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(2022)ThesisTwo-dimensional transition metal dichalcogenide (TMD) nanocrystals (NCs) exhibit unique optical and electrocatalytic properties. However, the growth of uniform and high-quality NCs of monolayer TMD remains a challenge. Until now, most of them are synthesized via solution-based hydrothermal process or ultrasonic exfoliation method, in which the capping ligands introduced from organic solution often quench the optical and electrocatalytic properties of TMD NCs. Moreover, it is difficult to homogeneously disperse the solution-based TMD NCs on a substrate for device fabrication since the dispersed NCs can easily aggregate. Here, we put forward a novel CVD method to grow closely-spaced TMD NCs and explored the growth mechanism and attempts on the size control. Their applications acting as electrocatalysts and adhesion layer for Au film deposition have been also well displayed. Through the whole chapters of this thesis, the following aspects are highlighted: 1. MoS2 and other TMD nanocrystals have been grown on the c-plane sapphire. The surface oxygen vacancies determine the density of TMD nanocrystals. The MoS2 nanocrystals demonstrate excellent hydrogen evolution reaction and surface-enhanced Raman scattering performance owing to the abundant edges. 2. Deep insights into the growth of MoS2 nanograins have been explored. The surface step edges and lattice structures of the underlying sapphire substrates have a significant influence on the growth behaviors. The step edges could modulate the aggregation of MoS2 nanograins to form unidirectional triangular islands. The Raman spectra of MoS2 demonstrate a linear relationship with the crystal size of MoS2. 3. The orientation of sapphire substrate has an of importance effect on the critical size of MoS2 nanocrystals. The MoS2 nanocrystals have the smallest size on the r-plane sapphire, besides, the MoS2 on r-plane sapphire demonstrates the sintering-resistance feature, which is attributed to the edge-pinning effect when MoS2 edges are anchored on the sapphire surface. 4. The MoS2 nanocrystalline layer was utilized as the adhesion layer for Au film depositing on a sapphire substrate. The Au films on MoS2 displayed superior transmittance and electrical conductivity as well as outstanding thermal stability, which lay in the strong binding of Au film with MoS2 nanocrystalline layer.
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(2022)ThesisDissolved organic carbon is stored and processed in groundwater in three ways. It is stored on minerals by adsorption, it is biologically processed through biodegradation, and it also undergoes a process to return to groundwater called desorption. This biophysiochemical research shows that the groundwater system is therefore a vital part of the global carbon cycle and carbon sink. This research fills a gap in the existing understanding of how to calculate the global carbon budget, as does not yet include the dissolved organic carbon that is stored in groundwater. This thesis exclusively explores processes determining dissolved organic carbon character and concentration in groundwater in different geological environments. This is new, useful knowledge to describe the biophysiochemical process. This research did not examine human interference in adding carbon to groundwater. This research found how dissolved organic carbon is stored and processed in groundwater due to biodegradation and desorption, and how it is adsorbed onto sediment surface. This research explored the characteristics and concentration of Dissolved organic carbon in groundwater by using Liquid Chromatography-Organic Carbon Detection, and other techniques, to examine dissolved organic carbon in terms of its fractions: humic substances, hydrophobic organic carbon, biopolymers, building blocks (BB), low molecular weight neutrals and low molecular weight acids. There were several key findings. First, the results showed that both semi-arid inland low sedimentary organic carbon environments – i.e., Maules Creek and Wellington – were a carbon source; while the high rainfall temperate coastal peatland environment of Anna Bay was a carbon sink. Secondly, another key finding was that dissolved organic carbon was not processed as a whole chemical compound, but it was processed by its fractions where each fraction was processed distinctly. For example, humic substances were only adsorbed/desorbed in groundwater; while low molecular weight neutrals were only consumed by microbes in the biodegradation process in groundwater.
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(2023)ThesisThis work explores how reversible light-induced pH changes can be increased and applied to control pH-responsive systems with light. Chapter 2 investigates how substitution patterns influence the acidity of merocyanine photoacids in the dark as well as under light irradiation. The parameters which are crucial for increasing light-induced pH changes are defined and applied to synthesized merocyanine photoacids. The light-induced pH changes starting from varying initial pH values are explored and a model is developed to estimate these based on experimentally defined parameters. Transient absorption spectroscopy was used to explore the influence of the protonation state of the merocyanine form (MCH vs MC) on the photoswitching efficiency. A python model is developed to describe the pH- recovery in the dark. Chapter 3 introduces an improved merocyanine photoacid, designed by principles outlined in Chapter 2. The acidity parameters and photoswitching abilities are characterized. The pH switching capacity is investigated and extended into the basic pH range. The light-induced pH switch by the improved photoacid is applied to control the protonation state of an indicator dye. Chapter 4 applies light-induced pH changes to influence the secondary structure of pH-sensitive DNA. The transient formation of these structures is explored. The influence of the initial pH value and a DNA binder on the ratio and kinetics of the system components is investigated. Chapter 5 applies light-induced pH changes to influence the properties of different types of supramolecular polymers. The challenges of applying merocyanine photoacids to generate structural changes of supramolecular polymers by influencing the components protonation state are highlighted. Chapter 6 presents brief conclusions and a future outlook for this research field.
