Chemistry - Doctoral Theses

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    The emission and atmospheric oxidation of biogenic volatile organic compounds from Sitka spruce
    (University College Cork, 2023) Furnell, Hayley; Wenger, John; Hellebust, Stig; Irish Research Council; Environmental Protection Agency
    Biogenic volatile organic compounds (BVOCs) emitted by plants undergo chemical reactions in the atmosphere resulting in the formation of oxidised products and secondary organic aerosols (SOA), which have a large impact on climate. In this work an on-line time-of-flight chemical ionisation mass spectrometer (ToF-CIMS) was used in laboratory studies to identify the main BVOCs emitted from the main plantation tree species in Ireland, Picea Sitchensis (Sitka spruce). Experiments have also been conducted to assess the atmospheric oxidation pathways of the BVOCs emitted by Sitka spruce and their SOA formation potential. The ToF-CIMS was used in combination with off-line gas chromatography-mass spectrometry to identify the BVOC emissions from three Sitka spruce trees maintained in a plant growth chamber under conditions relevant to the Irish climate. Fifty-two of the seventy-four BVOCs emitted from Sitka spruce were oxygenated compounds, with piperitone (C10H16O), an oxygenated monoterpene, being the dominant emission. Other prevalent emissions included isoprene and five monoterpenes (myrcene, β-phellandrene, δ-limonene, α-pinene, and camphene). Temperature, light intensity and stress were all found to alter the emission profiles, with different BVOCs exhibiting different responses. At the current conditions of the Irish climate the annual BVOC flux for isoprene was found to exceed that for piperitone, although this is expected to change in a warming climate. A series of simulation chamber experiments was performed to determine, for the first time, the kinetics, products and mechanisms for the gas-phase reaction of piperitone with the main atmospheric oxidant the hydroxyl radical (OH•). The rate coefficient was determined by the relative rate method and used to calculate an atmospheric lifetime of under 2 hours. Calculations based on structure activity relationships identified the reaction with OH• as the dominant loss pathway for piperitone and was used to identify its most reactive sites. The ToF-CIMS detected thirty-three gas-phase oxidation products, and formation mechanisms for seventeen of the products have been proposed. The results from these experiments provide new and useful information on the atmospheric fate of piperitone. Oxidation experiments were also conducted with OH• on all the BVOCs emitted by a Sitka spruce tree, to identify oxidation products, reaction pathways and determine the SOA formation potential of whole Sitka spruce BVOC emissions. Eight gas-phase BVOCs were identified as key reactive emissions, and upon reaction with OH• led to the formation of twenty-five gas-phase products and ninety-nine particle-phase products. Eight of these products were identified as originating from the oxidation of piperitone, myrcene and isoprene across the gas-phase and particle-phase, with the majority of the remining products resulting from oligomerisation reactions. Rapid SOA formation was observed soon after the onset of oxidation, likely due to the formation of low volatility oxidation products which caused new particle formation. SOA yields were estimated to be around 15%. Overall, this work has produced a wealth of new information on the emission and atmospheric oxidation of BVOCs emitted from Sitka spruce, which will be valuable to decision makers in the forestry sector. Moreover, the research highlights the importance of assessing BVOC emissions and the associated SOA formation potential prior to establishing tree plantations.
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    Studies in the synthesis and impurity profiling of pharmacologically active benzodifurans
    (University College Cork, 2022) O'Connor, Richard Eric; Keating, J J; Higher Education Authority
    Substituted 2,3-dihydrobenzofuran derivatives as well as their benzofuran and benzodifuranyl analogues are versatile heterocycles that are increasing in prominence as key building blocks in organic chemistry. In particular, benzodifuran-containing structures are gaining significant interest in medicinal chemistry as pharmacophores and in industrial chemistry as scaffolds for organic electroluminescent devices, organic field-effect transistors, solar cell sensitizers and semiconducting polymers. The synthesis of pharmacologically active benzodifurans are complex multi-step processes and each individual step has the potential for considerable side-product/impurity formation. This project focused on synthetic strategies to benzofuran and benzodifuran derivatives in addition to their hydrogenated and substituted analogues. The chosen synthetic routes to target molecules further focused on the propensity of synthetic steps to produce impurities, modifiable variables to modulate impurity formation and the impurity profile of each synthetic route explored. Organic process impurities identified were isolated and fully characterised where possible, in addition to intended products.
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    Development of rapid analytical separation methods for the detection of NSAIDs in wastewater
    (University College Cork, 2023) Alatawi, Hanan; Moore, Eric; Saudi Arabian Cultural Bureau
    Recently, non-steroidal anti-inflammatory drugs (NSAIDs) have been increasingly used in humans and animals. Despite being effective against a wide variety of diseases, they pose a threat to aquatic environments. Since NSAIDs are poorly degraded and highly water-soluble, they are able to pass through all-natural filtration processes. It has been well known that conventional wastewater treatment plants (WWTPs) were not made to completely remove these compounds because they were not intended to do so. As a result, several pharmaceuticals are released back into the environment. It is essential to develop fast, simple, and reliable analytical methods for detecting NSAIDs in environmental water. Capillary electrophoresis (CE) has been used for many years to determine various classes of pharmaceuticals in various sample matrices due to its advantages of high separation efficiency and rapid analysis time. The interest in CE has led to the miniaturization of microchip electrophoresis (ME). ME has advantages over traditional analysis techniques, such as fast separation, high separation efficiency, low reagent volume, decreased waste generation, and low-power requirement (the maximum voltage that can be used is 3 kV), and its potential of portability and disposability. The goal of this project was to develop novel methods for rapid separation and detection of NSAIDs in wastewater using capillary and microchip electrophoresis with UV and C4D detections. The methods were validated using solid phase extraction(SPE), and two different cartridges (C18 and Oasis HLB) were optimized to enhance the recoveries. The results of the research project showed that NSAIDs compounds could be well separated in less than 1 min and had excellent analytical performances with LODs ranging between 0.125 and 0.5 mg/L. The microchip system has proved to be an excellent analytical technique for fast and reliable environmental applications.
