No description available.

Inaug.-Diss.--Leipzig. / Vita.

Low-to-negative thermal expansion is an important property for materials in a wide range of applications including space applications, microwave components, construction, mirrors, dental fillings and high precision ion dilatometers. Powder X-ray diffraction (PXRD) has been used to investigate the thermoresponsive behavior of Nb6.7W10.3O47, Ta14.8W1.2O46, Ta16W18O94 and BaPbO3. Calibration and benchmarking of the diffractometer was performed to ensure accurate results are obtained. Continuous Online X-ray Analysis (COXA) enabled the close monitoring of phase transitions, changes in any lattice parameters in response to thermal stimuli. When COXA is coupled with Rietveld refinement, coefficients of thermal expansion (CTE) could be determined accurately. The tungstates were synthesized using a precipitation reaction and heat treatment from chlorides of the metals (NbCl5; TaCl5) and tungstic acid (H2WO4). The products, Nb6.7W10.3O47, Ta14.8W1.2O46 and Ta16W18O94, underwent a COXA analysis within the temperature range 30 ˚C to 900 ˚C. Nb6.7W10.3O47 has a mean volumetric CTE of 6.704 x 10-6 ˚C-1, and therefore has low positive thermal expansion. The tantalum tungstates were found to have low positive thermal expansion as well. Ta14.8W1.2O46 and Ta16W18O94 have mean volumetric CTEs of 2.101 x 10-5 ˚C-1 and 9.851 x 10-6 ˚C-1. BaPbO3 underwent two phase transitions between 30 ˚C and 550 ˚C from orthorhombic Imma to I4/mcm to cubic Pm-3m. The transition from Imma to I4/mcm took place at 270 ˚C. The phase transition from I4/mcm to Pm-3m took place at 390 ˚C.

Thesis (M.S.)--West Virginia University, 1998. / Title from document title page. "December 1998." Document formatted into pages; contains viii, 92 p. : ill. (some col.) Includes abstract. Includes bibliographical references (p. 73-78).

published_or_final_version / abstract / Physics / Doctoral / Doctor of Philosophy

