Chemistry - Doctoral Theses

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    Multiferroic investigations of Aurivillius phase thin films
    (University College Cork, 2023) Colfer, Louise; Keeney, Lynette; Long, Brenda; Royal Society; Science Foundation Ireland
    In recent years, the amount of data being created and processed is growing at a much faster rate than the rate of computational storage technology development. With CMOS technologies reaching their miniaturisation limits, new disruptive materials are needed to increase data storage capabilities. Technological road-maps have identified room temperature, non-volatile magnetoelectric multiferroic materials as promising candidates for memory scaling within future memory storage devices. Although multiferroic memory devices have the potential to revolutionise memory storage technologies, commercial devices successfully utilising multiferroics have not yet come to fruition. The focus of this thesis is to understand and optimise a rare example of a room temperature magnetoelectric multiferroic, Bi6TixFeyMnzO18 (B6TFMO; x = 2.80 to 3.04; Y = 1.32 to 1.52; Z = 0.54 to 0.64). Aurivillius phase materials, (Bi2O2)(An−1BnO3n+1), where ferroelectric perovskite units are interleaved between dielectric [Bi2O2]2+ layers, are flexible scaffolds for technological applications. While earlier studies indicated that B6TFMO is a promising material for future memory devices, my thesis presents significant advances in the characterisation, understanding and optimisation required towards implementing the material in fully realised devices. In this work, correlation between the octahedral tilting and atomic-level structural distortions with functional electronic and magnetic properties of B6TFMO were determined, revealing that crystal field splitting of the Ti4+ octahedra is influenced by its position within the Aurivillius unit cell. Theoretical calculations determined that this is predominantly driven by changes in the extent of tetragonal distortion along the c-direction. Atomic scale mapping of polar displacements reveals this has a direct impact on the ferroelectric properties. Polarisation is largest towards the outer perovskite cells, correlating with an increased extent of local tetragonal distortion of octahedral geometries. Experiments demonstrate that tilting of the BO6 octahedra competes with the extent of tetragonal distortion of the TiO6 octahedra, where the degree of octahedral tilting increases towards the central layers of this Aurivillius system, where the magnetic cations preferentially partition. This work presents the first indication that octahedral tilting might be an important enabler of long-range magnetic interactions and subsequent multiferroic behaviour in B6TFMO. Delving deeper into fundamental understandings of B6TFMO’s antipolar and magnetic behaviour, the purposeful inclusion of structural defects within the layered structure of B6TFMO and how they can impart elastic strain and electrostatic energy changes which in turn influence polar behaviour is explored. The findings show that the vicinal sapphire substrates (mis-cut angle 0.2 o to 10 o) are successful for promoting the propagation of sub-unit-cell defects and disruptions to the periodicity of the Aurivillius phases. This has a marked effect on the film morphology and ferroelectric properties. Macroscopic and local measurements show that defect, crystal grain and ferroelectric domain density increases with increasing substrate mis-cut angle. Atomic resolution polarisation mapping showed that charged domain walls alongside exotic polar vortices are facilitated by OPBs when two OPB defects are spaced 5 nm apart. This work provides insight into methods for successfully controlling defect levels and how polar vortex domain walls and charged domain walls are promoted within layered multiferroics by tailoring the underlying substrate that the film is grown on. Moving on from vicinal sapphire surfaces, patterned sapphire with 3D domes were used to encourage the growth of the Aurivillius grains towards an upright geometry. An increased number of non-(00l) reflections were present in the B6TFMO films on patterned sapphire along with evidence from STEM imaging showing that B6TFMO grains grow along the incline of the patterned sapphire domes. With the growth of the crystal grains towards an upright geometry it would be expected that access to the major a-axis polarisation via out-of-plane measurement would be improved, however with a maximum inclination angle of 60 ° achieved with the 3D dome architectures, the out-of-plane piezoresponse of the samples remained weaker than the in-plane piezoresponse. Studies of the magnetic properties of the films demonstrated that the B6TFMO samples were ferromagnetic at room temperature. These findings provide further evidence of room temperature multiferroic behaviour in B6TFMO. Lastly, the role of bismuth excess and substrate strain were investigated to optimise the epitaxial growth of B6TFMO via DLI-CVD. A single-step deposition method on epitaxial substrates was developed to allow the successful synthesis of continuous 45 nm thick B6TFMO films at thicknesses relevant to applications as piezoelectric actuators, sensors and energy harvesters. These films nucleated via a layer-by-layer growth mode and were found to have a strong in-plane ferroelectric response with isotropic domains. Film purity was enhanced with utilisation of epitaxial substrate with appropriate lattice match to B6TFMO and by optimising the amount of bismuth precursor used. In this work, progress was made towards the optimisation of epitaxially grown B6TFMO films, allowing greater control of film orientation and augmenting strain-induced enhancement of multiferroic properties in future data storage devices. Overall, this research has increased understanding of the fundamental mechanisms governing the ferroelectric and ferromagnetic properties of B6TFMO. The work has elucidated some of the key requirements fundamental to the manifestation of polar topologies and has created strategies for the tailoring of novel polar topologies. This combination of new material understanding and new growth optimisation of room temperature multiferroics contributes to solving the ‘big data’ problem. Application of B6TFMO in future technologies based on ultra-high density, energy efficient memory devices, spintronic devices, multilevel resistance control (memristive and synaptic devices) and energy-efficient neuromorphic “brain inspired” devices are envisioned.
