material. This research explores the ‘powder to power' development of alternative SOFC anode catalyst systems by impregnation of an A-site deficient La0.20Sr0.25Ca0.45TiO3 (LSCT[sub](A-)) anode ‘backbone' microstructure with coatings of ceria-based oxide ion conductors and metallic electrocatalyst particles, in order to create a SOFC anode which exhibits high redox stability, tolerance to sulphur poisoning and low voltage degradation rates under operating conditions. A 75 weight percent (wt. %) solids loading LSCT[sub](A-) ink, exhibiting ideal properties for screen printing of thick-film SOFC anode layers, was screen printed with 325 and 230 mesh counts (per inch) screens onto electrolyte supports. Sintering of anode layers between 1250 °C and 1350 °C for 1 to 2 hours indicated that microstructures printed with the 230 mesh screen provided a higher porosity and improved grain connectivity than those printed with the 325 mesh screen. Sintering anode layers at 1350 °C for 2 hours provided an anode microstructure with an advantageous combination of lateral grain connectivity and porosity, giving rise to an ‘effective' electrical conductivity of 17.5 S cm−1 at 850 °C. Impregnation of this optimised LSCT[sub](A-) anode scaffold with 13-16 wt. % (of the anode mass) Ce0.80Gd0.20O1.90 (CGO) and either Ni (5 wt. %), Pd, Pt, Rh or Ru (2-3 wt. %) and integration into SOFC resulted in achievement of Area Specific Resistances (ASR) of as low as 0.39 Ω cm−2, using thick (160 μm) 6ScSZ electrolytes. Durability testing of SOFC with Ni/CGO, Ni/CeO2, Pt/CGO and Rh/CGO impregnated LSCT[sub](A-) anodes was subsequently carried out in industrial button cell test rigs at HEXIS AG, Winterthur, Switzerland. Both Ni/CGO and Pt/CGO cells showed unacceptable levels of degradation (14.9% and 13.4%, respectively) during a ~960 hour period of operation, including redox/thermo/thermoredox cycling treatments. Significantly, by exchanging the CGO component for the CeO2 component in the SOFC containing Ni, the degradation over the same time period was almost halved. Most importantly, galvanostatic operation of the SOFC with a Rh/CGO impregnated anode for >3000 hours (without cycling treatments) resulted in an average voltage degradation rate of < 1.9% kh−1 which, to the author's knowledge, has not previously been reported for an alternative, SrTiO3-based anode material. Finally, transfer of the Rh/CGO impregnated LSCT[sub](A-) anode to industrial short stack (5 cells) scale at HEXIS AG revealed that operation in relevant conditions, with low gas flow rates, resulted in accelerated degradation of the Rh/CGO anode. During a 1451 hour period of galvanostatic operation, with redox cycles and overload treatments, a voltage degradation of 19.2% was observed. Redox cycling was noted to briefly recover performance of the stack before rapidly degrading back to the pre-redox cycling performance, though redox cycling does not affect this anode detrimentally. Instead, a more severe, underlying degradation mechanism, most likely caused by instability and agglomeration of Rh nanoparticles under operating conditions, is responsible for this observed degradation. Furthermore, exposure of the SOFC to fuel utilisations of >100% (overloading) had little effect on the Rh/CGO co-impregnated LSCT[sub](A-) anodes, giving a direct advantage over the standard HEXIS SOFC. Finally, elevated ohmic resistances caused by imperfect contacting with the Ni-based current collector materials highlighted that a new method of current collection must be developed for use with these anode materials.
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Buha, Jelena. "Nonaqueous syntheses of metal oxide and metal nitride nanoparticles." Phd thesis, Universität Potsdam, 2008. http://opus.kobv.de/ubp/volltexte/2008/1836/.
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Nanostructured materials are materials consisting of nanoparticulate building blocks on the scale of nanometers (i.e. 10-9 m). Composition, crystallinity and morphology can enhance or even induce new properties of the materials, which are desirable for todays and future technological applications. In this work, we have shown new strategies to synthesise metal oxide and metal nitride nanomaterials.
The first part of the work deals with the study of nonaqueous synthesis of metal oxide nanoparticles. We succeeded in the synthesis of In2O3 nanopartcles where we could clearly influence the morphology by varying the type of the precursors and the solvents; of ZnO mesocrystals by using acetonitrile as a solvent; of transition metal oxides (Nb2O5, Ta2O5 and HfO2) that are particularly hard to obtain on the nanoscale and other technologically important materials.
Solvothermal synthesis however is not restricted to formation of oxide materials only. In the second part we show examples of nonaqueous, solvothermal reactions of metal nitrides, but the main focus lies on the investigation of the influence of different morphologies of metal oxide precursors on the formation of the metal nitride nanoparticles. In spite of various reports, the number and variety of nanocrystalline metal nitrides is marginally small by comparison to metal oxides; hence preformed metal oxides as precursors for the preparation of metal nitrides are a logical choice. By reacting oxide nanoparticles with cyanamide, urea or melamine, at temperatures of 800 to 900 °C under nitrogen flow metal nitrides could be obtained. We studied in detail the influence of the starting material and realized that size, crystallinity, type of nitrogen source and temperature play the most important role. We have managed to propose and verify a dissolution-recrystallisation model as the formation mechanism. Furthermore we could show that the initial morphology of the oxides could be retained when ammonia flow was used instead.Nanostrukturierte Materialien sind Materialien, die aus nanopartikulären Baueinheiten in der Größenordnung von Nanonmetern (d.h. 10-9 m) bestehen. Zusammensetzung, Kristallinität und Morphologie können die natürlichen Eigenschaften dieser Materialien verbessern oder zusätzliche Eigenschaften erzeugen, die für heutige und zukünftige Anwendungen und Verfahren wünschenswert sind. In dieser Arbeit präsentieren wir neue Strategien zur Synthese von Nanopartikeln der Metaloxide und Metalnitride. Im einführenden Teil wird die nichtwässrige Synthese von Metaloxidnanopartikeln beschrieben. Uns gelang die Darstellung von In2O3 Nanopartikeln, deren Größe und Form wir durch die Wahl des Prekursors und des Lösemittels deutlich beeinflussen konnten; von ZnO Mesokristallen durch den Einsatz von Acetonitril als Lösemittel; von Übergangsmetalloxiden (Nb2O5, Ta2O5 and HfO2), die besonders schwer im Nanomaßstab zu erhalten sind und von anderen, technisch relevanten Materialien. Die Möglichkeiten der solvothermalen Synthese sind nicht mit der Darstellung von Oxidmaterialen erschöpft. Im zweiten Teil zeigen wir einige Beispiele nichtwässriger, solvothermaler Synthese von Metalnitriden auf; das Hauptaugenmerk liegt aber auf einer Betrachtung der Einflüsse der Morphologie von Metaloxidnanopartikelprekursoren auf die Bildung der Metalnitridnanopartikel. Die Anzahl und Vielfalt bekannter nanokristalliner Metalnitride ist verschwindend klein im Vergleich zu den Metaloxiden, die in der Fachliteratur etabliert sind und demzufolge einen reichen Baukasten an Prekursoren zur Darstellung von Metalnitriden liefern. Durch die Reaktion von Metaloxidnanopartikeln mit Cyanamid, Urea oder Melamine bei Temperaturen von 800 bis 900 °C unter Stickstofffluss konnten Metalnitride erhalten werden. Eine detaillierte Studie der Reaktionsbedingungen und des Reaktionsablaufs zeigte auf, dass Größe und Kristallinität der Metaloxide, die Art der Stickstoffquelle und die Temperatur die entscheidenden Faktoren sind und legte eine Auflösungs-Rekristallisation als Modelmechanismus dieser Art Reaktion nahe. Darüber hinaus konnte gezeigt worden, dass die anfängliche Morphologie des Oxids unter einem Ammoniafluss beibehalten werden konnte.
