Statistical learning methods for photovoltaic energy output prediction
- Authors: Magaya, Aphiwe
- Date: 2024-04
- Subjects: Photovoltaic power generation , Mathematical statistics , Statistics
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/64138 , vital:73656
- Description: Predicting solar energy accurately is important for the integration of more renewable energy into the grid, which can help to alleviate the energy demand on traditional coal-powered sources in South Africa. This study aims to assess several statistical learning models to predict the energy output of a 1MW photovoltaic system installed on the Nelson Mandela University South Campus in Gqeberha. Weather data (including temperature, wind speed, wind direction, precipitation, air pressure, and humidity) and solar irradiance data (including global horizontal radiation, diffuse radiation, and direct radiation) are used to predict the energy output of this system using Artificial Neural Networks (ANN), Support Vector Machines (SVM), Multiple Linear Regression (MLR), and Regression Trees (RT). The performance of each of the models was compared and the results indicated that the ANN model performed best. , Thesis (MSc) -- Faculty of Science, School of Computer Science, Mathematics, Physics and Statistics, 2024
- Full Text:
- Date Issued: 2024-04
- Authors: Magaya, Aphiwe
- Date: 2024-04
- Subjects: Photovoltaic power generation , Mathematical statistics , Statistics
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/64138 , vital:73656
- Description: Predicting solar energy accurately is important for the integration of more renewable energy into the grid, which can help to alleviate the energy demand on traditional coal-powered sources in South Africa. This study aims to assess several statistical learning models to predict the energy output of a 1MW photovoltaic system installed on the Nelson Mandela University South Campus in Gqeberha. Weather data (including temperature, wind speed, wind direction, precipitation, air pressure, and humidity) and solar irradiance data (including global horizontal radiation, diffuse radiation, and direct radiation) are used to predict the energy output of this system using Artificial Neural Networks (ANN), Support Vector Machines (SVM), Multiple Linear Regression (MLR), and Regression Trees (RT). The performance of each of the models was compared and the results indicated that the ANN model performed best. , Thesis (MSc) -- Faculty of Science, School of Computer Science, Mathematics, Physics and Statistics, 2024
- Full Text:
- Date Issued: 2024-04
Synthesis and applications of hydroxyl-functionalized chemosensors for selective detection of ions in aqueous systems
- Authors: Hamukoshi, Simeon Shiweda
- Date: 2024-04
- Subjects: Molecular recognition , Solution (Chemistry) , Water chemistry
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/63787 , vital:73613
- Description: Fluorescent molecular chemosensors are crucial tools for monitoring toxic metal ions and environmental compounds that pose risks to both humans and wildlife. Continuous sensing is essential for early detection, and chemosensors offer a sensitive and straightforward approach by detecting challenging analyte’s through optical absorption and fluorescence. Current detection methods, such as flame photometry and mass spectrometry, can be expensive, destructive, and impractical for continuous monitoring. Consequently, fluorescent-based methods present a promising, simple, and highly sensitive alternative for chemical recognition and monitoring. In this project, we successfully synthesized ten highly selective small hydroxyl containing molecule fluorescent and colorimetric sensors; Oxime Dye (OD), Small Sensor 1 (SS1), Small Sensor 2 (SS2), Quinoline Dye 1 (QD1), Quinoline Dye 2 (QD2), Quinoline Dye 3 (QD3), Coumarin Dye 1 (CD1), Coumarin Dye 2 (CD2), Naphthalene Dye 1 (ND1), Naphthalene Dye 2 (ND2). These chemosensors contained benzothiazole, naphthalene, quinoline, and coumarin fluorophores. These sensors facilitate both quantitative and qualitative assessment of cationic and anionic species in aqueous organic media. The chemosensors were synthesized using modified Schiff base, azo dye, and oxime-based reactions, enhancing binding and selectivity with analyte’s. They exhibited selectivity towards various metal ions (Cu2+, Fe2+, Ni2+, and Hg2+) and anions (hydroxyl and cyanate), characterized by distinct absorption bands and significant fluorescent quenching and enhancement. While some sensors were selective towards both cations and anions, others exclusively targeted cations, showing lower selectivity or sensitivity towards anions upon further testing. Conversely, certain sensors were selective towards anions, demonstrating reduced sensitivity or selectivity towards the tested cations. The oxime-based chemosensor, OD, was obtained through an oxime-based reaction. The sensor demonstrates remarkable selectivity for Cu2+ and cyanate ions. During titration experiments, the interaction of Cu2+ with OD resulted in a noticeable fluorescence quenching effect, while the presence of OCN ions led to fluorescence enhancement. These distinct behaviors strongly suggest the formation of specific 1:1 complexes between OD and Cu2+ or OCN ions, a conclusion supported by detailed analysis using the Jobs plot technique. In addition to the fluorescence studies, investigations into the influence of pH on the sensor OD, as well as its complexes with Cu2+ and OCN, were conducted to determine the optimum pH conditions for their operation. Moreover, reversible behavior of the complexes was explored in the presence of EDTA, revealing that only the OD-OCN complex displayed reversibility. Furthermore, molecular modeling studies were performed to validate the binding units and calculate the energy differences between the sensor and its respective complexes. Additionally, four chemosensors (SS1, SS2, CD2, and QD2) were synthesized and characterized using Schiff-based reactions, showcasing their unique absorption behaviors. SS1 and SS2, characterized by benzothiazole fluorophores, demonstrated high sensitivity to hydroxyl anions. Jobs plot studies revealed a stable 1:1 binding stoichiometry. Chemosensor CD2, incorporating a coumarin fluorophore, was structurally confirmed but showed no significant spectral changes when screened with various ions. Chemosensor QD2 exhibited remarkable selectivity for Fe2+ ions, and stable 1:1 complexes were confirmed. Further molecular modeling studies were conducted to identify potential binding sites. Furthermore, five chemosensors (CD1, CD3, QD1, ND1, and ND2) were synthesized and characterized using azo dye reactions, revealing their unique absorption behaviors. Chemosensor CD1 showed high selectivity towards Hg2+ under both absorption and emission spectroscopy. Job's plot studies confirmed a stable 1:1 complex formation. The presence of competing cations did not affect complex formation, emphasizing its stability and selectivity. Another coumarin-containing dye chemosensor, CD3, was synthesized as a novel chemosensor. In the presence of TBA anionic solutions, CD3 exhibited strong absorption bands and selectivity for OH- ions, forming a stable complex with them. Quantitative studies, including the determination of LOD and LOQ, were also conducted. The binding stoichiometry of 1:1 between CD3 and OH- was established through Job's plot analysis. Lastly, two naphthalene dyes were synthesized. However, they did not exhibit selectivity towards cations or anions. Interestingly, their absorption spectra were affected by the change in solvent system, a concept worth exploring in future work. Chemosensor ND1 and ND2 did not show any cation or anion selectivity. However, they demonstrated different spectra and colour responses to cations and anions in different water-DMSO solvent systems. , Thesis (PhD) -- Faculty of Science, School of Biomolecular & Chemical Sciences, 2024
- Full Text:
- Date Issued: 2024-04
- Authors: Hamukoshi, Simeon Shiweda
- Date: 2024-04
- Subjects: Molecular recognition , Solution (Chemistry) , Water chemistry
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/63787 , vital:73613
- Description: Fluorescent molecular chemosensors are crucial tools for monitoring toxic metal ions and environmental compounds that pose risks to both humans and wildlife. Continuous sensing is essential for early detection, and chemosensors offer a sensitive and straightforward approach by detecting challenging analyte’s through optical absorption and fluorescence. Current detection methods, such as flame photometry and mass spectrometry, can be expensive, destructive, and impractical for continuous monitoring. Consequently, fluorescent-based methods present a promising, simple, and highly sensitive alternative for chemical recognition and monitoring. In this project, we successfully synthesized ten highly selective small hydroxyl containing molecule fluorescent and colorimetric sensors; Oxime Dye (OD), Small Sensor 1 (SS1), Small Sensor 2 (SS2), Quinoline Dye 1 (QD1), Quinoline Dye 2 (QD2), Quinoline Dye 3 (QD3), Coumarin Dye 1 (CD1), Coumarin Dye 2 (CD2), Naphthalene Dye 1 (ND1), Naphthalene Dye 2 (ND2). These chemosensors contained benzothiazole, naphthalene, quinoline, and coumarin fluorophores. These sensors facilitate both quantitative and qualitative assessment of cationic and anionic species in aqueous organic media. The chemosensors were synthesized using modified Schiff base, azo dye, and oxime-based reactions, enhancing binding and selectivity with analyte’s. They exhibited selectivity towards various metal ions (Cu2+, Fe2+, Ni2+, and Hg2+) and anions (hydroxyl and cyanate), characterized by distinct absorption bands and significant fluorescent quenching and enhancement. While some sensors were selective towards both cations and anions, others exclusively targeted cations, showing lower selectivity or sensitivity towards anions upon further testing. Conversely, certain sensors were selective towards anions, demonstrating reduced sensitivity or selectivity towards the tested cations. The oxime-based chemosensor, OD, was obtained through an oxime-based reaction. The sensor demonstrates remarkable selectivity for Cu2+ and cyanate ions. During titration experiments, the interaction of Cu2+ with OD resulted in a noticeable fluorescence quenching effect, while the presence of OCN ions led to fluorescence enhancement. These distinct behaviors strongly suggest the formation of specific 1:1 complexes between OD and Cu2+ or OCN ions, a conclusion supported by detailed analysis using the Jobs plot technique. In addition to the fluorescence studies, investigations into the influence of pH on the sensor OD, as well as its complexes with Cu2+ and OCN, were conducted to determine the optimum pH conditions for their operation. Moreover, reversible behavior of the complexes was explored in the presence of EDTA, revealing that only the OD-OCN complex displayed reversibility. Furthermore, molecular modeling studies were performed to validate the binding units and calculate the energy differences between the sensor and its respective complexes. Additionally, four chemosensors (SS1, SS2, CD2, and QD2) were synthesized and characterized using Schiff-based reactions, showcasing their unique absorption behaviors. SS1 and SS2, characterized by benzothiazole fluorophores, demonstrated high sensitivity to hydroxyl anions. Jobs plot studies revealed a stable 1:1 binding stoichiometry. Chemosensor CD2, incorporating a coumarin fluorophore, was structurally confirmed but showed no significant spectral changes when screened with various ions. Chemosensor QD2 exhibited remarkable selectivity for Fe2+ ions, and stable 1:1 complexes were confirmed. Further molecular modeling studies were conducted to identify potential binding sites. Furthermore, five chemosensors (CD1, CD3, QD1, ND1, and ND2) were synthesized and characterized using azo dye reactions, revealing their unique absorption behaviors. Chemosensor CD1 showed high selectivity towards Hg2+ under both absorption and emission spectroscopy. Job's plot studies confirmed a stable 1:1 complex formation. The presence of competing cations did not affect complex formation, emphasizing its stability and selectivity. Another coumarin-containing dye chemosensor, CD3, was synthesized as a novel chemosensor. In the presence of TBA anionic solutions, CD3 exhibited strong absorption bands and selectivity for OH- ions, forming a stable complex with them. Quantitative studies, including the determination of LOD and LOQ, were also conducted. The binding stoichiometry of 1:1 between CD3 and OH- was established through Job's plot analysis. Lastly, two naphthalene dyes were synthesized. However, they did not exhibit selectivity towards cations or anions. Interestingly, their absorption spectra were affected by the change in solvent system, a concept worth exploring in future work. Chemosensor ND1 and ND2 did not show any cation or anion selectivity. However, they demonstrated different spectra and colour responses to cations and anions in different water-DMSO solvent systems. , Thesis (PhD) -- Faculty of Science, School of Biomolecular & Chemical Sciences, 2024
- Full Text:
- Date Issued: 2024-04
Synthesis and applications of novel coumarin-based chemosensors for the detection of metal ions using UV-visible spectroscopy
- Authors: Myburgh, Lisa
- Date: 2024-04
- Subjects: Biosensors , Molecular recognition , Chemical detectors
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/64239 , vital:73668
- Description: Current methods for ion detection are expensive and require trained personnel to operate the instruments. This led to the desire for alternative techniques that are quicker, easier to operate, cheaper, and highly efficient. With this in mind, coumarinbased derivatives were designed and synthesised using Knoevenagel condensation. These compounds were designed to incorporate different functional groups at the 3- position. Compounds S1, S2, and S3 contained keto, ester, and carboxylic acid groups, respectively. The structures of these compounds were confirmed using NMR, FT-IR, and X-ray crystal structures. During UV-Vis analysis, these compounds displayed a maximum absorption band between λmax= 289 and 295 nm, attributed to the coumarin moiety. Furthermore, the absorption behaviour of S2 was analysed in different solvent systems. It was noted that when S2 was dissolved in toluene, a significant absorbance increase and a hypsochromic shift were observed. The chemosensing capabilities of S1, S2 and S3 were investigated using UV-Vis for metal cations in acetonitrile. S1 and S3 showed selectivities towards Fe²⁺ ions, with S2 being selective for Fe³⁺ ions in a 1:1 binding ratio. Reversibility studies were performed using EDTA and revealed that S1 and S3 were partially reversible, with S2 showing nonreversibility properties. Lastly, the binding modes of these compounds with metal ions were determined using molecular modelling studies. These calculations concluded that the complexation occurs via the two carbonyl moieties from the coumarin ring and the ester group and is stabilised by nitrate counterions and water molecules. To change the selectivity of S2 towards Hg2+ ions, thiocarbonyl analogues of this compound were synthesised using Lawessons reagent. The reagent replaced the carbonyl oxygen of the coumarin backbone and the ester moiety with sulphur to form their respective analogues, S5 and S6. A switch in the selectivity of S5 and S6 was noted when tested as potential chemosensors for metal ions. S5 showed a high affinity for Hg²⁺, whereas S6 strongly interacted with both Hg²⁺ and Cu²⁺ ions in a 1:1 binding ratio. The mode of interaction was confirmed to occur between the thiocarbonyl and ester carbonyl group for S5 and between the two thiocarbonyl functional groups in S6. The viability of these novel chemosensors for detecting metal ions was then further tested in water samples obtained from local dams with positive results. , Thesis (MSc) -- Faculty of Science, School of Biomolecular & Chemical Sciences, 2024
- Full Text:
- Date Issued: 2024-04
- Authors: Myburgh, Lisa
- Date: 2024-04
- Subjects: Biosensors , Molecular recognition , Chemical detectors
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/64239 , vital:73668
- Description: Current methods for ion detection are expensive and require trained personnel to operate the instruments. This led to the desire for alternative techniques that are quicker, easier to operate, cheaper, and highly efficient. With this in mind, coumarinbased derivatives were designed and synthesised using Knoevenagel condensation. These compounds were designed to incorporate different functional groups at the 3- position. Compounds S1, S2, and S3 contained keto, ester, and carboxylic acid groups, respectively. The structures of these compounds were confirmed using NMR, FT-IR, and X-ray crystal structures. During UV-Vis analysis, these compounds displayed a maximum absorption band between λmax= 289 and 295 nm, attributed to the coumarin moiety. Furthermore, the absorption behaviour of S2 was analysed in different solvent systems. It was noted that when S2 was dissolved in toluene, a significant absorbance increase and a hypsochromic shift were observed. The chemosensing capabilities of S1, S2 and S3 were investigated using UV-Vis for metal cations in acetonitrile. S1 and S3 showed selectivities towards Fe²⁺ ions, with S2 being selective for Fe³⁺ ions in a 1:1 binding ratio. Reversibility studies were performed using EDTA and revealed that S1 and S3 were partially reversible, with S2 showing nonreversibility properties. Lastly, the binding modes of these compounds with metal ions were determined using molecular modelling studies. These calculations concluded that the complexation occurs via the two carbonyl moieties from the coumarin ring and the ester group and is stabilised by nitrate counterions and water molecules. To change the selectivity of S2 towards Hg2+ ions, thiocarbonyl analogues of this compound were synthesised using Lawessons reagent. The reagent replaced the carbonyl oxygen of the coumarin backbone and the ester moiety with sulphur to form their respective analogues, S5 and S6. A switch in the selectivity of S5 and S6 was noted when tested as potential chemosensors for metal ions. S5 showed a high affinity for Hg²⁺, whereas S6 strongly interacted with both Hg²⁺ and Cu²⁺ ions in a 1:1 binding ratio. The mode of interaction was confirmed to occur between the thiocarbonyl and ester carbonyl group for S5 and between the two thiocarbonyl functional groups in S6. The viability of these novel chemosensors for detecting metal ions was then further tested in water samples obtained from local dams with positive results. , Thesis (MSc) -- Faculty of Science, School of Biomolecular & Chemical Sciences, 2024
- Full Text:
- Date Issued: 2024-04
Synthesis of gatifloxacin, an important fluoroquinolone antibiotic using continuous flow technology
- Authors: Moyo, McQuillan
- Date: 2024-04