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    Development of ultrasensitive electrochemical sensors based on nanocomposites for environmental applications
    (University College Cork, 2023) Albalawi, Ibtihaj; Moore, Eric; Ministry of Education – Kingdom of Saudi Arabia
    Water quality assessment is an essential component of environmental monitoring, which affects not only aquatic life but the surrounding ecosystem as well. The presence of organic and inorganic micropollutants such as carbamate pesticides and heavy metals in water is a crucial water problem generated from industrial effluents, mining wastes, or domestic sewage, and the widespread use of pesticides in pest control in the environment. In the last years, heavy metals have risen significantly, especially in the developed country where most pollutants are used. According to the World Health Organisation (WHO), with only 8 % of the world’s population, Germany, the United States, and Russia consume about 75 % of the most widely used metals in the world. The United States only consumes approximately 20 % of the metal pollutants and 25 % of the production of fossil fuels each year. Heavy metals such as lead, and cadmium are among the most critical pollutants and the focus of international legislative bodies because of their nonbiodegradability and toxicity and their long-term negative health effect. Carbamate pesticide use is extensively reported, and the trend in their use is anticipated to rise significantly in the next few decades. Among them, carbaryl is extensively applied in grain and has an adverse impact on the cellular metabolic mechanism and mitochondrial function. Moreover, the pH of the water solution is another vital factor affecting biological and chemical processes in water, which in turn affects the environment and human health. Typically, the used conventional analytical techniques are expensive and time-consuming due to sample transportation, trained personnel, and failure to deliver water quality parameters in real-time. Therefore, electrochemical sensing technology has the potential to change the way we see quality control analysis in the environment. It can provide a cheap, sensitive, portable, and easy-to-use method of application in quality control analysis. Thus, this research aims to develop multi-sensors based on screen-printed electrodes, which have characteristics of low cost, high sensitivity, selectivity, and rapid analysis. The novel methods in this research proved their efficiency to detect analytes of interest in environmental media with high sensitivity, excellent stability, short response time, and have the potential to be integrated into a multi-parameter system sensing for on-field monitoring.
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    Two-dimensional transition metal dichalcogenides as next generation semiconductor materials
    (University College Cork, 2023) Coleman, Emma M.; Hurley, Paul; Cherkaoui, Karim; O'Dwyer, Colm; SFI Manufacturing; Horizon 2020 Framework Programme; European Research Council
    In recent years 2D materials, and more specifically transition metal dichalcogenisdes (TMD) MoS2 and WS2 have been investigated in the field of semiconductors as they exhibit energy gaps which span from semi-metals through to wide band gap semiconductors. Due to their thickness on an atomic scale, their properties differ from that of their bulk counterpart. The tunability of TMD bandgaps between the monolayers and bulk allows for a broader range of physical, electronic and optical properties and can be applied to a variety of applications including sensors, photode- tectors, flexible devices, optoelectronics, electronic (logic and memory) devices and green energy. This thesis focuses on the possible use of TMDs for the 3D back end of line (BEOL) integration of logic and memory and it investigates some of these challenges to help bridge the gap in the knowledge to strive for the reality of 3D BEOL. One of the approaches examined in this thesis is the mechanical exfoliation of TMD crystals. The interface properties of WS2 or MoS2 and insulating oxides is investigated with fabricated inverted MOSCAP (metal oxide semiconductor capacitor) structures, where a heavily doped silicon substrate is used as the back gate. With a variety of different devices, the impact of boundary defects is discussed along with a proposed bulk defect effects. Another important line of work is the improvement of TMD growth. Chemical vapour deposition (CVD) is a popular TMD growth process. Though high quality TMDs have been produced by CVD, there is a lack of knowledge about how to grow at lower temperature, in order to stay within the thermal budget of 3D BEOL. We investigate CVD grown MoS2 at temperatures lower than 550 °C and perform Hall data on transistors which provides positive mobility values and carrier concentrations. The significance of this work also shows findings in the nanoelectronic operation of atomic layer deposition (ALD) WS2. Insight is gained from Hall effect analysis and temperature dependent electronic studies, which are lacking in literature. Typically, for WS2 thin-films, the mobility values reported to date have been field effect mobility values extracted from transistor characteristics. More specifically, data includes the similarity of contact and sheet resistance temperature dependence in the WS2 device, indicating that both are dominated by the WS2 hole concentration temperature dependence. Moreover, rarely reported change in the TMD material, such as sheet resistance, due to device fabrication, is attributed to the chemicals and thermal treatments required to form the electronic devices. Finally, the aim of investigating laser annealed MoS2 was to show an in-depth investigation into synthetizing crystalline MoS2 layers on wafer scale area, where MoS2 films deposited on Si and Si/SiO2 surfaces are explored. This method shows that within the correct parameter range, the process can produce crystalline MoS2 films with small domains size of around 3.5 nm, from an initially amorphous MoS2 film. Field effect transistors formed in laser annealed MoS2 show limited Ids variation with Vgs consistent with the small domain size.