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Gu, Yanjuan. "Nanostructure of transition metal and metal oxide for electrocatalysis." Click to view the E-thesis via HKUTO, 2006. http://sunzi.lib.hku.hk/hkuto/record/B37774396.
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Kole, Pepijn Rombout. "Dynamics and morphology of metal and metal oxide surfaces." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610404.
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Makgae, Mosidi Elizabeth. "Environmental electrochemistry of organic compounds at metal oxide electrodes." Thesis, Stellenbosch : Stellenbosch University, 2004. http://hdl.handle.net/10019.1/49947.
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Dissertation (PhD)--Stellenbosch University, 2004.ENGLISH ABSTRACT: This study investigates the electrochemical oxidation of phenol. Phenol is a major toxin and water pollutant. In addition, during water treatment it reacts with chlorine to produce carcinogenic chlorophenols. lts treatment down to trace levels is therefore of increasing concern. For this purpose, dynamically stable anodes for the breakdown of phenols to carbon dioxide or other less harmful substances were developed and characterized. The anodes were prepared from mixed oxides of tin (Sn) and the precious metals ruthenium (Ru), tantalum (Ta) and iridium (Ir), which in tum were prepared using sol-gel techniques. This involved dip-coating the aqueous salts of the respective metals onto titanium substrates and heating to temperatures of several hundreds of degree Celsius. The properties of these mixed oxide thin films were investigated and characterized using thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), atomic force microscopy (AFM), elemental dispersive energy X-ray analysis (EDX), X-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS), particle induced X-ray emission (PIXE) and electrochemical measurements. A variety of different electrode materials including Til Sn02-Ru02-Ir02, Ti/Ta20s-Ir02 and Ti/RhOx-Ir02 were developed and tested for their potential as oxidation catalysts for organic pollutants in wastewaters. Depending on the anode type, phenol was found to be electrochemically degraded, to different extents, on these surfaces during electrolysis. It was however found that the oxidation rate not only depended on the chemical composition but also on the oxide morphology revealed, resulting from the preparation procedure. The Ti/SnOz-Ru02-Ir02 film was found to be the most efficient surface for the electrolytic breakdown of phenol. This film oxidized phenol at a potential of 200 mV vs Ag/AgC!. The activity of the catalytic systems was evaluated both on the basis of phenol removal efficiency as well as the kinetics of these reactions. Phenol removal efficiency was more than 90% for all the film surfaces prepared and the rate of the reaction followed first order kinetics. A pathway for the electrochemical degradation of phenol was derived using techniques such as HPLC to identify the breakdown products. These pathway products included the formation of benzoquinone and the further oxidation of benzoquinone to the carboxylic acids malic, malonic and oxalic.
AFRIKAANSE OPSOMMING: Die onderwerp van hierdie studie is die elektrochemiese oksidasie van fenol deur nuwe gemengde-oksied elektrodes. Fenol is 'n belangrike gifstof en besoedelingsmiddel in water. Daarbenewens kan fenolook met chloor reageer tydens waterbehandeling om sodoende karsinogeniese chlorofenole te vorm. Dit is dus belangrik dat metodes ondersoek word wat die konsentrasie van fenol in water verminder. Hierdie studie behels die bereiding en karakterisering van nuwe dinamiese stabiele anodes (DSA) vir die afbreek van fenol tot koolstofdioksied en ander minder gevaarlike verbindings. Hierdie nuwe anodes is berei vanaf die gemengde-okside van die edelmetale tin (Sn), ruthenium (Ru), tantalum (Ta) en iridium (Ir), met behulp van sol-gel tegnieke. Die finale stap in die bereiding behels kalsinering van die oksides by temperature van "n paar honderd grade Celsius. Hierdie nuwe elektrodes is later gebruik om die oksidasie van fenol te evalueer. Die gemengde-oksied dunlae/anodes IS d.m.v. die volgende analitiesetegnieke gekarakteriseer: termiese-gravimetriese analise (TGA), skandeerelektronmikroskopie (SEM), atoomkragmikroskopie (AFM), elementverstrooiingsenergie- X-straalanalise (EDX), X-straaldiffraksie (XRD), Rutherford terug-verstrooiingspektroskopie (RBS), partikel-geinduseerde X-straal emissie (PIXE), en elektrochemiese metings. 'n Verskeidenheid elektrodes van verskillende materiale is berei en hul potensiaal as oksidasie-kataliste vir organiese besoedelingsmiddels in afloopwater bepaal. Hierdie elektrodes het die volgende ingesluit: Ti/Sn02-Ru02-Ir02, Ti/Ta20s-Ir02 en Ti/RhOx-Ir02. Gedurende elektrolise is fenol elektrochemies afgebreek tot verskillende vlakke, afhangende van die tipe elektrode. Die oksidasietempo het egter nie alleen van die chemiese samestelling van die elektrode afgehang nie, maar ook van die morfologie van die okside, wat op hulle beurt van die voorbereidingsprosedure afgehang het. Daar is bevind dat die Ti/Sn02-Ru02-Ir02 elektrode die mees effektiewe oppervlakke vir die afbreek van fenol is. Hier het die oksidasie van fenol by 'n potensiaal van 200 mV plaasgevind. Die aktiwiteite van die katalitiese sisteme IS bepaal op grond van hulle fenolverwyderingsdoeltreffendheid. Die kinetika van die reaksies is ook bepaal. Al die elektrodes het >90% fenolverwyderingsdoeltreffendheid getoon en die reaksietempos was van die eerste-orde. Deur van analitiese tegnieke soos hoëdrukvloeistofchromatografie (HPLC) gebruik te maak is die afbreekprodukte van fenol geïdentifiseer en 'n skema vir die elektrochemiese afbreek van fenol uitgewerk. Daar is bevind dat bensokinoon gevorm het, wat later oksidasie ondergaan het om karboksielsure te vorm.