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(2023)ThesisProteins and enzymes are highly versatile materials that are involved in essentially every biological process, making them valuable tools and targets in the field of medicine. This thesis explores two distinct aspects of their applications: Part I focuses on the formation of responsive nanoparticles for drug delivery, while Part II delves into the development of small molecular inhibitors and their use in a novel protease assay. Each part will start with a separate literature review, to give the reader a brief background about the topic. Their biocompatibility, non-toxicity, and ability to specifically interact with cellular receptors make proteins and enzymes promising materials in the design of nanoparticles for drug-delivery applications. In many cases, a covalent modification of the protein is required to drive the formation of nanoparticles which can inadvertently change the properties of the underlying protein. One possibility to overcome this problem is to make the covalent modification reversible by the introduction of responsive linker molecules, which additionally allows targeting. Therefore, Part I of this thesis will explore nanoparticles that degrade in response to specific environmental cues, such as reducing agents, UV-light, or hypoxia. The first chapter is a comprehensive review of the literature on different protein-nanoparticle and the use of responsive linker systems in drug delivery applications. Chapter 2 of the thesis will present the synthesis of PEGylated enzyme nanoparticles designed for delivering catalytically active enzymes into cells. The results obtained will demonstrate the triggered disassembly of the nanoparticles and the subsequent release of catalytically active enzymes, leading to cellular toxicity. Moving on to Chapters 3 and 4, reductive-responsive nanoparticles composed of bovine serum albumin (BSA) and a hypoxia-responsive polymer will be featured as an intracellular drug delivery vehicle for nucleic acids. In Part II of the thesis, the focus is shifted to the design of small molecule inhibitors for acetylcholinesterase (AChE) and their use in the development of a novel protease assay. AChE has important implications in the treatment of Alzheimer's and other diseases. After a short literature review in Chapter 5 discussing the enzyme and past development of its inhibitors, Chapter 6 shows the journey in the design of potent, primary amine-containing inhibitors of AChE based on several known scaffolds. The increased polarity of the molecules hinders their ability to cross the blood-brain barrier, suggesting a potential application in the treatment of functional dyspepsia. Lastly, Chapter 7 deals with the development of a new proteases assay based on the inhibitors synthesized in the previous chapter. Proteases play a crucial role in many biological processes and are thus important medical markers for various diseases. The effect of the potency of the inhibitors after covalent modification with short peptides was evaluated and a mathematical model developed to predict the sensitivity of the assay.
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(2024)ThesisReceptor clustering is one of the most common mechanisms for controlling cell fate in nature, and strategies capable of directing this behaviour hold significant therapeutic potential. One prominent example is the TRAIL protein (TNF-related apoptosis inducing ligand), which selectively induces apoptosis in cancer cells by clustering death receptors DR4 and DR5. Although a potent chemotherapeutic, its clinical use has been hampered by its short circulation half-life. In this thesis, multivalent polymer scaffolds capable of presenting DR4/5 binding peptide ligands were developed as synthetic TRAIL mimics. In any synthetic protein mimic, directing the conformational structure to precisely control the spacing and orientation of multiple ligands is a major challenge. The two scaffolds in this thesis applied different strategies to achieve this. The first scaffold was a core-crosslinked micelle system with surface functionality for attachment of DR5 binding peptides. Micelles featuring varying peptide densities were synthesized and carefully characterized. These micelles successfully induce apoptosis in a colon cancer cell line (COLO205) via DR5 clustering. Micelles with a peptide density of 15% (roughly 1 peptide / 45 nm2) displayed the strongest activity with an IC50 value of 0.8 μM (relative to peptide), suggesting a statistical network of monomeric ligands may suffice to drive DR4/5 signalling. However, significantly improved activity could be achieved using star polymers with a hydrophobic core. Structural characterization by DOSY-NMR and surface plasmon resonance revealed that the improved activity came from the polymer folding in solution, which positioned the peptides in a well-defined manner on the periphery of the star, enhancing their accessibility to DR5. By varying the chemistry of the inner block, a new lead structure of 3-arm PBzA40-b-PDMA40-WDCL was identified in library screening with IC50 values in the low nanomolar range to COLO205. These leads show toxicities approaching that of the native TRAIL protein, but from a material that would be expected to show upwards of 20 h circulation half-lives in vivo.
