Photocatalytic reduction of CO2 by cobalt doped TiO2 and ZnO micro/nanostructured materials
- Authors: Mgolombane, Mvano
- Date: 2020
- Subjects: Nanostructures , Catalysis , Nanotechnology , Chemistry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/49171 , vital:41607
- Description: Large emissions of carbon dioxide (CO2) in the atmosphere have caused many harmful effects on humans and the environment. Carbon dioxide is a good source C and is used in a number of applications such as synthesis of fossil fuels. Redox reaction of CO2 and H2O with photocatalysts such as TiO2 and ZnO to produce solar fuels is a promising approach in reducing the environmental impacts of greenhouse gasses. This dissertation describes an in-depth synthesis of four photochemical catalysts and their photocatalytic conversion of CO2 to methanol, thereby addressing the above-mentioned problems by applying synthesised nano-based catalysts. Prior to photocatalytic reduction studies, catalysts such as TiO2, Co-doped TiO2, Co-doped TiO2/rGO, ZnO, Co-doped ZnO and Co-doped ZnO/rGO were synthesized and characterized using various spectroscopic and imaging techniques such as Powder X-Ray Diffraction (PXRD), Scanning Electron Microscopy (SEM), Transmission Electron Micrograph (TEM), X-ray Photoelectron Spectroscopy (XPS), Brunner- Emmet- Teller measurement (BET), Thermogravimetry Analysis (TGA) and UV-Vis Diffuse Reflectance Spectroscopy (UV-Vis-DRS). The conversion yield of CO2 to methanol on TiO2, Co-doped TiO2 and Co-doped TiO2/rGO reached 32.3 μmol/gcat, 730 μmol/gcat and 936 μmol/gcat, respectively, after 7 h of irradiation. Theoretical studies via Density functional theory (DFT) revealed that doping TiO2 with Co ions facilitated the formation of adsorbed carbonate or CO2•- species, as CO2 adsorbs onto Co-doped TiO2 surface with binding energy (BE) of -18.12 KJ/mol. The photocatalytic activities of ZnO-based nanomaterials found that Co-doped ZnO/rGO with high ratio of Co, reduced graphene (rGO) and large surface area (10.62 m2g-1) possessed higher CH3OH (30.1 μmol/g) in comparison with Co-doped ZnO (27.3 μmol/g) and ZnO (7.5 μmol/g). The research will deepen the understanding that TiO2 based photocatalyst show higher activity and the mole ratio (Ti/Zn:Co) influences nanocomposites performance and provide new ideas for designing efficient photocatalysts.
- Full Text:
- Date Issued: 2020
- Authors: Mgolombane, Mvano
- Date: 2020
- Subjects: Nanostructures , Catalysis , Nanotechnology , Chemistry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/49171 , vital:41607
- Description: Large emissions of carbon dioxide (CO2) in the atmosphere have caused many harmful effects on humans and the environment. Carbon dioxide is a good source C and is used in a number of applications such as synthesis of fossil fuels. Redox reaction of CO2 and H2O with photocatalysts such as TiO2 and ZnO to produce solar fuels is a promising approach in reducing the environmental impacts of greenhouse gasses. This dissertation describes an in-depth synthesis of four photochemical catalysts and their photocatalytic conversion of CO2 to methanol, thereby addressing the above-mentioned problems by applying synthesised nano-based catalysts. Prior to photocatalytic reduction studies, catalysts such as TiO2, Co-doped TiO2, Co-doped TiO2/rGO, ZnO, Co-doped ZnO and Co-doped ZnO/rGO were synthesized and characterized using various spectroscopic and imaging techniques such as Powder X-Ray Diffraction (PXRD), Scanning Electron Microscopy (SEM), Transmission Electron Micrograph (TEM), X-ray Photoelectron Spectroscopy (XPS), Brunner- Emmet- Teller measurement (BET), Thermogravimetry Analysis (TGA) and UV-Vis Diffuse Reflectance Spectroscopy (UV-Vis-DRS). The conversion yield of CO2 to methanol on TiO2, Co-doped TiO2 and Co-doped TiO2/rGO reached 32.3 μmol/gcat, 730 μmol/gcat and 936 μmol/gcat, respectively, after 7 h of irradiation. Theoretical studies via Density functional theory (DFT) revealed that doping TiO2 with Co ions facilitated the formation of adsorbed carbonate or CO2•- species, as CO2 adsorbs onto Co-doped TiO2 surface with binding energy (BE) of -18.12 KJ/mol. The photocatalytic activities of ZnO-based nanomaterials found that Co-doped ZnO/rGO with high ratio of Co, reduced graphene (rGO) and large surface area (10.62 m2g-1) possessed higher CH3OH (30.1 μmol/g) in comparison with Co-doped ZnO (27.3 μmol/g) and ZnO (7.5 μmol/g). The research will deepen the understanding that TiO2 based photocatalyst show higher activity and the mole ratio (Ti/Zn:Co) influences nanocomposites performance and provide new ideas for designing efficient photocatalysts.
- Full Text:
- Date Issued: 2020
Physical and thermal properties of binary and ternary blends of polypropylene, crumb rubber and wood flour
- Authors: Mosia, Lefika Ellen
- Date: 2020
- Subjects: Polypropylene , Polymers Materials science
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/49193 , vital:41609
- Description: The properties of binary and ternary blends of polypropylene (PP), crumb rubber (CR) and wood flour (WF), with and without ethylene-1-butene as a compatibiliser, were studied. The design of experiment (DoE) was used to determine the proportions of each component for various composites. The components were mixed using the Haake Thermo scientific Polylab QC internal mixer and the crumbs were then moulded into different shapes using the ARBURG 221-55-250 injection moulding machine. The properties of the blends were investigated using a scanning electron microscope (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanic analysis (DMA), tensile tester, water absorption and thickness swelling tests. The morphology of the blends showed the agglomeration of fillers (CR and WF) and more voids on untreated blends but on the treated blends fewer voids as well as improved distribution and dispersion were observed. PP bonded better with WF than with CR. The incorporation of both fillers improved the thermal stability, glass transition temperature, and melt temperature as well as crystallisation temperatures of the blends. Yet these fillers reduced the tensile strength and the yield strength of PP. The addition of WF increased the elongation at break and hardness of the blends but decreased the impact strength of the blends, whereas the addition of CR improved the elongation at break and impact strength of the blends and decreased the hardness of the blends. The blends with more WF absorbed more water and swelled more than the blends containing a high amount of CR. The incorporation of compatibiliser further decreased the tensile strength but improved the thermal stability and elongation at break of the blends. The water absorption and swelling of the blends seemed to decrease with the addition of the compatibiliser whereas the hardness increased. The impact strength of the blends containing more WF, increased after the addition of compatibiliser. The ternary blends showed better results than the binary blends.
- Full Text:
- Date Issued: 2020
- Authors: Mosia, Lefika Ellen
- Date: 2020
- Subjects: Polypropylene , Polymers Materials science
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/49193 , vital:41609
- Description: The properties of binary and ternary blends of polypropylene (PP), crumb rubber (CR) and wood flour (WF), with and without ethylene-1-butene as a compatibiliser, were studied. The design of experiment (DoE) was used to determine the proportions of each component for various composites. The components were mixed using the Haake Thermo scientific Polylab QC internal mixer and the crumbs were then moulded into different shapes using the ARBURG 221-55-250 injection moulding machine. The properties of the blends were investigated using a scanning electron microscope (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanic analysis (DMA), tensile tester, water absorption and thickness swelling tests. The morphology of the blends showed the agglomeration of fillers (CR and WF) and more voids on untreated blends but on the treated blends fewer voids as well as improved distribution and dispersion were observed. PP bonded better with WF than with CR. The incorporation of both fillers improved the thermal stability, glass transition temperature, and melt temperature as well as crystallisation temperatures of the blends. Yet these fillers reduced the tensile strength and the yield strength of PP. The addition of WF increased the elongation at break and hardness of the blends but decreased the impact strength of the blends, whereas the addition of CR improved the elongation at break and impact strength of the blends and decreased the hardness of the blends. The blends with more WF absorbed more water and swelled more than the blends containing a high amount of CR. The incorporation of compatibiliser further decreased the tensile strength but improved the thermal stability and elongation at break of the blends. The water absorption and swelling of the blends seemed to decrease with the addition of the compatibiliser whereas the hardness increased. The impact strength of the blends containing more WF, increased after the addition of compatibiliser. The ternary blends showed better results than the binary blends.
