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(2019)ThesisThis work provides a systematic study on engineering nickel hydroxide-based nanomaterials with enhanced electrochemical properties for the applications of supercapacitor and overall water splitting catalyst. Silver nanowires (Ag NWs) and Ni(OH)2 nanosheets based hybrid materials were prepared, which can simultaneously realize bifunctions of flexible transparent electrodes and all-solid supercapacitors. Ag NWs provide high conductivity while ensuring flexibility of the electrodes. Ni(OH)2 also has a variety of functions, one of which can reduce the contact resistance by compacting Ag NWs, and the second one is to act as a collector as a pseudo-capacitor. Through the combination of two multifunctional materials, all-solid-state supercapacitor with high cycle stability and flexibility has been demonstrated, which may have potential applications for flexible supercapacitor applications. Bifunctional overall water splitting catalysts based on Ni(OH)2 nanomaterials have been fabricated by the corporation of the hydrothermal method with calcination, which can enhance both oxygen evolution reaction and hydrogen evolution reaction capability. The morphology and crystal structure of hexagonal Ni(OH)2 nanosheets at different temperatures were investigated. It has proved that the content of nickel is an important factor for the improvement of electrochemical activity. Graphene contains a large number of defects which provided sufficient electrochemical active sites and improve the adhesion of the Ni(OH)2 nucleation process to the graphene substrate. It solves the poor catalytic stability attributed to the weak adhesion between catalysts and the conductive substrate.
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(2019)ThesisCurrent comprehension of circRNAs is relatively limited as compared to the extensive body of research available on other well-known coding and non-coding RNAs. CircRNAs have been implicated in gene regulatory functions and have been reported to display endogenous translational capacities. Current research demonstrates the conservation of circRNAs in mammalian brains, with humans having the most complex circular transcriptome currently known. In addition, expanding circular transcriptomes in ageing brains demonstrates the increase in circular network complexity alongside increasing complexity in maturing brain neural networks. Combined, the lack of knowledge of circRNAs could prove to be an understudied, and potentially fundamental, basis for the comprehension of brain evolution through time and amongst species. This research identified four conserved circRNAs between human and mouse cortex where 760 and 60 circRNAs had been discovered respectively; a fact that is indicative not only of some level of circular conservation between the mammalian brains, but also the potential impact of the independent circular transcriptomes on the evolution of the human brain as it is known today. The common circular transcriptome determined in human oligodendrocytes and neurons indicates a moderately interconnected basis of brain function and development; however, the distinct differences in cirexons being predominantly already annotated linear mRNA exons in the human cortex, compared to the high proportion of intronic/intergenic circRNA fragments comprising cirexons in human cell lines, could provide a novel distinct comprehension of human brain function and evolution through time. Current research of circRNA functions have not yielded results that provide a substantive understanding of their function. To the extent that this understanding remains elusive, it provides an incomplete foundation upon which to base interpretations of the reults from this research. Nevertheless, what is distinct is the increase in circRNAs in human brains and the postulated role of circRNAs being gene regulators, implicating circRNAs as definitive in human brain evolution with regard to functional capacity and complexity as compared to other mammals.
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(2019)ThesisThe morphologies of ceria nanocrystals play an essential role in determining their redox performance in many applications, yet the effect of synthesis variables on the formation of ceria nanoparticles of different morphologies and their related growth mechanisms are poorly understood. The present thesis investigates the morphological development of nanoceria through the examination of the key processing variables for precipitation and hydrothermal synthesis at high Ce and NaOH concentrations. The characterization included the analytical techniques XRD, TEM, HRTEM, XPS, BET, and laser Raman microspectroscopy. A comprehensive survey of the effects of experimental conditions on the resultant morphologies of nanoceria during precipitation and hydrothermal synthesis is presented. The key experimental variables [Ce], [NaOH], temperature, and time are observed to have significant effects on the morphological evolution and grain growth. Detailed schematic mapping of nanoceria in the form of nanorods and nanocubes indicates that high [Ce] and low temperature facilitate chain formation and subsequent coalescence into hexagonal nanorods. With increasing temperature and time, these structurally destabilise and re-form into nanospheres and nanocubes. The present work is elucidated through a range of mechanistic interpretations that underpin a new morphological map for high [Ce]; this incorporates not only morphological development but also grain growth effects of nanoceria. The experimental data and morphological map have allowed the derivation of the comprehensive schematic mapping that explains, for the first time, the effects of the four key experimental variables on the generation of the different morphologies that have been observed and reported in the literature.