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Ng, Yew Sun. "Studies of metal ion - Phosphine oxide and arsine oxide interactions." Thesis, University of Canterbury. Chemistry, 1997. http://hdl.handle.net/10092/7303.
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This thesis reports a study of metal complexes of trimethyl-phosphine and trimethylarsine oxides. X-ray crystal structure determinations and other physical studies, notably infrared and nmr, were used to assess the factors that influence the stereo-chemistries of these complexes.
It was observed that the compounds, (Mg(Me₃AsO)₅)(ClO₄)₂, (Ni(Me₃AsO)₅)(ClO₄)₂ and (Mg(Me₃PO)₅)(ClO₄)₂, readily adopt the square-pyramidal geometry. Two unusual features have been found in these complexes. The axial metal-oxygen bonds are consistently shorter than the corresponding basal metal-oxygen bonds, and the penultimate atoms (phosphorus and arsenic) of the basal ligands are coplanar with the square-base of the pyramid. This latter feature produces a large space in the region of the vacant sixth coordination site. The shorter axial metal-oxygen bond is discussed in terms of a stronger π interaction in the axial direction while the stability of the square-pyramidal geometry is explained in terms of electrostatic interactions between adjacent basal oxygen and arsenic atoms. Further evidence of this type of interaction was obtained from coulombic calculations.
The crystal structures of (Mg(Me₃PO)₅)(ClO₄)₂ and (Mg(Me₃PO)₅H₂O)(ClO₄)₂ enable the influence of a sixth ligand on the coordination geometry to be assessed. The significance of the formation of the five-coordinate square-pyramidal geometry and the stereochemical effects of the binding of a sixth ligand are discussed in relation to the possible importance of these geometrical features in the biological function of calcium and magnesium ions.
Comparisons between the donor powers of the phosphine oxide and arsine oxide are made. While arsine oxide has a greater σ donor strength, phosphine oxide is capable of a stronger π interaction.
An interesting dinuclear structure was determined for a calcium arsine oxide complex. This complex, (Ca₂(Me₃AsO)₉)(ClO₄)₄, was found to be bridged by arsine oxide ligands. The different donor capacities of the terminal and bridging ligands are discussed in relation to X-ray and nmr results.
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Liu, Dameng. "High-K gate oxides for future complementary metal-oxide-semiconductor transistors." Thesis, University of Cambridge, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.611517.
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Snyder, Mark Q. "Modification of Semi-metal Oxide and Metal Oxide Powders by Atomic Layer Deposition of Thin Films." Fogler Library, University of Maine, 2007. http://www.library.umaine.edu/theses/pdf/SnyderMQ2007.pdf.
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Popa, Tiberiu. "Metal oxide catalysts for green applications." Laramie, Wyo. : University of Wyoming, 2009. http://proquest.umi.com/pqdweb?did=1955861591&sid=1&Fmt=2&clientId=18949&RQT=309&VName=PQD.
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Astuti, Yeni. "Bio-functionalised nanostructured metal oxide electrodes." Thesis, Imperial College London, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.429459.
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Ng, Yip-hang, and 吳業恆. "Photocatalytic application of metal oxide nanostructures." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2014. http://hdl.handle.net/10722/197505.
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Metal oxides are important materials that are being developed for use in research and health-related applications. In particular, TiO2 and ZnO nanomaterials for applications in antibacterial coatings, pollutant purification, and photovoltaic devices have been extensively studied. The photocatalytic performances are highly dependent on morphology and crystal structure. However, there are few studies are comparing pollutant purification and antibacterial behavior of different TiO2 nanostructures and less studies of antibacterial activity related to fundamental properties of ZnO. In this study, the details of proposed mechanism and principle of antibacterial mechanisms of metal oxide nanostructures has been examined. Different TiO2 nanostructures (nanotubes, nanorods) have been successfully synthesized and their photocatalytic properties have been studied. In addition, studies of basic properties of commercial ZnO nanoparticles related to antibacterial activity have been performed.published_or_final_version
Physics
Master
Master of Philosophy
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Yeates, Rachel Marie. "Photoreactivity of porous metal-oxide frameworks." Thesis, University of Aberdeen, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.415549.
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The photoreactivity of three different types of porous metal-oxide frameworks have been investigated. The porous metal-oxide frameworks assessed are germanate, titanosilicate and vanadosilicate materials. A number of materials were synthesised, ASU-7, AUG-1, AUG-2, NH4-Ge-PHA, Li-ex-Ge-PHA. Mesoporous germanates, K-Ti-Si-PHA, AM-6 and ETVS-10. All materials synthesised were characterised using a number of techniques; x-ray diffraction, electron microscopy, solid state NMR, FT-IR, Raman, UV-vis, EXAFS, XPS, TGA and DTA. The photoreactivity of selected materials were investigated using EPR spectroscopy. The photoreactivity of two forms of the germanate pharmacosiderite material (NH4Ge-PHA and Li-ex-Ge-PHA) was explored. These materials are shown to have limited potential as photocatalyst due to their limited photoreactivity and their low thermal stability. However, on comparison to the non-porous metal oxide (h-GeO2) an improvement in photoreactivity was observed. The titanosilicate material showed limited photoreduction in the presence of ethene and methanol. However, when irradiated in the presence of oxygen a relatively stable and intense mononuclear O- species is formed. This species is found as a result of positive holes trapped at lattice oxide ions. A trapped hole signal with this stability has not previously been reported. AM-6 is shown to be a fully substituted vanadium form of ETS-10. The vanadium present is vanadium (IV) ions in octahedral coordination linking to form V-O chains. EXAFS analysis shows that the vanadium is in fact in significantly distorted octahedral sites. It is also shown that the free electrons are delocalised along the length of the vanadium-oxygen chains within the structure. ETVS-10 is a partially substituted vanadium form of ETS-10. The vanadium-oxygen chains present are interrupted by titanium sites, resulting in a reduction of the delocalisation of electrons along the chains. A photoreactivity study of these materials was problematical due to the intensity of the vanadium (IV) signal this made analysis of changes occurring upon irradiation in oxygen and methanol complicated.
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Bender, Edward Thomas. "Spectroscopic Characterization of Metal Oxide Nanofibers." University of Akron / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=akron1145294467.
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Beck, Michael Peter. "Thermal conductivity of metal oxide nanofluids." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/26488.