- Full Text:
- Date Issued: 2020
Prediction of mass spectra for natural products using an ab initio approach
- Authors: Novokoza, Yolanda
- Date: 2020
- Subjects: Molecular dynamics , Molecular dynamics -- Computer simulation , Mass spectroscopy , Electron impact ionization
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/167166 , vital:41443
- Description: Mass spectrometry (MS) is a technique that measures the fragmentation of molecules, dependent on the molecule’s chemical composition and structure, by first introducing a charge on the molecules. The instrument records the mass to charge ratio, but the energy from the ionization process causes the molecule to fragment. The resultant mass spectrum is highly indicative of not only the molecule analyzed, but also its chemical composition. MS is used in research and industry for both routine and research purposes. One such way to ionize molecules for MS is by bombarding the molecule with electrons which is the basis of electron impact mass spectrometry (EIMS). Although EIMS is widely used, prediction of electron impact mass spectra from first principles is a challenging problem due to a need to accurately determine the probability of different fragmentation pathways of a molecule. Ab initio molecular dynamics based methods are able to explore in an automatic fashion the energetically available fragmentation paths thus give reaction mechanisms in an unbiased way. The mass spectra of five molecules have been explored in work-flows leading to the prediction of mass spectra. These molecules include three natural products alpha-hispanolol, PFB oxime derivative and boronolide (for which experimental mass spectra were not available) and two compounds from the NIST database (for which experimental mass spectra were available). For each of these systems many random conformations were generated using the RDKit library. To all conformations random velocities were applied to each atom. Ab initio molecular dynamics was performed on each conformer, using these initial random velocities using CP2K software, at DFTB+ level at a variety of highly raised temperatures (to accelerate the formation of fragments) Fragmentation was monitored by iterating through all bonds, and identifying bond breakages during dynamics. Graph theoretical packages were used then to track distinct fragments generated. For each of these fragments, charges were determined from Mulliken analysis for all atoms on the fragment from the QM calculations and sum of atomic spin densities per fragment was also plotted. The fragment with the greatest charge (corresponding to the formation of a cation fragment) was taken for plotting on the mass spectrum. Finally, from the mass of the fragment and its elemental composition, the isotopic distribution for the fragment was determined, and this distribution was included by addition in to the mass spectrum. For all trajectories, the sum of all isotopic distributions determined the final mass spectrum.
- Full Text:
- Date Issued: 2020
- Authors: Novokoza, Yolanda
- Date: 2020
- Subjects: Molecular dynamics , Molecular dynamics -- Computer simulation , Mass spectroscopy , Electron impact ionization
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/167166 , vital:41443
- Description: Mass spectrometry (MS) is a technique that measures the fragmentation of molecules, dependent on the molecule’s chemical composition and structure, by first introducing a charge on the molecules. The instrument records the mass to charge ratio, but the energy from the ionization process causes the molecule to fragment. The resultant mass spectrum is highly indicative of not only the molecule analyzed, but also its chemical composition. MS is used in research and industry for both routine and research purposes. One such way to ionize molecules for MS is by bombarding the molecule with electrons which is the basis of electron impact mass spectrometry (EIMS). Although EIMS is widely used, prediction of electron impact mass spectra from first principles is a challenging problem due to a need to accurately determine the probability of different fragmentation pathways of a molecule. Ab initio molecular dynamics based methods are able to explore in an automatic fashion the energetically available fragmentation paths thus give reaction mechanisms in an unbiased way. The mass spectra of five molecules have been explored in work-flows leading to the prediction of mass spectra. These molecules include three natural products alpha-hispanolol, PFB oxime derivative and boronolide (for which experimental mass spectra were not available) and two compounds from the NIST database (for which experimental mass spectra were available). For each of these systems many random conformations were generated using the RDKit library. To all conformations random velocities were applied to each atom. Ab initio molecular dynamics was performed on each conformer, using these initial random velocities using CP2K software, at DFTB+ level at a variety of highly raised temperatures (to accelerate the formation of fragments) Fragmentation was monitored by iterating through all bonds, and identifying bond breakages during dynamics. Graph theoretical packages were used then to track distinct fragments generated. For each of these fragments, charges were determined from Mulliken analysis for all atoms on the fragment from the QM calculations and sum of atomic spin densities per fragment was also plotted. The fragment with the greatest charge (corresponding to the formation of a cation fragment) was taken for plotting on the mass spectrum. Finally, from the mass of the fragment and its elemental composition, the isotopic distribution for the fragment was determined, and this distribution was included by addition in to the mass spectrum. For all trajectories, the sum of all isotopic distributions determined the final mass spectrum.
- Full Text:
- Date Issued: 2020
Profitable day-neutral strawberry variety and planting date combination for year-round strawberry fruit production in the Southern Cape
- Authors: Parehwa, Patience
- Date: 2020
- Subjects: Strawberries -- Fertilizers
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/48599 , vital:40894
- Description: South Africa’s strawberry production is currently limited to winter and spring production. Strawberry growers have not been able to extend the growing season for year-round strawberry production primarily due to variety- and climatic limitations. Consumers world-wide, however, demand year-round supply of strawberries on their markets. Delayed planting and robust day-neutral varieties may allow growers to extend the marketing season. To investigate the most profitable variety and planting date combination for season extension in the Southern Cape, trials were conducted at Groeneweide Farm, George. Day-neutral strawberry varieties Monterey, San Andreas and Albion were planted at 30-day intervals from April to September for 3 seasons. They were planted in single layer, standard coir grow-bags at a density of 75 000/ha. Analyses of variance (ANOVA) were performed on vegetative growth stages (crown and runner formation), yield (flowering and fruit yield), fruit quality (fruit mass and total soluble solids content) and gross income. The analysis encompassed variety, month and planting month × variety interaction. ‘Monterey’ significantly outperformed ‘San Andreas’ which in turn significantly (p<0.05) outperformed ‘Albion’ for crown number, flower number, yield, fruit size and margin above cost. ‘San Andreas’ produced significantly fewer runners than ‘Monterey’ and ‘Albion’. ‘Albion’ produced significantly higher TSS followed by ‘Monterey’ and ‘San Andreas’. Over all, the three day-neutral varieties had no significant differences in yield within all planting dates. However, August and September planting dates produced significantly more runners, flowers and higher margin above cost, but significantly smaller fruit and lower total soluble solids (TSS). ‘Monterey’ planted in April and May produced the highest margin above cost and brought earliness to the production window. Together with ‘San Andreas’ planted in August, which extended the harvest season and gave similar margin above cost, it is possible to maximise profitability, extend both ends of the harvest season and also minimise hygiene costs associated with weekly runner removal. Since the strawberry price is very responsive, to quantity supplied, an oversupply out of the normal season, may however lead to lower prices affecting gross income.
- Full Text:
- Date Issued: 2020
- Authors: Parehwa, Patience
- Date: 2020
- Subjects: Strawberries -- Fertilizers
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/48599 , vital:40894
- Description: South Africa’s strawberry production is currently limited to winter and spring production. Strawberry growers have not been able to extend the growing season for year-round strawberry production primarily due to variety- and climatic limitations. Consumers world-wide, however, demand year-round supply of strawberries on their markets. Delayed planting and robust day-neutral varieties may allow growers to extend the marketing season. To investigate the most profitable variety and planting date combination for season extension in the Southern Cape, trials were conducted at Groeneweide Farm, George. Day-neutral strawberry varieties Monterey, San Andreas and Albion were planted at 30-day intervals from April to September for 3 seasons. They were planted in single layer, standard coir grow-bags at a density of 75 000/ha. Analyses of variance (ANOVA) were performed on vegetative growth stages (crown and runner formation), yield (flowering and fruit yield), fruit quality (fruit mass and total soluble solids content) and gross income. The analysis encompassed variety, month and planting month × variety interaction. ‘Monterey’ significantly outperformed ‘San Andreas’ which in turn significantly (p<0.05) outperformed ‘Albion’ for crown number, flower number, yield, fruit size and margin above cost. ‘San Andreas’ produced significantly fewer runners than ‘Monterey’ and ‘Albion’. ‘Albion’ produced significantly higher TSS followed by ‘Monterey’ and ‘San Andreas’. Over all, the three day-neutral varieties had no significant differences in yield within all planting dates. However, August and September planting dates produced significantly more runners, flowers and higher margin above cost, but significantly smaller fruit and lower total soluble solids (TSS). ‘Monterey’ planted in April and May produced the highest margin above cost and brought earliness to the production window. Together with ‘San Andreas’ planted in August, which extended the harvest season and gave similar margin above cost, it is possible to maximise profitability, extend both ends of the harvest season and also minimise hygiene costs associated with weekly runner removal. Since the strawberry price is very responsive, to quantity supplied, an oversupply out of the normal season, may however lead to lower prices affecting gross income.