- Subjects: Antibiotics , Drug resistance in microorganisms , Chemical processes
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10948/64204 , vital:73664
- Description: Gatifloxacin belongs to an important class of antibiotics known as fluoroquinolones (the fourth generation). Bristol-Myers Squibb (BMS) introduced gatifloxacin to the market in 1999 under the brand name Tequin® for treating respiratory tract infections. It has recently been widely employed as an ophthalmic solution for treating bacterial conjunctivitis. There is limited literature describing the complete synthesis of gatifloxacin; however, ciprofloxacin, a similar fluoroquinolone, has received much attention recently and is a good guide in the synthesis. Even though there are several similarities between ciprofloxacin and gatifloxacin, key reactions towards the synthesis of gatifloxacin have not been reported, which forms a knowledge gap, for instance, the three steps leading to the synthesis of the benzoyl chloride intermediate. It is estimated that 70-90 % of the active pharmaceutical ingredients (APIs) in drugs consumed in sub-Saharan Africa are imported, mainly from India, China and Europe. To reduce dependence and improve access to life-saving drugs, Africa needs to develop cutting-edge technology that is more advanced than traditional means. We envisage that employing continuous flow technology in synthesising gatifloxacin, previously developed in a batch setup, will offer an improved, future-proof process. Thus, this research aimed to create a more efficient multi-step continuous flow process for synthesising gatifloxacin compared to the current batch methods. The first chapter of this thesis provides an extensive literature review on the synthesis of gatifloxacin and its sister drug, ciprofloxacin. The foreground is based on the manufacture and consumption of APIs, particularly antibiotics. Continuous flow technology is also introduced and discussed as the solution to bridging the gap in Africa’s demand for API manufacturing, which significantly lags. Chapter two describes the results and discusses findings on the continuous flow synthesis of gatifloxacin. A seven-step process is described with reaction optimisation studies for each step, starting from 2,4,5-trifluoro-3-hydroxybenzoic acid. An alternative shorter route (with six steps) is also offered, incorporating microwave-assisted technology instead of the traditional batch process. We also describe several elegant multistep processes for synthesising gatifloxacin and its intermediates, achieved by combining several compatible, optimised steps. Subsequently, Chapter 3 describes all the experimental details of our research. In this study, efficient continuous flow procedures were developed to synthesise gatifloxacin. The seven-step continuous flow procedure we developed afforded gatifloxacin (54 % overall isolated yield) in a total residence time of 15.6 mins, a significant improvement from the reported batch process (52 % overall yield and over 103 hours reaction time). , Thesis (PhD) -- Faculty of Science, School of Biomolecular & Chemical Sciences, 2024
- Full Text:
- Date Issued: 2024-04
- Authors: Moyo, McQuillan
- Date: 2024-04
- Subjects: Antibiotics , Drug resistance in microorganisms , Chemical processes
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10948/64204 , vital:73664
- Description: Gatifloxacin belongs to an important class of antibiotics known as fluoroquinolones (the fourth generation). Bristol-Myers Squibb (BMS) introduced gatifloxacin to the market in 1999 under the brand name Tequin® for treating respiratory tract infections. It has recently been widely employed as an ophthalmic solution for treating bacterial conjunctivitis. There is limited literature describing the complete synthesis of gatifloxacin; however, ciprofloxacin, a similar fluoroquinolone, has received much attention recently and is a good guide in the synthesis. Even though there are several similarities between ciprofloxacin and gatifloxacin, key reactions towards the synthesis of gatifloxacin have not been reported, which forms a knowledge gap, for instance, the three steps leading to the synthesis of the benzoyl chloride intermediate. It is estimated that 70-90 % of the active pharmaceutical ingredients (APIs) in drugs consumed in sub-Saharan Africa are imported, mainly from India, China and Europe. To reduce dependence and improve access to life-saving drugs, Africa needs to develop cutting-edge technology that is more advanced than traditional means. We envisage that employing continuous flow technology in synthesising gatifloxacin, previously developed in a batch setup, will offer an improved, future-proof process. Thus, this research aimed to create a more efficient multi-step continuous flow process for synthesising gatifloxacin compared to the current batch methods. The first chapter of this thesis provides an extensive literature review on the synthesis of gatifloxacin and its sister drug, ciprofloxacin. The foreground is based on the manufacture and consumption of APIs, particularly antibiotics. Continuous flow technology is also introduced and discussed as the solution to bridging the gap in Africa’s demand for API manufacturing, which significantly lags. Chapter two describes the results and discusses findings on the continuous flow synthesis of gatifloxacin. A seven-step process is described with reaction optimisation studies for each step, starting from 2,4,5-trifluoro-3-hydroxybenzoic acid. An alternative shorter route (with six steps) is also offered, incorporating microwave-assisted technology instead of the traditional batch process. We also describe several elegant multistep processes for synthesising gatifloxacin and its intermediates, achieved by combining several compatible, optimised steps. Subsequently, Chapter 3 describes all the experimental details of our research. In this study, efficient continuous flow procedures were developed to synthesise gatifloxacin. The seven-step continuous flow procedure we developed afforded gatifloxacin (54 % overall isolated yield) in a total residence time of 15.6 mins, a significant improvement from the reported batch process (52 % overall yield and over 103 hours reaction time). , Thesis (PhD) -- Faculty of Science, School of Biomolecular & Chemical Sciences, 2024
- Full Text:
- Date Issued: 2024-04
The Algoa Bay region groundwater cycle – linking source to coast
- Authors: Dodd, Carla
- Date: 2024-04
- Subjects: Ecohydrology , Hydrology , Groundwater -- Management
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/63722 , vital:73592
- Description: Groundwater is a crucial component of freshwater supply globally, especially in water-scarce regions such as semi-arid climatic areas where surface water resources are climatically limited and further constrained during droughts. Groundwater resources are also important from an ecological perspective as they support numerous surface ecosystems including wetlands and rivers. Coastal groundwater discharge along the South African coast sustains supratidal spring-fed living microbialite ecosystems (SSLiME). These systems act as potential analogues for Earth’s earliest ecosystems and are therefore useful from a palaeoscientific and evolutionary perspective. The Southern Cape coast of South Africa is characterised by both fractured and intergranular aquifers and hosts the most extensive network of SSLiME reported globally. However, the region is frequently affected by water scarcity crises and consequently groundwater development and usage has increased. Yet, it is unclear to what extent coastal discharge is linked to inland aquifers and whether anthropogenic activities influence the quantity and quality of groundwater that flows into SSLiME. This thesis aims to assess the groundwater cycle of the Algoa Bay region along the Southern Cape coast by means of a multi-tracer study. Specifically, it endeavours to develop a better understanding of the hydrogeochemical connectivity between inland groundwater resources and coastal microbialite ecosystems. To achieve this, four groups of hydrochemical tracers were used: H- and O-isotope ratios, major cations and anions, organic micropollutants and macronutrients. Sampling strategies included monthly precipitation collection over twelve months (stable water isotopes), once-off groundwater collection from boreholes, inland springs and coastal discharge (all tracers). In addition, coastal groundwater discharge was sampled during a once-off repeat campaign (all tracers) and seasonally at selected sites (macronutrients). A local meteoric water line (LMWL) for the region was established and compared to the isotopic signature of groundwater. The results indicate that groundwater is likely recharged directly and with little evaporation. Furthermore, similarities in isotopic signatures between inland and coastal aquifer systems suggest some level of hydrogeological connectivity or similar environmental drivers of recharge, such as precipitation amount and moisture source. This is also supported by the physico-chemistry and major ionic composition of the groundwater samples. However, the major ion composition of groundwater is variable and, although it predominantly reflects the sodium-chloride nature of precipitation, lithological and spatial trends are apparent. For example, coastward trends such as increasing conductivity, calcium, total alkalinity, and nitrogen is evident. While isotopes and major ions inform on the environmental drivers and geogenic influence on groundwater recharge, the organic micropollutants and macronutrients provide insight into the nature of anthropogenic impacts on groundwater quality. Micropollutants quantified in the groundwater samples included artificial sweeteners, pharmaceuticals, a biocide, and an illicit drug. These compounds are mostly classed as wastewater indicators and indicate aquifer contamination from leaking reticulation systems and septic tanks. The highest concentrations are associated with the urban and coastal peri-urban areas, while groundwater from rural areas is often devoid of any micropollutants except sulfamic acid, which may be introduced during recharge from precipitation. Furthermore, the presence of selected compounds in groundwater discharge signifies that at least a component of the groundwater is derived from recent infiltration. Similarly, the macronutrient content of groundwater reflects the proximal land use. As such, coastal groundwater discharge sites adjacent to coastal villages reflect higher concentrations compared to rural sites. In addition, the nutrient load supplied to and discharged from SSLiME systems is quantified and the nutrient attenuation is estimated. This thesis contributes recent hydrogeochemical information for a structurally complex semi-arid area under both natural (drought conditions) and human (increased water use, degradation of aquifers) pressures. Collectively, the results indicate that coastal groundwater discharge is likely a mixture of both the intergranular and fractured aquifers and that anthropogenic activities in the hinterland is contaminating the groundwater. This study is an important addition to the baseline hydrological information available for the region and may be useful in terms of sustainable groundwater management strategies and development toward a socio-ecological optimum, especially as related to coastal microbialite system. , Thesis (PhD) -- Faculty of Science, School of Environmental Sciences, 2024
- Full Text:
- Date Issued: 2024-04
- Authors: Dodd, Carla
- Date: 2024-04
- Subjects: Ecohydrology , Hydrology , Groundwater -- Management
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/63722 , vital:73592
- Description: Groundwater is a crucial component of freshwater supply globally, especially in water-scarce regions such as semi-arid climatic areas where surface water resources are climatically limited and further constrained during droughts. Groundwater resources are also important from an ecological perspective as they support numerous surface ecosystems including wetlands and rivers. Coastal groundwater discharge along the South African coast sustains supratidal spring-fed living microbialite ecosystems (SSLiME). These systems act as potential analogues for Earth’s earliest ecosystems and are therefore useful from a palaeoscientific and evolutionary perspective. The Southern Cape coast of South Africa is characterised by both fractured and intergranular aquifers and hosts the most extensive network of SSLiME reported globally. However, the region is frequently affected by water scarcity crises and consequently groundwater development and usage has increased. Yet, it is unclear to what extent coastal discharge is linked to inland aquifers and whether anthropogenic activities influence the quantity and quality of groundwater that flows into SSLiME. This thesis aims to assess the groundwater cycle of the Algoa Bay region along the Southern Cape coast by means of a multi-tracer study. Specifically, it endeavours to develop a better understanding of the hydrogeochemical connectivity between inland groundwater resources and coastal microbialite ecosystems. To achieve this, four groups of hydrochemical tracers were used: H- and O-isotope ratios, major cations and anions, organic micropollutants and macronutrients. Sampling strategies included monthly precipitation collection over twelve months (stable water isotopes), once-off groundwater collection from boreholes, inland springs and coastal discharge (all tracers). In addition, coastal groundwater discharge was sampled during a once-off repeat campaign (all tracers) and seasonally at selected sites (macronutrients). A local meteoric water line (LMWL) for the region was established and compared to the isotopic signature of groundwater. The results indicate that groundwater is likely recharged directly and with little evaporation. Furthermore, similarities in isotopic signatures between inland and coastal aquifer systems suggest some level of hydrogeological connectivity or similar environmental drivers of recharge, such as precipitation amount and moisture source. This is also supported by the physico-chemistry and major ionic composition of the groundwater samples. However, the major ion composition of groundwater is variable and, although it predominantly reflects the sodium-chloride nature of precipitation, lithological and spatial trends are apparent. For example, coastward trends such as increasing conductivity, calcium, total alkalinity, and nitrogen is evident. While isotopes and major ions inform on the environmental drivers and geogenic influence on groundwater recharge, the organic micropollutants and macronutrients provide insight into the nature of anthropogenic impacts on groundwater quality. Micropollutants quantified in the groundwater samples included artificial sweeteners, pharmaceuticals, a biocide, and an illicit drug. These compounds are mostly classed as wastewater indicators and indicate aquifer contamination from leaking reticulation systems and septic tanks. The highest concentrations are associated with the urban and coastal peri-urban areas, while groundwater from rural areas is often devoid of any micropollutants except sulfamic acid, which may be introduced during recharge from precipitation. Furthermore, the presence of selected compounds in groundwater discharge signifies that at least a component of the groundwater is derived from recent infiltration. Similarly, the macronutrient content of groundwater reflects the proximal land use. As such, coastal groundwater discharge sites adjacent to coastal villages reflect higher concentrations compared to rural sites. In addition, the nutrient load supplied to and discharged from SSLiME systems is quantified and the nutrient attenuation is estimated. This thesis contributes recent hydrogeochemical information for a structurally complex semi-arid area under both natural (drought conditions) and human (increased water use, degradation of aquifers) pressures. Collectively, the results indicate that coastal groundwater discharge is likely a mixture of both the intergranular and fractured aquifers and that anthropogenic activities in the hinterland is contaminating the groundwater. This study is an important addition to the baseline hydrological information available for the region and may be useful in terms of sustainable groundwater management strategies and development toward a socio-ecological optimum, especially as related to coastal microbialite system. , Thesis (PhD) -- Faculty of Science, School of Environmental Sciences, 2024
- Full Text:
- Date Issued: 2024-04
The Camdeboo-Mountain Zebra mega-reserve as an opportunity to protect viable populations of medium- to large-sized mammals
- Authors: Davis, Kristen
- Date: 2024-04
- Subjects: Mammals -- Ecology -- South Africa -- Eastern Cape , Conservation of natural resources -- South Africa -- Eastern Cape , Wildlife conservation -- South Africa -- Eastern Cape
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/63711 , vital:73590
- Description: Conservation planning has focused extensively on representation of species in protected areas (PAs), rather than achieving the persistence of these species in PAs. Consequently, most PAs do not support viable populations of many species represented within them, particularly large mammals, resulting in extinction debt risks. The challenge is therefore to identify opportunities to achieve viable populations and to develop and implement conservation plans to achieve this, e.g., expand and connect existing PAs. A recent meta-analysis provides a minimum viable population (MVP) estimate of 5 000 individuals for mammals. This value was used as the target for modelling conservation opportunities for the South African endemic Cape mountain zebra (Equus zebra zebra), blesbok (Damaliscus pygargus phillipsi), black wildebeest (Connochaetes gnou) and co-existing medium- and large-sized mammal species. This study focused on the region between the Camdeboo and Mountain Zebra national parks (ca. 736 000 ha). Within the envisaged Camdeboo-Mountain Zebra (C-MZ) mega-reserve, a spreadsheet model was used to estimate potential herbivore population sizes, spatial requirement data were used to estimate potential omnivore and insectivore population sizes, and herbivore densities were used to estimate potential large carnivore population sizes. I show that 12 (the three endemic grazers and nine co-existing species) of the 28 modelled medium- and large-sized mammal species will potentially exceed 5 000 individuals, the MVP target, within the envisaged mega-reserve. The remaining 16 species show potential to reach substantial population sizes, however, will likely require ongoing metapopulation management. Using a conservation planning approach, I identify priority areas for the conservation of suitable habitat for Cape mountain zebra, blesbok, and black wildebeest within the envisaged mega-reserve, thus indirectly identifying priority areas for the conservation of these endemic species. I show that the potential incorporation of these priority areas within the envisaged mega-reserve will contribute considerably to the conservation of all focal species. In addition, the potential incorporation of these priority areas will contribute to PA expansion and significantly improve connectivity between existing PAs within the envisaged C-MZ mega-reserve. The importance of adequately-sized PAs to support viable populations of focal species is thus evident, and will ensure their long-term survival and ability to persist by allowing population and evolutionary scale processes. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2024