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Thesis (Ph.D)--Chemical Engineering, Georgia Institute of Technology, 2009.Committee Chair: Teja, Amyn S.; Committee Member: Abdel-Khalik, Said I.; Committee Member: Meredith, Carson; Committee Member: Nair, Sankar; Committee Member: Skandan, Ganesh. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Uddin, Md Tamez. "Metal oxide heterostructures for efficient photocatalysts." Phd thesis, Université Sciences et Technologies - Bordeaux I, 2013. http://tel.archives-ouvertes.fr/tel-00879226.
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Photocatalytic processes over semiconducting oxide surfaces have attracted worldwide attention aspotentially efficient, environmentally friendly and low cost methods for water/air purification as well as forrenewable hydrogen production. However, some limitations to achieve high photocatalytic efficiencies havebeen found due to the fast recombination of the charge carriers. Development of heterostucture photocatalystsby depositing metals on the surface of semiconductors or by coupling two semiconductors with suitable bandedge position can reduce recombination phenomena by vectorial transfer of charge carriers. To draw newprospects in this domain, three different kinds of heterostructures such as n-type/n-type semiconductor(SnO2/ZnO), metal/n-type semiconductor (RuO2/TiO2 and RuO2/ZnO) and p-type/n-type semiconductor(NiO/TiO2) heterojunction nanomaterials were successfully prepared by solution process. Their composition,texture, structure and morphology were thoroughly characterized by FTIR, X-ray diffraction (XRD), Ramanspectroscopy, transmission electron microscopy (TEM) and N2 sorption measurements. On the other hand, asuitable combination of UV-visible diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy(XPS) and ultraviolet photoemission spectroscopy (UPS) data provided the energy band diagram for eachsystem. The as-prepared heterojunction photocatalysts showed higher photocatalytic efficiency than P25 TiO2for the degradation of organic dyes (i.e. methylene blue and methyl orange) and the production of hydrogen.Particularly, heterostructure RuO2/TiO2 and NiO/TiO2 nanocomposites with optimum loading of RuO2 (5 wt %)and NiO (1 wt %), respectively, yielded the highest photocatalytic activities for the production of hydrogen.These enhanced performances were rationalized in terms of suitable band alignment as evidenced by XPS/UPSmeasurements along with their good textural and structural properties. This concept of semiconductingheterojunction nanocatalysts with high photocatlytic activity should find industrial application in the future toremove undesirable organics from the environment and to produce renewable hydrogen.
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LAMBERTI, ANDREA. "Metal-oxide nanostructures for energy applications." Doctoral thesis, Politecnico di Torino, 2013. http://hdl.handle.net/11583/2506221.
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One of the most important challenges for our society is providing powerful devices for energy conversion and storage. The number of proposed technologies in today’s green and renewable energy science is large and still increasing: among all the dye-sensitized solar cells (for energy generation) and Li-ions batteries (for energy storage) have attracted a lot of interest thanks to the easy fabrication processes and the cheap materials involved.
Great attention has been paid on the investigation of one-dimensional metal-oxide nanostructures for a new generation of power sources, because of their unique electronic properties, such as high electron mobility and low carrier recombination rate, high surface-to-volume ratio and excellent surface activity.
Among the large number of semiconductive metal oxide nanostructures, TiO2 and ZnO are of particular interest due to the fact that they are the best candidates as active materials in electrochemical devices thanks to their chemical and electronic properties.
Several approaches have been proposed for TiO2 nanostructure synthesis and among them anodic oxidation is now a well-established technique that can provide large area uniform nanotubular arrays on Ti foil with relatively high specific surface.
Regarding zinc oxide, many papers report on the synthesis of ZnO nanostructures performed by means of different techniques. Most of them exploits high temperature processes often using catalyst particles, requires the presence of a sacrificial template, introduces chemical contamination or exhibit slow kinetics.
This PhD thesis investigates the fabrication of different metal-oxide nanostructures and their integration as electrodes into DSCs and LiBs: in particular the work deals with TiO2 nanotube arrays obtained by anodic oxidation and with ZnO sponge-like films obtained by combined sputtering/thermal oxidation techniques.
Vertically oriented TiO2 NTs were obtained by anodic oxidation of titanium foil and fully characterized in terms of stoichiometry, crystalline phase and morphology. TiO2 nanotubes were tested both in DSC and in LiBs showing improved charge transport properties due to the 1-dimensional structures and a reduced recombination rate (and a subsequent higher carrier lifetime value) that could be attributed to the reduced presence of defects and trap-sites in the nanotubes with respect to the nanoparticle-based electrodes.
As competitive alternative to TiO2 nanotubes, porous ZnO films were obtained by a simple two-step method, involving the sputtering deposition of a sponge-like layer of metallic zinc, followed by a low-temperature treatment allowing for the complete oxidation of zinc, thus forming sponge-like ZnO films. Also in this case ZnO nanostructured films were fully characterized tested both in DSC and in LiBs showing interesting performance. Thanks to the its 3D nanostructuration, the superimposition of small branches able to grow in length almost isotropically and forming a complex topography, ZnO sponge-like can combine the fast transport properties of one dimensional material and the needed surface area usually provided by nanocrystalline electrodes.
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Soole, Julian B. D. "Surface plasmon effects in planar metal-oxide-metal tunnel junctions." Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.236032.
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This thesis gives an account of experiments which investigate the detection of light by, and the emission of light from, planar metal-oxide-metal (M-O-M) tunnel junctions. The particular focus of attention is the mediation of these processes by surface plasmons, or surface electromagnetic waves bound to metal-dielectric interfaces, in the two processes. It describes how the coupling of incident bulk radiation to a surface plasmon supported by the junction structure may enhance the response of the device when used as a photodetector. This idea is then extended to cover other electromagnetic resonances supported by the junction system in different operating configurations. There is a brief departure from M-O-M devices to consider how a metal-semiconductor Schottky barrier diode may also have its photoresponse enhanced in a similar manner by coupling to a surface plasma wave localised at the metal-vacuum interface before returning to M-O-M devices to show that, in addition to their use as discrete detectors, they may also be used as integrated detectors of guided radiation. Attention is then turned onto the reverse process of light emission from M-O-M tunnel junctions. When these devices are 'rough' or are corrugated in some manner and pass a current they emit broadband light with an upper frequency cut-off determined by the applied bias, hv= eVbias. This light emission process is mediated by the surface plasmons of the structure, of which there are three in the energy range considered. Experimental results on the light emission from residually rough and deliberately roughened junctions are reported. In particular, the results of an experiment are presented which show that the majority of the radiation outcoupled from statistically rough devices is derived from the 'fast' surface plasmon localised at the outer metal surface.
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Aksomaityte, Gabriele. "Synthesis of metal and metal oxide nanoparticles in supercritical fluids." Thesis, University of Nottingham, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.523001.