- Full Text:
- Date Issued: 2020
Retrospective analysis of birth HIV PCR testing and follow-up of positive HIV PCR results in Nelson Mandela Bay Health District
- Authors: Makubalo, Nomlindo Princess
- Date: 2020
- Subjects: HIV infections -- South Africa -- Nelson Mandela Bay
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/46351 , vital:39580
- Description: BACKGROUND HIV infection contributes significantly to infant morbidity and mortality, especially in high-prevalence, low-income countries. In view of this evidence-based knowledge, South Africa’s National Department of Health, in April 2015, released the National Consolidated Guidelines of Human Immunodeficiency Virus (HIV) stipulating that all HIV-exposed babies should have a HIV Polymer Chain Reaction (PCR) test performed at birth. Early infant diagnosis (EID) means early initiation of combined antiretroviral treatment (cART) and a reduction in the incidence of early infant HIV-related mortality. However, these guidelines can only be successful if implemented properly across all public sector healthcare institutions. Thus,the research question was,“How well has the Nelson Mandela Bay Health District implemented the EID?”AIM The aim of the study was to review the impact of the consolidated HIV guidelines on birth HIV-PCR testing and initiation of treatment in the Nelson Mandela Bay Health District. METHOD A retrospective quantitative longitudinal non-experimental design was used.The study consisted of two components,namely,analysis of NHLS databases, particularly HIV birth PCR results of infants over a three-year period (June 2015 to June 2018),and analysis of feedback received from the primary health care clinics. The feedback focused on infants with a positive-birth PCR test, using a purpose-designed data collection tool that was used by the clinics for the duration of the same three-year period. The paper-based tool documented antenatal care attendance, enrolment into the prevention of mother-to-child transmission (PMTCT) programme and initiation of ART. RESULTS Over the three-year period, there were approximately 13,096 live births to HIV-positive women in the study area, and a total of 11,066 HIV birth PCR tests were done over xiiithe three-year study period (84.5% of HIV-exposed infants). The birth HIV PCR was negative in 10,909 (98.6%) neonates, while 130 (1.2%) of neonates had positive-birth HIV PCR tests,and a further 27 (0.2%) had indeterminate results. The birth HIV PCR positivity rate reduced from 1.4%(2015)to 1%(2018)over the three-year study period. Of the 130 infants with positive-birth HIV PCR, the files of 42 children were excluded, and further analysis conducted on the files of 88 infants. cART was initiated within seven days in only nine of the 88 infants (10.2%). ARV initiation was delayed for 58 infants (65.9%) and 21 neonates (23.9%) were never initiated on cART. Among the 88 mothers of infants, more than one-third (38.6%) of pregnant women did not attend antenatal care, thus,compromising their opportunity to be enrolled on the PMTCT programme. Of those who attended antenatal care, only 39.1% were reported to attend antenatal care before 20 weeks CONCLUSION AND RECOMMENDATIONS The incidence of positive-birth HIV PCR has reduced from 1.4% in 2015 to 1% in 2018 whilst there has been an increase in birth HIV PCR testing. However, initiation of cART within seven days was achieved in only 10.2% of infants with positive-birth HIV PCR test results. Implementation of point-of-care birth HIV PCR testing would ensure that results are immediately available resulting in increasing the proportion of infants initiated on cART within seven days.
- Full Text:
- Date Issued: 2020
- Authors: Makubalo, Nomlindo Princess
- Date: 2020
- Subjects: HIV infections -- South Africa -- Nelson Mandela Bay
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/46351 , vital:39580
- Description: BACKGROUND HIV infection contributes significantly to infant morbidity and mortality, especially in high-prevalence, low-income countries. In view of this evidence-based knowledge, South Africa’s National Department of Health, in April 2015, released the National Consolidated Guidelines of Human Immunodeficiency Virus (HIV) stipulating that all HIV-exposed babies should have a HIV Polymer Chain Reaction (PCR) test performed at birth. Early infant diagnosis (EID) means early initiation of combined antiretroviral treatment (cART) and a reduction in the incidence of early infant HIV-related mortality. However, these guidelines can only be successful if implemented properly across all public sector healthcare institutions. Thus,the research question was,“How well has the Nelson Mandela Bay Health District implemented the EID?”AIM The aim of the study was to review the impact of the consolidated HIV guidelines on birth HIV-PCR testing and initiation of treatment in the Nelson Mandela Bay Health District. METHOD A retrospective quantitative longitudinal non-experimental design was used.The study consisted of two components,namely,analysis of NHLS databases, particularly HIV birth PCR results of infants over a three-year period (June 2015 to June 2018),and analysis of feedback received from the primary health care clinics. The feedback focused on infants with a positive-birth PCR test, using a purpose-designed data collection tool that was used by the clinics for the duration of the same three-year period. The paper-based tool documented antenatal care attendance, enrolment into the prevention of mother-to-child transmission (PMTCT) programme and initiation of ART. RESULTS Over the three-year period, there were approximately 13,096 live births to HIV-positive women in the study area, and a total of 11,066 HIV birth PCR tests were done over xiiithe three-year study period (84.5% of HIV-exposed infants). The birth HIV PCR was negative in 10,909 (98.6%) neonates, while 130 (1.2%) of neonates had positive-birth HIV PCR tests,and a further 27 (0.2%) had indeterminate results. The birth HIV PCR positivity rate reduced from 1.4%(2015)to 1%(2018)over the three-year study period. Of the 130 infants with positive-birth HIV PCR, the files of 42 children were excluded, and further analysis conducted on the files of 88 infants. cART was initiated within seven days in only nine of the 88 infants (10.2%). ARV initiation was delayed for 58 infants (65.9%) and 21 neonates (23.9%) were never initiated on cART. Among the 88 mothers of infants, more than one-third (38.6%) of pregnant women did not attend antenatal care, thus,compromising their opportunity to be enrolled on the PMTCT programme. Of those who attended antenatal care, only 39.1% were reported to attend antenatal care before 20 weeks CONCLUSION AND RECOMMENDATIONS The incidence of positive-birth HIV PCR has reduced from 1.4% in 2015 to 1% in 2018 whilst there has been an increase in birth HIV PCR testing. However, initiation of cART within seven days was achieved in only 10.2% of infants with positive-birth HIV PCR test results. Implementation of point-of-care birth HIV PCR testing would ensure that results are immediately available resulting in increasing the proportion of infants initiated on cART within seven days.
- Full Text:
- Date Issued: 2020
Seasonal trends of rainfall intensity, ground cover and sediment dynamics in the Little Pot River and Gqukunqa River catchments, South Africa
- Authors: Herd-Hoare, Sean
- Date: 2020
- Subjects: Land degradation -- Control -- South Africa -- Eastern Cape , Vegetation mapping -- South Africa -- Eastern Cape , Rain and rainfall -- South Africa -- Eastern Cape , Gqukunqa River catchment (South Africa) , Little Pot River catchment (South Africa) , Tsitsa River catchment (South Africa)
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/146288 , vital:38512
- Description: Natural rangelands provide a variety of ecosystem services including livestock production which occurs on land under freehold land tenure and on land under communal tenure. There is an ongoing debate around the extent to which land degradation is occurring on these rangelands under different land management and land tenure systems and what the main degradation drivers are. Over-grazing, rainfall and soil type are key drivers of rangeland dynamics and the resultant sediment yield in the river systems, however, over-grazing is an outcome of land management while rainfall and soil type are natural drivers. This study explores the relationship between rainfall and daily sediment flux as well as the seasonal trends of vegetation cover and the study is part of a greater research effort called the Tsitsa Project which is based in the Tsitsa River catchment (near Maclear, Eastern Cape, South Africa). The Tsitsa Project aims at developing and managing both land and water in a sustainable way by improving the land, water and lives of people living in the Tsitsa River catchment. The restoration efforts of the Tstisa Project will aid in extending the lifespan of both the proposed dams on the Tsitsa River. The Tsitsa River catchment is characterised by grasslands, steep topography, highly erodible soils with many large gullies present and a very high sediment yield in the Tsitsa River which allowed for the exploration of some of the system drivers of sediment yield in this catchment. The study involved two sub-catchments of the Upper Tsitsa River catchment of different land management strategies: one dominated by commercial livestock farms (Little Pot River catchment) and one dominated by communal rangelands (Gqukunqa River catchment). The aim of this study was to determine the seasonal trends of rainfall intensity, ground cover and sediment dynamics in the Little Pot River and Gqukunqa River catchments. The purpose of the findings was to improve management strategies in degraded areas and catchments. In order to achieve this aim a variety of field and desktop methods were used. Field methods involved measuring variables including: vegetation biomass, vegetation cover, soil surface hardness, biocrust cover and slope angle for a range of Normalized Difference Vegetation Index (NDVI) values from the Sentinel-2A sensor. The study assessed the system response of the field variables in both catchments over one rainfall season (2018-2019). Desktop methods included various NDVI analyses as well as analyses of trends and relationships between vegetation dynamics, rainfall and sediment. The relationship between erosive rainfall events, daily rainfall, antecedent rainfall and daily sediment flux was explored over the time period of January 2016 to January 2019 and October 2015 to January 2019 for the Little Pot River catchment and the Gqukunqa River catchment respectively. NDVI was explored as a proxy for vegetation cover to extrapolate across the catchments and monitoring period. NDVI was found to have a weak positive relationship with vegetation cover and biomass (R2 values ranged from 0,04 to 0,525). Mean monthly catchment NDVI values, biomass and vegetation cover increased throughout the wet season of 2018-2019 in both catchments. Mean monthly NDVI values increased from 0,26 to 0,55 in the Little Pot River catchment and from 0,29 to 0,53 in the Gqukunqa River catchment over the course of the 2018-2019 wet season. NDVI, biomass and vegetation cover was found to be higher on south-facing slopes than north-facing slopes in both catchments for the majority of the wet season. The Gqukunqa River has significantly higher daily sediment fluxes than the Little Pot River despite similar NDVI and rainfall intensities which is owed to the dispersive soils in the Gqukunqa River catchment. Soil surface hardness results were inconclusive due to rainfall before or during every field trip which changed the properties of the soil. The largest erosive rainfall, daily rainfall and daily sediment events occurred from January to March each wet season in both catchments. Rainfall intensity and sediment fluxes were found to have a weak relationship, however, there was a stronger relationship found between antecedent rainfall and sediment flux. The larger daily sediment fluxes in each catchment often did not result from an erosive rainfall event on the same day but rather from multiple days of rainfall which can result in saturated soils and runoff leading to surface and sub-surface erosion. The possibility of sub-surface erosion via chemical processes contributing to the larger sediment events was also explored to explain the stronger relationship between antecedent rainfall and daily sediment flux.
