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(2021) Chua, StephanieThesisImprovements in liquid lithium-ion battery electrolytes using of metal organic frameworks (MOFs) as a functional decoration on polymer membrane separators were investigated using a combination of experimental and theoretical methods. Zirconium-based MOF UiO-66 was introduced to the polymer support using the mixed matrix membrane (MMM) method. The method allowed the one-step manufacture of a robust, mechanically pliable polymer-MOF membrane composite of high MOF loading. MOF-MMMs imparted improved electrochemical behaviours such as a widened potential operating window, near-unity transference number, and increased presence of solid electrolyte interphase (SEI) components crucial to battery performance. Density functional theory (DFT) calculations were also performed to provide insights regarding electrolyte solvation in the presence of MOF. A simple dip-coating technique was utilised to modify the surface of the MOF-MMMs with polydopamine (PDA) for further improvement of the electrochemical properties. Increased transference numbers, as well as stability during rate cycling, were observed with the resulting PDA-MMM owing to the improved electrode/electrolyte interface. However, surface analyses using x-ray photoelectron spectroscopy (XPS) showed that there are reduced amounts vital SEI components compared to the original MOF-MMM support. The last section further explores the versatility of UiO-66 and tackled the preparation of gel polymer electrolytes (GPEs) decorated with UiO-66 via phase inversion technique. Using the phase inversion method, the fabricated GPE contained pores from both polymer substrate and the intrinsic pores of the 3D nanomaterial for improvement of electrochemical properties. It was demonstrated in this work that the MOF GPE is equally inert and suitable in ether or carbonate-based electrolytes. Overall, this study demonstrated the versatility of UiO-66 metal organic frameworks for use as a functional nanofiller for electrolyte membranes. With the use of inexpensive membrane fabrication methods, the composites obtained are viable for lithium-metal battery applications. Similarly, insights drawn can provide a springboard towards future study of MOF-based electrolytes.
(2022) Wang, ShuangyueThesisTwo-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.
The processes determining dissolved organic carbon (DOC) character and concentration in groundwater in different geological environments(2022) Oudone, PhetdalaThesisDissolved 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.
(2023) Abbasi, RoozbehThesisLow melting point post-transition metals are a class of materials that melt below 330 ℃. Their low melting points offer distinctive physical and chemical properties that are yet to be fully explored. The study of properties of low melting point post-transition metals in various organic or inorganic systems enable insights into the field of biomaterials. The first stage of this thesis reports the synthesis of a liquid metal-polymer system which has the potential for patterning of liquid metals on different substrates. A sonication method is utilised for dispersion of eutectic mix of gallium and indium (EGaIn) particles into a photo-polymer. After characterisation of this inorganic-organic system, patterning of the dispersion is demonstrated through conductive tracks on flexible and rigid substrates. This method provides straightforward patterning of conductive EGaIn liquid metal traces. In the second stage, the physical, mechanical and biocompatibility properties of another liquid metal system known as Field’s metal (a eutectic mix of indium, tin and bismuth) was explored. Field’s metal (FM) has a melting point of 61 ℃. Two eutectic mixes of FM and FM-with zinc were synthesised and compared. A proof-of-concept application was demonstrated for the two biocompatible materials shaped into body implants for clinical applications. The removal of these implants from within a tissue mimic was demonstrated by utilising a mild non-contact heat source. This approach was shown to negate the need for invasive surgery for removal of implants from the body to potentially improving the health of patients. In the third stage, another liquid metal system was investigated based on gallium as the reaction media. Magnesium/bismuth intermetallic was formed on the surface of gallium through selective solidification. The intermetallic system, with a very high intrinsic melting point, formed at low temperature and hexagonal shaped domains of intermetallics on the surface were established. This inorganic system was then studied to show favourable antibacterial properties in comparison to pure gallium control. The work was a successful experimental demonstration on the possibility of the usage of liquid metal media for the formation of various mixes and intermetallic species in mild thermal conditions. Altogether, the outcomes of this successful PhD thesis will provide fundamental insights into surface chemistry of liquid metals with potential benefits in biomedical applications.
(2023) Wimberger, LauraThesisThis 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.
Stimuli-responsive Nanoparticles for Drug Delivery and Novel Acetylcholinesterase Inhibitors and their Use as Protease Sensors(2023) Kaltbeitzel, JonasThesisProteins 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.