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Alam, Tanvir E. "Metal Oxide Graphene Nanocomposites for Organic and Heavy Metal Remediation." Scholar Commons, 2012. http://scholarcommons.usf.edu/etd/3945.
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This thesis consists of two research problems in the water decontamination area. In the first work, the main focus is to understand the structure and photocatalytic activity of titanium dioxide with graphene (G-TiO2) which is synthesized by using sol-gel method. The photocatalytic activity of TiO2 is limited by the short electron hole pair recombination time. Graphene, with high specific surface area and unique electronic properties, can be used as a good support for TiO2 to enhance the photocatalytic activity. The obtained G-TiO2 photocatalysts has been characterized by X-Ray Diffraction (XRD), Raman Spectroscopy, Transmission Electron Microscopy (TEM), FTIR Spectroscopy and Ultraviolet visible (UV-vis) Spectroscopy. This prepared G-TiO2 nanocomposite exhibited excellent photocatalysis degradation on methyl orange (MO) under irradiation of simulated sunlight. Such enthralling photocatalyst may find substantial applications in various fields.
The primary objective of the second work is to understand the nanocomposite structure of SiO2 coated over graphene (G) nanoplatelets. An attempt has been made to synthesize G-SiO2 nanocomposite using sol-gel technique. The G-SiO2 nanocomposite is characterized using Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Raman spectroscopy, FTIR spectroscopy, and Electrochemical and Electrical measurement technique, respectively. In this work, G-SiO2 nanoparticles with the water containing salts of zinc is added, and allowed to settle in water. The ZnCl2
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concentration displays a whitish color solution which has turned to colorless within one or two hours of treatment with G-SiO2 nanocomposites. The presence of heavy metal is tested using electrochemical cyclic voltammetry (CV) technique. The CV measurement on the water treated with G-SiO2 has been tested for several days to understand the presence of heavy metals in water. Interestingly, the near complete separation has been observed by treating the heavy metal contaminated water sample for one to two days in presence of G-SiO2 nanoparticles. The redox potential observed for the heavy metal has been found to diminish as a function of treatment with respect to time, and no redox peak is observed after the treatment for four to five days. Further test using EDS measurement indicates that the heavy metal ions are observed within the G-SiO2 nanocomposite. The recovery of G-SiO2 nanocomposite is obtained by washing using deionized water. Our experimental finding indicates that the G-SiO2 nanocomposite could be exploited for potential heavy metals cleaning from waste or drinking water.
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Krupski, Katarzyna Jadwiga. "Growth and characterisation of metal alloy and metal oxide surfaces." Thesis, University of Warwick, 2017. http://wrap.warwick.ac.uk/102621/.
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Optimisation of epitaxial anatase TiO2 thin films grown on LaAlO3(001) -substrates was performed using ultra-high vacuum based pulsed laser deposition -(PLD) and studied by in-situ reflection high-energy electron diffraction (RHEED). In -addition, ex-situ X-ray diffraction (XRD), atomic force microscopy (AFM), and -scanning transmission electron microscopy (STEM) were performed to characterise -the bulk properties of these thin films. The deposited TiO2 thin film is demonstrated -to have anatase phase and bonded directly to the LaAlO3(001) substrate. In a separate -ultra-high vacuum system low-energy electron diffraction (LEED) and scanning -tunnelling microscopy (STM) measurements were performed and a well-ordered twodomain -(1 ́4) and (4 ́1) reconstruction of anatase surface was observed. Analysis of -the STM measurements indicates the coexistence of atomic steps of both 2.5 Å and 5.0 -Å, confirming the existence of two TiO2 domains. The atomic resolution STEM -images reveal that the TiO2/LaAlO3 interface to be terminated with LaO layer and that -the anatase-TiO2 reconstruction was found to be stable during the film growth. Low-energy electron diffraction (LEED), scanning tunneling microscopy (STM) -and density functional theory (DFT) calculations have been used to investigate the -atomic and electronic structure of gold deposited (between 0.8 and 1.0 monolayer) on -the Pt(111) face in ultrahigh vacuum at room temperature. The analysis of LEED and -STM measurements indicates two-dimensional growth of the first Au monolayer. -Change of the measured surface lattice constant equal to 2.80 Å after Au adsorption -was not observed. Based on DFT, the distance between the nearest atoms in the case -of bare Pt(111) and Au/Pt(111) surface is equal to 2.83 Å, which gives 1% difference -in comparison with STM values. The first and second interlayer spacing of the clean -Pt(111) surface are expanded by +0.87% and contracted by −0.43%, respectively. The -adsorption energy of the Au atom on the Pt(111) surface is dependent on the adsorption -position, and there is a preference for a hollow fcc site. For the Au/Pt(111) surface, the -top interlayer spacing is expanded by +2.16% with respect to the ideal bulk value. -Changes in the electronic properties of the Au/Pt(111) system below the Fermi level -connected to the interaction of Au atoms with Pt(111) surface are observed. Detailed structural properties of the Pt3Ti(111) surface have been studing with -the use of ab initio density functional theory calculations and scanning tunelling -microscopy measurements. The DFT calculations show that the atoms composition of -the second and third atomic layer have influence upon the top surface of the Pt3Ti.
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Dorval, Courchesne Noémie-Manuelle. "Biologically-templated metal oxide and metal nanostructures for photovoltaic applications." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/98705.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemical Engineering, 2015.Cataloged from PDF version of thesis. Vita. Page 296 blank.
Includes bibliographical references.
In several electronic, electrochemical and photonic systems, the organization of materials at the nanoscale is critical. Specifically, in nanostructured heterojunction solar cells, active materials with high surface area and continuous shapes tend to improve charge transport and collection, and to minimize recombination. Organizing nanoparticles, quantum dots or organic molecules intro three-dimensional structures can thus improve device efficiency. To do so, biotemplates with a wide variety of shapes and length scales can be used to nucleate nanoparticles and to organize them into complex structures. In this work, we have used microorganisms as templates to assemble metal oxide and metal nano- and microstructures that can enhance the performance of photovoltaic devices. First, we used M13 bacteriophages for their high aspect ratio and ability to bind noble metal nanoparticles, to create plasmonic nanowire arrays. We developed a novel process to assemble bacteriophages into nanoporous thin films via layer-by-layer assembly, and we mineralized the structure with titania. The resulting porous titania network was infiltrated with lead sulfide quantum dots to construct functional solar cells. We then used this system as a platform to study the effects of morphology and plasmonics on device performance, and observed significant improvements in photocurrent for devices containing bacteriophages. Next, we developed a process to magnesiothermally reduce biotemplated and solution-processed metal oxide structures into useful metallic materials that cannot be otherwise synthesized in solution. We applied the process to the synthesis of silicon nanostructures for use as semiconductors or photoactive materials. As starting materials, we obtained diatomaceous earth, a natural source of biotemplated silica, and we also mineralized M13 bacteriophages with silica to produce porous nanonetworks, and Spirulina major, a spiral-shaped algae, to produce micro-coils. We successfully reduced all silica structures to nanocrystalline silicon while preserving their shape. Overall, this work provides insights into incorporating biological materials in energy-related devices, doping materials to create semiconductors, characterizing their morphology and composition, and measuring their performance. The versatility and simplicity of the bottom-up assembly processes described here could contribute to the production of more accessible and inexpensive nanostructured energy conversion devices.
by Noémie-Manuelle Dorval Courchesne.