- Full Text:
- Date Issued: 2020
- Authors: Herd-Hoare, Sean
- Date: 2020
- Subjects: Land degradation -- Control -- South Africa -- Eastern Cape , Vegetation mapping -- South Africa -- Eastern Cape , Rain and rainfall -- South Africa -- Eastern Cape , Gqukunqa River catchment (South Africa) , Little Pot River catchment (South Africa) , Tsitsa River catchment (South Africa)
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/146288 , vital:38512
- Description: Natural rangelands provide a variety of ecosystem services including livestock production which occurs on land under freehold land tenure and on land under communal tenure. There is an ongoing debate around the extent to which land degradation is occurring on these rangelands under different land management and land tenure systems and what the main degradation drivers are. Over-grazing, rainfall and soil type are key drivers of rangeland dynamics and the resultant sediment yield in the river systems, however, over-grazing is an outcome of land management while rainfall and soil type are natural drivers. This study explores the relationship between rainfall and daily sediment flux as well as the seasonal trends of vegetation cover and the study is part of a greater research effort called the Tsitsa Project which is based in the Tsitsa River catchment (near Maclear, Eastern Cape, South Africa). The Tsitsa Project aims at developing and managing both land and water in a sustainable way by improving the land, water and lives of people living in the Tsitsa River catchment. The restoration efforts of the Tstisa Project will aid in extending the lifespan of both the proposed dams on the Tsitsa River. The Tsitsa River catchment is characterised by grasslands, steep topography, highly erodible soils with many large gullies present and a very high sediment yield in the Tsitsa River which allowed for the exploration of some of the system drivers of sediment yield in this catchment. The study involved two sub-catchments of the Upper Tsitsa River catchment of different land management strategies: one dominated by commercial livestock farms (Little Pot River catchment) and one dominated by communal rangelands (Gqukunqa River catchment). The aim of this study was to determine the seasonal trends of rainfall intensity, ground cover and sediment dynamics in the Little Pot River and Gqukunqa River catchments. The purpose of the findings was to improve management strategies in degraded areas and catchments. In order to achieve this aim a variety of field and desktop methods were used. Field methods involved measuring variables including: vegetation biomass, vegetation cover, soil surface hardness, biocrust cover and slope angle for a range of Normalized Difference Vegetation Index (NDVI) values from the Sentinel-2A sensor. The study assessed the system response of the field variables in both catchments over one rainfall season (2018-2019). Desktop methods included various NDVI analyses as well as analyses of trends and relationships between vegetation dynamics, rainfall and sediment. The relationship between erosive rainfall events, daily rainfall, antecedent rainfall and daily sediment flux was explored over the time period of January 2016 to January 2019 and October 2015 to January 2019 for the Little Pot River catchment and the Gqukunqa River catchment respectively. NDVI was explored as a proxy for vegetation cover to extrapolate across the catchments and monitoring period. NDVI was found to have a weak positive relationship with vegetation cover and biomass (R2 values ranged from 0,04 to 0,525). Mean monthly catchment NDVI values, biomass and vegetation cover increased throughout the wet season of 2018-2019 in both catchments. Mean monthly NDVI values increased from 0,26 to 0,55 in the Little Pot River catchment and from 0,29 to 0,53 in the Gqukunqa River catchment over the course of the 2018-2019 wet season. NDVI, biomass and vegetation cover was found to be higher on south-facing slopes than north-facing slopes in both catchments for the majority of the wet season. The Gqukunqa River has significantly higher daily sediment fluxes than the Little Pot River despite similar NDVI and rainfall intensities which is owed to the dispersive soils in the Gqukunqa River catchment. Soil surface hardness results were inconclusive due to rainfall before or during every field trip which changed the properties of the soil. The largest erosive rainfall, daily rainfall and daily sediment events occurred from January to March each wet season in both catchments. Rainfall intensity and sediment fluxes were found to have a weak relationship, however, there was a stronger relationship found between antecedent rainfall and sediment flux. The larger daily sediment fluxes in each catchment often did not result from an erosive rainfall event on the same day but rather from multiple days of rainfall which can result in saturated soils and runoff leading to surface and sub-surface erosion. The possibility of sub-surface erosion via chemical processes contributing to the larger sediment events was also explored to explain the stronger relationship between antecedent rainfall and daily sediment flux.
- Full Text:
- Date Issued: 2020
Securing software development using developer access control
- Authors: Ongers, Grant
- Date: 2020
- Subjects: Computer software -- Development , Computers -- Access control , Computer security -- Software , Computer networks -- Security measures , Source code (Computer science) , Plug-ins (Computer programs) , Data encryption (Computer science) , Network Access Control , Data Loss Prevention , Google’s BeyondCorp , Confidentiality, Integrity and Availability (CIA) triad
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/149022 , vital:38796
- Description: This research is aimed at software development companies and highlights the unique information security concerns in the context of a non-malicious software developer’s work environment; and furthermore explores an application driven solution which focuses specifically on providing developer environments with access control for source code repositories. In order to achieve that, five goals were defined as discussed in section 1.3. The application designed to provide the developer environment with access control to source code repositories was modelled on lessons taken from the principles of Network Access Control (NAC), Data Loss Prevention (DLP), and Google’s BeyondCorp (GBC) for zero-trust end-user computing. The intention of this research is to provide software developers with maximum access to source code without compromising Confidentiality, as per the Confidentiality, Integrity and Availability (CIA) triad. Employing data gleaned from examining the characteristics of DLP, NAC, and Beyond- Corp—proof-of-concept code was developed to regulate access to the developer’s environment and source code. The system required sufficient flexibility to support the diversity of software development environments. In order to achieve this, a modular design was selected. The system comprised a client side agent and a plug-in-ready server component. The client side agent mounts and dismounts encrypted volumes containing source code. Furthermore, it provides the server with information of the client that is demanded by plug-ins. The server side service provided encryption keys to facilitate the mounting of the volumes and, through plug-ins, asked questions of the client agent to determine whether access should be granted. The solution was then tested with integration and system testing. There were plans to have it used by development teams who were then to be surveyed as to their view on the proof of concept but this proved impossible. The conclusion provides a basis by which organisations that develop software can better balance the two corners of the CIA triad most often in conflict: Confidentiality in terms of their source code against the Availability of the same to developers.
- Full Text:
- Date Issued: 2020
- Authors: Ongers, Grant
- Date: 2020
- Subjects: Computer software -- Development , Computers -- Access control , Computer security -- Software , Computer networks -- Security measures , Source code (Computer science) , Plug-ins (Computer programs) , Data encryption (Computer science) , Network Access Control , Data Loss Prevention , Google’s BeyondCorp , Confidentiality, Integrity and Availability (CIA) triad
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/149022 , vital:38796
- Description: This research is aimed at software development companies and highlights the unique information security concerns in the context of a non-malicious software developer’s work environment; and furthermore explores an application driven solution which focuses specifically on providing developer environments with access control for source code repositories. In order to achieve that, five goals were defined as discussed in section 1.3. The application designed to provide the developer environment with access control to source code repositories was modelled on lessons taken from the principles of Network Access Control (NAC), Data Loss Prevention (DLP), and Google’s BeyondCorp (GBC) for zero-trust end-user computing. The intention of this research is to provide software developers with maximum access to source code without compromising Confidentiality, as per the Confidentiality, Integrity and Availability (CIA) triad. Employing data gleaned from examining the characteristics of DLP, NAC, and Beyond- Corp—proof-of-concept code was developed to regulate access to the developer’s environment and source code. The system required sufficient flexibility to support the diversity of software development environments. In order to achieve this, a modular design was selected. The system comprised a client side agent and a plug-in-ready server component. The client side agent mounts and dismounts encrypted volumes containing source code. Furthermore, it provides the server with information of the client that is demanded by plug-ins. The server side service provided encryption keys to facilitate the mounting of the volumes and, through plug-ins, asked questions of the client agent to determine whether access should be granted. The solution was then tested with integration and system testing. There were plans to have it used by development teams who were then to be surveyed as to their view on the proof of concept but this proved impossible. The conclusion provides a basis by which organisations that develop software can better balance the two corners of the CIA triad most often in conflict: Confidentiality in terms of their source code against the Availability of the same to developers.