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    Ordered macroporous metal oxides and carbonaceous composites for Li-ion and beyond Li-ion batteries
    (University College Cork, 2023) Carroll, Aoife; O'Dwyer, Colm; Irish Research Council
    This thesis provides an in-depth investigation of three-dimensional ordered macroporous materials, specifically inverse opal materials, for electrochemical energy storage systems, particularly rechargeable batteries. Exploring the potential of composite structures, this research focuses on TiO2/GeO2 nanocomposites and C/TiO2 inverse opal anodes in Li-ion batteries, and carbon inverse opal anodes in Na-ion and K-ion batteries. Employing comprehensive characterization techniques, this research studies intricate material properties and electrochemical responses inherent in these structures. The composite materials exhibit promising features such as enhanced electrolyte penetration, improved specific capacities and coulombic efficiency, and robust structural integrity during extended charge-discharge cycling. The study findings shed light on the unique advantages of inverse opal composites for application in next-generation battery technologies. Highly ordered, macroporous inverse opal structures were fabricated as TiO2/GeO2 nanocomposites with varying GeO2 content, showcasing coulombic efficiency and capacity retention. The overall capacity of these interconnected binder-free anodes was affected by the Ge content and its distribution at both slow and fast rates. Characterization techniques such as X-ray diffraction, high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction, energy-dispersive X-ray spectroscopy, and electron energy loss spectroscopy were employed to analyse these anodes. The electrochemical response over 2000 cycles and at various rates elucidated the impact of the composite on key metric in battery cells. The results indicated that a composite of intercalation and alloying compounds yielded good specific capacity and excellent coulombic efficiency (>99%), even with low quantities of the GeO2. The cycling life reveals an increase in capacity with improved coulombic efficiency with suspicion that the GeO2 material becomes electrochemically active within the composite matrix, undergoing modifications during cycling. C/TiO2 composite were synthesized from sucrose as the carbon precursor to form interconnected, porous inverse opal structures. Material characterization revealed amorphous TiO2 and disordered carbon with a large pore size of ~400 nm. An atomic ratio of ~8:1 in favour of carbon yielded promising electrochemical responses with high specific capacity and capacity retention at 150 mA/g rate. Diffusion processes were shown to be the dominant contributor to current responses for all scan rates, with double-layer capacitance accounting for less than ~45 % even at the high scan rate of 1000 mV/s. When compared to individual carbon and TiO2 inverse opals the composite demonstrated improved coulombic efficiency and high-rate performance attributed to the synergistic benefits of combining these two intercalation materials. Carbon inverse opals were fabricated in a similar way from sucrose to study the effect of the macroporous structure on performance in sodium-ion and potassium-ion batteries. Composed of disordered carbon with short-range graphitic regions, the storage mechanism involved primarily diffusion processes at lower scan rate with capacitive behaviour governing the current response at faster scan rates. Structural integrity was maintained in all cells after 250 cycles showcasing impressive resistance to structural stresses. Comparing the inverse opal material to thin films of the same composition highlighted the improved capacity retention and cycling stability inherent to the three-dimensional ordered macroporous structure.
