Biocompatible anatase TiO2 single-crystals with 27 % -- 50 % chemically reactive facets were obtained in 90 minutes by using a microwave-assisted method. The preparation involved an aqueous solution of titanium tetrafluoride and an ionic liquid (1-methyl-imidazolium tetrafluoroborate). The as-obtained TiO2 single-crystals exhibited a truncated tetragonal bipyramidal shape. By simply changing the concentration of the ionic liquid, the level of reactive facets can be continuously tuned from 27 % to 50 %. The use of microwave heating is critical as it allows rapid and uniform heating of the reaction mixture. The TiO2 single-crystals were characterized by XRD, TEM, XPS and FESEM. The products exhibited excellent photocatalytic efficiency for both oxidation of nitric oxide in air and degradation of organic compounds in aqueous solution under UV light irradiation. The relationship between the physicochemical properties and the photocatalytic performance of the samples was discussed. The TiO2 single-crystals were found to be nontoxic using Zebrafish (D. rerio) as a model. / Bismuth oxyhalide semiconductors (BiOBr, BiOCl) with marigold-like open architectures were also prepared by a solvothermal method involving imidazolium-based ionic liquids and ethylene glycol. The 3D self-assembled marigold-like materials were effective photocatalysts for degrading organic pollutants and generating hydrogen. The main advantages of the new materials were large surface area, high surface-to-bulk ratio, facile species transportation, and ease of recovery and regeneration. / By using a microwave-assisted hydrothermal method involving titanium tetrafluoride and a tetrafluoroborate-based ionic liquid (1-butyl-3-methyl-imidazolium-tetrafluoroborate), a micro-sheet anatase TiO2 single crystal photocatalyst with remarkable 80 % reactive facets was synthesized. The as-obtained TiO2 single-crystal exhibited a truncated tetragonal bipyramidal shape. The high reactivity of facets made these single crystals highly photocatalytically active. They were easily recyclable and thermally stable up to 800 °C. / Furthermore, a simple and environmentally benign approach for the synthesis of photocatalytically active rutile TiO2 mesocrystals was developed. It was a microwave-assisted hydrothermal method involving titanium(III) chloride as the only reactant. The resulting 1D rutile nanowires could easily assemble into 3D hierarchical architectures without the help of surfactants or additives. The average aspect ratio for the nanowires was 267. The BET specific surface area of the mesocrystal was 16 m2/g. / Part I: Size-tunable monodispersed hierarchical metallic Ni nanocrystals (58-190 nm in diameter) were prepared by the reduction of Ni2+ with hexadecylamine under atmospheric pressure. The diameter of the particles could be tuned by simply changing the reaction time. A reaction mechanism was proposed and the relationships between the size, hierarchical surfaces and the magnetic properties were investigated. The as synthesized Ni crystals exhibited higher coercivities than the bulk metallic material owing to the reduced size and the hierarchical surface structure. The saturation magnetization (Ms) and the ratio of remanence to saturation (Mr/Ms) increased with increasing particle size. / Part II: A facile microwave-assisted solvothermal method was developed for the controlled synthesis of novel 3D CdS structures. Dendrite-, star-, popcorn- and hollow sphere-like CdS structures could be obtained by changing the reaction conditions including the reaction temperature and the amounts of reagents and solvents. The results revealed that the final structures were related to the solvent properties such as surface tension and viscosity. The degree of supersaturation was also responsible for the morphology variation and it could be adjusted by the reaction temperature. The CdS products with different morphologies exhibited interesting shape-dependent optical properties and photocatalytic activities. / The optical band energy of the product exhibited an obvious red-shift of 0.2 eV with aspect to that of pure rutile TiO2. This red-shift effect may be ascribed to the high aspect ratio of the rutile nanowires. The products showed excellent photocatalytic activity for NO removal in air and the activity was well maintained after three cycles. Gold modification on the rutile TiO2 resulted in a 50 % improvement in the photocatalytic performance. / This thesis focuses primarily on the preparation of various functional materials with controllable structures and properties. The first part describes the synthesis of materials by solvothermal methods. The second part describes the rapid fabrication of novel semiconductor materials by microwave-assisted methods. / Zhang, Dieqing. / Source: Dissertation Abstracts International, Volume: 72-04, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references (leaves 189-190). / 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.