- Full Text:
- Date Issued: 2020
Sexual attraction and mating compatibility between Thaumatotibia leucotreta populations and implications for semiochemical dependent technologies
- Authors: Upfold, Jennifer Kate
- Date: 2020
- Subjects: Cryptophlebia leucotreta -- South Africa , Cryptophlebia leucotreta -- Reproduction , Citrus -- Disease and pests -- Control -- South Africa , Insect sterilization -- South Africa , Pheromones , Pheromone traps
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/148526 , vital:38747
- Description: False codling moth (FCM), Thaumatotibia leucotreta (Meyrick), is the most important pest for the cultivation of citrus in South Africa. False codling moth is indigenous to southern Africa and is a regulated pest of many international markets for phytosanitary concerns. Considerable research efforts have been invested in the past decades to develop semiochemcial technologies, such as monitoring with sex pheromones, attract-and-kill, mating disruption and the sterile insect technique. One of the potential obstacles identified with semiochemical control is the differences in the ratio of the compounds comprising the sex pheromone at different geographical locations, resulting in what is known as regional attraction. This has been identified in FCM populations from three different countries, however, regional attraction within South African FCM populations was unknown. Therefore, the study assessed the genetic integrity of five laboratory-reared FCM populations originating from geographically isolated populations in South Africa using the AFLP technique in order to assess regional attractiveness within the country. The results found isolated populations from Addo, Citrusdal, Marble Hall, Nelspruit and a fifth group found to be closely related to Addo and Citrusdal called the ‘Old’ colony. These five genetically isolated populations as well as a population from Xsit (Pty) Ltd, used for the sterile insect technique (SIT), were used in regional attractiveness trials. Males were significantly (P = <0.05) more attracted to females originating from the same population. No significant attraction could be determined from the sterile males, as the recapture rates in the trap were too low. Furthermore, regional attractiveness was assessed through choice/ no-choice mating compatibility trials. Significant sexual isolation (ISI) occurred between mating combinations Addo × Nelspruit (ISI = 0,13; t2 = 6.23; p = 0.02), Addo × Marble Hall (ISI = 0,11; t2 = 4.72; p = 0.04), Citrusdal × Nelspruit (ISI = 0,11; t2 = 4.95; p = 0.04), and Citrusdal × Marble Hall (ISI = 0,12; t2 = 4.31; p = 0.04). In these combinations, Addo and Citrusdal males were found to have outcompeted Nelspruit and Marble Hall males for more mating events. Significant sexual isolation was also recorded for Sterile × Marble Hall (ISI = 0.12; t2 = 4.98; p =0.01) and Sterile × Citrusdal (ISI = 0.13; t2 = 3.96; p = 0.01) populations. The male relative performance index was significant in both combinations, indicating that non-sterile laboratory males outcompeted the sterile males in these two combinations. When given no choice, evaluated as spermatophore transfer/ female/ 48h, all males (including sterile) were successful in transferring spermatophores to all FCM populations, with no significant differences. These results indicate that there may be incipient pre-isolation mechanisms affected by local natural selection, resulting in localised sexual attraction via differences in the sex pheromone ratios. These findings provide important information for semiochemical technologies and the implication of these results with regard to monitoring with sex pheromones, attract-and-kill, mating disruption and sterile insect technique are discussed.
- Full Text:
- Date Issued: 2020
- Authors: Upfold, Jennifer Kate
- Date: 2020
- Subjects: Cryptophlebia leucotreta -- South Africa , Cryptophlebia leucotreta -- Reproduction , Citrus -- Disease and pests -- Control -- South Africa , Insect sterilization -- South Africa , Pheromones , Pheromone traps
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/148526 , vital:38747
- Description: False codling moth (FCM), Thaumatotibia leucotreta (Meyrick), is the most important pest for the cultivation of citrus in South Africa. False codling moth is indigenous to southern Africa and is a regulated pest of many international markets for phytosanitary concerns. Considerable research efforts have been invested in the past decades to develop semiochemcial technologies, such as monitoring with sex pheromones, attract-and-kill, mating disruption and the sterile insect technique. One of the potential obstacles identified with semiochemical control is the differences in the ratio of the compounds comprising the sex pheromone at different geographical locations, resulting in what is known as regional attraction. This has been identified in FCM populations from three different countries, however, regional attraction within South African FCM populations was unknown. Therefore, the study assessed the genetic integrity of five laboratory-reared FCM populations originating from geographically isolated populations in South Africa using the AFLP technique in order to assess regional attractiveness within the country. The results found isolated populations from Addo, Citrusdal, Marble Hall, Nelspruit and a fifth group found to be closely related to Addo and Citrusdal called the ‘Old’ colony. These five genetically isolated populations as well as a population from Xsit (Pty) Ltd, used for the sterile insect technique (SIT), were used in regional attractiveness trials. Males were significantly (P = <0.05) more attracted to females originating from the same population. No significant attraction could be determined from the sterile males, as the recapture rates in the trap were too low. Furthermore, regional attractiveness was assessed through choice/ no-choice mating compatibility trials. Significant sexual isolation (ISI) occurred between mating combinations Addo × Nelspruit (ISI = 0,13; t2 = 6.23; p = 0.02), Addo × Marble Hall (ISI = 0,11; t2 = 4.72; p = 0.04), Citrusdal × Nelspruit (ISI = 0,11; t2 = 4.95; p = 0.04), and Citrusdal × Marble Hall (ISI = 0,12; t2 = 4.31; p = 0.04). In these combinations, Addo and Citrusdal males were found to have outcompeted Nelspruit and Marble Hall males for more mating events. Significant sexual isolation was also recorded for Sterile × Marble Hall (ISI = 0.12; t2 = 4.98; p =0.01) and Sterile × Citrusdal (ISI = 0.13; t2 = 3.96; p = 0.01) populations. The male relative performance index was significant in both combinations, indicating that non-sterile laboratory males outcompeted the sterile males in these two combinations. When given no choice, evaluated as spermatophore transfer/ female/ 48h, all males (including sterile) were successful in transferring spermatophores to all FCM populations, with no significant differences. These results indicate that there may be incipient pre-isolation mechanisms affected by local natural selection, resulting in localised sexual attraction via differences in the sex pheromone ratios. These findings provide important information for semiochemical technologies and the implication of these results with regard to monitoring with sex pheromones, attract-and-kill, mating disruption and sterile insect technique are discussed.
- Full Text:
- Date Issued: 2020
Shrub and bird community response to fire in dune thicket of the southeastern Cape, South Africa
- Authors: Strydom, Tiaan
- Date: 2020
- Subjects: Fire prevention -- Research -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/47635 , vital:40260
- Description: Fire studies within the Cape Floristic Region (CFR) are restricted to the impacts of fire on plants and birds in fire-prone fynbos while little is known about post-fire responses of shrubs and birds in fire-avoiding subtropical dune thicket, which coexists with fynbos but burns on much longer cycles. Fire is deemed important for maintaining the boundaries between fynbos and thicket. It has been hypothesised that high-intensity fires prevent fire-dependent fynbos from being replaced by fireavoiding subtropical thicket (hereafter thicket) on dune landscapes of the CFR. I posit that (1) fire-related thicket shrub mortality would be size dependent, with smaller individuals suffering higher mortality than larger ones; and (2) that survival and resprouting vigour of thicket shrubs would be negatively correlated with fire intensity. In relation to the response of birds to fire I posit that (1) fire reduces bird species richness and bird abundance in thicket during the first two years post-fire; and (2) fire changes feeding guild composition and results in the loss of frugivorous birds. Extensive fires in dune thicket along the southeastern Cape coast presented the opportunity to assess the responses of thicket shrubs and birds to fire. For the thicket shrubs I assessed survival and resprouting vigour of thicket shrubs post-fire in relation to fire intensity and pre-fire shrub size at two dune landscapes (Cape St Francis and Knysna) in the CFR. I furthermore compared bird species richness, bird abundance and feeding guild composition between burnt and unburnt thicket (only at Knysna). A total of 29 species and 1112 individuals of thicket shrub were surveyed, with post-fire survival being high (83-85%). Smaller shrubs had a lower probability of post-fire survival than larger individuals but there was no consistent relationship between shrub mortality and fire intensity. Fire intensity had a positive effect on resprouting shoot count but a variable effect on resprouting volume. In the bird study a total of 66 bird species and 2404 individuals were recorded of which 52 species and 1176 individuals were in burnt thicket and 60 species and 1228 individuals were in unburnt thicket. Ten species occurred only in burnt thicket and 13 species only in unburnt thicket. Insectivores and generalists were the most common feeding guilds in terms of richness and abundance in both burnt and unburnt thicket. Frugivores were more abundant in unburnt thicket than burnt thicket, whereas granivores were more abundant in burnt thicket than unburnt thicket. I conclude that thicket shrubs and bird communities are resilient to fire. Prescribed high-intensity fires in dune landscapes are unlikely to reduce the extent of thicket in fynbos or radically change the bird communities. The effects of fire on thicket shrubs and birds are likely to be short-lived as thicket shrubs resprout vigorously after fire resulting in rapid recovery of vegetation and thus bird habitat structure. However, frequent fires may prevent the encroachment of thicket shrub juveniles into fynbos, owing to the greater vulnerability of small shrubs to fire. Most recruitment of thicket shrub individuals into fynbos is via ramets that likely originate from well-established plants in mature thicket stands. These mature unburnt thicket stands provide habitat for various forest bird species and can function as refuge areas for birds and other wildlife in fire-prone landscapes. However, there is no need for managers to take any precautions when implementing controlled burns or controlling wildfires because not all thicket patches in the landscape are likely to burn.