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(2019)ThesisPhotocatalytic and photoelectrochemical water splitting can play an important role in future renewable energy systems by allowing solar energy to be stored in the form of hydrogen. Tungsten oxide (WO3) has some promising properties as a photocatalytic material, but as a simple binary oxide, is has limitations on its optoelectronic properties. In order to improve the visible-light absorption efficiency for photocatalytic applications, the band gap should be further reduced. Moving to ternary compounds can be a strategic method to achieve this, as ternary compounds provide a much greater variety in compositions and hence properties. In this work, the effect of introducing a second metal cation into tungsten oxide is studied by Density Functional Theory (DFT) calculations using the HSE06 functional. The compounds investigated include AWO4 tungstates (A = Sn, Fe), M2WO6 tungstates (M = Bi, Sb), tungstite (WO3·H2O) and hydrotungstite (WO3·2H2O). The band gaps are found to be 2.98 eV (WO3), 1.65 eV (SnWO4), 2.03 eV (FeWO4), 2.83 eV (Bi2WO6), 2.91 eV (Sb2WO6), 2.27 eV (WO3·H2O), 2.51 eV (WO3·2H2O). The band gaps of all the tungstates studied in this work are lower than that of binary WO3. The valence bands of these ternary oxides are formed by the oxygen 2p orbitals and the s orbitals of the second metal cations, which contribute to the band gap narrowing compared to WO3. Structural properties are also strongly correlated with the band energies; the spacing between layers of WO6 octahedra was found to be related to the conduction band edge, with larger spacing causing a shift in the band edge to a more negative potential compared to WO3. The tungstates studied are found to have either a small band gap (SnWO4, FeWO4, WO3·H2O and WO3·2H2O), and hence can potentially give a high efficiency for visible-light absorption, or a more negative conduction band edge than WO3 (Bi2WO6, Sb2WO6), which means they may be able to achieve the overall water splitting. The defect properties of several intrinsic defects in α-SnWO4 are also evaluated; a SnW antisite defect and oxygen vacancy (VO) are found to be the most two probable defects to form in α-SnWO4. Furthermore, SnW defects may lead to an enhancement of the photocatalytic performance under sunlight, while VO are expected to decrease the performance.
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(2019)ThesisRecent development of wearable devices in healthcare, wearable and soft robotics has generated increasing demand for memory devices which are more compact with higher data storage capacity and mechanical flexibility, as well as lower fabrication costs. Resistive random access memory (RRAM), which is an emerging technology, has unique advantage of high response speed, low power consumption, and 3D stack architecture. In this research, a sandwich structure (Au/CeO2/Au/Si) based RRAM device has been developed. Scanning electron microscope (SEM), transmission electron microscopy (TEM) were applied to analyze the phase and microstructure for both inks and the thin films. The electrical properties including current-voltage (I-V) response were systematically tested by auto-lab and source meter. A stretching test also was done with a thermoplastic polyurethane (TPU) based device. A suspension ink with controlled shape of CeO2 nanocrystals was prepared. A series of samples have been prepared with solvent, toluene or hexane, by using CeO2 as core material for the ink. The thin film was deposited by spin coating or drop-coating following with plasma treatment. Both silicon and TPU based device have been used as substrates for comparison. Shape controlled CeO2 nanocrystals and printable inks have been successfully fabricated. Different solvent was used to vary the properties of the ink and improve the cracking-free films. A large area cracking-free CeO2 thin film was obtained by plasma processing. Ink jet printing method was also involved as one method of film fabrication. The memory behaviour could be more clearly demonstrated with obvious characteristic from the I-V curve both at silicon and TPU elastic substrates. Thus, the plasma treatment with different treatment time and power could help improve the thin film performance. A simple flexible device had been manufactured with a basic memory behaviour. In summary, the project provided a systematic study on developing metal oxide based nanocrystals towards crack-free thin film and memory devices applications, which may have potential applications in future printed, flexible data storage devices.
