Includes bibliographical references (p. 121-129).

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

No description available.

M.Tech. / Among the materials being used for gas sensors, metal oxides are the most important materials because of their potential to detect many gases at low concentrations. Nevertheless, sensors made of metal oxide need to be operated at high temperatures (above 200°C) and have a weak sel ectivity. In order to overcome this difficulty, the materials are being investigated for gas sensing applications. Carbon nanotubes (CNTs) are promising materials with unique properties, such as high electrical conductivity, mechanical strength, nanometer–scale sizes, and high aspect ratio. Their adsorption ability and high surface area make them attractive as gas sensing materials, which have been intensively studied. CNTs can be used solely or combined with metals and oxides materials in order to constitute efficient gas sensors. In the present research, multi–walled CNTs (MWCNTs) were coated with tin dioxide (SnO2) and incorporated into two epoxy resins with widely different mechanical properties in order to study the effect of CNTs on the morphology, mechanical, electrical, and sensing properties of the composites. In the MWCNT/polymer composite study, Epon 828 was used as the polymer matrix and D–2000 (which gives rubbery composites) and T–403 (which gives glassy composites) as the hardeners. Composite were prepared with 0.1 wt.% MWCNTs in an epoxy matrix. Pristine MWCNTs (MWCNTs not treated with any acid and therefore used as received) and SnO2–MWCNTs were used for comparison and a two–step curing procedure was used with initial temperature set at 75°C for 3 hours, followed by additional 3 hours at 125°C. The sample s were characterized for morphology, mechanical, thermo–mechanical and electrical properties using scanning electron microscopy (SEM), an Instron tensile tester, dynamic mechanical analysis (DMA) and Cascade Microtech four–point probe, respectively. In both cases, strong covalent bonds were created as a bridge between the CNTs and matrix, but due to differences in viscosity, the nanotubes dispersion was much better in the rubbery epoxy resin than in the glassy epoxy resin. A 77% increase in tensile modulus was observed in the rubbery system using 0.1 wt.% SnO2–MWCNTs compared to the neat rubbery epoxy. As for the glassy epoxy based composite, only a 3% improvement in tensile modulus could be observed. In addition to the mechanical properties, the presence of CNTs has demonstrated a material with high vi electrical conductivity. But for the surface measurements during the gas sensing analysis, the conductivity was very low for the composites to be used for this application as envisioned. MWCNTs coated with SnO2 nanoparticles used in the present study, were synthesized by a microwave synthesis method. The composite samples were characterized by X–ray diffraction (XRD), Raman spectroscopy, high resolution transmission electron microscopy (HRTEM), scanning electron microscopy, Fourier transform infrared spectroscopy (FTIR) and Brunauer–Emmet–Teller (BET) surface area analysis. These techniques gave evidence for surface and chemical modifications of the synthesized composites. The results showed microwave synthesis to be a very efficient method in producing CNTs that are densely coated and well dispersed with SnO2 nanoparticles in a very short time (total reaction time of 10 minutes). Microwave synthesis is particularly interesting because of the energy used, the higher temperature homogeneity and the shorter reaction times led to nanoparticles with high crystallinity and a narrow particle size distribution. Controlling the morphology by varying synthesis conditions such as temperature, pressure and time is also possible.

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

No description available.

by Yip Yeuk Lan = 已發生液態調幅分離的過冷「鈀八十二硅十八」合金熔融體的結晶行為 / 葉若蘭. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2003. / Includes bibliographical references (leaves 51-52). / Text in English; abstracts in English and Chinese. / by Yip Yeuk Lan = Yi fa sheng ye tai diao fu fen li de guo leng "ba ba shi er gui shi ba" he jin rong rong ti de jie jing xing wei / Ye Ruolan. / Acknowledgments --- p.ii / Abstract --- p.iii / 摘要 --- p.iv / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Introduction / Chapter 1.2 --- Properties of Nanocrystalline Materials / Chapter 1.3 --- Fabrication of Nanocrystalline Materials / Chapter 1.4 --- Fabrication of Nanocrystalline Material by Spinodal Decomposition / Chapter 1.5 --- Aim of the Thesis / References / Figures / Chapter Chapter 2 --- Experimental --- p.28 / Chapter 2.1 --- Introduction / Chapter 2.2 --- Preparation of Fused Silica Tubes / Chapter 2.3 --- Sample Preparation / Chapter 2.4 --- Sample Preparation for Microstructure Analysis / Chapter 2.5 --- Microstructure Characterization by TEM / Chapter 2.6 --- Annealing a TEM sample / References / Figures / Chapter Chapter 3 --- Results and Discussions --- p.44 / Results / Discussions / References / Figures

In this study, two kinds of effective VLD photocatalysts, AgBr-Ag-Bi 2WO6 nanojunction and Zn:In(OH)ySz solid solution nanoplates have been synthesized and characterized. Zn:In(OH) ySz solid solution nanoplates (Synthesis conditions: 45 mmol L-1 thiourea, 26 mmol L-1 SDS, 0.4≤X≤0.7) have high VLD photocatalytic activities on the degradation of Rhodamine B (RhB), which is due to their suitable band gap and potentials of conduction band and valence band as well as their uniform and small diameter sizes (about 10 nm in width and about 15 nm in length). AgBr-Ag-Bi2WO6 nanojunction exhibits excellent VLD photocatalytic performance both on the degradation of Procion Red MX-5B and pentachlorophenol, and on the disinfection of various bacteria including Escherichia coli, Pseudomonas fluorescens and Alteromonas macleodii. Its excellent performance results from the broadened visible-light response and the synergic effect among the three components under the visible light irradiation, namely the vectorial electron transfer of Bi2WO6→Ag→AgBr. / Moreover, a novel and versatile partition setup has been first constructed to investigate the fundamental mechanism of photocatalytic process. The results indicate that the functional reactive species produced by VLD Zn:In(OH) ySz solid solution nanoplates mainly remain on the surface, thus the direct contact between Zn:In(OH)ySz solid solution nanoplates and RhB is a prerequisite for the degradation of RhB during the photocatalytic process. However, the functional reactive species produced by AgBr-Ag-Bi2WO6 nanojunction can diffuse into the bulk, thus the direct contact between the AgBr-Ag-Bi2WO6 nanojunction and bacteria is unnecessary for the photocatalytic disinfection of bacteria. / Recent years, environmental problems related to organic pollutants and pathogenic microorganisms have emerged as a high national and international priority. To address these significant problems, photocatalysis causes increasing interest as a kind of green and energy-saving technology. However, the traditional photocatalyst TiO2 can only be excited by ultraviolet or near-ultraviolet radiation, which merely occupies about 4% of the solar light spectrum. Notably, the visible region covers the largest proportion of the solar spectrum (about 48%). In order to efficiently utilize solar light, the development of visible-light-driven (VLD) photocatalysts with excellent performances has been urged. / Therefore, in this work, the exploration of VLD photocatalyst gives us the opportunities to utilize solar energy to solve the environmental problems and energy crisis, and the investigation of fundamental mechanism provides us more deep understanding for photocatalytic process. / Zhang, Lisha. / Adviser: P. K. Wong. / Source: Dissertation Abstracts International, Volume: 72-04, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references (leaves 159-171). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. Ann Arbor, MI : ProQuest Information and Learning Company, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

Wu Ling. / "Dec 2004." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.