- Full Text:
- Date Issued: 2020
- Authors: Strydom, Tiaan
- Date: 2020
- Subjects: Fire prevention -- Research -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/47635 , vital:40260
- Description: Fire studies within the Cape Floristic Region (CFR) are restricted to the impacts of fire on plants and birds in fire-prone fynbos while little is known about post-fire responses of shrubs and birds in fire-avoiding subtropical dune thicket, which coexists with fynbos but burns on much longer cycles. Fire is deemed important for maintaining the boundaries between fynbos and thicket. It has been hypothesised that high-intensity fires prevent fire-dependent fynbos from being replaced by fireavoiding subtropical thicket (hereafter thicket) on dune landscapes of the CFR. I posit that (1) fire-related thicket shrub mortality would be size dependent, with smaller individuals suffering higher mortality than larger ones; and (2) that survival and resprouting vigour of thicket shrubs would be negatively correlated with fire intensity. In relation to the response of birds to fire I posit that (1) fire reduces bird species richness and bird abundance in thicket during the first two years post-fire; and (2) fire changes feeding guild composition and results in the loss of frugivorous birds. Extensive fires in dune thicket along the southeastern Cape coast presented the opportunity to assess the responses of thicket shrubs and birds to fire. For the thicket shrubs I assessed survival and resprouting vigour of thicket shrubs post-fire in relation to fire intensity and pre-fire shrub size at two dune landscapes (Cape St Francis and Knysna) in the CFR. I furthermore compared bird species richness, bird abundance and feeding guild composition between burnt and unburnt thicket (only at Knysna). A total of 29 species and 1112 individuals of thicket shrub were surveyed, with post-fire survival being high (83-85%). Smaller shrubs had a lower probability of post-fire survival than larger individuals but there was no consistent relationship between shrub mortality and fire intensity. Fire intensity had a positive effect on resprouting shoot count but a variable effect on resprouting volume. In the bird study a total of 66 bird species and 2404 individuals were recorded of which 52 species and 1176 individuals were in burnt thicket and 60 species and 1228 individuals were in unburnt thicket. Ten species occurred only in burnt thicket and 13 species only in unburnt thicket. Insectivores and generalists were the most common feeding guilds in terms of richness and abundance in both burnt and unburnt thicket. Frugivores were more abundant in unburnt thicket than burnt thicket, whereas granivores were more abundant in burnt thicket than unburnt thicket. I conclude that thicket shrubs and bird communities are resilient to fire. Prescribed high-intensity fires in dune landscapes are unlikely to reduce the extent of thicket in fynbos or radically change the bird communities. The effects of fire on thicket shrubs and birds are likely to be short-lived as thicket shrubs resprout vigorously after fire resulting in rapid recovery of vegetation and thus bird habitat structure. However, frequent fires may prevent the encroachment of thicket shrub juveniles into fynbos, owing to the greater vulnerability of small shrubs to fire. Most recruitment of thicket shrub individuals into fynbos is via ramets that likely originate from well-established plants in mature thicket stands. These mature unburnt thicket stands provide habitat for various forest bird species and can function as refuge areas for birds and other wildlife in fire-prone landscapes. However, there is no need for managers to take any precautions when implementing controlled burns or controlling wildfires because not all thicket patches in the landscape are likely to burn.
- Full Text:
- Date Issued: 2020
Solid waste management practices in Joe Slovo township, Nelson Mandela Bay Municipality
- Mngomezulu, Sibongangani Khonelihle
- Authors: Mngomezulu, Sibongangani Khonelihle
- Date: 2020
- Subjects: Refuse and refuse disposal -- Management , Refuse and refuse disposal -- Environmental aspects Refuse and refuse disposal -- South Africa -- Port Elizabeth -- Management
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/46185 , vital:39512
- Description: Solid waste management practice is one of the essential service deliveries that should exist in all places. The method of handling, storage and processing solid waste at household is key and it plays a significant role in public health, ensuring a safe environment and in the efficiency of municipal solid waste. Previous research has revealed that solid waste management is a global issue and the lack of awareness and involvement of communities is escalating the problem. In addition, studies also disclosed that solid waste produced by inhabitants is recyclable, therefore waste management practice must implement new systems that are sustainable, to improve waste management practices. Hence, addressing solid waste management challenges would have a positive impact on the goals of achieving a health-city concept which promotes sustainable development. The aim of this study was to examine solid waste management practices that hinder sustainable human settlements. The methodology used included an extensive literature review, field observation and a field study conducted in Joe Slovo West Township. A quantitative study approach that is based on a positivism paradigm and a random sampling technique was adopted. The descriptive method of data analysis was employed, and the findings and the interpretations are presented through tables, graphs and images. Analysis of the findings revealed that institutional, fiscal/economic, development, socio-economic and policy matters are the factors holding back existing solid waste management practices in Joe Slovo Township. Key recommendations include that the solid waste management system needs to be improved and that enhancing the ease of waste recycling as an economic activity and as a practice should be pursued and that residents should be educated and encouraged to separate their waste before disposal while an incentive should be provided for this to stimulate community participation.
- Full Text:
- Date Issued: 2020
- Authors: Mngomezulu, Sibongangani Khonelihle
- Date: 2020
- Subjects: Refuse and refuse disposal -- Management , Refuse and refuse disposal -- Environmental aspects Refuse and refuse disposal -- South Africa -- Port Elizabeth -- Management
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/46185 , vital:39512
- Description: Solid waste management practice is one of the essential service deliveries that should exist in all places. The method of handling, storage and processing solid waste at household is key and it plays a significant role in public health, ensuring a safe environment and in the efficiency of municipal solid waste. Previous research has revealed that solid waste management is a global issue and the lack of awareness and involvement of communities is escalating the problem. In addition, studies also disclosed that solid waste produced by inhabitants is recyclable, therefore waste management practice must implement new systems that are sustainable, to improve waste management practices. Hence, addressing solid waste management challenges would have a positive impact on the goals of achieving a health-city concept which promotes sustainable development. The aim of this study was to examine solid waste management practices that hinder sustainable human settlements. The methodology used included an extensive literature review, field observation and a field study conducted in Joe Slovo West Township. A quantitative study approach that is based on a positivism paradigm and a random sampling technique was adopted. The descriptive method of data analysis was employed, and the findings and the interpretations are presented through tables, graphs and images. Analysis of the findings revealed that institutional, fiscal/economic, development, socio-economic and policy matters are the factors holding back existing solid waste management practices in Joe Slovo Township. Key recommendations include that the solid waste management system needs to be improved and that enhancing the ease of waste recycling as an economic activity and as a practice should be pursued and that residents should be educated and encouraged to separate their waste before disposal while an incentive should be provided for this to stimulate community participation.
- Full Text:
- Date Issued: 2020
Spatio-temporal variation of the land surface parameters in Temperature, in King Williams Town, Eastern Cape Province, South Africa
- Authors: Willie, Yanga Adrian
- Date: 2020
- Subjects: Environmental sciences
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10353/12106 , vital:39152
- Description: The world is currently experiencing unprecedented urban growth. The influx of people into urban areas from rural areas is motivated by both economic and social factors such as increased employment opportunities. The latter is a result of, in part, industrialization, and the perceived higher standard of living that is often associated with access to better infrastructure. Surface Heat Island (SHI) is a phenomenon whereby urban areas experience higher surface temperatures than the surrounding rural areas. The presence of the SHI in urban areas has a negative impact not only on city dwellers, but also on the environment and the economy. The development of SHI is often associated with patterns of land use and land cover in urban areas. Numerous methods exist that can be used to study SHI’s. Literature suggests that Land Surface Temperature (LST), derived from satellite imagery, is a proven method that produces reliable results. The aim of this study was to evaluate the SHI in King Williams Town by studying the relationship between land surface temperatures, land cover and land cover indices. The derived indices are the Normalized Difference Vegetation Index (NDVI) and Normalized Difference Built up Index (NDBI). These indices were selected because they are representative of the land cover scheme used in the research study. This study was conducted in the King Williams town area between the years 1995 and 2018 the land surface temperature was derived from Landsat ETM + high thermal band data. The findings from this study provide an idea on the correlation between satellite derived land surface temperature and the land modification which occurred during the urbanization of King Williams Town during a 23 year period between1995 and 2018. The built up land category was the most influential in the development of high land surface temperature levels , vegetation had an opposite effect as a series of data sets illustrated that vegetated areas had a iv cooling effect on the surface. Water bodies in the study area had an insignificant effect on the Surface temperature levels while the grass lands weren’t as cooling as the vegetation but provided a cooling environment in the study area .The spatial distribution of areas of high surface temperature (hot spots) was discovered to be concentrated in the urban areas of the study area which is in the northwest region of the study area and correlates to the land cover and land cover indices associated with built up and artificial surfaces. The cooler areas or patches of land with lower values of land surface temperature were distributed on the outskirts of the study area away from the CBD and residential areas. This was the case because of the high concentration of vegetation and thicker grass lands in those regions.