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(2018)ThesisPhotocatalytic materials such as TiO2 have the potential to be used for air and water purification applications. However, TiO2 has a high band gap and thus only UV radiation can cause the activation of the material, leading to low efficiencies in sunlight. An improvement of the photocatalytic performance can be achieved by loading of noble metals such as gold (Au) on the surface of TiO2 such that they form localised Schottky junctions. Thus with a sufficient extent of surface decoration, an efficient charge separation of the light generated electron-hole pairs can occur leading to an improvement in photocatalytic efficiencies. First principle calculations were conducted to determine the effects of loading gold (Aun) clusters of varying sizes on the surface of titanium dioxide (TiO2). In terms of geometry, planar geometries of Aun clusters are generally preferred to be adsorbed on the surface of the TiO2 slab. The work showed that Aun loading on TiO2 resulted in the introduction of occupied Au MIGS (metal-induced gap states) which resulted in a significant reduction in the band gap in comparison to unloaded TiO2. Moreover, the difference in the electronic structures of clusters with even and odd numbers of Au atoms resulted in an odd-even oscillation in the band gap energy. Odd-numbered Aun clusters with unpaired electronic states had a relatively narrow bandgap, while the even-numbered Aun clusters, in which all the electronic states are paired, had wider band gaps. The odd-even oscillation trend was observed in the formation energy variations such that even-numbered Aun clusters on the TiO2 slab showed a higher stability than the odd-numbered Aun clusters. Experimental work was conducted involving the synthesis of gold nanoparticles of varying morphologies and their loading on TiO2 coatings fabricated by anodisation. Nanorods and clustered particles were fabricated; however, only the nanorods were used for deposition owing to their high aspect ratios 1.8 and monodispersed nature, which would be expected to show superior catalytic activity. TiO2 coatings were prepared by anodisation on titanium alloy (Ti6Al4V) substrates in 1 M H2SO4 acid electrolyte. The gold nanoparticles (AuNPs) were deposited on TiO2 (2-6 deposition cycles) by spin coating and then the samples were annealed at 200ºC or 300ºC. The mineralogies were identified by GAXRD while the microstructures were examined using SEM and AFM. The film thicknesses were determined using FIB. The surface compositions of the film were examined by XPS. The band gap, which is an indicative property for photocatalytic performance, was measured by using UV-Vis reflectance spectrophotometry. Finally, the photocatalytic performance was assessed in terms of the degradation of methylene blue (MB). In general, there were no significant differences observed for the mineralogy and microstructure of TiO2 coating with varying layers of AuNPs deposition; however, the thickness of films appears to have increased with increasing deposition layer and this is believed to be owing to the expansion of the organic-containing layer owing to pyrolysis during heat treatment. XPS analysis of the samples after MB testing showed that four possible mechanisms can affect the stability and performance of AuNPs in contact with photocatalytic TiO2 these include chemisorption, physisorption, organic binding, and physical entrapment. The best performance was seen for 4 cycles of AuNPs, which was similar to that of the unloaded film at 48 h (30% MB degradation). The loss of particles during testing is believed to cause the deterioration of photocatalytic performance at longer test times. Reflectance data showed low levels of light absorption with deposition of AuNPs leading to an increase of the band gap. It is possible that there was some limited charge transfer between the AuNPs and TiO2, which improved the photocatalytic effect.
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(2018)ThesisCampylobacter concisusis a Gram-negative bacterium with a singular polar flagellum and curved morphology that enables it to traverse the mucus layer and directly contact the intestinal epithelium, providing the opportunity to trigger intestinal inflammation and facilitate the progression of inflammatory diseases to cancer. This thesis reports novel findings regarding the adaptation of different genomospecies of C. concisus to the human gastrointestinal tract and the potential for C. concisus to affect the PD-1 and PD-L1 pathway and thus the development of inflammatory-driven cancer. C. concisus was previously reported to be associated with inflammatory bowel disease (IBD). It has two genomospecies (GS) that carry distinct and specific genes, suggesting they may have different pathogenic potentials. Previous studies have found that GS2 C. concisus strains are invasive to intestinal epithelial cells, suggesting that they may contribute to the initiation of IBD. However, no clinical studies to date have demonstrated GS2 strains to be more associated with IBD. In Chapter 2, the colonization of the human gastrointestinal tract by GS1 and GS2 C. concisus is systematically examined in patients with IBD and in healthy controls. This chapter provides novel information regarding the adaptation of different genomospecies of C. concisus to the human gastrointestinal tract. Two new PCR methods were developed and validated for detecting and quantifying C. concisus strains, based on polymorphisms of the 23S rRNA gene. These PCR methods were used to evaluate GS1 and GS2 C. concisus prevalence in 56 oral and enteric samples. Quantitative PCR showed significantly higher level of GS2 C. concisus than GS1 C. concisus in samples collected from the upper and lower gastrointestinal tracts of both patients with IBD and healthy controls, indicating that GS2 C. concisus is better adapted to the human gastrointestinal tract. A meta-analysis of the compositions of GS1 and GS2 C. concisus strains