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    Multifaceted computational modelling in pharmaceutical research and development
    (University College Cork, 2023) Vinay Kumar Reddy, Cheemarla; Tiana, Davide; Lawrence, Simon; Swiss Forum for International Agricultural Research; National Institute of Neurological Disorders and Stroke
    Drug development is a multi-step process and takes around 12 to 15 years for a new drug to get approved. In the current scenario, to accelerate the drug development process and to reduce the time frame, most pharmaceutical companies have in-house developed workflows comprised of a hybrid use of computational and experimental approaches. This thesis was focused on employing state-of-the-art molecular modelling methods in three significant areas of pharmaceutical research and development. This thesis comprises an introductory part (chapter 1) and a productive part (chapter 3 to chapter 5). The first chapter of this thesis is the literature review, outlining the foundational studies and research framework used in chapters 3 to 5. The second chapter describes the thesis structure and objectives of the other three chapters. The third chapter explores the hit identification process, utilising docking to screen a small database of phytopharmaceuticals against sclerostin protein followed by an investigation of the stability of the protein-ligand complexes through standard molecular dynamics and funnel meta dynamics. The fourth chapter involves the modelling of adsorption and diffusion of doxorubicin, paclitaxel, carboplatin, and gemcitabine anticancer drugs and also drug combinations such as doxorubicin with carboplatin, paclitaxel with gemcitabine and carboplatin employing NUIG-4 metal-organic framework as drug delivery agents. In this chapter, the comprehensive understanding of molecular interactions governing drug adsorption and diffusion was studied using Grand Canonical Monte Carlo (GCMC) and Molecular Dynamics (MD) simulations. The fifth chapter focuses on investigating the mechanism of chiral Bronsted acid catalysed asymmetric synthesis of homoallyl alcohols from ortho vinyl benzaldehydes and allyl boron pinacol ester using density functional theory methods (DFT), QTAIM, and NCI analysis. Furthermore, a comparative analysis of transition structures of Ortho vinyl and ortho alkynyl benzaldehyde substrates was studied.
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    Studies in synthesis using CO2 and H2 gases
    (University College Cork, 2023) Lowry, Amy; Mcglacken, Gerard P.; Byrne, Peter; Irish Research Council; Higher Education Authority
    This thesis is split into two parts based on two different areas of research. Part 1 Part 1 is sub-divided into four chapters. Chapter 1 involves a review of the existing research conducted in this area. Chapter 2 provides details on the research carried out in this project on the development of a Wittig CO2 utilisation methodology for the synthesis of α,β unsaturated carboxylic acids. Chapter 3 involves discussion on the development of protocols for purification of the α,β-unsaturated carboxylic acids synthesised. The Conclusions and Future Work section relating to this area of research is found at the end of Chapter 3. Chapter 4 outlines the experimental work for Part 1. CO2 utilisation continues to capture the attention of chemists due to the ever-increasing levels of CO2 and the negative effects of global warming. CO2 is an inexpensive and environmentally friendly C1 building block, which can be used in the synthesis of value-added chemicals. Many medicinally important compounds and natural products contain the elements of CO2 within their structure, including carboxylic acids, enoates, and carbamates. In particular, α,β unsaturated carboxyl compounds are typically accessed by metal-catalysed transformations or condensation reactions, which often require hydrolysis of the ester product to furnish the corresponding acid. In this project, a telescoped process was developed, that not only achieves CO2 activation, but exploits a novel application of the Wittig reaction, enabling direct installation of the carboxyl group by two successive carbon-carbon bond forming events. Reaction optimisation and purification studies were carried out and 34 α,β-unsaturated carboxylic acids were synthesised using the method, containing a wide range of functional groups, as well as a number of pharmaceutical precursors, in moderate to excellent yields. As part of this work, a novel method for purification of α,β-unsaturated carboxylic acids was developed. Part 2 Part 2 is sub-divided into three chapters. Chapter 5 involves a discussion on the background of the project and a review of the existing research conducted in the area. Chapter 6 involves a discussion of the research carried out in this project on the dearomatisation of benzofuroquinolines by a Pd-catalysed hydrogenation reaction. The Conclusions and Future Work section relating to this part of the thesis is found at the end of Chapter 6. Chapter 7 outlines the experimental work for Part 2. Within the McGlacken group, development of C-H activation methodologies has been a large area of research, and, in particular, benzofuroquinolines have been synthesised via direct intramolecular arylation of 4-phenoxyquinolines. The quinoline nucleus is one of the most frequently occurring ring systems in approved drugs, and hydrogenation of the quinoline nucleus and the selectivity thereof, has been reported in the literature. In addition, increasing interest in the concept of ‘escaping flatland’, whereby the saturation of compounds is increased, allowing for the exploration of more architecturally complex molecules that will potentially give rise to enhanced biological activities. In this part of the thesis, a range of differently substituted benzofuroquinolines were hydrogenated to generate 18 selectively dearomatised benzofuroquinolines. Investigations were carried out into different reaction conditions tolerated by the reaction, and the fate of halogen substituents in the reaction. In addition, a double reduction product side-product was identified and characterised, opening up the methodology to the formation of a new class of novel compounds.