金屬氧化物納米材料因其優異的催化、光、電性能，在催化、環境修復、氣敏、光電裝置、鋰電及能源存儲等領域具有廣泛的潛在應用價值。科學研究表明，材料的性能取決于其組成、晶相、形貌和尺寸等，因此，對金屬氧化物納米材料的結構和形貌可控合成的研究具有重要意義。 / 本論文的主要研究內容包括：在純溶劑或混合溶劑中，采用無模板的水熱/溶劑熱方法合成了形貌可控的金屬氧化物納米材料，并系統研究了反應物及其濃度、反應溫度、時間和反應介質等參數對材料形貌的影響。此外，基於詳細的實驗數據，我們提出了各金屬氧化物納米材料的可能形成機理並對這些材料的光學性能和環境修複應用進行了深入研究。 / 在純水溶劑中，我們只采用一種反應物Zn(CH₃COO)₂·2H₂O 成功合成了由納米顆粒組合而成的六邊形氧化鋅“微米杯“和“微米環“材料。此前驅體在反應中不僅作爲鋅源，還提供了一種有效的侵蝕劑CH₃COOH，此侵蝕劑對氧化鋅晶體材料空心結構的形成起著關鍵作用。在混合溶劑乙醇/乙二醇體系中，我們成功合成了氧化鋅納米顆粒，并可以通過改變溶劑的體積比調控納米顆粒的粒徑，還對其尺寸依賴的光學性質進行了詳細研究。而介孔氧化鎂納米線和“微米花“則是通過無模板溶劑熱合成並煅燒而制得。實驗結果表明，反義介質對前驅體氫氧化鎂納米結構的形貌控制起了決定性的作用，在極性大的純水中更有利於氫氧化鎂的極性生長，從而生成直徑約80 nm 的納米線；而在極性较小的水/乙醇混合溶劑（其體積比小於2:1）中则得到由納米片組成的“微米花“超結構，並且隨著水/乙醇體積比的減小，納米片的厚度以及“微米花“的尺寸都相應地增大。我們還進行了氧化鎂納米結構對有機染料甲基橙的吸附能力測試，結果顯示氧化鎂納米線和“微米花“都具有很高的吸附容量，分別為48.9 mg g⁻¹ 和56.8 mg g⁻¹，而商品氧化鎂對甲基橙的吸附量僅為13.6 mg g⁻¹，其原因可歸結于制备的納米材料具有孔結構和較大的比表面積。此外，我們希望通過把氧化鋅摻入到氧化鎂中得到(ZnO)x(MgO)₁-x 納米片，將氧化鎂較強的吸附能力和氧化鋅的光催化特性整合在一起，從而提高其對甲基橙的去除效果，甲基橙的紫外光降解測試結果表明結合兩種優勢的(ZnO)x(MgO)₁-x 納米片具有很好的光催化性能。我們還利用紫外可見吸收光譜和陰極發光發射光譜研究了(ZnO)x(MgO)₁₋x 納米片的光學性質，前者顯示樣品的能帶隨著氧化鋅的摻入量而發生改變，後者表明(ZnO)x(MgO)₁-x 納米片的表面具有明顯的氧空位等缺陷。 / Metal oxides nanomaterials have the potential for a wide variety of applications such as catalysis, environmental remediation, gas sensors, optoelectronic devices, lithium ion batteries, and energy storage. It is because of their unique catalytic, optical, and electrical properties. Moreover, it has been demonstrated that these properties are strongly dependent on their compositions, phases, shapes, and sizes. Therefore, the studies on structure and morphology controlled synthesis of nanomaterials are of great interest and are actively being pursued. / In this thesis, we present an environmentally friendly and template-free hydro/solvothermal synthetic method for the morphology-controlled synthesis of metal oxides nanomaterials in pure solvent or in mixed solvent systems. Moreover, the effects of the reaction parameters including reactants and their concentration, reaction temperature, time, and reaction medium on the morphology of the target products were investigated systematically in this work. The possible formation mechanisms of these metal oxides nanostructures were also discussed in-depth on the basis of detailed experimental data. In addition, their shape and size-dependent optical properties as well as their applications in environmental remediation were also investigated. / In this work, hexagonal ZnO micro-cups and micro-rings assembled by nanoparticles were obtained by using only one reactant Zn(CH₃COO)₂·2H₂O in pure water system. The precursor not only served as the zinc source, but also provided an effective etchant CH₃COOH that played a strategic role in the formation of the hollow structures in the ZnO crystals. We also synthesized ZnO nanoparticles with controllable size in a mixed solvent system. The average size of the nanoparticles could be tailored by adjusting the volume ratio of ethanol/ethylene glycol (EG). Mesoporous MgO nanowires and microflowers were prepared by a template-free solution phase synthetic method combined with subsequent calcination. Our results indicated that the reaction medium played a crucial role in the morphological control of the precursor Mg(OH)₂ nanostructures. The high polarity of pure water favored the polar growth of the precursor, resulting in the formation of nanowires with a diameter of 80 nm, whereas water/ethanol mixtures with a lower polarity, at a volume ratio of and below 2:1, generally led to the formation of microflowers composed of nanoplates. Moreover, as the volume ratio of the water/ethanol mixture reduced, both the thickness of the nanoplates and the size of microflowers increased. In addition, the removal capacities of the mesoporous MgO nanostructures for organic dye MO from water were studied and calculated to be 48.9 mg g⁻¹ and 56.8 mg g⁻¹ for MgO nanowires and microflowers, respectively, which were higher than that of commercial MgO powder (13.6 mg g⁻¹). The superior removal performance was attributed to the excellent porous structure and high surface area of the as-prepared MgO nanostructures. In order to improve the removal performance, we had combined these two merits in terms of the adsorption ability of MgO and photocatalytic property of ZnO together by doping ZnO into MgO nanostructures. Thus, mesoporous (ZnO)x(MgO)₁-x nanoplates were obtained. The UV-induced degradation of MO indicated that the mesoporous (ZnO)x(MgO)₁-x nanoplates with the combinative merits had high photocatalytic performance and would be a promising candidate for environmental remediation. Moreover, their optical properties were also investigated by the UV-vis absorption and room temperature cathodoluminescence (CL) emission spectroscopy. The UV-vis absorption spectra showed the band gap variation of the as-prepared samples, due to the presence of ZnO in the MgO nanostructures. The result indicated that the design of surface structure could produce oxide nanocrystals with controlled optical properties. The CL spectra showed strong broad peaks in visible range from 450 to 700 nm, which implied there were significant oxygen vacancy defects created on the surface of (ZnO)x(MgO)₁-x nanoplates. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Lian, Jiabiao = 金屬氧化物納米材料的無模板水熱/溶劑熱合成、表徵及其應用 / 連加彪. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2013. / Includes bibliographical references. / Abstracts also in Chinese. / Lian, Jiabiao = Jin shu yang hua wu na mi cai liao de wu mu ban shui re/rong ji re he cheng, biao zheng ji qi ying yong / Lian jia biao. / Abstract --- p.i / 摘要 --- p.iv / Acknowledgment --- p.vi / Table of Contents --- p.viii / List of Figure Captions --- p.xi / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Nanomaterials --- p.1 / Chapter 1.1.1 --- Definitions and Classfications --- p.1 / Chapter 1.1.2 --- Characteristics and Applications --- p.3 / Chapter 1.1.3 --- Fabrication Methods --- p.8 / Chapter 1.1.4 --- Metal Oxides Nanomaterials --- p.12 / Chapter 1.2 --- Methodology of This Work --- p.16 / Chapter 1.2.1 --- Method and Experimental Setups for Sample Preparation --- p.17 / Chapter 1.2.2 --- Techniques for Sample Characterizations --- p.20 / Chapter 1.2.2.1 --- Thermogravimetric Analysis (TGA) --- p.20 / Chapter 1.2.2.2 --- X-ray Powder Diffractometry (XRD) --- p.20 / Chapter 1.2.2.3 --- Scanning Electron Microscopy (SEM) --- p.21 / Chapter 1.2.2.4 --- Transmission Electron Microscopy (TEM) --- p.22 / Chapter 1.2.2.5 --- Ultraviolet-visible (UV-vis) Absorption Spectroscopy --- p.22 / Chapter 1.2.2.6 --- Cathodoluminescence (CL) Emission Spectroscopy --- p.24 / Chapter 1.2.2.7 --- N2 Adsorption Surface Analysis --- p.24 / Chapter 1.2.3 --- Evaluation of MO Adsorption or Degradation --- p.25 / Chapter 1.3 --- Objectives of This Work --- p.27 / References --- p.30 / Chapter Chapter 2 --- Hexagonal ZnO Micro-cups and Micro-rings --- p.34 / Chapter 2.1 --- Introduction --- p.35 / Chapter 2.2 --- Experiments --- p.36 / Chapter 2.2.1 --- Samples Preparation --- p.36 / Chapter 2.2.2 --- Instruments and Characterizations --- p.37 / Chapter 2.3 --- Results and Discussion --- p.37 / Chapter 2.4 --- Conclusions --- p.44 / References --- p.45 / Chapter Chapter 3 --- ZnO Nanoparticles with Controllable Size and Size-Dependent Optical Properties --- p.47 / Chapter 3.1 --- Introduction --- p.47 / Chapter 3.2 --- Experiments --- p.49 / Chapter 3.2.1 --- Samples Preparation --- p.49 / Chapter 3.2.2 --- Instruments and Characterizations --- p.49 / Chapter 3.3 --- Results and Discussion --- p.49 / Chapter 3.4 --- Conclusions --- p.54 / References --- p.55 / Chapter Chapter 4 --- Mesoporous MgO Nanostructures --- p.56 / Chapter 4.1 --- Introduction --- p.56 / Chapter 4.2 --- Experiments --- p.58 / Chapter 4.2.1 --- Samples Preparation --- p.58 / Chapter 4.2.2 --- Instruments and Characterizations --- p.59 / Chapter 4.2.3 --- Water Treatment Experiments --- p.59 / Chapter 4.3 --- Results and Discussion --- p.60 / Chapter 4.3.1 --- Structure Characterization --- p.60 / Chapter 4.3.2 --- Morphology Characterization --- p.62 / Chapter 4.3.3 --- Reaction Mechanisms --- p.66 / Chapter 4.3.4 --- Treatment of Polluted Water --- p.68 / Chapter 4.4 --- Conclusions --- p.70 / References --- p.72 / Chapter Chapter 5 --- Mesoporous (ZnO)x(MgO)₁-x Nanoplates --- p.74 / Chapter 5.1 --- Introduction --- p.74 / Chapter 5.2 --- Experiments --- p.77 / Chapter 5.2.1 --- Samples Preparation --- p.77 / Chapter 5.2.2 --- Samples Characterization --- p.78 / Chapter 5.2.3 --- Water Treatment Experiments --- p.78 / Chapter 5.3 --- Results and Discussion --- p.79 / Chapter 5.3.1 --- Structure Characterization --- p.79 / Chapter 5.3.2 --- Morphology Characterization --- p.83 / Chapter 5.3.3 --- Reaction Mechanisms --- p.85 / Chapter 5.3.4 --- Optical Properties --- p.85 / Chapter 5.3.5 --- Treatment of Polluted Water --- p.88 / Chapter 5.4 --- Conclusions --- p.93 / References --- p.94 / Chapter Chapter 6 --- Conclusions and Suggestions for Future Work --- p.97 / Chapter 6.1 --- Conclusions --- p.97 / Chapter 6.2 --- Suggestions for Future Work --- p.99 / References --- p.100

H.Y. Tsoi. / Thesis (M.Phil.)--Chinese University of Hong Kong. / Bibliography: leaf [3]

No description available.

Thèse : Sciences physiques : Paris, Faculté des sciences : 1880. / Titre provenant de l'écran-titre.

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