isolated in previous studies was also conducted, and showed similar findings except that a significantly lower number of GS2 strains were isolated from faecal samples of healthy individuals; this suggests a potential difference between healthy controls and patients with gastrointestinal diseases in either colonizing strains or the enteric environment. Overall, the human gastrointestinal tract harbours a complex community of bacteria, some of which are pathogens capable of establishing chronic infections. These microbes may be involved in the development of inflammation-driven cancer. The immune system uses various effector cells and molecules to control and eradicate infectious agents and cancer cells. In particular, cytotoxic T cells (CTL) are major effector cells in anti-tumour immune responses. However, the functions of these effector cells can be inhibited by immune checkpoint proteins and molecules in tumour environments; this inhibition contributes to cancer cell immune evasion. Accordingly, the blockade of immune checkpoint proteins and molecules, such as PD-1 and its ligand PD-L1, has shown great promise in cancer treatment. Previous studies have shown that some microbes capable of establishing chronic infections in humans, such as Helicobacter pylori, also increase host PD-L1 and PD-1 expression on both mRNA and protein level; these microbes might be involved in the development of inflammation-driven cancer through assisting immune evasion of cancer cells. However, whether other bacterial species associated with chronic inflammation in the human gastrointestinal tract have effects on the PD-1 and PD-L1 pathway remains to be investigated. In the case of C. concisus, its curved morphology and flagellum enable it to pass through the intestinal mucus layer and contact intestinal epithelial cells. Previous studies have shown that colonization of the intestinal tract by C. concisus can induce epithelial production of proinflammatory cytokines such as IFN-γ and TNF-α. Interestingly, IFN-γ and TNF-α were previously reported to play important roles in upregulating PD-L1 mRNA and protein expression in intestinal cells. Evidence of T cell infiltration at the jejunum and colon after infection with C. concisus in mice suggests that C. concisus might be involved in the development of cancers through shaping interactions between PD-1 and PD-L1. In Chapter 3, the effects of GS1 and GS2 C. concisus strains on PD-L1 expression in human epithelial cells are investigated. Briefly, the expression levels of PD-L1 mRNA and protein in human epithelial cells were analysed after C. concisus infection. The results suggest that human epithelial cells do express PD-L1 mRNA but barely expressed PD-L1 protein on their surfaces. Treatment of these cells with IFN-γ can induce PD-L1 protein expression. Also, some C. concisus strains can regulate PD-L1 expression at the mRNA level, but effects depended upon strain rather than genomospecies. In contrast, PD-L1 protein expression was not statistically different for different infecting strains or genomospecies. In conclusion, this thesis reports novel findings regarding the adaptation of different genomospecies of C. concisus to the human gastrointestinal tract. Furthermore, it provides information regarding the effects of different genomospecies of C. concisus on PD-L1 expression in human intestinal epithelial cells. These data may provide a better understanding of the pathogenicity of this opportunistic bacterium.
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(2018)ThesisMagnetic nanostructures have been of interest for long due to their various applications such as bioapplications, including hyperthermia, drug delivery and magnetic resonance image, magnetic recording media or spintronic devices. The shape of nanostructures strongly affects the magnetic properties. For example, due to its vortex structure, magnetic nanorings have high magnetization and low coercivity, suitable for the bioapplications mentioned above, thus been extensively investigated. However, there are few reports on the compounds with magnetic nanorings and gold nanoparticles, which are both promising candidate for bioapplications. Diluted magnetic semiconductor is one of promising materials for spintronic devices. However, dopant accumulation at the interface is a major problem for oxide based diluted magnetic semiconductor. Recently emerged 2D based diluted magnetic semiconductor has the potential to solve the problem. In this work, the synthesis and magnetic properties of gold nanoparticles decorated Fe3O4 nanorings were investigated. Moreover, transition metal doped MoS2 2D based diluted magnetic semiconductor is fabricated and studied. Gold nanoparticles supported magnetic iron oxide nanorings were fabricated by three steps. Firstly, hematite nanorings was synthesized through an anion-assisted hydrothermal route. Secondly, the nanorings were decorated with uniform-sized gold nanoparticles by deposition-precipitation method. Finally, gold supported hematite nanorings were reduced in H2 to obtain magnetic nanorings. As the fabrication of nanorings is sensitive to temperature, it's difficult to reduce gold supported hematite nanorings into gold supported Fe3O4 nanorings. By optimizing the fabrication parameters, we successfully achieved gold supported Fe3O4 nanorings. However, a small amount of unreduced hematite still exists. Hence, the saturation magnetization is smaller than reported. MoS2 nanosheets doped with vanadium and cobalt with various concentrations were synthesized by hydrothermal method. EDX, XPS and EPR results demonstrated the successful n-type substitutional doping of V and Co at the Mo sites of MoS2. As the concentration of Co increased, it became the dominate dopants instead of V. Further magnetic properties analysed by SQUID indicates that pure MoS2 is magnetic, maybe due to the zigzag defects or vacancies. V and Co doping leads to some ferromagnetic coupling. However, the majority of the film shows paramagnetic signal.