Ph. D.
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Tejpal, Jyoti. "The use of metal and metal oxide nanoparticles against biofilms." Thesis, De Montfort University, 2016. http://hdl.handle.net/2086/13114.
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The persistence of biofilms in hospital settings are associated with Healthcare Associated Infections (HCAI), causing increased morbidity, mortality and healthcare costs. The resistance of biofilms against commonly used hospital disinfectants has been well reported. Metal and metal oxide nanoparticles (NP) such as silver (Ag), copper (Cu), zinc oxide (ZnO) and copper oxide (CuO) exhibit antimicrobial properties against various pathogens. Methods: Biofilm formation of Pseudomonas aeruginosa and Staphylococcus aureus in a Centre for Disease Control (CDC) biofilm reactor and a 96 well plate was compared. A three stage approach including Minimum Biofilm Reduction Concentration (MBRC), R2 values and log(10) reductions was used to assess the efficacy of Ag and ZnO NPs both alone and in combination against P. aeruginosa and S. aureus biofilms. Atomic Absorption Spectroscopy (AAS), Scanning Electron Microscopy (SEM) and Confocal Laser Scanning Microscopy (CLSM) was used to further assess the antimicrobial ability of the metal and metal oxide NPs. The prevention of P. aeruginosa and S. aureus adherence on Ag and ZnO thin film coating on silicon (Si) surfaces was also investigated, as well as icaC, ebpS and fnbB gene expression in S. aureus biofilms. Results: The CDC biofilm reactor demonstrated to be the most effective method for P. aeruginosa and S. aureus biofilm production in comparison to 96 well plates, with lower standard errors of the mean (SE) and higher replicability. Individual MBRC of ZnO and Ag NPs in suspension were 256 and 50 µg/ml for P. aeruginosa and 16 and 50 µg/ml for S. aureus respectively. The concentrations in combination were reduced by at least a half, with concentrations of 32/25 µg/ml of ZnO/Ag NPs in suspension resulting in a significant (p ≤0.05) reduction of 3.77 log(10) against P. aeruginosa biofilms and 8/12 µg/ml of ZnO/Ag NPs in suspension resulted in a 3.91 log(10) (p ≤0.05) against S. aureus biofilms. Both combinations showed an additive effect. Time point analysis confirmed that a 24 hour treatment is vital for any significant (p ≤0.05) antimicrobial activity. AAS data suggested that the Ag+ ions quenched Zn2+ ions, therefore the antimicrobial efficacy of the combination is mainly due to Ag+ ions. Damage of the biofilms from Ag and ZnO NPs was observed in the SEM imaging and energy dispersive X-ray (EDX) analysis confirmed the adherence of Zn and Ag within the biofilms. CLSM imaging showed dead (red) cells of P. aeruginosa and S. aureus biofilms throughout the depth of the biofilm. P. aeruginosa formation was reduced by 1.41 log(10) and 1.43 log(10) on Ag and ZnO thin film coatings respectively. For S. aureus, a reduction of 1.82 log(10) and 1.65 log(10) was obtained for Ag and ZnO coating respectively. Only low levels of ribonucleic acid (RNA) were achieved so no further gene analysis could occur. Conclusion: Reductions of ≥3 log(10) were observed for P. aeruginosa and S. aureus biofilm treatment with ZnO/Ag NP suspensions. It can be concluded that the ZnO/Ag NP suspensions had greater antimicrobial activity than Ag and ZnO coated surfaces owing to large concentrations of Ag+ and Zn2+ ions acting upon the biofilms. The slower release of ions from coated surfaces suggest an inadequate concentration of ions in the media, which are therefore unable to prevent biofilm formation as rapidly as NP suspensions, however provide a sustained release of ions over time. The results from this investigation propose that Ag and ZnO NPs in suspension could be a potential alternative to disinfectants for use in nosocomial environments against P. aeruginosa and S. aureus biofilms.
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Chen, Youjiang. "Fundamental Aspects of Electrocatalysis at Metal and Metal Oxide Electrodes." Case Western Reserve University School of Graduate Studies / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=case1284390270.
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Loney, Charles Nicholas. "Characterization of Polyproline Peptide Monolayers on Metal / Metal Oxide Substrates." Case Western Reserve University School of Graduate Studies / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=case159163938348028.
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Reeder, Askia Enrico. "STUDY OF THE STRUCTURE AND THE ELECTRONIC PROPERTIES OF THE OXIDE/OXIDE INTERFACES IN MIXED METAL OXIDES." Doctoral thesis, Università degli studi di Padova, 2014. http://hdl.handle.net/11577/3423844.
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A very important role is played by metal oxides in many areas of chemistry, physics, and materials science. Transition metal and rare-earth metal elements are able to form a large diversity of oxide compounds which can adopt an ample array of atomic structures and electronic properties that can exhibit metallic, semiconductor, or insulator characteristics. In technological applications, metal oxides are used in the fabrication of microelectronic components, sensors, fuel cells, coatings to protect surfaces against corrosion, and as catalysts. In this thesis we have decided to study two known catalytic materials Zirconia-Titania and Ceria-Titania mixed oxides. For both materials bibliography principally concerns powders thus in order to better study their interfaces, of which a deeper study is still lacking, we decided to deposit zirconia and ceria as thin films onto rutile TiO2(110).
We first studied the zirconia-titania system by depositing an ultra-thin film of zirconium oxide via a metal-organic precursor: Zirconium Tetra tert-Butoxide. The deposition was carried at three different substrate temperatures 677 K, 738 K, 773 K in five stages of a minute each and the results were traced by using XPS. The chemical characterization via XPS showed an interesting chemistry undergoing on the substrate’s surface and we have observed the formation of carbonaceous species at the interface. Zirconium appeared to be at its highest oxidation state while titanium was seen to undergo reduction with each successive deposited layer. The ratio of the Zr/Ti signals showed that zirconia didn’t completely wet the surface. Furthermore, no long range order was observed via LEED. XPD measurements showed that zirconia does not form a substitutional oxide with titania. However with the aid of computer simulation we deduced that very likely zirconia forms nanochains on the surface of TiO2(110). This surface was exposed to 100 L of pyridine to test its acidity.