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Development of Barium Titanate Nanomaterials for Applications in Piezocatalysis and Cathode Coatings(2024)ThesisThe environment and energy are two areas of great concern today. Dye pollution control and research on lithium-ion batteries (LIBs) performance are branches of these two fields, respectively. The use of piezoelectric materials to achieve piezoelectric catalysis is a relatively novel method for degrading dyes. Barium titanate (BTO), as an excellent piezoelectric material, has been widely used in the field of piezoelectric catalysis. In addition, as a bimetallic oxide with excellent stability, it also has the potential to be used to protect the cathode material of LIBs. In this thesis, BTO nanoparticles were synthesized utilizing three different methodologies: sol-gel, hydrothermal and molten salt to control the phase and microstructure. BTO nanocubes, characterized by a diameter ranging between 20-30 nm, were procured through sol-gel and hydrothermal methods, and their tetragonal phase and spontaneous polarization were achieved through annealing and ball milling processes, respectively. A subsequent modification of BTO was carried out using a Ti3C2Tx (MXene) coating, resulting in an over 90% degradation ratio of Rhodamine B (RhB) within a span of 15 min. Compared to BTO, which degrades by 40% in 15 minutes, the efficiency has approximately doubled. Additionally, this prepared composite exhibited significant outcomes in the photocatalytic and synergistic (piezo-photo) catalytic degradation of RhB. The photocatalytic degradation efficiency of unmodified BTO stood at approximately 20% after 90 minutes. In contrast, the MXene-modified BTO achieved an efficiency of around 70%, representing a significant enhancement. When subjected to simultaneous light and ultrasound exposure, the degradation efficiency witnesses a marked increase. The MXene-modified BTO degraded over 90% of RhB in just 15 minutes, while the unmodified BTO achieved 70%. The MXene-modified BTO exhibited relatively good stability. After three cycles of usage, it sustained a degradation efficiency of approximately 80%. In the context of LIBs applications, a BTO coating was applied to the surface of the cathode electrode material, which is Li(Ni0.8Co0.15Al0.05)O2 (NCA), to enhance its electrochemical properties. With the BTO coating, a relatively uniform film formed on the surface of NCA. At a concentration fraction of 1%, this coating positively impacted NCA. Performance evaluations of the battery revealed that the incorporation of the BTO coating contributed to an enhanced cycle and rate performance. Remarkably, post 200 cycles, a discharge capacity of 144 mAh/g and a retention of 86.9% of the discharge capacity was observed. Compared with 64.6% of pristine NCA, it was a relatively good improvement. In conclusion, this work provides a facile approach to controlling the phase and morphology of barium titanate nanomaterials with enhanced piezoelectric catalysis. In addition, the as-prepared barium titanate nanomaterials have been utilized as cathode coatings to prevent the side reactions between the cathode materials and electrolytes. This work demonstrates that barium titanate is a promising, multifunctional material with wide applications in energy and environment related areas.
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(2023)ThesisHollow fibre (HF) membrane modules implemented in submerged membrane bioreactors (MBR) and pressurised applications have been widely accepted for both wastewater treatment and polishing wastewater treatment plant (WWTP) effluents. Further innovations in membrane technologies and wastewater treatment market competitiveness, however, are restricted by high manufacturing and operational costs, where a trade-off exists between membrane system design and filtration performance. In the current work, the effects of HF lengths, physical characteristics and system fouling mitigation techniques were investigated to further optimize filtration performance. The following experimental approaches were considered, (1) small-scale filtration experiments with various HF membrane lengths and fibre dimensions, (2) the development of theoretical filtration models and the assessment of filtration simulations, and (3) pilot-scale filtration performance of prototype large-scale membrane modules in wastewater. Two mathematical models for constant TMP filtration using dead-end HF membranes were developed using firstly the Darcy friction factor, and secondly, the Hagen–Poiseuille model. The models allowed for the overall theoretical lumen pressure drop values, local flux distributions and overall filtration performance to be extensively studied. Laboratory-scale filtration experiments using HF membranes of different lengths (0.5 – 2.0 m) were undertaken with the objective of demonstrating the influence of lumen pressure drop in overall filtration performance. Though greater permeate volumes were obtained when using modules prepared with longer HF membranes, such systems experienced greater lumen pressure loss. These losses reduced the operating TMPs effectiveness, resulting in greater non-uniformity in local fluxes across the length of the HF membranes. The magnitude of losses and degree of non-uniformity in such longer systems were extensively studied, allowing for the identification of effective loss reduction techniques, such as the incorporation of HF membranes with larger inner diameters (ID) in the membrane modules. Pilot scale investigations were undertaken to evaluate the influence of HF length on overall performance in real wastewater feeds. Prototype full-scale modules were prepared with HF membrane of different lengths (1.6 – 2.0 m) and ID. Longer modules demonstrated greater filtration performance as the influence of increased lumen pressure drop due to longer fibre lengths was effectively offset by the enhanced fibre dimensions. Overall, the results presented in this study reveal that a significant interplay exists between module design (including length, packing density, slack, and fibre size), filtration process design (feedwater quality, biomass concentration, aeration rate, aeration/shear efficiency) and the critical flux (of threshold flux) conditions. In conclusion, the incorporation of longer length HF membranes in pressurised and submerged MBR modules has been proven to be a promising innovation which offers enhanced filtration capabilities.