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(2018)ThesisThis project aimed to synthesize fused-ring systems derived from flavanones and isoflavanones by utilizing the chemistry of the highly reactive ortho-quinone methide (o-QM) intermediate. The synthesis of cis-4-arylisoflavan and isoflavene derivatives was also explored by employing different metal catalysts. The fused-ring systems were synthesized via inverse electron-demand Diels Alder (iEDDA) reaction between dienophiles and o-QM intermediate, which was generated in situ by thermolysis of the corresponding Mannich base. The reaction proceeded in a highly regioselective way, which can be explained by the charge distribution of the reacting partners. However, in the case of 7-hydroxyflavanone, the cycloadduct mixture contained both ring-closed flavanone product and ring-opened chalcone product. The iEDDA reactions were found to give cycloadducts in high yields when electron-rich alkenes were used. In contrast, electron-poor dienophiles remained unreactive in this reaction. The chemistry of o-QM was further studied using dihydrodaidzein, an isoflavanone-type compound as a scaffold. The ability of o-QM to undergo both [4+2] cycloaddition reaction with dienophiles and Michael addition with nucleophiles was explored. However, under certain conditions, the isoflavanone core underwent ring-opening, a process which was proposed to involve the formation of a propenone intermediate. Electron-rich arenes such as 3,5-dimethoxyphenol and 3,5-dimethoxyaniline participated in a Michael addition reaction to furnish the biarylmethane analogues, possessing a methylene bridge which connected the C8 of dihydrodaidzein with the arene moiety. Interestingly, with sulfur-containing arenes, the resulting products possessed a thioether linkage. A rationale for this observation has been proposed. 4-Arylisoflavans and isoflavenes were reported to exhibit promising anticancer activities. The synthesis of these derivatives was explored by utilizing metal catalysts. cis-4-Arylisoflavans were prepared in moderate to good yields by catalytic hydrogenation of the corresponding 4-arylisoflavenes. Suzuki-Miyaura cross-coupling reactions between the key intermediate 3-iodo-4-phenyl-2H-chromene and various phenylboronic acids or heterocyclic boronic acids allowed the generation of 4-arylisoflavene analogues. A gold(I) catalyst was also successfully used in preparing isoflavenes without a phenyl ring at the C4 position. The anticancer activity of the isoflavan and isoflavene analogues was investigated. The results paved the way for some structural modifications in order to generate more active analogues.
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(2019)ThesisIn our research, we carried out several analyses in order to investigate the effect of nanoparticle sizes and softness on drug delivery. In first section, poly (2-hydroxyethyl acrylate) (pHEA) in three different molecular weight were synthesized via RAFT polymerization and mono-dispersed gold nanoparticles in various sizes were produced through seeded growth techniques. Afterwards, the polymers were grafted to the surface of gold nanoparticles via “grafting-to” technique. The nanoparticle sizes and softness were characterized in various methods. In second section, the cellular uptake of synthesized pHEA-coated gold nanoparticles was investigated for drug delivery purposes. The investigations, including the in-vitro cytotoxicity, protein adsorption, differences in endocytosis pathway and cancer cellular uptake in 2D and 3D models were conducted. After the proof of the non-cytotoxicity in cancer cell line A549, the nanoparticles in various sizes and softness by coating pHEA chain in different thickness were compared in the extent of cellular uptake and the differences of endocytosis pathway. The investigation proved that the degree of cellular uptake is affected by both nanoparticles sizes and pHEA chain thickness. The cellular uptake imparity in 2D and 3D models also proved the various pathways in endocytosis.