In the case of ceria, we have deposited the oxide on a heated TiO2(110) substrate via metal evaporation from a Mo crucible since the process is rather easy and garners clean deposits. During deposition the substrate was kept at 677 K and in an O2 environment of 5.2•10-6mbar, and, in order to obtain an ordered homogeneous surface the sample was further annealed in the same environment at 900 K. Through LEED imaging different phases were observed and were dependent on sample history and film thickness. Via computer simulation these phases were then referred to the parent oxide in order to better comprehend the difference in respect to the bulk phase. All films showed cerium present at Ce(III). Ultra-violet Photoelectron Spectroscopy showed the electronic properties of the film showing a binding energy shift and the population of Ce4f states due to stabilization of Ce(III) by TiO2(110). The reactivity of the ceria-titania system was the probed by using methanol and ethanol. Results showed that the addition of ceria opened the dehydrogenation path from alcohol to aldehyde. We have observed that oxygen pre-oxidation of the CeOx-TiO2(110) system had an impact on its selectivity by opening also a dehydration path from methanol and ethanol to respectively, methane and ethylene. This alternative path was viable only for low cerium oxide coverages as interaction with the substrate was needed for dehydration to occur. Aldehyde formation was seen to occur at mild temperatures (330 K) and was independent of film thickness. Subsequently, ceria-titania mixed oxide powders were characterized via XPS and we have observed that for increasing amount of cerium the element gradually became present at its highest oxidation state Ce(IV). By XPS we have also determined the formation of a very intimate composite between the two oxides by observing the increasing the full width at half maximum of the Ti2p peak for increasing amounts of cerium. Furthermore, compositional calculation showed that cerium had the tendency to disperse within the titania particles. These data helped to uncover a possibly good recipe for the formation of cerium titanate a composite with good oxygen storage capacity.Un ruolo molto importante è svolto dagli ossidi metallici in molti settori della chimica, fisica e scienza dei materiali. I metalli di transizione e le terre rare sono in grado di formare una grande diversità di composti ossidici che possono adottare un'ampia gamma di strutture atomiche ed proprieta’ elettroniche che possono esibire caratteristiche metalliche, semiconduttrici o isolanti. In applicazioni tecnologiche, gli ossidi metallici sono impiegati nella fabbricazione di componenti microelettronici, sensori, celle a combustibile, rivestimenti per proteggere le superfici dalla corrosione, e come catalizzatori. In questa tesi abbiamo deciso di studiare due noti materiali catalitici: gli ossidi misti di Zirconia-Titania Ceria-Titania. Per entrambi i materiali la bibliografia riguarda principalmente le polveri quindi, al fine di studiare meglio le loro interfacce, di cui uno studio più approfondito e’ tuttora neccessario, abbiamo deciso di depositare film sottili di ossido di zirconio e ossido di cerio su rutilo TiO2(110). Abbiamo prima studiato il sistema zirconia-titania depositando un film ultra-sottile di ossido di zirconio mediante un precursore metallo-organico: Zirconio Tetra tert-butossido. La deposizione è stata effettuata a tre diverse temperature del substrato 677. K, 738 K, 773 K in cinque fasi di un minuto ciascuno. La caratterizzazione mediante XPS ha mostrato una chimica interessante sulla superficie del substrato e abbiamo osservato la formazione di specie carboniose all'interfaccia. Lo zirconio sembrava essere nel suo piu’ alto stato di ossidazione mentre il titanio è stato visto gradualmente ridursi con ogni successive strato di deposito. Il rapporto dei segnali Zr/Ti ha mostrato che la zirconia non ha completamente coperto la superficie. Inoltre,tramite LEED non si e’ osservato nessun ordine a lungo raggio. Misure XPD ha mostrato che la zirconia non forma un ossido di sostituzione con la titania. Tuttavia, con l'ausilio di simulazione al computer abbiamo dedotto che la zirconia forma, molto probabilmente nanocatene sulla superficie di TiO2(110). Questa superficie è stato esposta a 100 L di pyridinina per testarne la acidita’. Nel caso di ceria, abbiamo depositato l'ossido su un substrato riscaldato di TiO2 (110) tramite evaporazione del metallo da un crogiolo Mo poiché il processo è piuttosto facile e fornisce depositi puliti. Durante la deposizione il substrato è stata mantenuto a 677 K in un ambiente di 5,2 • 10 -6 mbar di O2, e, al fine di ottenere una superficie omogenea e ordinata il campione è stato ulteriormente sottoposto a trattamento termico nello stesso ambiente a 900 K. Tramite la tecnica LEED sono state osservate differenti fasi dipendenti dalla storia del campione e dallo spessore del film. Tramite simulazione al computer queste fasi sono stati poi riferite rispetto al biossido di cerio per meglio comprendere le differenze rispetto alla fase massiva. Tutti i film hanno mostrato cerio presenti come Ce(III). La Spettroscopia Fotoelettronica a Ultravioletti ha mostrato le proprietà elettroniche del film che mostra uno spostamento in energia di legame e un popolamento degli stati Ce4f. Questo e’ dovuto alla stabilizzazione di Ce (III) da parte di TiO2 (110). Si e’ volute osservare la reattività del sistema ceria-titania nei confronti di metanolo ed etanolo. I risultati hanno mostrato che l'aggiunta di ceria ha aperto il percorso della deidrogenazione degli alcoli ad aldeidi. Abbiamo osservato che la pre-ossidazione con ossigeno del sistema CeOx-TiO2(110) ha avuto un impatto sulla sua selettività aprendo anche un percorso di disidratazione di metanolo ed etanolo rispettivamente a metano ed etilene. Questa via alternativa era valida solo per basse coperture di ossido di cerio avendo osservato che l’interazione con il substrato è stato necessario perche’ avvenga la disidratazione. La formazione di aldeidi fu osservata avvenire a temperature piuttosto (330 K) ed essere indipendente dallo spessore del film. Successivamente sono state caratterizzate tramite XPS delle polveri di ossidi misti di ceria e titania. Abbiamo osservato che per quantità crescenti di cerio l'elemento diventa gradualmente sempre piu’ presente al suo stato di ossidazione più alto Ce (IV). Con XPS abbiamo anche determinato la formazione di un composito molto intimo tra i due ossidi osservando l'aumento della larghezza a metà altezza del picco Ti2p per quantità crescenti di cerio. Inoltre, la determinazione della composizione ha mostrato che il cerio ha la tendenza di disperdersi all'interno delle particelle di titania. Questi dati hanno contribuito a scoprire una possibile buona ricetta per la formazione di cerio titanato; un composito con buona capacità di stoccaggio di ossigeno.
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Tse, Koon-Yiu. "High-K gate oxides and metal gate materials for future complementary metal-oxide-semiconductor field-effect transistors." Thesis, University of Cambridge, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.611979.
