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(2022)ThesisWastewater processing conditions in manufacturing environments often involve the three key factors for optimum bacterial growth - water, ideal temperature, and a constant food source. Bacteria are problematic because they can reduce product yield by consuming product and metabolise it into organic acids which lower the process pH, requiring large amounts of chemicals to control. At a casestudy wastewater treatment plant, a site-wide analysis of the impacts of chemical sanitation methods had not been conducted and the efficacy of these chemicals had not been established. To understand the impacts of current sanitation practices, standard microbiological plating techniques combined with HPLC testing to measure lactic acid as a proxy for microbial activity were used. Nitrogensource determination and solids analysis were used extensively to provide a comprehensive picture of the stream properties throughout the plant. I show that current microbial control methods are ineffective for significantly limiting microbial growth in the water treatment plant. The most important factors impacting this are the concentration of nitrogen-sources followed by total organic solids at chemical dosing sites, which react more rapidly with oxidative sanitisers than bacteria do. These findings indicate that chemical sanitisers would be more effective if dosed in locations with minimal concentrations of nitrogen-sources and organic solids. In practice, this is difficult to achieve in an existing plant without significant capital expenditure and so investigation of alternative, nonchemical methods of sanitation in combination with more effective use of chemical methods is recommended.
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(2022)ThesisWith the increasing demand for large electronic devices, such as electric vehicle (EV), hybrid vehicles (HEV), energy storage devices have become more prominent. Lithium-ion rechargeable batteries have been one of the most popular vital topics in this area. For developing the next generation lithium-ion batteries with higher energy capacity and safety, solid-state electrolytes play an important role in improving ionic conductivity and preventing leakage in lithium-ion batteries. Lithium lanthanum titanate (Li3xLa2/3–xTiO3, LLTO) is a ceramic oxide solid-state electrolyte material, which has attracted many interests due to its high chemical stability, wide voltage window and high ionic conductivity (10-3 S/cm). However poor grain boundary conductivity of LLTO and electrode/electrolyte inter-facial problem limit the overall ionic conductivity and rate capacity of LLTO based solid battery systems. Therefore, optimizing the grain boundary conductivity, minimizing the interface issues and increasing the total conductivity of LLTO solid-state electrolytes are imminent. In this thesis, three approaches for enhancing ionic conductivity of LLTO based materials were developed: spark plasma sintering technology, oxygen vacancy manipulation and SiO2 doping. Spark plasma sintering technology enhances the processing methodology of LLTO to prevent lithium-ions loss at grain boundary, thus improving the grain boundary conductivity of LLTO to 1.624×10-6 S/cm. Oxygen vacancy manipulation uses post-annealing procedures to tailor oxygen levels of LLTO, which influenced the crystal structure and changed lithium-ions conduction mechanism of LLTO, resulting an enhanced overall ionic conductivity to 3.38×10-5 S/cm. SiO2 doping process creates the amorphous layers at grain boundary of LLTO to minimize the grain boundary resistance effect, thereby further improving the grain boundary conductivity to 1.96×10-4 S/cm. The purpose of this study is to understand Lithium-ions migration mechanism and optimize the electrochemical performance of LLTO solid-state electrolyte.