- Full Text:
- Date Issued: 2020
- Authors: Willie, Yanga Adrian
- Date: 2020
- Subjects: Environmental sciences
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10353/12106 , vital:39152
- Description: The world is currently experiencing unprecedented urban growth. The influx of people into urban areas from rural areas is motivated by both economic and social factors such as increased employment opportunities. The latter is a result of, in part, industrialization, and the perceived higher standard of living that is often associated with access to better infrastructure. Surface Heat Island (SHI) is a phenomenon whereby urban areas experience higher surface temperatures than the surrounding rural areas. The presence of the SHI in urban areas has a negative impact not only on city dwellers, but also on the environment and the economy. The development of SHI is often associated with patterns of land use and land cover in urban areas. Numerous methods exist that can be used to study SHI’s. Literature suggests that Land Surface Temperature (LST), derived from satellite imagery, is a proven method that produces reliable results. The aim of this study was to evaluate the SHI in King Williams Town by studying the relationship between land surface temperatures, land cover and land cover indices. The derived indices are the Normalized Difference Vegetation Index (NDVI) and Normalized Difference Built up Index (NDBI). These indices were selected because they are representative of the land cover scheme used in the research study. This study was conducted in the King Williams town area between the years 1995 and 2018 the land surface temperature was derived from Landsat ETM + high thermal band data. The findings from this study provide an idea on the correlation between satellite derived land surface temperature and the land modification which occurred during the urbanization of King Williams Town during a 23 year period between1995 and 2018. The built up land category was the most influential in the development of high land surface temperature levels , vegetation had an opposite effect as a series of data sets illustrated that vegetated areas had a iv cooling effect on the surface. Water bodies in the study area had an insignificant effect on the Surface temperature levels while the grass lands weren’t as cooling as the vegetation but provided a cooling environment in the study area .The spatial distribution of areas of high surface temperature (hot spots) was discovered to be concentrated in the urban areas of the study area which is in the northwest region of the study area and correlates to the land cover and land cover indices associated with built up and artificial surfaces. The cooler areas or patches of land with lower values of land surface temperature were distributed on the outskirts of the study area away from the CBD and residential areas. This was the case because of the high concentration of vegetation and thicker grass lands in those regions.
- Full Text:
- Date Issued: 2020
Structure and interaction studies of beta-amyloid in the search for new lead compounds for the treatment of Alzheimer’s disease
- Authors: Mtini, Onke
- Date: 2020
- Subjects: Alzheimer's disease -- Chemotherapy , Alzheimer's disease -- Treatment , Amyloid beta-protein , Oxidative stress , Protein binding , South African Natural Compounds Database
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/167574 , vital:41493
- Description: Alzheimer’s disease (AD) is the most devastating neurodegenerative disorder that effects the aging population worldwide. In this study three hypotheses of AD are explored, the β-amyloid cascade hypothesis, the β-amyloid metal binding hypothesis and the oxidative stress hypothesis are explored. In the first case compounds from the South African Natural Compounds Database (SANCDB) are docked to models of β-amyloid fibrils and the properties of these fibrils under pulling simulations are compared to a known small molecule disruptor of β-amyloid, wgx-50. In these simulations SANCDB compounds are identified that disrupt β-amyloid in a similar manner to wgx-50. In these simulations the disruption to the free energy of binding of chains to the fibrils is quantified. For metal binding and oxidative stress hypotheses, problems in simulation arise due to only fragments of β-amyloid being present in the Research Collaboratory for Structural Bioinformatics protein data bank (RCSB PDB), as determined from NMR experiments. In this work, β-amyloid is set up under periodic boundary conditions to simulate a fibril under reasonable computational time. Within these periodic boundary conditions, β-amyloid has been solvated in copper and zinc rich environments and diffusion of these metals around the fibrils has been explored. The localization of these metals (in simulation only using van der Waal’s and electrostatic terms) around the fibril has led us to explore other possible metal binding sites. Metal bound to the infinite fibril has been optimized at the QM/MM level and some of the reactive oxygen species in the presence of the fibril are quantified.
- Full Text:
- Date Issued: 2020
- Authors: Mtini, Onke
- Date: 2020
- Subjects: Alzheimer's disease -- Chemotherapy , Alzheimer's disease -- Treatment , Amyloid beta-protein , Oxidative stress , Protein binding , South African Natural Compounds Database
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/167574 , vital:41493
- Description: Alzheimer’s disease (AD) is the most devastating neurodegenerative disorder that effects the aging population worldwide. In this study three hypotheses of AD are explored, the β-amyloid cascade hypothesis, the β-amyloid metal binding hypothesis and the oxidative stress hypothesis are explored. In the first case compounds from the South African Natural Compounds Database (SANCDB) are docked to models of β-amyloid fibrils and the properties of these fibrils under pulling simulations are compared to a known small molecule disruptor of β-amyloid, wgx-50. In these simulations SANCDB compounds are identified that disrupt β-amyloid in a similar manner to wgx-50. In these simulations the disruption to the free energy of binding of chains to the fibrils is quantified. For metal binding and oxidative stress hypotheses, problems in simulation arise due to only fragments of β-amyloid being present in the Research Collaboratory for Structural Bioinformatics protein data bank (RCSB PDB), as determined from NMR experiments. In this work, β-amyloid is set up under periodic boundary conditions to simulate a fibril under reasonable computational time. Within these periodic boundary conditions, β-amyloid has been solvated in copper and zinc rich environments and diffusion of these metals around the fibrils has been explored. The localization of these metals (in simulation only using van der Waal’s and electrostatic terms) around the fibril has led us to explore other possible metal binding sites. Metal bound to the infinite fibril has been optimized at the QM/MM level and some of the reactive oxygen species in the presence of the fibril are quantified.
- Full Text:
- Date Issued: 2020
Symmetry and asymmetry in electrocatalysis: enhancing the electrocatalytic activity of phthalocyanines through synergy with doped graphene quantum dots
- Nkhahle, Reitumetse Precious
- Authors: Nkhahle, Reitumetse Precious
- Date: 2020
- Subjects: Phthalocyanines , Quantum dots , Graphene
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/117585 , vital:34529
- Description: An exploration on the enhancement of the electrocatalytic activity of phthalocyanines (Pcs) through coupling with a series of graphene quantum dots (GQDs) is undertaken. The preliminary studies using symmetrical Pcs, a cobalt and an iron chloride tetra substituted diethylaminophenoxy Pc (complexes 1 and 2), for the electro-oxidation of nitrite revealed through the various sequential modifications that doped GQDs fare better than their pristine counterparts with respect to improving the electrocatalytic behaviour of Pcs, in particular, the nitrogen-doped GQDs (NGQDs). Following up on this, a series of asymmetric Pc complexes; 2,9,16-tris-(4-tert-butylphenoxy) mono carboxyphenoxy phthalocyanato cobalt (II) (3), 2,9,16-tris-(4-tert-butylphenoxy) mono aminophenoxy phthalocyanato cobalt (II) (4), 2,9,16-tris-(3-diethylamino)phenoxy) mono carboxyphenoxy phthalocyanato cobalt (II) (5) and 2,9,16-tris-(3-diethylamino)phenoxy) mono aminophenoxy phthalocyanato cobalt (II) (6) was prepared in which push-pull systems were compared to other asymmetric complexes that lack this effect towards the electrocatalytic sensing of hydrazine. All asymmetric complexes (3-6) were π-stacked to the NGQDs while those with an NH2 group (4 and 6), were also covalently linked to the NGQDs. These complexes and their corresponding conjugates were characterized accordingly and applied as electrocatalysts in the oxidation of hydrazine. The electrochemical studies revealed that π π stacking yields better responses (higher sensitivities and lower limits of detection) than covalent linking because there are less forces acting on the graphene network. Covalent linking introduces both tensile and compressive forces which in turn results in an increase in the ID/IG ratio and that is unfavourable for electrocatalysis. In comparing the electrodes composed of the π-stacked conjugates to those altered through sequential modifications, despite the conditions not being the same, it can be inferred that the magnitude of the electrostatic forces between the Pcs and the GQDs also plays a significant role in electrocatalysis. The π-stacked conjugates, owing to the manner in which they were prepared, have stronger electrostatic forces acting between the Pc and GQDs hence they were able to elicit a better electrochemical response than the sequentially modified electrodes. In addition to that, it appears that asymmetric Pcs are better electrocatalysts in comparison to the symmetric Pcs.