- Full Text:
- Date Issued: 2024-04
- Authors: Davis, Kristen
- Date: 2024-04
- Subjects: Mammals -- Ecology -- South Africa -- Eastern Cape , Conservation of natural resources -- South Africa -- Eastern Cape , Wildlife conservation -- South Africa -- Eastern Cape
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/63711 , vital:73590
- Description: Conservation planning has focused extensively on representation of species in protected areas (PAs), rather than achieving the persistence of these species in PAs. Consequently, most PAs do not support viable populations of many species represented within them, particularly large mammals, resulting in extinction debt risks. The challenge is therefore to identify opportunities to achieve viable populations and to develop and implement conservation plans to achieve this, e.g., expand and connect existing PAs. A recent meta-analysis provides a minimum viable population (MVP) estimate of 5 000 individuals for mammals. This value was used as the target for modelling conservation opportunities for the South African endemic Cape mountain zebra (Equus zebra zebra), blesbok (Damaliscus pygargus phillipsi), black wildebeest (Connochaetes gnou) and co-existing medium- and large-sized mammal species. This study focused on the region between the Camdeboo and Mountain Zebra national parks (ca. 736 000 ha). Within the envisaged Camdeboo-Mountain Zebra (C-MZ) mega-reserve, a spreadsheet model was used to estimate potential herbivore population sizes, spatial requirement data were used to estimate potential omnivore and insectivore population sizes, and herbivore densities were used to estimate potential large carnivore population sizes. I show that 12 (the three endemic grazers and nine co-existing species) of the 28 modelled medium- and large-sized mammal species will potentially exceed 5 000 individuals, the MVP target, within the envisaged mega-reserve. The remaining 16 species show potential to reach substantial population sizes, however, will likely require ongoing metapopulation management. Using a conservation planning approach, I identify priority areas for the conservation of suitable habitat for Cape mountain zebra, blesbok, and black wildebeest within the envisaged mega-reserve, thus indirectly identifying priority areas for the conservation of these endemic species. I show that the potential incorporation of these priority areas within the envisaged mega-reserve will contribute considerably to the conservation of all focal species. In addition, the potential incorporation of these priority areas will contribute to PA expansion and significantly improve connectivity between existing PAs within the envisaged C-MZ mega-reserve. The importance of adequately-sized PAs to support viable populations of focal species is thus evident, and will ensure their long-term survival and ability to persist by allowing population and evolutionary scale processes. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2024
- Full Text:
- Date Issued: 2024-04
The demographic-specific prey preferences of lions and cheetahs, and potential impacts on prey populations
- Authors: Dreyer, Nicola Bondi
- Date: 2024-04
- Subjects: Predation (Biology) , Animal populations , Animal ecology
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/63733 , vital:73593
- Description: Understanding prey selection offers predictive insights into predator-prey interactions, which can be extended to explore the impacts of predators on prey populations. Prey availability and vulnerability vary across species, demographic classes, body sizes, and seasons. Traditional prey selection models for large carnivores, based on estimates of prey body size, assume uniform vulnerability across prey demographic classes and seasons, failing to account for these variations. This study aims to contrast seasonal shifts in demographic-specific prey preferences between lions and cheetahs and examine the potential impact of their demographic-specific predation patterns on a range of prey species across a body size spectrum. It was predicted that cheetahs would shift their selection from adults and juveniles of smaller prey species in the dry season to neonates and juveniles of both smaller and larger prey species in the wet season, while lions would select adults irrespective of the season. Additionally, predation focusing on adults would have a greater impact on prey populations compared to predation focusing on non-adults. Furthermore, it was predicted that prey populations experiencing demographic-specific selection from both lions and cheetahs would be impacted more than species selected by only one predator. Degrees of preference (DOP) were estimated based on prey availability (camera traps) and prey use (GPS clusters) for lion and cheetah populations in Lapalala Wilderness Reserve. Generalized Additive Models for Location, Scale, and Shape (GAMLSS) were used to determine seasonal shifts in demographic-specific prey preferences. The seasonal-demographic specific predation patterns of lion and cheetah, along with prey vital rates extracted from the literature, were then used to model potential predation impacts on prey populations using both Leslie-Usher and Lefkovitch matrix models. Lions preferred larger adult prey such as blue wildebeest, eland, and buffalo, while cheetahs preferred smaller prey, particularly juveniles of small to intermediate-sized species like impala, kudu, blue wildebeest, and zebra. Both predators showed seasonal shifts in demographic-specific prey preferences, with lions selecting adult buffalo during the dry season and juvenile buffalo in the wet season, and cheetahs selecting juveniles in the dry season and neonates and juveniles during the wet season. Lions and cheetahs exerted the highest degree of top-down limitations on their preferred prey. Predation on adult prey had a greater effect on prey population growth rates than predation on non-adults, especially in the dry season. Intermediate-sized prey species experienced the highest predation pressures, while larger prey species were more affected than smaller ones, contrary to the size-nested predation hypothesis. My study represents a first effort in the southern hemisphere to model the demographic impacts of multiple predators on diverse prey species, incorporating seasonal and demographic-specific prey preferences. The findings emphasise the importance of incorporating prey demographics and seasonality in predator-prey studies as these refined studies have implications for the management and conservation of both predator and prey populations. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2024
- Full Text:
- Date Issued: 2024-04
- Authors: Dreyer, Nicola Bondi
- Date: 2024-04
- Subjects: Predation (Biology) , Animal populations , Animal ecology
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/63733 , vital:73593
- Description: Understanding prey selection offers predictive insights into predator-prey interactions, which can be extended to explore the impacts of predators on prey populations. Prey availability and vulnerability vary across species, demographic classes, body sizes, and seasons. Traditional prey selection models for large carnivores, based on estimates of prey body size, assume uniform vulnerability across prey demographic classes and seasons, failing to account for these variations. This study aims to contrast seasonal shifts in demographic-specific prey preferences between lions and cheetahs and examine the potential impact of their demographic-specific predation patterns on a range of prey species across a body size spectrum. It was predicted that cheetahs would shift their selection from adults and juveniles of smaller prey species in the dry season to neonates and juveniles of both smaller and larger prey species in the wet season, while lions would select adults irrespective of the season. Additionally, predation focusing on adults would have a greater impact on prey populations compared to predation focusing on non-adults. Furthermore, it was predicted that prey populations experiencing demographic-specific selection from both lions and cheetahs would be impacted more than species selected by only one predator. Degrees of preference (DOP) were estimated based on prey availability (camera traps) and prey use (GPS clusters) for lion and cheetah populations in Lapalala Wilderness Reserve. Generalized Additive Models for Location, Scale, and Shape (GAMLSS) were used to determine seasonal shifts in demographic-specific prey preferences. The seasonal-demographic specific predation patterns of lion and cheetah, along with prey vital rates extracted from the literature, were then used to model potential predation impacts on prey populations using both Leslie-Usher and Lefkovitch matrix models. Lions preferred larger adult prey such as blue wildebeest, eland, and buffalo, while cheetahs preferred smaller prey, particularly juveniles of small to intermediate-sized species like impala, kudu, blue wildebeest, and zebra. Both predators showed seasonal shifts in demographic-specific prey preferences, with lions selecting adult buffalo during the dry season and juvenile buffalo in the wet season, and cheetahs selecting juveniles in the dry season and neonates and juveniles during the wet season. Lions and cheetahs exerted the highest degree of top-down limitations on their preferred prey. Predation on adult prey had a greater effect on prey population growth rates than predation on non-adults, especially in the dry season. Intermediate-sized prey species experienced the highest predation pressures, while larger prey species were more affected than smaller ones, contrary to the size-nested predation hypothesis. My study represents a first effort in the southern hemisphere to model the demographic impacts of multiple predators on diverse prey species, incorporating seasonal and demographic-specific prey preferences. The findings emphasise the importance of incorporating prey demographics and seasonality in predator-prey studies as these refined studies have implications for the management and conservation of both predator and prey populations. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2024
- Full Text:
- Date Issued: 2024-04
The effects of selected samples on the bio-stimulatory capacity and anti-aging effects of red light on human skin cells
- Authors: Rudolph, Carlen
- Date: 2024-04
- Subjects: Cell culture -- Technique , Dermatologic agents , Collagen , Biochemistry -- Technique
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/64347 , vital:73677
- Description: Photobiomodulation (PBM) has gained a remarkable interest in the cosmeceutical industry, with research demonstrating supporting evidence for its use as anti-aging and skin-rejuvenating strategies. It is defined as photons at a non-thermal irradiance or non-ionizing photonic energy that trigger photochemical changes within the cellular structure to alter certain biological activities. Lasers were the main focus during the developmental years of light-based treatments, but since the introduction of non-ablative, light-emitting diode (LED) devices, the focus has changed because of the reduced concerns associated with lasers, such as costs, ablation cutting, thermally coagulating tissue, no downtime needed after treatment, and no trained staff needed for operation. The precise biochemical mechanism for PBM is still to be elucidated; however, accepted theories suggest that it has an influence on the activity of cytochrome c oxidase, a complex located in the electron transport chain, or on the viscosity of the interfacial water layer (IWL) of the mitochondrial membrane. The interaction of those cellular components with the light then leads to the primary responses of increased ROS, ATP production, and intracellular calcium, which ultimately leads to the stimulation of secondary responses that are desired for skin rejuvenation and anti-aging, such as cell proliferation and collagen production. There is controversy surrounding photobiomodulation (PBM), mostly because of the incomplete understanding behind its biochemical mechanism and the number of parameters that require optimization; however, it still poses as a promising field for research into anti-aging properties, as seen in the literature. Besides the use of devices for skin rejuvenation and anti-aging strategies, it is not uncommon to see plant extracts and other natural products being used in current skin care products for the same reason? This is mostly because of their promising bioactivities, some of which include antioxidant, anti-inflammatory, anti-bacterial, collagen-stimulating, and cell-proliferating activities. The aim of this study was to investigate the bio-stimulatory capacity of red light on skin cells and to evaluate possible effects it could have in combination with samples that already show promising anti-aging properties in research. The samples that were selected for this study are: Aspalathus linearis (rooibos) unfermented extract, L-ascorbic acid 2-phosphate, mangrove bee honey, stingless bee honey, Sargassum oligocystum (brown seaweed) and Ulva fasciata (green seaweed).It was found that red light irradiation did indeed stimulate the primary responses of ROS, ATP production, and intracellular calcium levels in HaCaT keratinocytes, as proposed in the hypothesised theory. However, none of the proposed secondary responses to cell proliferation or collagen production were demonstrated. In fact, the opposite was observed for cell proliferation and collagen production, where red light irradiation seemed to be cytostatic towards Hs27 fibroblast cells and caused significant decreases in collagen production. Red light energy dosages of 10, 20 and 30 J/cm2, yielded different primary responses with 20 and 30 J/cm2 generally causing more significant stimulation than that of 10 J/cm2. It should also be noted that even if the desired secondary responses were not observed in this study, it does not mean that red light does not have the capacity to still stimulate them. It is clear that the responses are energy dosage-dependent, and it is suggested that lower energy dosages could possibly lead to cell proliferation and that longer incubation periods post-irradiation are required before measuring the endpoint of collagen production. For the combination of red light irradiation and selected test samples, it was demonstrated that the order of samples that yielded the best outcomes is: stingless bee honey > mangrove bee honey > U. fasciata > S. oligocystum > 2-PAA > green rooibos. Unexpected results were demonstrated for green rooibos in the presence and absence of red light, which included decreased ATP production and collagen biosynthesis. Further investigation is therefore needed to have a better understanding of these unanticipated results. , Thesis (MSc) -- Faculty of Science, School of Biomolecular & Chemical Sciences, 2024
- Full Text:
- Date Issued: 2024-04
- Authors: Rudolph, Carlen
- Date: 2024-04
- Subjects: Cell culture -- Technique , Dermatologic agents , Collagen , Biochemistry -- Technique
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/64347 , vital:73677
- Description: Photobiomodulation (PBM) has gained a remarkable interest in the cosmeceutical industry, with research demonstrating supporting evidence for its use as anti-aging and skin-rejuvenating strategies. It is defined as photons at a non-thermal irradiance or non-ionizing photonic energy that trigger photochemical changes within the cellular structure to alter certain biological activities. Lasers were the main focus during the developmental years of light-based treatments, but since the introduction of non-ablative, light-emitting diode (LED) devices, the focus has changed because of the reduced concerns associated with lasers, such as costs, ablation cutting, thermally coagulating tissue, no downtime needed after treatment, and no trained staff needed for operation. The precise biochemical mechanism for PBM is still to be elucidated; however, accepted theories suggest that it has an influence on the activity of cytochrome c oxidase, a complex located in the electron transport chain, or on the viscosity of the interfacial water layer (IWL) of the mitochondrial membrane. The interaction of those cellular components with the light then leads to the primary responses of increased ROS, ATP production, and intracellular calcium, which ultimately leads to the stimulation of secondary responses that are desired for skin rejuvenation and anti-aging, such as cell proliferation and collagen production. There is controversy surrounding photobiomodulation (PBM), mostly because of the incomplete understanding behind its biochemical mechanism and the number of parameters that require optimization; however, it still poses as a promising field for research into anti-aging properties, as seen in the literature. Besides the use of devices for skin rejuvenation and anti-aging strategies, it is not uncommon to see plant extracts and other natural products being used in current skin care products for the same reason? This is mostly because of their promising bioactivities, some of which include antioxidant, anti-inflammatory, anti-bacterial, collagen-stimulating, and cell-proliferating activities. The aim of this study was to investigate the bio-stimulatory capacity of red light on skin cells and to evaluate possible effects it could have in combination with samples that already show promising anti-aging properties in research. The samples that were selected for this study are: Aspalathus linearis (rooibos) unfermented extract, L-ascorbic acid 2-phosphate, mangrove bee honey, stingless bee honey, Sargassum oligocystum (brown seaweed) and Ulva fasciata (green seaweed).It was found that red light irradiation did indeed stimulate the primary responses of ROS, ATP production, and intracellular calcium levels in HaCaT keratinocytes, as proposed in the hypothesised theory. However, none of the proposed secondary responses to cell proliferation or collagen production were demonstrated. In fact, the opposite was observed for cell proliferation and collagen production, where red light irradiation seemed to be cytostatic towards Hs27 fibroblast cells and caused significant decreases in collagen production. Red light energy dosages of 10, 20 and 30 J/cm2, yielded different primary responses with 20 and 30 J/cm2 generally causing more significant stimulation than that of 10 J/cm2. It should also be noted that even if the desired secondary responses were not observed in this study, it does not mean that red light does not have the capacity to still stimulate them. It is clear that the responses are energy dosage-dependent, and it is suggested that lower energy dosages could possibly lead to cell proliferation and that longer incubation periods post-irradiation are required before measuring the endpoint of collagen production. For the combination of red light irradiation and selected test samples, it was demonstrated that the order of samples that yielded the best outcomes is: stingless bee honey > mangrove bee honey > U. fasciata > S. oligocystum > 2-PAA > green rooibos. Unexpected results were demonstrated for green rooibos in the presence and absence of red light, which included decreased ATP production and collagen biosynthesis. Further investigation is therefore needed to have a better understanding of these unanticipated results. , Thesis (MSc) -- Faculty of Science, School of Biomolecular & Chemical Sciences, 2024