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(2022)ThesisMultijunction solar cells based on silicon are predicted to achieve an efficiency of 40-45% for a top cell with a band gap of 1.6-1.9 eV. However, there are currently no known materials with suitable band gaps able to deliver high efficiencies. Two classes of materials that have been proposed for top cells are alloys of CuGaSe2 and alloyed oxide perovskites. CuGaSe2 has a suitable band gap (1.68 eV) for a top cell on silicon, but the maximum efficiency achieved is only 11%, while that of the closely-related CuInGaSe2 (band gap 1.14 eV) is 23.35%. The low efficiency of CuGaSe2 has been attributed to anti-site defects. Therefore, suppressing this defect formation is critical to achieving higher efficiencies. On the other hand, most oxide perovskites have band gaps that are too high (>2 eV) to be used as top cells on silicon, hence strategies such as alloying are required to lower their band gaps. In this work, the effects of alloying CuGaSe2 with Ag, Na, K, Al, In, La and S were investigated using Density Functional Theory (DFT) calculations. The band gaps of the alloyed compounds and formation energies of anti-site defects were calculated to find alloying elements that can increase the defect formation energy but maintain the band gap. CuGaSe2 alloyed with Al at 50at% showed the highest increase (compared to unalloyed CuGaSe2) in the defect formation energy (by ~0.20 eV) followed by Na (~0.15 eV) and S (~0.10 eV), both at 50at%. However, the band gap of the Al alloy (~2.15 eV) is too high for a top cell, while those of Na (~1.95 eV) and S (~1.91 eV) are slightly above the upper limit. Thus, alloying with these elements is not an ideal route towards significantly increasing the formation energy of anti-site defects while maintaining the band gap of CuGaSe2. However, some of the factors that influence the defect formation energy are identified, potentially leading to design rules for future work. Defect formation energies were found to be higher in structures with more positively charged Ga and negatively charged Se atoms. Analysis of bond lengths revealed a positive correlation between shorter Ga and Se bonds and higher defect formation energies. Band gaps of various alloyed oxide perovskites were calculated using DFT. BiFeO3 was alloyed with Y and Sb; LaFeO3 with Cr and Sb and YFeO3 with Bi and Sb. YFeO3 alloyed with Sb at 50at%, was found to have a band gap of 1.4-2.1 eV (depending on the basis set used) which is in the range for a top cell.
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(2022)ThesisThe in-depth characterisation of protein–small molecule complexes is of paramount importance to both drug discovery and fundamental molecular biology. Understanding the structural and thermodynamic properties of such biomolecular assemblies can enable the rational development of new therapeutics, assist in the elucidation of protein function, or provide insights into the molecular mechanisms through which biological activity is regulated. Native mass spectrometry (MS) has emerged as a powerful tool for the investigation of protein–small molecule interactions within heterogenous biomolecular systems. Using native MS, numerous protein–small molecule complexes can be resolved in a single mass spectrum, allowing for the quantitative characterisation of multiple ligand binding events. This is in stark contrast to most established biophysical techniques, which are typically unable to characterise multiple protein–ligand interactions simultaneously. This thesis aims to explore proven applications of native MS in the study of protein–small molecule interactions, and to identify novel methods that facilitate the investigation of complex biochemical systems using such approaches. Chapter 1 provides a comprehensive review of the relevant literature, exploring the critical developments in MS instrumentation and methodologies that have enabled the high-resolution characterisation of protein–ligand complexes. Through a critical analysis of past investigations, the review outlines major challenges facing the field and suggests potential approaches for addressing many of these issues. The second chapter of this thesis outlines a novel native MS-based method for the direct identification of protein–ligand complexes formed from natural extracts containing more than 5,000 potential small-molecule binders. Using this approach, several novel ligands of a key human drug target are identified. Improvements in method efficiency are subsequently made to ensure that the approach could be employed for large-scale pharmaceutical screening campaigns or used for the elucidation of novel interactions between protein complexes and endogenous metabolites. Finally, chapter three aims to identify novel chemical additives that can reduce the charge of protein–ligand complexes in native MS. Charge-reducing agents for positive-mode native MS have been previously shown to facilitate accurate quantitative analysis of protein–small molecule interactions, by increasing the kinetic stability of the gas-phase ions. In this chapter the author explores the properties of several chemical agents that reduce the charge of anionic protein complexes. The effect of these agents on the charge state of various model proteins is characterised to critically evaluate their analytical utility. Furthermore, their effect on the gas-phase stability of a labile protein–ligand complex is also explored. Such agents may prove useful in the quantification of weak interactions that cannot be accurately characterised using standard native MS-based approaches.