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Almar, Liante Laura. "Ordered mesoporous metal oxides for solid oxide fuel cells and gas sensors." Doctoral thesis, Universitat de Barcelona, 2014. http://hdl.handle.net/10803/283997.
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Nanomaterials have received increasing attention during the last decades in the solid state field since they play a major role as catalyst and catalyst supports for many applications including fuel cells or gas sensors. The interest is mainly due to their high specific surface area, which leads to an increase of performance and a cost-effective solution for expensive or rare materials. However, many studies have reported the collapse of nanostructures at high temperature as one of the main drawbacks for their implementation in real devices and therefore, routes to thermally stabilize these materials must be explored.
In this thesis, the unique features of ordered mesoporous materials fabricated by nanocasting are exploited to create quasi-universal thermal stabilization methodologies, allowing implementing and evaluating them in high temperature energy applications e.g. solid oxide fuel cells.
The work developed is divided into seven parts. The first chapter introduces the basics of mesoporous materials, solid oxide fuel cells, catalysis and gas sensors. The second chapter focuses on the experimental procedures and the characterization tools employed. In the third chapter, a novel route to thermally stabilize 3-D open mesoporous structures is presented. The next three chapters, show the fabrication and evaluation of thermal stable mesoporous materials as electrodes for solid oxide fuel cells. Finally, chapter seven presents the suitability of mesoporous ceramic oxides as functional materials in humidity sensors.Los nano-materiales han recibido especial atención durante estas últimas décadas en el campo del estado sólido dado el importante papel que desempeñan como catalizadores y/o soportes catalíticos en diversas aplicaciones, tales como las pilas de combustible o los sensores de gas. Este interés se debe principalmente a su elevada área específica, que da lugar a una mejora del rendimiento y es una solución efectiva para aquellas aplicaciones que requieran materiales de elevado coste. Sin embargo tal y como señalan muchos estudios, el colapso de estas nano-estructuras a elevadas temperaturas es uno de los mayores inconvenientes para su implementación en dispositivos reales, siendo por tanto necesario explorar nuevas rutas que consigan estabilizar estos materiales térmicamente. El objetivo de la presente tesis es desarrollar metodologías cuasi-universales de estabilización térmica, mediante la explotación de las características exclusivas que poseen los materiales mesoporosos ordenados fabricados a partir de un template. Lo cual nos permite implementarlos y evaluarlos en aplicaciones energéticas que operan a elevada temperatura p.ej. pilas de combustible de óxido sólido. El trabajo desarrollado se divide en siete partes. El primer capítulo introduce los fundamentos de los materiales mesoporosos, las pilas de combustible de óxido sólido, la catálisis y los sensores de gas. En el segundo capítulo se detallan los procedimientos experimentales y las técnicas de caracterización empleados. El tercer capítulo presenta una nueva metodología para estabilizar térmicamente los materiales mesoporosos de estructura 3-D abierta. Los siguientes tres capítulos, muestran la fabricación y el comportamiento electroquímico de materiales mesoporosos térmicamente estables trabajando como electrodos de pilas de combustible de óxido sólido. Por último, en el capítulo siete se demuestra la viabilidad de los óxidos cerámicos mesoporosos como materiales funcionales en sensores de humedad.
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Låte, Leiv. "Oxygen-assisted conversion of propane over metal and metal oxide catalysts." Doctoral thesis, Norwegian University of Science and Technology, Department of Chemical Engineering, 2002. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-1536.
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杨纯臻 and Chunzhen Yang. "Metal/metal oxide nanoparticles supported on nanostructured carbons for electrochemical applications." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2013. http://hdl.handle.net/10722/193414.
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Among various electrochemical devices that have been developed for energy storage and conversion, electric double layer capacitors (EDLCs) and direct methanol fuel cells (DMFC) have received much research attention. Nanostructured carbon materials have been playing an important role in the development of these devices, due to such characteristics as good electrical conductivity, high chemical stability, high surface area and large pore volumes and etc. In an EDLC, nanostructured carbon electrodes, possessing pores of varied length scales, can deliver electric energy at high current loadings. This kind of pore structure also benefits the deposition of metal catalysts and the transport of reactants and products in the methanol oxidation reaction.
In order to systematically study the structural effects on the electrochemical capacitance and ionic transport, a series of three-dimensional hierarchical carbons with hollow core-mesoporous shell (HCMS) structure were template-synthesized. Periodically ordered macroscopic hollow cores of 330 nm in diameter were surrounded by a mesoporous shell containing uniform pores of 3.9 nm. The shell thickness was stepwise increased from 0, 25, 50 to 100 nm. The HCMS structure was modeled by a 5-level transmission line model to study the capacitance contribution from the pores at different length scale. Results revealed that the HCMS carbon with thicker mesoporous shells can provide high capacitance, while thinner shells could deliver high power output.
A series of HCMS carbon sphere supported Pt nanoparticles were synthesized via the “Carbonization over Protected and Dispersed Metal” (CPDM) method. Contrary to the conventional “polyol” synthetic method, whereas most of Pt nanoparticles were deposited on the external surface of carbon spheres; the Pt nanoparticles synthesized via the CPDM method were found encapsulated in the mesoporous carbon shells and highly dispersed throughout the carbon texture. „Accelerated stress tests‟ (ASTs) were conducted to investigate the nanopores confinement effect toward the electrochemical stability of these Pt catalysts. Results revealed that (1) the nanopores confined Pt nanoparticles on HCMS carbon spheres exhibited a stable electrochemical active surface area (ECSA) and catalytic activity; and (2) thick mesoporous carbon shells could provide better protection over the Pt nanoparticles. This “CPDM” method was further extended to synthesize highly alloyed PtRu nanoparticles supported electrocatalysts. It is expected that this CPDM method can also be applied to synthesize other metal/metal oxide supported catalysts with stable electrochemical performance.
WO3 has been demonstrated as a promsing co-catalyst for Pt in the methanol oxidation reaction (MOR). The synthesis of Pt-WO3/C catalyst with well-controlled nanoparticle size (2.5 nm) and composition was achieved via a microwave-assisted water-oil microemulsion reaction. Hydrogen adsorption, CO-stripping and Cu- stripping methods were used to estimate the ECSA of Pt in the Pt-WO3/C catalysts. Among these, Cu-stripping method was relatively more reliable due to the overlapping involvement of the WO3 component in the other methods. The methanol oxidation measurement shows that a 1:1 Pt:W ratio catalyst exhibits the highest Pt-mass current density of 271 mA mg-1-Pt, 1.4 times higher than that of commercial E-TEK catalyst.published_or_final_version
Chemistry
Doctoral
Doctor of Philosophy