- Full Text:
- Date Issued: 2024-04
The host potential of wheel-and-axle polyaromatic compounds
- Authors: Vorgers, Jarryd Allister
- Date: 2024-04
- Subjects: Supramolecular chemistry
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/64426 , vital:73704
- Description: In this work, wheel-and-axle compounds 1,4-phenylene-bis(diphenylmethanol) (H1), 1,4-phenylene-bis(di-p-tolylmethanol) (H2) and 1,4-phenylene-bis(di-p-fluorophenylmethanol) (H3) were investigated for their host behaviour in various pyridyl and heterocyclic guest mixtures. These host compounds were readily synthesized by means of Grignard addition reactions on dimethyl terephthalate, employing the aryl halides bromobenzene for H1 (73% yield), p-bromotoluene for H2 (69%) and p-bromofluorobenzene for H3 (70%). Molecular modelling calculations demonstrated that the various C-C-C angles differed between the computed low energy host conformers and those in the host molecules from their PYR-containing crystal structures. However, specified ‘torsion’ angles were in close agreement. Compound 1,4-phenylene-bis(diphenylmethanol) (H1) possessed the ability to form 1:2 host-guest (H:G) complexes with each of pyridine (PYR) and 2-, 3- and 4-methylpyridine (2MP, 3MP and 4MP). Furthermore, H1 showed preferential behaviour towards PYR and 4MP when presented with various mixtures of these four pyridines. Due to the high selectivity coefficients calculated in many instances (the selectivity coefficient, K, is a measure of the selectivity of a host compound for one particular guest in a mixture), it was demonstrated that H1 would be suitable for separations/purifications for many of the mixtures investigated in this work through host-guest chemistry strategies. (These pyridines are difficult to separate by means of the more conventional fractional distillations because of very similar boiling points.) Single crystal X-ray diffraction (SCXRD) analyses revealed that 4MP and 3MP experienced hydrogen bonds with the host molecule which were similar in distance, while the hydrogen bond distance between H1 and 4MP was shorter than that between H1 and 2MP. Furthermore, the hydrogen bond angles in complexes with the preferred PYR and 4MP guest species were more linear than in those having 2MP and 3MP. Additionally, preferred PYR and 4MP experienced significant π‧‧‧π contacts with nearby guest molecules, while disfavoured 2MP and 3MP did not interact in this fashion. Hirshfeld surface analyses demonstrated that PYR and 4MP (favoured) were involved in a greater percentage of (guest)N‧‧H(host) , Thesis (MSc) -- Faculty of Science, School of Biomolecular & Chemical Sciences, 2024
- Full Text:
- Date Issued: 2024-04
- Authors: Vorgers, Jarryd Allister
- Date: 2024-04
- Subjects: Supramolecular chemistry
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/64426 , vital:73704
- Description: In this work, wheel-and-axle compounds 1,4-phenylene-bis(diphenylmethanol) (H1), 1,4-phenylene-bis(di-p-tolylmethanol) (H2) and 1,4-phenylene-bis(di-p-fluorophenylmethanol) (H3) were investigated for their host behaviour in various pyridyl and heterocyclic guest mixtures. These host compounds were readily synthesized by means of Grignard addition reactions on dimethyl terephthalate, employing the aryl halides bromobenzene for H1 (73% yield), p-bromotoluene for H2 (69%) and p-bromofluorobenzene for H3 (70%). Molecular modelling calculations demonstrated that the various C-C-C angles differed between the computed low energy host conformers and those in the host molecules from their PYR-containing crystal structures. However, specified ‘torsion’ angles were in close agreement. Compound 1,4-phenylene-bis(diphenylmethanol) (H1) possessed the ability to form 1:2 host-guest (H:G) complexes with each of pyridine (PYR) and 2-, 3- and 4-methylpyridine (2MP, 3MP and 4MP). Furthermore, H1 showed preferential behaviour towards PYR and 4MP when presented with various mixtures of these four pyridines. Due to the high selectivity coefficients calculated in many instances (the selectivity coefficient, K, is a measure of the selectivity of a host compound for one particular guest in a mixture), it was demonstrated that H1 would be suitable for separations/purifications for many of the mixtures investigated in this work through host-guest chemistry strategies. (These pyridines are difficult to separate by means of the more conventional fractional distillations because of very similar boiling points.) Single crystal X-ray diffraction (SCXRD) analyses revealed that 4MP and 3MP experienced hydrogen bonds with the host molecule which were similar in distance, while the hydrogen bond distance between H1 and 4MP was shorter than that between H1 and 2MP. Furthermore, the hydrogen bond angles in complexes with the preferred PYR and 4MP guest species were more linear than in those having 2MP and 3MP. Additionally, preferred PYR and 4MP experienced significant π‧‧‧π contacts with nearby guest molecules, while disfavoured 2MP and 3MP did not interact in this fashion. Hirshfeld surface analyses demonstrated that PYR and 4MP (favoured) were involved in a greater percentage of (guest)N‧‧H(host) , Thesis (MSc) -- Faculty of Science, School of Biomolecular & Chemical Sciences, 2024
- Full Text:
- Date Issued: 2024-04
The on-demand continuous flow generation, separation, and utilization of monosilane gas, a feedstock for solar-grade silicon
- Authors: Mathe, Francis Matota
- Date: 2024-04
- Subjects: Chemistry, Organic , Chemistry , Silicon -- Synthesis
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10948/64179 , vital:73660
- Description: This research is dedicated to the development of a continuous flow process for the production and utilization of monosilane gas. The utilization of continuous flow techniques was instrumental in addressing the challenges and conditions associated with the handling of monosilane gas. Furthermore, the integration of Process Analytical Technologies (PAT) facilitated in-process monitoring and analysis. Chapter one of this research provides an extensive background and literature review encompassing the purification methods of silicon, the latest advancements in the direct synthesis of alkoxysilanes, current synthesis methods for monosilane, the various applications of monosilane, as well as the utilization of continuous flow technology and process analytical technologies. In chapter two, a detailed account of the experimental procedures employed in this research is presented. Chapter three delves into the results derived from each section of the research. The first section discusses an attempt to upscale the continuous flow synthesis of triethoxysilane, based on previous group research. Process Analytical Technologies (PAT), specifically thermocouples, were utilized in this endeavor. The study revealed temperature inconsistencies along the packed bed reactor, which had a notable impact on the reaction capabilities. The subsequent section explores the continuous flow synthesis of monosilane from triethoxysilane. A Design of Experiment (DoE) approach was employed to identify the optimal reaction conditions and compare the effectiveness of two catalysts. The study determined that Amberlyst-A26 emerged as the superior catalyst, offering stability and reasonable conversions over a 24-hour period. In a residence time of 6 minutes and at a temperature of 55 °C, the maximum triethoxysilane conversion of 100% was achieved. PAT, particularly inline FT-IR, was instrumental in monitoring catalyst activity, while continuous flow gas separation techniques facilitated the separation of monosilane. The research also demonstrated further applications of continuous flow techniques in the synthesis of monosilane from tetraethoxysilane and magnesium silicide. The former aimed to , Thesis (PhD) -- Faculty of Science, School of Biomolecular & Chemical Sciences, 2024
- Full Text:
- Date Issued: 2024-04
- Authors: Mathe, Francis Matota
- Date: 2024-04
- Subjects: Chemistry, Organic , Chemistry , Silicon -- Synthesis
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10948/64179 , vital:73660
- Description: This research is dedicated to the development of a continuous flow process for the production and utilization of monosilane gas. The utilization of continuous flow techniques was instrumental in addressing the challenges and conditions associated with the handling of monosilane gas. Furthermore, the integration of Process Analytical Technologies (PAT) facilitated in-process monitoring and analysis. Chapter one of this research provides an extensive background and literature review encompassing the purification methods of silicon, the latest advancements in the direct synthesis of alkoxysilanes, current synthesis methods for monosilane, the various applications of monosilane, as well as the utilization of continuous flow technology and process analytical technologies. In chapter two, a detailed account of the experimental procedures employed in this research is presented. Chapter three delves into the results derived from each section of the research. The first section discusses an attempt to upscale the continuous flow synthesis of triethoxysilane, based on previous group research. Process Analytical Technologies (PAT), specifically thermocouples, were utilized in this endeavor. The study revealed temperature inconsistencies along the packed bed reactor, which had a notable impact on the reaction capabilities. The subsequent section explores the continuous flow synthesis of monosilane from triethoxysilane. A Design of Experiment (DoE) approach was employed to identify the optimal reaction conditions and compare the effectiveness of two catalysts. The study determined that Amberlyst-A26 emerged as the superior catalyst, offering stability and reasonable conversions over a 24-hour period. In a residence time of 6 minutes and at a temperature of 55 °C, the maximum triethoxysilane conversion of 100% was achieved. PAT, particularly inline FT-IR, was instrumental in monitoring catalyst activity, while continuous flow gas separation techniques facilitated the separation of monosilane. The research also demonstrated further applications of continuous flow techniques in the synthesis of monosilane from tetraethoxysilane and magnesium silicide. The former aimed to , Thesis (PhD) -- Faculty of Science, School of Biomolecular & Chemical Sciences, 2024
- Full Text:
- Date Issued: 2024-04
Trophic ecology and breeding success of Brown Skuas (Catharacta antarctica)
- Authors: Walker, Tegan
- Date: 2024-04
- Subjects: Birds -- Conservation , Birds -- Ecology , Birds -- Behavior -- Evolution
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/64437 , vital:73710
- Description: Invasive species can impact island ecosystem processes by altering species interactions through direct competition for the same resources or by predation on insular species. Seabirds on sub-Antarctic islands are naïve to any new predators and are most at risk of local extirpation. Successful eradications of invasive mammals have yielded positive ecological responses from several seabird species. On sub-Antarctic Marion Island, populations of burrowing petrels, largely targeted by Feral Cats Felis catus, have indicated slow recovery despite the successful eradication of cats in the early 1990s. House Mice Mus musculus, have since proliferated on Marion Island, aided by a warmer climate, and are severely impacting several defenceless populations of burrowing petrels. In this thesis, I investigated the contemporary breeding productivity and diet of Brown Skuas Catharacta antarctica. At Marion Island, Brown Skua breeding productivity was associated to diet, which varied between years. Skuas feeding mostly on burrowing petrels exhibited higher breeding success than pairs mostly feeding on penguins. Higher contributions of burrowing petrels were seen in the contemporary diet of skuas compared to previous diet work. The importance of penguin prey compared to their 1980 and 2010/11 diet, was largely reduced during the 2021/22 and 2022/23 breeding seasons (53 and 51%, respectively) despite a historically high dependence on this prey (78% in 1980 and 67% in 2010/11). Penguin populations have been decreasing at the island and this may be reflected in the current skua diet. Breeding productivity was not influenced by the other factors tested, i.e. weather data (daily minimum, average and maximum air temperature; daily minimum, average, maximum wind speed; daily precipitation), distance to closest penguin colony, species of penguin or number of conspecifics in a 100 m radius around the nest. Brown Skuas breeding on Marion, Gough and Mayes islands were also used as biosamplers of burrowing petrels. These birds form a large part of the skua diet and are reflected in regurgitated skua pellets. Temporal comparisons for Marion Island indicated significant changes in burrowing petrel composition since the 1980s. Blue Petrels Halobaena caerulea and Salvin’s Prions Pachyptila salvini remained the highest contributors of skua pellets, but their proportions differed with three-fold increase in Blue Petrel and 25% decrease in Salvin’s Prion remains compared to previous studies. Further, my study indicated that smaller species of burrowing petrels such as the storm-petrels and diving petrels may be returning to Marion Island, 30 years after the eradication of cats. Pellet analyses at Marion, Gough and Mayes islands also indicated that skua diet may underrepresent larger species of petrels and soft-bodied prey. Despite these limitations, skua diet can indicate the presence of burrowing petrels during summer months, more so at Marion and Mayes islands than Gough Island, where pellet collection is difficult due to dense vegetation. Prey remains, such as wings in middens, may be a more appropriate method to investigate skua diet at Gough Island. Dominant burrowing petrels indicated by pellets at each island generally reflected the most abundant breeding species; Blue Petrels and Salvin’s Prions at Marion Island, Great Shearwaters Puffinus gravis and prion Pachyptila spp. at Gough Island, and Blue Petrels and Slender-billed Prions Pachyptila belcheri at Mayes Island. Pellets provide a non-invasive method for studying species of burrowing petrels that are challenging to monitor. This method is appropriate for studies conducted during summer months, while other studies (e.g., observations, camera traps, acoustic recordings and genetics) may be more reflective of the presence of burrowing species that breed in winter or could be used in combination with skua pellets during summer months. Population monitoring is an important part of conservation as it provides insights into population change. This thesis adds to the baseline data in terms of breeding productivity and updated trophic ecology of Brown Skuas, which will be used to inform the recovery of burrowing petrels once mice have been eradicated from Marion Island. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2024
- Full Text:
- Date Issued: 2024-04
- Authors: Walker, Tegan
- Date: 2024-04
- Subjects: Birds -- Conservation , Birds -- Ecology , Birds -- Behavior -- Evolution
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/64437 , vital:73710
- Description: Invasive species can impact island ecosystem processes by altering species interactions through direct competition for the same resources or by predation on insular species. Seabirds on sub-Antarctic islands are naïve to any new predators and are most at risk of local extirpation. Successful eradications of invasive mammals have yielded positive ecological responses from several seabird species. On sub-Antarctic Marion Island, populations of burrowing petrels, largely targeted by Feral Cats Felis catus, have indicated slow recovery despite the successful eradication of cats in the early 1990s. House Mice Mus musculus, have since proliferated on Marion Island, aided by a warmer climate, and are severely impacting several defenceless populations of burrowing petrels. In this thesis, I investigated the contemporary breeding productivity and diet of Brown Skuas Catharacta antarctica. At Marion Island, Brown Skua breeding productivity was associated to diet, which varied between years. Skuas feeding mostly on burrowing petrels exhibited higher breeding success than pairs mostly feeding on penguins. Higher contributions of burrowing petrels were seen in the contemporary diet of skuas compared to previous diet work. The importance of penguin prey compared to their 1980 and 2010/11 diet, was largely reduced during the 2021/22 and 2022/23 breeding seasons (53 and 51%, respectively) despite a historically high dependence on this prey (78% in 1980 and 67% in 2010/11). Penguin populations have been decreasing at the island and this may be reflected in the current skua diet. Breeding productivity was not influenced by the other factors tested, i.e. weather data (daily minimum, average and maximum air temperature; daily minimum, average, maximum wind speed; daily precipitation), distance to closest penguin colony, species of penguin or number of conspecifics in a 100 m radius around the nest. Brown Skuas breeding on Marion, Gough and Mayes islands were also used as biosamplers of burrowing petrels. These birds form a large part of the skua diet and are reflected in regurgitated skua pellets. Temporal comparisons for Marion Island indicated significant changes in burrowing petrel composition since the 1980s. Blue Petrels Halobaena caerulea and Salvin’s Prions Pachyptila salvini remained the highest contributors of skua pellets, but their proportions differed with three-fold increase in Blue Petrel and 25% decrease in Salvin’s Prion remains compared to previous studies. Further, my study indicated that smaller species of burrowing petrels such as the storm-petrels and diving petrels may be returning to Marion Island, 30 years after the eradication of cats. Pellet analyses at Marion, Gough and Mayes islands also indicated that skua diet may underrepresent larger species of petrels and soft-bodied prey. Despite these limitations, skua diet can indicate the presence of burrowing petrels during summer months, more so at Marion and Mayes islands than Gough Island, where pellet collection is difficult due to dense vegetation. Prey remains, such as wings in middens, may be a more appropriate method to investigate skua diet at Gough Island. Dominant burrowing petrels indicated by pellets at each island generally reflected the most abundant breeding species; Blue Petrels and Salvin’s Prions at Marion Island, Great Shearwaters Puffinus gravis and prion Pachyptila spp. at Gough Island, and Blue Petrels and Slender-billed Prions Pachyptila belcheri at Mayes Island. Pellets provide a non-invasive method for studying species of burrowing petrels that are challenging to monitor. This method is appropriate for studies conducted during summer months, while other studies (e.g., observations, camera traps, acoustic recordings and genetics) may be more reflective of the presence of burrowing species that breed in winter or could be used in combination with skua pellets during summer months. Population monitoring is an important part of conservation as it provides insights into population change. This thesis adds to the baseline data in terms of breeding productivity and updated trophic ecology of Brown Skuas, which will be used to inform the recovery of burrowing petrels once mice have been eradicated from Marion Island. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2024