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    Macroporous metal oxide battery electrode performance analysis and operando spectroscopy
    (University College Cork, 2023) Grant, Alex; O'Dwyer, Colm; Irish Research Council for Science, Engineering and Technology
    Vast consumption of fossil fuels has catapulted greenhouse gas emissions which have contributed to increasing the global average temperature at a frightening rate. Thankfully, sun, wind and tides have massive potential to provide energy in an environmentally friendly way. However, maintaining these energy sources at the global scale required to realise the transition from fossil fuels to renewable energy is difficult, given that their supply is often location and weather dependent. Fortunately, there is a solution, and energy storage is the key to a green energy future. Currently, battery systems are the most suitable option. These systems can be implemented in large-scale grid storage facilities, electric vehicles (EVs), portable electronics like laptops and mobile phones, right down to fingernail-sized microbatteries for medical devices and hearing aids. Despite decades of research, the demand for increased functionality has grown at such a rate that the development of appropriate technology has proven difficult. Additionally, the materials typically used in production of commercial batteries such as cobalt, graphite and Li are coupled with concerns related to ethics, CO2 emissions, and availability. This thesis delves into three realms, all related to the development and optimisation of battery electrode materials, and efficient approaches to monitor their deterioration. The first realm is optical analysis of opal photonic crystals (PhCs) which are used as templates for battery electrodes. PhCs are a particular type of nanostructure which demonstrate iridescent colours when exposed to light. The observed colours originate from a phenomenon known as the photonic band gap (PBG), the band of frequencies which are reflected from the crystal. The PBG is dependent on the structure and refractive index contrast of the material. Consequently, the PBG can be controlled by changing the structural parameters of the crystal. Opals are a type of PhC which are used as templates for inverse opals (IOs), which have shown promise as battery electrodes due to their high surface area to volume ratio, thin pore walls and interconnectivity, which removes the need for conductive additives and binders. The most fascinating aspect of their potential is the correlation between their structural properties and their optical response since the primary route of battery performance deterioration is through the structural degradation of the battery electrode materials. Opals of different thicknesses can be constructed while the reflected colours remain unchanged once the periodicity of the crystal is maintained. However, the intensities of the reflected frequencies are thickness dependent. The optical response of these materials can therefore be used to determine crystal thickness, and vice versa. Optimising the electrochemical performance of IO (IO) battery electrodes requires formation of an excellent opal template which can be directed and evaluated by this non-destructive optical spectroscopy approach. With a method established for perfecting opal quality established, the second realm explores the electrochemical performance of sustainable battery systems, in the form of SnO2-based electrode materials in lithium-ion (Li-ion)and sodium-ion (Na-ion) chemistries. Li-ion is the most widely used commercial battery chemistry. As Li reserves are depleted, alternatives must be considered. Na stands as a practically infinite resource, extracted easily from sea salt. Na-ion batteries operate under similar principles to Li-ion, but optimisation of appropriate electrode materials has proved challenging. Graphite stands as the gold standard anode material for Li-ion, but its capacity is dramatically reduced in Na-ion systems. Furthermore, the carbon emissions from the processing of natural graphite and production of synthetic graphite are worrying. SnO2 is one of the thirty most abundant elements on earth and stands as a promising replacement for graphite in Na-ion batteries. However, massive volume expansion prevents its widespread adoption. Routes to overcome this volume expansion involve the design of state-of-the-art nanostructures, the route taken in this thesis using the IO architecture. While this electrochemical exploration provides an explanation of the underlying chemistry governing the rate behaviour and stability of the IO electrodes, the structural changes which arise in the electrode during cycling prompt deeper investigations. Furthermore, the rapid nature of the associated electrochemical processes prompt real-time measurements, which are addressed next in the thesis in the form of operando Raman spectroscopy. The third realm is the application of operando methods to battery performance analysis, an approach which litters the literature in recent years. Traditionally, analysis of battery electrodes and the electrolyte were performed ex-situ. The battery was disassembled, the materials were removed and analysed. Ex-situ analysis is useful prior to cycling and for postmortem analysis. A more effective analytical approach is the use of in-situ techniques. These involve stopping the battery at a certain voltage, disassembly, and analysing the electrodes and electrolyte in that state. This approach is useful for determining what changes occur to the battery at different states of charge. However, these materials are often sensitive to the environment, and the in-situ results are not representative of the state of the material prior to disassembly. Furthermore, electrochemical reactions can occur over nanoseconds or even less, while the structural changes can be short-lived. As a result, in-situ analysis can fail to capture many of the changes which occur during cycling. Operando techniques involve analysis of battery components during electrochemical cycling. Disassembly is not required, and structural changes can be tracked continuously, capturing any metastable and ultrashort phases. Operando Raman spectroscopy can be used to monitor structural changes to the electrode at the atomic scale, along with evolution of the electrolyte non-destructively. This thesis has been written to showcase the benefits of combining optical, structural, and electrochemical analysis, moving from ex-situ to operando techniques, and optimising performance of sustainable battery technologies with a view to transitioning from Li-ion to Na-ion chemistry with environmentally friendly electrode materials to develop the first PhC, lab-based operando battery diagnostics system.