Surface passivation of semiconductor quantum dots is essential to preserve their efficient and robust light emitting properties. By using a lattice matched (mismatch = 0.5%) lead halide perovskite matrix, we achieve shell-like passivation of lead sulfide QDs in crystalline films, leading to efficient infrared light emission. These structures are made from a simple one-step spin coating process of an electrostatically stabilized colloidal suspension. Photoluminescence and transient absorption spectroscopy indicate rapid energy transfer between the perovskite matrix and the QDs, suggesting an interface with few trap states. In addition to housing the efficient infrared QD emitters, lead halide perovskites themselves have good carrier mobilities and low trap densities, making these solution-processable heterostructures an attractive option for electrically pumped light emitting devices. The highest performing quantum dots for visible light applications are CdE (E=chalcogenide) core/shell heterostructures. Again, surface passivation plays a huge role in determining the brightness and robustness of visible QD emitters. Multilayer shell passivation is usually used to produce the highest quantum yield particles. Surface trap states are shown to be detrimental to luminescence output, even in thick-shelled particles. Spherical quantum wells allow for thicker shells and with good surface passivation, show promising reduction of biexciton auger recombination, as measured by a time correlated single photon counting (TCSPC) microscope. TCSPC methods were used to diagnose and identify QD architectures for LED applications and explore fundamental recombination dynamics using photon antibunching measurements, and statistical analysis of blinking traces.Introducing new surfaces onto graphitic substrates can be a useful for introducing new electronic properties, patterning device-specific geometries, or appending molecular catalysts. Metal nanoparticles were used to act as a catalyst for the gasification and etching of graphite and graphene. Several methods of controlling the initiation, propagation, and density of these trenches were explored. Patterning defects helped control where initiation occurred, while faceting existing defect sites could also enable more facile initiation and control the direction at the beginning of etching, due to the wetting mechanism of particle movement. Patterning the metal also was shown as a promising avenue to limit unwanted gasification and promote etching in specific, patterned regions. Surface functionalization using reactive gases was performed and characterized with outlook for future experiments.

Graduation date: 1993

The field of Tissue Engineering has developed in response to the shortcomings associated to the replacement of tissues lost to disease or trauma: donor tissue rejection, chronic inflammation, and donor tissue shortages. The driving force behind Tissue Engineering is to avoid these problems by creating biological substitutes capable of replacing the damaged tissue. This is done by combining scaffolds, cells and signals in order to create living, physiological, three-dimensional tissues.Scaffolds are porous biodegradable structures that are meant to be colonised by cells and degrade in time with tissue generation. Scaffold design and development is mainly an engineering challenge, and is the goal of this PhD thesis.The main aim of this thesis is to develop and characterise scaffolds for Tissue Engineering applications. Specifically, its objectives are: 1. To study, optimise and characterise two scaffold processing methods: Solvent Casting and Phase Separation. This is done by experiment design analysis. 2. To characterise the degradation, surface properties, and cellular behaviour of the scaffolds produced. The scaffolds are made of a composite of polylactic acid polymer and a calcium phosphate soluble glass. The comparison of the two processing methods reveals that in general, the solvent cast scaffolds have higher porosities and lower mechanical properties than the phase-separated ones. Two compositions containing 20 weight % and 50 weight % of glass particles were chosen for further characterisations including degradation, surface properties and cellular behaviour. The degradation of the scaffolds was studied for a period of 10 weeks. The evolution of various parameters such as: morphology, weight loss, mechanical properties, thermal transitions and porosity, was monitored. Scaffolds produced via solvent casting were found to be more severely affected by degradation than phase-separated ones. The surface properties of the scaffolds were measured by modelling the scaffold pore walls as thin composite films. The morphology, topography, surface energy and protein adsorption of the films was characterised thoroughly. Again, the processing method was critical in determining scaffold properties. Films made via phase-separation processing had markedly different properties due to extensive coating of the glass particles by the polymer. This made the surfaces rougher and more hydrophobic. When the glass particles are not completely coated with polymer, they increase the material's hydrophilic and protein adsorption properties, thus confirming the potential biological benefits of the inclusion of the calcium phosphate glass.The biological behaviour of the scaffolds was characterised by means of in vitro cell cultures with primary osteoblast stem cells and cells from a stable cell line, under static and dynamic conditions. Their morphology, proliferation and differentiation were monitored. Both types of scaffolds sustained osteblastic cell growth. The solvent cast scaffolds were easily colonised by cells which migrated throughout their structure. The cells on the phase-separated scaffolds, however, tended to form thick layers on the scaffold surface. Finally, an alternative characterisation technique was explored applying Synchrotron X-Ray Microtomography and in-situ micromechanical testing. These experiments allowed for the qualitative and quantitative analysis of the microstructure of the scaffolds both at rest and under strain. A finite element model of the solvent cast scaffolds was developed and a preliminary analysis was performed. This technique could be used to complement and overcome some of the limitations of traditional mechanical characterisation of these highly porous materials.

Thesis (Ph. D.)--University of Hong Kong, 2009. / Includes bibliographical references. Also available online.

Thesis (Ph.D.) -- University of Texas at Arlington, 2008.

Thesis (Ph. D.)--University of Hong Kong, 2009. / Includes bibliographical references. Also available in print.

A numerical method is developed to determine the dynamic behavior of delamination and transverse cracks in multilayered plates. The plate is subjected to a time dependent antiplane shear stress field which is acting on the plate surfaces. The interaction of waves diffracted at the crack tip with those reflected at the plate boundaries and transmitted at the material interface makes the problem very complicated, so analytical study of this problem cannot be carried out with our present state of knowledge; hence the problem is solved numerically. The finite element equations are obtained by variational calculus applied in the frequency domain. Thus time intregration schemes are avoided, but time dependent response can still be obtained after inverting the frequency dependent response spectra numerically by Fast Fourier Transform (FFT) routine. Another advantage of the frequency domain analysis is that the resonance frequency can be easily detected from the sharp peaks of the response spectra. The numerical difficulty associated with the singular behavior of the stress field near the crack tip has been avoided by using quarter point elements. The numerical results obtained from this investigation are compared with analytical results to verify the accuracy of the method.

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