- Full Text:
- Date Issued: 2024-04
A Combined Experimental and Computational Study of Hydridospirophosphorane Ligand Systems Featuring Halogenated Mandelic Acids
- Authors: Maritz, Marius Johann
- Date: 2023-12
- Subjects: Organic compounds -- Synthesis , Heterocyclic compounds , catalysis -- South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/62096 , vital:71911
- Description: The search for new stereoselective catalysts remains important for the isolation of enantiomeric products from racemic mixtures. The need exists for these catalysts to be more efficient, to be more cost effective as well as be stable over time without undergoing changes in molecular structure and selectivity. The purpose of this research project was to experimentally synthesise and characterise asymmetric catalysts for the use in enantioselective synthesis. The catalysts consisted of the main group element phosphorous as central atom, with the phenyl rings of mandelic acid ligands monosubstituted with halogen atoms fluorine, chlorine and bromine in different configurations. Ligand binding resulted in the formation of hydridospirophosphorane structures, from which the molecular properties and binding geometry of these molecules could be explained by the theory of apicophilicity. Characterization was performed by NMR and IR spectroscopy as well as diffraction studies that provided the experimental crystal structures. The structural, energetic and spectroscopy results were compared to the theoretically obtained molecular properties using DFT analysis. Various interand intramolecular interactions that existed between molecules found in crystal packing environments were discussed. Additional properties that were investigated included modelling solvation effects, molecular orbital analysis, Hirshfeld surfaces, orbital and atomic energy and population analysis as well as ESP energy calculations with the optimized crystal structures as input. Molecular overlay comparisons were also performed between the experimental and optimized structures where the effectiveness of various DFT functionals and basis sets could be determined. The method with the best overall cost-to-accuracy ratio was found to be the triple-zeta def2-tzvp basis set with B3LYP functional theory and the addition of Grimme’s dispersion correction. Results indicated differences in crystal packing depending largely on the given halogen atoms present in the substituted phenyl rings, with differences observed in electronegativity and steric effects. One of the crystal systems showed additional interactions with solvent molecules, giving the impression that obtaining crystal void formation was possible. Alterations in the transition state activation energies between the isomers of each molecule were found to be present and supported the theory behind the mechanism of stereochemical induction. The studied compounds were therefore effective in isolating different enantiomeric ligands by means of energy differences between conformers and displayed unique catalytic properties resulting from the phosphorous main group element. The hydridospirophosphoranes conformers responsible for the lowest theoretically calculated activation energy induced crystallization as was seen by diffraction results for all compounds. Even as an intriguing observation, crystallization will largely depend on solubility rather than a specific conformer’s amount in solution. , Thesis (MSc) -- Faculty of Science, School of Biomolecular and Chemical Sciences, 2023
- Full Text:
- Date Issued: 2023-12
- Authors: Maritz, Marius Johann
- Date: 2023-12
- Subjects: Organic compounds -- Synthesis , Heterocyclic compounds , catalysis -- South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/62096 , vital:71911
- Description: The search for new stereoselective catalysts remains important for the isolation of enantiomeric products from racemic mixtures. The need exists for these catalysts to be more efficient, to be more cost effective as well as be stable over time without undergoing changes in molecular structure and selectivity. The purpose of this research project was to experimentally synthesise and characterise asymmetric catalysts for the use in enantioselective synthesis. The catalysts consisted of the main group element phosphorous as central atom, with the phenyl rings of mandelic acid ligands monosubstituted with halogen atoms fluorine, chlorine and bromine in different configurations. Ligand binding resulted in the formation of hydridospirophosphorane structures, from which the molecular properties and binding geometry of these molecules could be explained by the theory of apicophilicity. Characterization was performed by NMR and IR spectroscopy as well as diffraction studies that provided the experimental crystal structures. The structural, energetic and spectroscopy results were compared to the theoretically obtained molecular properties using DFT analysis. Various interand intramolecular interactions that existed between molecules found in crystal packing environments were discussed. Additional properties that were investigated included modelling solvation effects, molecular orbital analysis, Hirshfeld surfaces, orbital and atomic energy and population analysis as well as ESP energy calculations with the optimized crystal structures as input. Molecular overlay comparisons were also performed between the experimental and optimized structures where the effectiveness of various DFT functionals and basis sets could be determined. The method with the best overall cost-to-accuracy ratio was found to be the triple-zeta def2-tzvp basis set with B3LYP functional theory and the addition of Grimme’s dispersion correction. Results indicated differences in crystal packing depending largely on the given halogen atoms present in the substituted phenyl rings, with differences observed in electronegativity and steric effects. One of the crystal systems showed additional interactions with solvent molecules, giving the impression that obtaining crystal void formation was possible. Alterations in the transition state activation energies between the isomers of each molecule were found to be present and supported the theory behind the mechanism of stereochemical induction. The studied compounds were therefore effective in isolating different enantiomeric ligands by means of energy differences between conformers and displayed unique catalytic properties resulting from the phosphorous main group element. The hydridospirophosphoranes conformers responsible for the lowest theoretically calculated activation energy induced crystallization as was seen by diffraction results for all compounds. Even as an intriguing observation, crystallization will largely depend on solubility rather than a specific conformer’s amount in solution. , Thesis (MSc) -- Faculty of Science, School of Biomolecular and Chemical Sciences, 2023
- Full Text:
- Date Issued: 2023-12
A digital transformation framework for municipalities in the Eastern Cape
- Authors: Luke, Lamla Lonwabo Leadley
- Date: 2023-12
- Subjects: Internet in public administration , Information technology -- Political aspects , Electronic government information
- Language: English
- Type: Master's thesis , text
- Identifier: http://hdl.handle.net/10948/62506 , vital:72779
- Description: Digital transformation (DT) integrates technology into all business areas, fundamentally changing how businesses operate and deliver value to their clients. It is also a cultural change that requires organisations to continually challenge the status quo, experiment and get comfortable with change. Smart Municipalities in South Africa have various challenges concerning integrating services and information flow among departments within the municipalities, thus preventing the creation of value for the citizens. The ongoing digital transformation revolutionises urban development and governance, offering opportunities for enhanced citizen services, resource optimisation, and sustainable growth. However, the complexity of implementing smart city initiatives demands a structured approach. Due to urbanisation, municipal management in developing nations must deal with issues like increased energy consumption, pollution, the disposal of toxic wastes, resource depletion, ineffective management of urban infrastructures, ineffective planning processes, overloaded transportation networks, endemic congestion, as well as social inequality and socioeconomic disparity. The extent of digital adoption in the South African province of the Eastern Cape has provided municipalities with a learning opportunity to change into data-driven Smart Municipalities in order to increase productivity, growth, employment, and the need for people with a variety of skills. This study required a review of the literature to examine digital transformation, Smart Municipalities, Smart Municipalities at national and international levels, and Smart Municipality models. The literature review also helped to create a Smart Municipality conceptual model. Data for this study were collected in four Eastern Cape municipalities, namely: DR. AB. Xuma, Enoch Mgijima, Intsika Yethu Local municipalities, and their critical stakeholder Chris Hani District Municipality. The population was all municipal workers, including Municipal Managers, Councillors, Executive Management, ICT officials, Unit Managers, Computer Users and other municipal employees who were using IT to do their job responsibilities within the municipalities. This research study followed a positivistic approach using quantitative methods of analysis. Accordingly, the conceptual model was hypothesised and tested using a questionnaire to collect data and the data were statistically analysed. The study followed a descriptive research designwith a quantitative approach. Various statistical analyses were conducted, including descriptive statistics, reliability and validity metrics of the research instrument, correlation coefficients and Exploratory Factor Analysis (EFA). South Africa has provided municipalities with a learning opportunity to change into data-driven Smart Municipalities to increase productivity, growth, and employment supported by the need for people with a variety of skills. A Value Alignment Smart City Stakeholder (VASCS) model was created in previous research and identified nine dimensions of a smart city, namely Smart Economy, Smart Environment, Smart Governance, Smart Living, Smart Mobility, Smart Organisation, Smart People, Smart Policies and Smart Technology. Due to lack of DT framework and guidelines that guides municipalities on how they can adopt Smart Municipality concept, the objective of this study was to propose and evaluate a Value Alignment Smart Municipality Stakeholder (VASMS) model for municipalities in the Eastern Cape. The nine dimensions were empirically evaluated by stakeholders in four Eastern Cape municipalities. The results depict a change towards the importance of developing a Smart Municipality in the four municipalities, while following appropriate planning, designing, management, operations and governance guidelines. The respondents regarded the smart policy dimension as the most important dimension in the proposed VASMS model. This study further provided practical guidelines for the adoption of smart municipalities in the Eastern Cape Province of South Africa. This proposed VASMS model aims to address the unique challenges faced by municipalities in the Eastern Cape as they embark on their digital transformation journey. It outlines a stepby- step process encompassing strategic planning, technological integration, stakeholder engagement, and governance restructuring. Moreover, it emphasises the importance of fostering a collaborative ecosystem between government agencies, private sector partners, and citizens. By offering this VASMS model, this research contributes to the advancement of Smart Municipality initiatives in the Eastern Cape, ultimately paving the way for more efficient, resilient, and citizen-centric urban environments. , Thesis (MCom) -- Faculty of Science, School of Computing Sciences, 2023
- Full Text:
- Date Issued: 2023-12
- Authors: Luke, Lamla Lonwabo Leadley
- Date: 2023-12
- Subjects: Internet in public administration , Information technology -- Political aspects , Electronic government information
- Language: English
- Type: Master's thesis , text
- Identifier: http://hdl.handle.net/10948/62506 , vital:72779
- Description: Digital transformation (DT) integrates technology into all business areas, fundamentally changing how businesses operate and deliver value to their clients. It is also a cultural change that requires organisations to continually challenge the status quo, experiment and get comfortable with change. Smart Municipalities in South Africa have various challenges concerning integrating services and information flow among departments within the municipalities, thus preventing the creation of value for the citizens. The ongoing digital transformation revolutionises urban development and governance, offering opportunities for enhanced citizen services, resource optimisation, and sustainable growth. However, the complexity of implementing smart city initiatives demands a structured approach. Due to urbanisation, municipal management in developing nations must deal with issues like increased energy consumption, pollution, the disposal of toxic wastes, resource depletion, ineffective management of urban infrastructures, ineffective planning processes, overloaded transportation networks, endemic congestion, as well as social inequality and socioeconomic disparity. The extent of digital adoption in the South African province of the Eastern Cape has provided municipalities with a learning opportunity to change into data-driven Smart Municipalities in order to increase productivity, growth, employment, and the need for people with a variety of skills. This study required a review of the literature to examine digital transformation, Smart Municipalities, Smart Municipalities at national and international levels, and Smart Municipality models. The literature review also helped to create a Smart Municipality conceptual model. Data for this study were collected in four Eastern Cape municipalities, namely: DR. AB. Xuma, Enoch Mgijima, Intsika Yethu Local municipalities, and their critical stakeholder Chris Hani District Municipality. The population was all municipal workers, including Municipal Managers, Councillors, Executive Management, ICT officials, Unit Managers, Computer Users and other municipal employees who were using IT to do their job responsibilities within the municipalities. This research study followed a positivistic approach using quantitative methods of analysis. Accordingly, the conceptual model was hypothesised and tested using a questionnaire to collect data and the data were statistically analysed. The study followed a descriptive research designwith a quantitative approach. Various statistical analyses were conducted, including descriptive statistics, reliability and validity metrics of the research instrument, correlation coefficients and Exploratory Factor Analysis (EFA). South Africa has provided municipalities with a learning opportunity to change into data-driven Smart Municipalities to increase productivity, growth, and employment supported by the need for people with a variety of skills. A Value Alignment Smart City Stakeholder (VASCS) model was created in previous research and identified nine dimensions of a smart city, namely Smart Economy, Smart Environment, Smart Governance, Smart Living, Smart Mobility, Smart Organisation, Smart People, Smart Policies and Smart Technology. Due to lack of DT framework and guidelines that guides municipalities on how they can adopt Smart Municipality concept, the objective of this study was to propose and evaluate a Value Alignment Smart Municipality Stakeholder (VASMS) model for municipalities in the Eastern Cape. The nine dimensions were empirically evaluated by stakeholders in four Eastern Cape municipalities. The results depict a change towards the importance of developing a Smart Municipality in the four municipalities, while following appropriate planning, designing, management, operations and governance guidelines. The respondents regarded the smart policy dimension as the most important dimension in the proposed VASMS model. This study further provided practical guidelines for the adoption of smart municipalities in the Eastern Cape Province of South Africa. This proposed VASMS model aims to address the unique challenges faced by municipalities in the Eastern Cape as they embark on their digital transformation journey. It outlines a stepby- step process encompassing strategic planning, technological integration, stakeholder engagement, and governance restructuring. Moreover, it emphasises the importance of fostering a collaborative ecosystem between government agencies, private sector partners, and citizens. By offering this VASMS model, this research contributes to the advancement of Smart Municipality initiatives in the Eastern Cape, ultimately paving the way for more efficient, resilient, and citizen-centric urban environments. , Thesis (MCom) -- Faculty of Science, School of Computing Sciences, 2023
- Full Text:
- Date Issued: 2023-12
An architecture for feedback-driven learning analytics
- Authors: Winfield, Philip John
- Date: 2023-12
- Subjects: Educational statistics -- Data processing , Education -- Research -- Statistical methods , Teacher-student relationships
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/62744 , vital:72935
- Description: Feedback from students provides an opportunity to gain insights into students’ learning behaviour and participation in higher education learning and teaching. Academic staff are expected to constantly review and improve the learning and teaching environment where feedback contributes vital information toward pedagogical decision-making. Reviewing student feedback is essential but time-consuming, making it crucial to explore more effective and efficient ways to analyse and present feedback that encourages intervention and support. The general design science research evaluation pattern guided the construction and evaluation of a Feedback-Driven Architecture (FDA) for Learning Analytics (LA) to address this problem. An FDA implementation using a suitable case demonstrated each component validating the feasibility and effectiveness of the proposed design. The components identified for inclusion in the FDA were integrated within layers of a three-tiered architecture pattern. The data layer incorporates the collection, preparation and storage of learning management system data which includes free-form narrative student feedback. The application layer contains logic to support the analysis of free-form narrative student feedback and extraction of learning analytics. Arrangement and visualisation of information in the presentation layer aim to promote appropriate intervention and support. Evaluation using a case study showed that the FDA provided necessary guidelines for developing an implementation that produced feedbackdriven learning analytics. Data preparation transformed unstructured data into a suitable representation for effective analysis. Cohorts within narrative feedback responses were identified using the k-means clustering algorithm and latent Dirichlet allocation. Logistic regression and support vector machines were applied as predictive models and trained using extracted quantitative markers to predict academic success. , Thesis (MSc) -- Faculty of Science, School of Computer Science, Mathematics, Physics and Statistics, 2023
- Full Text:
- Date Issued: 2023-12
- Authors: Winfield, Philip John
- Date: 2023-12
- Subjects: Educational statistics -- Data processing , Education -- Research -- Statistical methods , Teacher-student relationships
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/62744 , vital:72935
- Description: Feedback from students provides an opportunity to gain insights into students’ learning behaviour and participation in higher education learning and teaching. Academic staff are expected to constantly review and improve the learning and teaching environment where feedback contributes vital information toward pedagogical decision-making. Reviewing student feedback is essential but time-consuming, making it crucial to explore more effective and efficient ways to analyse and present feedback that encourages intervention and support. The general design science research evaluation pattern guided the construction and evaluation of a Feedback-Driven Architecture (FDA) for Learning Analytics (LA) to address this problem. An FDA implementation using a suitable case demonstrated each component validating the feasibility and effectiveness of the proposed design. The components identified for inclusion in the FDA were integrated within layers of a three-tiered architecture pattern. The data layer incorporates the collection, preparation and storage of learning management system data which includes free-form narrative student feedback. The application layer contains logic to support the analysis of free-form narrative student feedback and extraction of learning analytics. Arrangement and visualisation of information in the presentation layer aim to promote appropriate intervention and support. Evaluation using a case study showed that the FDA provided necessary guidelines for developing an implementation that produced feedbackdriven learning analytics. Data preparation transformed unstructured data into a suitable representation for effective analysis. Cohorts within narrative feedback responses were identified using the k-means clustering algorithm and latent Dirichlet allocation. Logistic regression and support vector machines were applied as predictive models and trained using extracted quantitative markers to predict academic success. , Thesis (MSc) -- Faculty of Science, School of Computer Science, Mathematics, Physics and Statistics, 2023
- Full Text:
- Date Issued: 2023-12
Assessing land degradation and the effectiveness of calcrete bontveld rehabilitation in a grassridge PPC cement mining area using multi-sensor remotely sensed data and machine learning techniques
- Authors: Mpisane, Khanyisa
- Date: 2023-12
- Subjects: Land degradation -- South Africa , Environmental degradation , Mines and mineral resources -- South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/62527 , vital:72821
- Description: This study uses multi-temporal remote sensing data to spatially visualise and quantify land degradation due to mining as well as Calcrete Bontveld rehabilitation at the Grassridge PPC Cement mine, Gqeberha formerly known as Port Elizabeth in the Eastern Cape, South Africa. Botanical field data is also used to verify the suasses of rehabilitation in the area. SPOT-6 and Landsat multi-spectral images were compared, and Support Vector Machine and Random Forest algorithms were used for classification in order to determine which yields more accurate results for a limestone mine. Support Vector Machine analysis using SPOT-6 images yielded the best results. This was due to the high spatial resolution of SPOT-6 compared to Landsat and Support Vector Machine classifier was able to classify images with fewer training points compared to Random Forest. The spatio-temporal land cover change at the mine was then determined between the years 2000, 2015 and 2020. Land cover classification is useful for monitoring land degradation and, in this case, was able to show the extent of rehabilitation success. For the year 2020, a 17% area was rehabilitated; however, the algorithm could not distinguish between unmined Calcrete Bontveld matrix and rehabilitation sites that were older than five years. The performed change detection also showed that 29.50% of unmined Calcrete Bontveld matrix had changed to “mature rehabilitation” (rehabilitation sites older than five years). Again, for this percentage in some areas the algorithm could not distinguish between the unmined Calcrete Bontveld matrix and rehabilitation sites that were older than five years due to high similarities between the two land cover types. Area changes of the different land cover classes could also be used to demonstrate how rehabilitation areas have matured over time and lead to the conclusion that most of the Calcrete Bontveld which was mined, has over the years been successfully rehabilitated. Vegetation analysis was conducted to further validate the rehabilitation success of Calcrete Bontveld matrix. Multivariant Detrended Correspondent Analysis showed that rehabilitation sites which were younger than five years (2–year-old rehabilitation plots that were sampled) had great dissimilarity to the natural unmined Calcrete Bontveld matrix and that rehabilitation sites older than five years, in this case 16–years older, had high similarity and resemblance to natural unmined Calcrete Bontveld matrix and therefore could be considered as being mature. This was a more definitive assessment as it considers all aspects of the vegetation. Species cover and species richness also showed that Calcrete Bontveld matrix rehabilitation sites which have been rehabilitated for more than 5 years had greater similarity to natural unmined vegetation compared to areas that have been rehabilitated for less than five years. This study, therefore, demonstrates that due to the high similarity between mature rehabilitation sites and unmined Calcrete Bontveld, rehabilitation has been successful. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2023
- Full Text:
- Date Issued: 2023-12
- Authors: Mpisane, Khanyisa
- Date: 2023-12
- Subjects: Land degradation -- South Africa , Environmental degradation , Mines and mineral resources -- South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/62527 , vital:72821
- Description: This study uses multi-temporal remote sensing data to spatially visualise and quantify land degradation due to mining as well as Calcrete Bontveld rehabilitation at the Grassridge PPC Cement mine, Gqeberha formerly known as Port Elizabeth in the Eastern Cape, South Africa. Botanical field data is also used to verify the suasses of rehabilitation in the area. SPOT-6 and Landsat multi-spectral images were compared, and Support Vector Machine and Random Forest algorithms were used for classification in order to determine which yields more accurate results for a limestone mine. Support Vector Machine analysis using SPOT-6 images yielded the best results. This was due to the high spatial resolution of SPOT-6 compared to Landsat and Support Vector Machine classifier was able to classify images with fewer training points compared to Random Forest. The spatio-temporal land cover change at the mine was then determined between the years 2000, 2015 and 2020. Land cover classification is useful for monitoring land degradation and, in this case, was able to show the extent of rehabilitation success. For the year 2020, a 17% area was rehabilitated; however, the algorithm could not distinguish between unmined Calcrete Bontveld matrix and rehabilitation sites that were older than five years. The performed change detection also showed that 29.50% of unmined Calcrete Bontveld matrix had changed to “mature rehabilitation” (rehabilitation sites older than five years). Again, for this percentage in some areas the algorithm could not distinguish between the unmined Calcrete Bontveld matrix and rehabilitation sites that were older than five years due to high similarities between the two land cover types. Area changes of the different land cover classes could also be used to demonstrate how rehabilitation areas have matured over time and lead to the conclusion that most of the Calcrete Bontveld which was mined, has over the years been successfully rehabilitated. Vegetation analysis was conducted to further validate the rehabilitation success of Calcrete Bontveld matrix. Multivariant Detrended Correspondent Analysis showed that rehabilitation sites which were younger than five years (2–year-old rehabilitation plots that were sampled) had great dissimilarity to the natural unmined Calcrete Bontveld matrix and that rehabilitation sites older than five years, in this case 16–years older, had high similarity and resemblance to natural unmined Calcrete Bontveld matrix and therefore could be considered as being mature. This was a more definitive assessment as it considers all aspects of the vegetation. Species cover and species richness also showed that Calcrete Bontveld matrix rehabilitation sites which have been rehabilitated for more than 5 years had greater similarity to natural unmined vegetation compared to areas that have been rehabilitated for less than five years. This study, therefore, demonstrates that due to the high similarity between mature rehabilitation sites and unmined Calcrete Bontveld, rehabilitation has been successful. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2023
- Full Text:
- Date Issued: 2023-12
Assessing the effects of fish stock management on Cape gannet foraging behaviour in South Africa
- Strydom, Zanri, Grémillet, David, Pichegru, Lorien
- Authors: Strydom, Zanri , Grémillet, David , Pichegru, Lorien
- Date: 2023-12
- Subjects: Gannets -- South Africa , Birds of prey -- Behavior -- South Africa , Fish stock assessment
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10948/62622 , vital:72887
- Description: Seabirds are one of the most threatened groups of birds under both marine and terrestrial pressures. Among seabirds, the Cape gannet Morus capensis is a southern African endemic species facing several pressures of anthropogenic origin, including competition with industrial fisheries on small pelagic fish stocks. Cape gannets, being a long-lived species that is sensitive to environmental changes, are sentinels of change in oceanic environments granting it important to understand which factors influence their foraging behaviour and breeding outputs. For example, factors like age can result in a loss of physical capabilities which can lead to behavioral compensation and subsequent changes in chick provisioning rates and amounts. With the current fisheries management the fish stocks are continually decreasing, indicating the importance of an updated fine-scale assessment on the spatiotemporal overlap between foraging gannets and fisheries. The first objective of this thesis was to determine the influence of adult Cape gannets’ age and sex on their foraging characteristics and energy expenditure during foraging. I equipped chick-rearing Cape gannets of known age and sex with a 3D accelerometer and GPS device. Foraging effort (trip duration, foraging path and maximum distance to the nest) did not differ between sexes nor with age in Cape gannets. Both sexes rested less on the water with age. Aging females also spent more time in flight than males. The age- and sexual differences in energy expenditure prevalent in our study might reflect niche and/or risk partitioning strategies to ensure adequate provisioning to the chick. The second objective of this thesis was to determine the influence of fisheries catch rates, sardine and anchovy biomass, and adult foraging effort on chick growth rates in Cape gannets, using a long-term dataset collected between 2005 and 2020 on Malgas Island. I equipped chick-rearing adults with a GPS device and I weighed the chicks for between 3 to 6 increments to calculate the average daily mass increment. Of all the variables, foraging trip duration was the main determinant of daily growth rates, with chicks benefitting from parents’ shorter foraging trip durations. Chicks tended to grow slower when fisheries catch of sardine and anchovy were higher, possibly an effect of competition with fisheries. Chicks also grew faster when fish biomass was higher. This long-term monitoring demonstrated the possible effect of food competition between Cape gannets and fisheries, with negative impacts on gannet fitness as determined via chick growth rates. The third objective of this thesis was to determine the influence of both the biomass and fisheries catch rates of sardine and anchovy on Cape gannet foraging effort at a spatial and temporal scale. This was achieved by equipping a total of 668 chick-rearing Cape gannets with a GPS device. With an increase in fisheries catch there was an increase in the birds’ foraging effort. To reduce competition between the gannets and fisheries, the gannets’ core foraging areas seldomly overlapped with the fisheries catch locations, at the cost of the gannets’ increased foraging effort. One method to halt the Cape gannet population decline would be to conserve the fish resources close to the breeding colonies. This would reduce the birds’ foraging whereby increasing their fitness. Safeguarding small pelagic fish to ensure the perseverance of the remaining Benguela seabird populations, would lead to preserving the Benguela marine ecosystem as a whole. My study provided new insight into effects of fish stock management on Cape gannet foraging behaviour in South Africa, and the need for adequate management to ensure population persistence. , Thesis (PhD) -- Faculty of Science, School of Environmental Sciences, 2023
- Full Text:
- Date Issued: 2023-12
- Authors: Strydom, Zanri , Grémillet, David , Pichegru, Lorien
- Date: 2023-12
- Subjects: Gannets -- South Africa , Birds of prey -- Behavior -- South Africa , Fish stock assessment
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10948/62622 , vital:72887
- Description: Seabirds are one of the most threatened groups of birds under both marine and terrestrial pressures. Among seabirds, the Cape gannet Morus capensis is a southern African endemic species facing several pressures of anthropogenic origin, including competition with industrial fisheries on small pelagic fish stocks. Cape gannets, being a long-lived species that is sensitive to environmental changes, are sentinels of change in oceanic environments granting it important to understand which factors influence their foraging behaviour and breeding outputs. For example, factors like age can result in a loss of physical capabilities which can lead to behavioral compensation and subsequent changes in chick provisioning rates and amounts. With the current fisheries management the fish stocks are continually decreasing, indicating the importance of an updated fine-scale assessment on the spatiotemporal overlap between foraging gannets and fisheries. The first objective of this thesis was to determine the influence of adult Cape gannets’ age and sex on their foraging characteristics and energy expenditure during foraging. I equipped chick-rearing Cape gannets of known age and sex with a 3D accelerometer and GPS device. Foraging effort (trip duration, foraging path and maximum distance to the nest) did not differ between sexes nor with age in Cape gannets. Both sexes rested less on the water with age. Aging females also spent more time in flight than males. The age- and sexual differences in energy expenditure prevalent in our study might reflect niche and/or risk partitioning strategies to ensure adequate provisioning to the chick. The second objective of this thesis was to determine the influence of fisheries catch rates, sardine and anchovy biomass, and adult foraging effort on chick growth rates in Cape gannets, using a long-term dataset collected between 2005 and 2020 on Malgas Island. I equipped chick-rearing adults with a GPS device and I weighed the chicks for between 3 to 6 increments to calculate the average daily mass increment. Of all the variables, foraging trip duration was the main determinant of daily growth rates, with chicks benefitting from parents’ shorter foraging trip durations. Chicks tended to grow slower when fisheries catch of sardine and anchovy were higher, possibly an effect of competition with fisheries. Chicks also grew faster when fish biomass was higher. This long-term monitoring demonstrated the possible effect of food competition between Cape gannets and fisheries, with negative impacts on gannet fitness as determined via chick growth rates. The third objective of this thesis was to determine the influence of both the biomass and fisheries catch rates of sardine and anchovy on Cape gannet foraging effort at a spatial and temporal scale. This was achieved by equipping a total of 668 chick-rearing Cape gannets with a GPS device. With an increase in fisheries catch there was an increase in the birds’ foraging effort. To reduce competition between the gannets and fisheries, the gannets’ core foraging areas seldomly overlapped with the fisheries catch locations, at the cost of the gannets’ increased foraging effort. One method to halt the Cape gannet population decline would be to conserve the fish resources close to the breeding colonies. This would reduce the birds’ foraging whereby increasing their fitness. Safeguarding small pelagic fish to ensure the perseverance of the remaining Benguela seabird populations, would lead to preserving the Benguela marine ecosystem as a whole. My study provided new insight into effects of fish stock management on Cape gannet foraging behaviour in South Africa, and the need for adequate management to ensure population persistence. , Thesis (PhD) -- Faculty of Science, School of Environmental Sciences, 2023
- Full Text:
- Date Issued: 2023-12
Characterization of the coastal Aquifer of Gqeberha, South Africa : Developing a conceptual understanding
- Authors: Vandala, Bamanye
- Date: 2023-12
- Subjects: Aquifers -- South Africa -- Port Elizabeth , Groundwater ecology , Hydrogeology
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/62710 , vital:72932
- Description: The aquifer systems in Gqeberha are poorly understood due to a lack of groundwater studies within the area, and this is particularly the case for the coastal aquifer of Gqeberha. Amidst the water crisis the city is currently facing, groundwater has become crucial, with over 1000 boreholes reportedly drilled in the coastal area, most of which are residential. This has resulted in the need to conduct more groundwater studies in the area and in Nelson Mandela Bay. This study presents a detailed hydrogeological characterization of the coastal aquifer of Gqeberha. This was achieved through the use of different techniques, which include field mapping, geophysics, hydrochemistry, and pumping test analysis. The work was done on the coastal seeps of the Algoa Group Formation and the fractured aquifer of the Peninsula Formation. The results through mapping indicated an abundance of folds, faults, and fractures which all have implications for groundwater flow. The majority of fractures are striking in the NE-SW and NW-SE directions. The pumping test analysis also indicated fractal flow with significant matrix flow resulting in a dual porosity system up to at least 200m in depth. The transmissivity and storativity values range from 6.78 – 44.5 m2/day and 0.0172 – 0.0325, respectively. This is highly dependent on the fracture interconnectivity, which varies across the area and is higher at shallow depths, as suggested by the geophysical profiles. Geophysical profiles indicate that the contact between the Algoa Group Formations and the Peninsula Formation results in coastal seeps due to the difference in hydraulic conductivities. The hydrochemical analysis suggests that the seeps generally have Na-Cl and Ca-Mg-Cl water types. The groundwater in the eastern area has a Ca-HCO3 water type, and the groundwater in the western region has a Ca-Mg-Cl water type, with the Chelsea-Noordhoek Fault system separating the two groundwater signatures. Groundwater at greater depths has a Na-Cl water type with higher TDS values. The chemical signatures seen are due to external factors, which include sea sprays, anthropogenic activities, rock-water processes, and possibly connate water in the Peninsula Formation aquifer. The findings of this study offer valuable insights into the present conditions of the aquifer in Gqeberha. This research serves as a foundational study that can provide a baseline for future hydrogeological investigations in the area. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2023
- Full Text:
- Date Issued: 2023-12
- Authors: Vandala, Bamanye
- Date: 2023-12
- Subjects: Aquifers -- South Africa -- Port Elizabeth , Groundwater ecology , Hydrogeology
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/62710 , vital:72932
- Description: The aquifer systems in Gqeberha are poorly understood due to a lack of groundwater studies within the area, and this is particularly the case for the coastal aquifer of Gqeberha. Amidst the water crisis the city is currently facing, groundwater has become crucial, with over 1000 boreholes reportedly drilled in the coastal area, most of which are residential. This has resulted in the need to conduct more groundwater studies in the area and in Nelson Mandela Bay. This study presents a detailed hydrogeological characterization of the coastal aquifer of Gqeberha. This was achieved through the use of different techniques, which include field mapping, geophysics, hydrochemistry, and pumping test analysis. The work was done on the coastal seeps of the Algoa Group Formation and the fractured aquifer of the Peninsula Formation. The results through mapping indicated an abundance of folds, faults, and fractures which all have implications for groundwater flow. The majority of fractures are striking in the NE-SW and NW-SE directions. The pumping test analysis also indicated fractal flow with significant matrix flow resulting in a dual porosity system up to at least 200m in depth. The transmissivity and storativity values range from 6.78 – 44.5 m2/day and 0.0172 – 0.0325, respectively. This is highly dependent on the fracture interconnectivity, which varies across the area and is higher at shallow depths, as suggested by the geophysical profiles. Geophysical profiles indicate that the contact between the Algoa Group Formations and the Peninsula Formation results in coastal seeps due to the difference in hydraulic conductivities. The hydrochemical analysis suggests that the seeps generally have Na-Cl and Ca-Mg-Cl water types. The groundwater in the eastern area has a Ca-HCO3 water type, and the groundwater in the western region has a Ca-Mg-Cl water type, with the Chelsea-Noordhoek Fault system separating the two groundwater signatures. Groundwater at greater depths has a Na-Cl water type with higher TDS values. The chemical signatures seen are due to external factors, which include sea sprays, anthropogenic activities, rock-water processes, and possibly connate water in the Peninsula Formation aquifer. The findings of this study offer valuable insights into the present conditions of the aquifer in Gqeberha. This research serves as a foundational study that can provide a baseline for future hydrogeological investigations in the area. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2023
- Full Text:
- Date Issued: 2023-12
Chemical analysis and biological activities of crude extracts and essential oil of selected medicinal plants from the Eastern Cape, South Africa, and Volta Region of Ghana
- Authors: Agbo, Irene Adzo
- Date: 2023-12
- Subjects: Medicinal plants , Lantana camara , Peptic ulcer -- Treatment , Traditional medicine - South Africa -- Eastern Cape , Traditional medicine -- Ghana
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/62431 , vital:72728
- Description: Lantana camara and Khaya grandifoliola extracts are among many plants found traditionally effective for the treatment of wounds and ulcers. This study assessed the phytochemical content, isolation and identification of single compounds from methanol and ethyl acetate extracts of Lantana camara and Khaya grandifoliola. Further, the bioactivity testing including antioxidant, antimicrobial and cytoxicity of the extracts was done to confirm the wound healing potential discovered by the traditional healers. Materials and methods: Extraction was done successively using maceration method with 100 % ethyl acetate and 100 % methanol with a biomass-to-solvent ratio of 1:3 (w/v) to obtain L. camara ethyl acetate extracts of berry (ELB), flower (ELF) and leaf (ELL) and methanol extracts of MLB, MLF, MLL and K. grandifoliola ethyl acetate extracts of leaf (EKL), root (EKR) and stem bark (EKSB) and methanol extracts of MKL, MKR, MKSB respectively. L. camara leaf essential oil (EO) was extracted using the hydro-distillation method with a Clevenger apparatus. Total phytochemical content was assessed for each extract using spectrophotometric methods and a calibration curve of standards: bromocresol green method with atropine; Folin–Ciocalteu colorimetric method with gallic acid, aluminium chloride colorimetric method with quercetin and concentrated sulphuric acid chloroform with linalool for total alkaloid, phenolic, flavonoid and terpenoid contents respectively. Single compound isolation and purification was conducted using chromatographic techniques. Elucidation of single compounds was done using spectrometric method, high resolution- mass spectrometry, and one and two-dimensional (1D and 2D)-NMR. Stereochemistry of each compound was confirmed using electronic circular dichroism spectra. A Crystalline compound was identified by single crystal X-ray diffraction using CuKα-radiation. In vitro bioactivities were assessed with methods such as 3-[4,5-dimethylthiazole-2-yl]-2,5-diphenyltetrazolium bromide, free radical scavenging activity of 1,1-diphenyl-2-picrylhydrazyl, inhibitory effect on nitric oxide production in lipopolysaccharide-activated RAW 264.7 macrophages, and 96-well plate micro dilution for cytotoxicity, ant-inflammatory and antimicrobial activity testing. Results: Methanol extracts of both plants retained high phytochemical concentrations of all the phytoconstituents investigated compared with the ethyl acetate extracts which retained lower concentrations. The results of the L. camara methanol extracts include; total alkaloid content (TAC) (2.05±0.18, 1.87±1.54 and 2.60±1.10 mg AEQ/100 mg); total phenolic content (TPC) (14.05±4.04, 34.59±3.01 and 18.58±1.87 mg GAEQ/100 mg); the total flavonoid content(TFC) of flower (12.45±1.87, 20.41±2.69 and mg QEQ/100 mg); total terpenoids (TTC) (20.74±2.34, 20.74±2.34 and 15.97±1.19 mg LIN EQ/100mg) of MLB, MLF and MLL respectively. Whereas that of the K. grandifoliola methanol extracts include; TAC (7.32±0.14,8.49±0.34, 10.67±0.22 mg AEQ/100 mg); TPC (37.49±1.40, 44.41±0.69, 53.57±1.50 mgGAEQ/100 mg); TFC (6.54±0.55, 9.58±0.89 and 10.26±0.92 mg QEQ/100 mg); TTC(10.16±1.41, 35.78±2.14 and 23.45±1.76 mg LIN EQ/100mg) of MKL, MKR and MKSB respectively. The major components of essential oil, out of the 71 constituents identified include Davanone D (32.91 %), Caryophyllene (5.07 %), Nerolidol 2 (3.56 %) and GermacreneD (3.13 %). Compounds 3.47 was isolated from the methanol extract of L. camara flowers. This compound is reported for the first time from the L. camara flower extract. Two compounds, compounds 4.23, and 4.26, were isolated from the methanol extract of K. grandifoliola roots, compound 4.22 was isolated from the ethyl acetate root extract while compounds 4.24 and 4.25 were isolated from the ethyl acetate stem bark extract as isomers in a mixture. Compounds 4.22 and 4.23 are reported from K. grandifoliola root for the first time. The isolated compounds (compounds 3.47 and 4.23) were nontoxic to the Vero cell line and this may contribute to possible stimulation of cell proliferation, promoting wound healing. Cytotoxicity describes extract virulence to Vero cell line. MLF and ELB were found nontoxic even at the highest concentration of 200 μg/mL. The MKSB and MKR, as well as the EKSB were nontoxic. Antioxidant activity results, described by the percentage inhibition in the DPPH assay, showed that MLF and MKSB had the highest antioxidant activities compared with the ascorbic acid standard, with IC50 of 38.68±5.09 and 37.03±11.95 μg/mL for L. camara and K. grandifoliola respectively. ELB exhibited a significant anti-inflammatory activity inhibiting NO• radical generation in the LPS-stimulated RAW 264.7 macrophages at concentration ranging from 50 and 100 μg/mL. EKSB and MKR showed significant anti-inflammatory activity at 100 and 200 μg/ml respectively. ELL and ELF demonstrated potent growth inhibition against S. pyogenes with an MIC value ≤ 0.125 mg/mL, while the MICs of the ELB and MLL were 0.5 mg/mL and 2 mg/mL respectively. MKSB and MKR and EKSB extract exhibited an effective growth inhibition against S. aureus with MIC of 1 mg/mL. The growth of S. pyogenes was supressed by both ethyl acetate and methanol extracts of all plant parts tested with MIC ranging from 0.25–2 mg/mL. Conclusion: The potent bioactivity shown in the results of the cytotoxicity, antioxidant activity, anti-inflammatory and antimicrobial activity testing, and the nontoxic singlecompounds of L. camara and K. grandifoliola extracts led to the conclusion that the two plants had wound healing potential. The study therefore confirmed their traditional uses for treatment of wounds. , Thesis (PhD) -- Faculty of Science, School of Biomolecular and Chemical Sciences, 2023
- Full Text:
- Date Issued: 2023-12
- Authors: Agbo, Irene Adzo
- Date: 2023-12
- Subjects: Medicinal plants , Lantana camara , Peptic ulcer -- Treatment , Traditional medicine - South Africa -- Eastern Cape , Traditional medicine -- Ghana
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/62431 , vital:72728
- Description: Lantana camara and Khaya grandifoliola extracts are among many plants found traditionally effective for the treatment of wounds and ulcers. This study assessed the phytochemical content, isolation and identification of single compounds from methanol and ethyl acetate extracts of Lantana camara and Khaya grandifoliola. Further, the bioactivity testing including antioxidant, antimicrobial and cytoxicity of the extracts was done to confirm the wound healing potential discovered by the traditional healers. Materials and methods: Extraction was done successively using maceration method with 100 % ethyl acetate and 100 % methanol with a biomass-to-solvent ratio of 1:3 (w/v) to obtain L. camara ethyl acetate extracts of berry (ELB), flower (ELF) and leaf (ELL) and methanol extracts of MLB, MLF, MLL and K. grandifoliola ethyl acetate extracts of leaf (EKL), root (EKR) and stem bark (EKSB) and methanol extracts of MKL, MKR, MKSB respectively. L. camara leaf essential oil (EO) was extracted using the hydro-distillation method with a Clevenger apparatus. Total phytochemical content was assessed for each extract using spectrophotometric methods and a calibration curve of standards: bromocresol green method with atropine; Folin–Ciocalteu colorimetric method with gallic acid, aluminium chloride colorimetric method with quercetin and concentrated sulphuric acid chloroform with linalool for total alkaloid, phenolic, flavonoid and terpenoid contents respectively. Single compound isolation and purification was conducted using chromatographic techniques. Elucidation of single compounds was done using spectrometric method, high resolution- mass spectrometry, and one and two-dimensional (1D and 2D)-NMR. Stereochemistry of each compound was confirmed using electronic circular dichroism spectra. A Crystalline compound was identified by single crystal X-ray diffraction using CuKα-radiation. In vitro bioactivities were assessed with methods such as 3-[4,5-dimethylthiazole-2-yl]-2,5-diphenyltetrazolium bromide, free radical scavenging activity of 1,1-diphenyl-2-picrylhydrazyl, inhibitory effect on nitric oxide production in lipopolysaccharide-activated RAW 264.7 macrophages, and 96-well plate micro dilution for cytotoxicity, ant-inflammatory and antimicrobial activity testing. Results: Methanol extracts of both plants retained high phytochemical concentrations of all the phytoconstituents investigated compared with the ethyl acetate extracts which retained lower concentrations. The results of the L. camara methanol extracts include; total alkaloid content (TAC) (2.05±0.18, 1.87±1.54 and 2.60±1.10 mg AEQ/100 mg); total phenolic content (TPC) (14.05±4.04, 34.59±3.01 and 18.58±1.87 mg GAEQ/100 mg); the total flavonoid content(TFC) of flower (12.45±1.87, 20.41±2.69 and mg QEQ/100 mg); total terpenoids (TTC) (20.74±2.34, 20.74±2.34 and 15.97±1.19 mg LIN EQ/100mg) of MLB, MLF and MLL respectively. Whereas that of the K. grandifoliola methanol extracts include; TAC (7.32±0.14,8.49±0.34, 10.67±0.22 mg AEQ/100 mg); TPC (37.49±1.40, 44.41±0.69, 53.57±1.50 mgGAEQ/100 mg); TFC (6.54±0.55, 9.58±0.89 and 10.26±0.92 mg QEQ/100 mg); TTC(10.16±1.41, 35.78±2.14 and 23.45±1.76 mg LIN EQ/100mg) of MKL, MKR and MKSB respectively. The major components of essential oil, out of the 71 constituents identified include Davanone D (32.91 %), Caryophyllene (5.07 %), Nerolidol 2 (3.56 %) and GermacreneD (3.13 %). Compounds 3.47 was isolated from the methanol extract of L. camara flowers. This compound is reported for the first time from the L. camara flower extract. Two compounds, compounds 4.23, and 4.26, were isolated from the methanol extract of K. grandifoliola roots, compound 4.22 was isolated from the ethyl acetate root extract while compounds 4.24 and 4.25 were isolated from the ethyl acetate stem bark extract as isomers in a mixture. Compounds 4.22 and 4.23 are reported from K. grandifoliola root for the first time. The isolated compounds (compounds 3.47 and 4.23) were nontoxic to the Vero cell line and this may contribute to possible stimulation of cell proliferation, promoting wound healing. Cytotoxicity describes extract virulence to Vero cell line. MLF and ELB were found nontoxic even at the highest concentration of 200 μg/mL. The MKSB and MKR, as well as the EKSB were nontoxic. Antioxidant activity results, described by the percentage inhibition in the DPPH assay, showed that MLF and MKSB had the highest antioxidant activities compared with the ascorbic acid standard, with IC50 of 38.68±5.09 and 37.03±11.95 μg/mL for L. camara and K. grandifoliola respectively. ELB exhibited a significant anti-inflammatory activity inhibiting NO• radical generation in the LPS-stimulated RAW 264.7 macrophages at concentration ranging from 50 and 100 μg/mL. EKSB and MKR showed significant anti-inflammatory activity at 100 and 200 μg/ml respectively. ELL and ELF demonstrated potent growth inhibition against S. pyogenes with an MIC value ≤ 0.125 mg/mL, while the MICs of the ELB and MLL were 0.5 mg/mL and 2 mg/mL respectively. MKSB and MKR and EKSB extract exhibited an effective growth inhibition against S. aureus with MIC of 1 mg/mL. The growth of S. pyogenes was supressed by both ethyl acetate and methanol extracts of all plant parts tested with MIC ranging from 0.25–2 mg/mL. Conclusion: The potent bioactivity shown in the results of the cytotoxicity, antioxidant activity, anti-inflammatory and antimicrobial activity testing, and the nontoxic singlecompounds of L. camara and K. grandifoliola extracts led to the conclusion that the two plants had wound healing potential. The study therefore confirmed their traditional uses for treatment of wounds. , Thesis (PhD) -- Faculty of Science, School of Biomolecular and Chemical Sciences, 2023
- Full Text:
- Date Issued: 2023-12
Dietary assessment of Cape Gannets (Morus capensis) and African Penguins (Spheniscus demersus) in Algoa Bay using molecular scatology
- Bowmaker - Falconer, Kezia, Von Der Heyden, Sophie
- Authors: Bowmaker - Falconer, Kezia , Von Der Heyden, Sophie
- Date: 2023-12
- Subjects: Gannets , Gannets -- Food , Sea birds -- South Africa -- Bird Island, Algoa Bay.
- Language: English
- Type: Master's theses
- Identifier: http://hdl.handle.net/10948/62420 , vital:72675
- Description: Seabirds are important marine sentinels, providing valuable information about ecosystem health and condition. Dietary studies of seabirds can inform on ecosystem functioning through identifying the condition and changes occurring in their surrounding environment. Dietary studies are also crucial as they can identify threats that seabirds face. Until recently, the diets of southern African endemic and Endangered Cape Gannets Morus capensis and African Penguins Spheniscus demersus were solely investigated through stomach content analyses, which allows for the identification and quantification of prey remains. To overcome some of the limitations associated with stomach content analysis, stable isotope and fatty acid analyses were proposed. However, these methods still require bird handling and thus impose some stress on the birds. DNA metabarcoding of faecal matter shows promise as a completely noninvasive method for seabird dietary studies. This thesis first examined whether DNA metabarcoding could be used to determine the diet of Cape Gannet and African Penguin breeding in Algoa Bay, South Africa. Then, this method was used to investigate the influence of intrinsic (both seabird species) and extrinsic (African Penguins) factors on the diet of the two seabird species. For the first data chapter, stomach content samples and faecal matter were collected concurrently from breeding Cape Gannets and African Penguins on Bird Island. DNA was successfully extracted from most faecal matter samples and the primers (18S_SSU, 16S_Fish) used for group, taxa and fish prey identification allowed amplification of prey DNA for both study species. A similar piscivorous diet was determined by both dietary methods for Cape Gannets with Sardine Sardinops sagax and Atlantic Saury Scomberesox saurus dominating the diet. Sardine also dominated the African Penguin diet in both dietary methods. In addition, DNA metabarcoding in African Penguins revealed a more diverse diet compared to the one determined by stomach content analysis. This was likely due to the limitations on the allowed number of stomach content samples to be collected for that Endangered species. Non-invasive DNA metabarcoding of faecal matter was then used to investigate whether the diet varied with breeding stages (incubation, chick-rearing) and age classes (chick-rearing adults, chicks) in both seabird species, but also breeding colonies (Algoa Bay: Bird Island, St Croix Island) in African Penguins. DNA metabarcoding revealed that breeding stages influenced the diet of Cape Gannets and African Penguins on Bird Island where prey species diversity was greater for incubating adults. On the contrary, the diet of incubating and chick-rearing penguins on St Croix Island was similar. When comparing the diet of African Penguins between Bird Island and St Croix Island, there was an increased overlap in diet composition between incubating and chick-rearing adults on St Croix Island when compared to Bird Island. Importantly, DNA metabarcoding indicated an increase in fishery interactions in Algoa Bay, particularly for Cape Gannets and the hake Merluccius spp. fishery, where the contribution of hake to chick-rearing adults and chick diet was considerably greater than incubating adult diet. In this study, I showed that DNA metabarcoding of faecal matter provides an opportunity for non-invasive dietary studies in two southern African endemic and Endangered seabird species. Incorporating non-invasive methods as a complement to other dietary methods for monitoring seabird trophic ecology is crucial when considering the worsening status of several seabird species. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2023
- Full Text:
- Date Issued: 2023-12
- Authors: Bowmaker - Falconer, Kezia , Von Der Heyden, Sophie
- Date: 2023-12
- Subjects: Gannets , Gannets -- Food , Sea birds -- South Africa -- Bird Island, Algoa Bay.
- Language: English
- Type: Master's theses
- Identifier: http://hdl.handle.net/10948/62420 , vital:72675
- Description: Seabirds are important marine sentinels, providing valuable information about ecosystem health and condition. Dietary studies of seabirds can inform on ecosystem functioning through identifying the condition and changes occurring in their surrounding environment. Dietary studies are also crucial as they can identify threats that seabirds face. Until recently, the diets of southern African endemic and Endangered Cape Gannets Morus capensis and African Penguins Spheniscus demersus were solely investigated through stomach content analyses, which allows for the identification and quantification of prey remains. To overcome some of the limitations associated with stomach content analysis, stable isotope and fatty acid analyses were proposed. However, these methods still require bird handling and thus impose some stress on the birds. DNA metabarcoding of faecal matter shows promise as a completely noninvasive method for seabird dietary studies. This thesis first examined whether DNA metabarcoding could be used to determine the diet of Cape Gannet and African Penguin breeding in Algoa Bay, South Africa. Then, this method was used to investigate the influence of intrinsic (both seabird species) and extrinsic (African Penguins) factors on the diet of the two seabird species. For the first data chapter, stomach content samples and faecal matter were collected concurrently from breeding Cape Gannets and African Penguins on Bird Island. DNA was successfully extracted from most faecal matter samples and the primers (18S_SSU, 16S_Fish) used for group, taxa and fish prey identification allowed amplification of prey DNA for both study species. A similar piscivorous diet was determined by both dietary methods for Cape Gannets with Sardine Sardinops sagax and Atlantic Saury Scomberesox saurus dominating the diet. Sardine also dominated the African Penguin diet in both dietary methods. In addition, DNA metabarcoding in African Penguins revealed a more diverse diet compared to the one determined by stomach content analysis. This was likely due to the limitations on the allowed number of stomach content samples to be collected for that Endangered species. Non-invasive DNA metabarcoding of faecal matter was then used to investigate whether the diet varied with breeding stages (incubation, chick-rearing) and age classes (chick-rearing adults, chicks) in both seabird species, but also breeding colonies (Algoa Bay: Bird Island, St Croix Island) in African Penguins. DNA metabarcoding revealed that breeding stages influenced the diet of Cape Gannets and African Penguins on Bird Island where prey species diversity was greater for incubating adults. On the contrary, the diet of incubating and chick-rearing penguins on St Croix Island was similar. When comparing the diet of African Penguins between Bird Island and St Croix Island, there was an increased overlap in diet composition between incubating and chick-rearing adults on St Croix Island when compared to Bird Island. Importantly, DNA metabarcoding indicated an increase in fishery interactions in Algoa Bay, particularly for Cape Gannets and the hake Merluccius spp. fishery, where the contribution of hake to chick-rearing adults and chick diet was considerably greater than incubating adult diet. In this study, I showed that DNA metabarcoding of faecal matter provides an opportunity for non-invasive dietary studies in two southern African endemic and Endangered seabird species. Incorporating non-invasive methods as a complement to other dietary methods for monitoring seabird trophic ecology is crucial when considering the worsening status of several seabird species. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2023
- Full Text:
- Date Issued: 2023-12
Effects of annealing on the structural and optical properties of nanostructured TiO2
- Talla, Assane, Urgessa, Zelalem
- Authors: Talla, Assane , Urgessa, Zelalem
- Date: 2023-12
- Subjects: Titanium dioxide , Nanostructured materials , Nanotubes
- Language: English
- Type: Doctorial theses , text
- Identifier: http://hdl.handle.net/10948/62655 , vital:72907
- Description: In this thesis, the structural, morphological and optical properties of titanium dioxide (TiO2) are investigated. Titanium dioxide (TiO2) nanotubes are prepared by anodic oxidation of titanium foil. The as-anodised samples are thermally annealed at various temperatures in nitrogen, air, oxygen and vacuum. The purpose is to study how the annealing conditions affect the properties of the nanostructures, including the anatase to rutile phase transformation. In all annealing atmospheres, except in vacuum, the dominant phase is found to be anatase when annealing is performed up to 600 oC. Above 700 oC the rutile phase becomes dominant. The anatase phase is stable above 600 oC in vacuum and does not evolve significantly up to 900 oC. The morphologies of the tubes tend to deteriorate with increased annealing temperature, in nitrogen, air and oxygen atmospheres, due to sintering effects. However, the integrity of the nanotubes is maintained up to 900 oC in vacuum. The photoluminescence (PL) spectra suggest mainly the presence of oxygen vacancies and self-trapped excitons, with respective emission bands around 2.5 eV and 2.3 eV. The results show that both the annealing temperature and atmosphere strongly influence the crystalline and optical properties of the TiO2 nanotubes. In addition, the phase transformation from anatase to rutile for samples annealed in an oxygen-rich environment is investigated in detail. Complementary structural information obtained from transmission electron microscopy and Raman analysis for oxygen-annealed samples reveals that the nucleation of the rutile phase starts from the titanium substrate and then propagates along the tubes. The results provide suitable annealing conditions to control the phase content and morphology of anodic TiO2 nanotubes. The PL characteristics of bulk crystalline anatase TiO2, namely virgin and hydrogen-annealed at 600 oC for 1 h, are studied. The low temperature PL spectra at 5.5 K shows near band edge (NBE) emissions with two dominant lines ascribed to shallow donor bound exciton and possibly free to bound recombination. The two main transitions are assisted by optical phononmodes. Temperature-dependent PL measurements performed on these anatase crystals reveal that the donor bound exciton is stable below 90 K. Hydrogen trapped in oxygen vacancies is proposed to be the shallow donor. In addition, two activation processes are involved for the thermal quenching of donor bound excitons. The total activation energy is found to correlate well with the localisation energy of the bound exciton. Site-selective PL spectra obtained from anodic TiO2 tubes reveals that the luminescence of the nanostructures depends on the morphology. The result shows unusual near-band edge emission (NBE) for these structures, which is rarely observed in indirect band gap TiO2. , Thesis (PhD) -- Faculty of Science, School of Biomolecular and Chemical Sciences, 2023
- Full Text:
- Date Issued: 2023-12
- Authors: Talla, Assane , Urgessa, Zelalem
- Date: 2023-12
- Subjects: Titanium dioxide , Nanostructured materials , Nanotubes
- Language: English
- Type: Doctorial theses , text
- Identifier: http://hdl.handle.net/10948/62655 , vital:72907
- Description: In this thesis, the structural, morphological and optical properties of titanium dioxide (TiO2) are investigated. Titanium dioxide (TiO2) nanotubes are prepared by anodic oxidation of titanium foil. The as-anodised samples are thermally annealed at various temperatures in nitrogen, air, oxygen and vacuum. The purpose is to study how the annealing conditions affect the properties of the nanostructures, including the anatase to rutile phase transformation. In all annealing atmospheres, except in vacuum, the dominant phase is found to be anatase when annealing is performed up to 600 oC. Above 700 oC the rutile phase becomes dominant. The anatase phase is stable above 600 oC in vacuum and does not evolve significantly up to 900 oC. The morphologies of the tubes tend to deteriorate with increased annealing temperature, in nitrogen, air and oxygen atmospheres, due to sintering effects. However, the integrity of the nanotubes is maintained up to 900 oC in vacuum. The photoluminescence (PL) spectra suggest mainly the presence of oxygen vacancies and self-trapped excitons, with respective emission bands around 2.5 eV and 2.3 eV. The results show that both the annealing temperature and atmosphere strongly influence the crystalline and optical properties of the TiO2 nanotubes. In addition, the phase transformation from anatase to rutile for samples annealed in an oxygen-rich environment is investigated in detail. Complementary structural information obtained from transmission electron microscopy and Raman analysis for oxygen-annealed samples reveals that the nucleation of the rutile phase starts from the titanium substrate and then propagates along the tubes. The results provide suitable annealing conditions to control the phase content and morphology of anodic TiO2 nanotubes. The PL characteristics of bulk crystalline anatase TiO2, namely virgin and hydrogen-annealed at 600 oC for 1 h, are studied. The low temperature PL spectra at 5.5 K shows near band edge (NBE) emissions with two dominant lines ascribed to shallow donor bound exciton and possibly free to bound recombination. The two main transitions are assisted by optical phononmodes. Temperature-dependent PL measurements performed on these anatase crystals reveal that the donor bound exciton is stable below 90 K. Hydrogen trapped in oxygen vacancies is proposed to be the shallow donor. In addition, two activation processes are involved for the thermal quenching of donor bound excitons. The total activation energy is found to correlate well with the localisation energy of the bound exciton. Site-selective PL spectra obtained from anodic TiO2 tubes reveals that the luminescence of the nanostructures depends on the morphology. The result shows unusual near-band edge emission (NBE) for these structures, which is rarely observed in indirect band gap TiO2. , Thesis (PhD) -- Faculty of Science, School of Biomolecular and Chemical Sciences, 2023
- Full Text:
- Date Issued: 2023-12