- Full Text:
- Date Issued: 2020
- Authors: Nkhahle, Reitumetse Precious
- Date: 2020
- Subjects: Phthalocyanines , Quantum dots , Graphene
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/117585 , vital:34529
- Description: An exploration on the enhancement of the electrocatalytic activity of phthalocyanines (Pcs) through coupling with a series of graphene quantum dots (GQDs) is undertaken. The preliminary studies using symmetrical Pcs, a cobalt and an iron chloride tetra substituted diethylaminophenoxy Pc (complexes 1 and 2), for the electro-oxidation of nitrite revealed through the various sequential modifications that doped GQDs fare better than their pristine counterparts with respect to improving the electrocatalytic behaviour of Pcs, in particular, the nitrogen-doped GQDs (NGQDs). Following up on this, a series of asymmetric Pc complexes; 2,9,16-tris-(4-tert-butylphenoxy) mono carboxyphenoxy phthalocyanato cobalt (II) (3), 2,9,16-tris-(4-tert-butylphenoxy) mono aminophenoxy phthalocyanato cobalt (II) (4), 2,9,16-tris-(3-diethylamino)phenoxy) mono carboxyphenoxy phthalocyanato cobalt (II) (5) and 2,9,16-tris-(3-diethylamino)phenoxy) mono aminophenoxy phthalocyanato cobalt (II) (6) was prepared in which push-pull systems were compared to other asymmetric complexes that lack this effect towards the electrocatalytic sensing of hydrazine. All asymmetric complexes (3-6) were π-stacked to the NGQDs while those with an NH2 group (4 and 6), were also covalently linked to the NGQDs. These complexes and their corresponding conjugates were characterized accordingly and applied as electrocatalysts in the oxidation of hydrazine. The electrochemical studies revealed that π π stacking yields better responses (higher sensitivities and lower limits of detection) than covalent linking because there are less forces acting on the graphene network. Covalent linking introduces both tensile and compressive forces which in turn results in an increase in the ID/IG ratio and that is unfavourable for electrocatalysis. In comparing the electrodes composed of the π-stacked conjugates to those altered through sequential modifications, despite the conditions not being the same, it can be inferred that the magnitude of the electrostatic forces between the Pcs and the GQDs also plays a significant role in electrocatalysis. The π-stacked conjugates, owing to the manner in which they were prepared, have stronger electrostatic forces acting between the Pc and GQDs hence they were able to elicit a better electrochemical response than the sequentially modified electrodes. In addition to that, it appears that asymmetric Pcs are better electrocatalysts in comparison to the symmetric Pcs.
- Full Text:
- Date Issued: 2020
Synthesis and application of fluorescent triazolyl-coumarin based chemosensors
- Authors: Schoeman, Stiaan
- Date: 2020
- Subjects: Chemistry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/47454 , vital:39992
- Description: The search for a fluorescent chemosensor with high selectivity and sensitivity that can be used for the detection of trace amounts of a toxic transition metal or heavy metal ions have gained immense popularity in recent years. Coumarin derivatives have been widely used as the basis of these fluorescent chemosensors by which a 1,2,3-triazole ring is used as the binding site for such metal ions. The benefits of chemosensors include nearly eliminating the need for tedious sample preparation and highly skilled operators. Therefore, enabling quantitative and qualitative measurement in both a lab setting and on-site. In addition, chemosensors provide a more sensitive and selective detection method at low-cost. A variety of chemosensors were designed and synthesized, in which some synthesis steps were refined to obtain better yields and purer products. Chemosensors designed, in this study, can be divided into novel triazolyl-coumarin derivatives without a spacer 1C – 1D and with a spacer between the coumarin and triazole ring (2D and 2E). 1C – 1D were characterized by 1H NMR, 13C NMR and IR and photophysical properties were investigated in DMF. 2D and 2E could not be purified and further investigation was discontinued. An overall enhancement was observed for the chemosensors 1C – 1D in the presence of 24 different ions that were tested. 1C had a quenching effect in the presence of Cd2+, however, competition studies revealed that 1C is not selective in the presence of competing metal cations. Molecular modelling studies were performed on sensors 1C – 1G in the presence of various ions. The molecular modelling studies provided invaluable insights into the binding of the selected metal ions as well as revealed a variety of binding sites. In addition, the space-filled depictions offered insights into the overlapping during binding which had an effect in the electrostatic potential maps of the chemosensors..
- Full Text:
- Date Issued: 2020
- Authors: Schoeman, Stiaan
- Date: 2020
- Subjects: Chemistry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/47454 , vital:39992
- Description: The search for a fluorescent chemosensor with high selectivity and sensitivity that can be used for the detection of trace amounts of a toxic transition metal or heavy metal ions have gained immense popularity in recent years. Coumarin derivatives have been widely used as the basis of these fluorescent chemosensors by which a 1,2,3-triazole ring is used as the binding site for such metal ions. The benefits of chemosensors include nearly eliminating the need for tedious sample preparation and highly skilled operators. Therefore, enabling quantitative and qualitative measurement in both a lab setting and on-site. In addition, chemosensors provide a more sensitive and selective detection method at low-cost. A variety of chemosensors were designed and synthesized, in which some synthesis steps were refined to obtain better yields and purer products. Chemosensors designed, in this study, can be divided into novel triazolyl-coumarin derivatives without a spacer 1C – 1D and with a spacer between the coumarin and triazole ring (2D and 2E). 1C – 1D were characterized by 1H NMR, 13C NMR and IR and photophysical properties were investigated in DMF. 2D and 2E could not be purified and further investigation was discontinued. An overall enhancement was observed for the chemosensors 1C – 1D in the presence of 24 different ions that were tested. 1C had a quenching effect in the presence of Cd2+, however, competition studies revealed that 1C is not selective in the presence of competing metal cations. Molecular modelling studies were performed on sensors 1C – 1G in the presence of various ions. The molecular modelling studies provided invaluable insights into the binding of the selected metal ions as well as revealed a variety of binding sites. In addition, the space-filled depictions offered insights into the overlapping during binding which had an effect in the electrostatic potential maps of the chemosensors..
- Full Text:
- Date Issued: 2020
Synthesis and characterisation of lanthanide complexes with potential nitrogen- and oxygen-donor schiff base ligands
- Authors: Pikoli, Sibongile
- Date: 2020
- Subjects: Rare earths , Schiff bases
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/47050 , vital:39778
- Description: This research describes the coordination chemistry of lanthanide complexes with potentially multidentate nitrogen- and oxygen-donor Schiff base derivatives. The studies were performed using various physico-chemical techniques including melting point, IR and NMR spectroscopy, UV-Vis spectroscopy, elemental analyses, conductivity measurements, X-ray crystallography and cyclic voltammetry. The reaction of [Ln(NO3)3·xH2O] (Ln = Nd, Gd, Yb; x = 6 for Nd and Gd, x = 5 for Yb) with the flexible salen-type Schiff base ligand 1,3-bis(o-hydroxybenzylideneamino)propane (H2L1) produced three polynuclear complexes with the general formulae {[Nd(µH2L1)4(NO3)3]·2H2O}n and [Ln(µ-H2L1)2(NO3)6(H2L1)] (Ln = Gd and Yb). Single-crystal Xray crystallography revealed a ten-coordinate polymeric Nd(III) complex that crystallised in the monoclinic space group P21/c, and isostructural nine-coordinate binuclear Gd(III) and Yb(III) complexes (triclinic system, space group P-1). The lanthanide contraction effect is clear across the series. The flexible nature of HL2 results in the self-assembly of the Nd(III) complex in a 1D polymer chain by acting as the bridge between the metal ions. The Nd-Ophenolate bond distances are 2.403(18), 2.463(17), 2.379(17) and 2.367(19) Å and the average Nd-Onitrate bond length is 2.671 Å. Furthermore, the electronic absorption spectra displays 4f→4f transitions solely for the neodymium(III) compound. The syntheses and characterisation of the lanthanide complexes, [La(HL2)3(NO3)3], [Dy(HL2)2(NO3)3] and [Dy(HL2)2Cl3(H2O)]·2CH2Cl2 with the o-vanillin-derived Schiff base ligand 2-methoxy-6-[(E)-(phenylimino)methyl]phenol (HL2) are reported. The nitro-stabilised La(III) and Dy(III) compounds are ten-coordinate with metabidiminished icosahedron and sphenocorona geometries, respectively. Substitution of the nitrate with chloride ions in the starting metal compounds yielded an eight-coordinate Dy(III) complex that adopts the biaugmented trigonal prism geometry. For all three complexes, HL2 exists as a zwitterion that is bound to the metal centre in a mono- and bidentate fashion via the phenolate and methoxy oxygen atoms. The dysprosium(III) chloride complex is stabilised by both intramolecular N−H···O and intermolecular O−H···C1 hydrogen bonds, while the crystal packing of the Ln(III) nitrate complexes is ensured by mainly intramolecular N−H···O hydrogen bonds. Fluorescence studies displayed characteristic Dy(III) f→f transitions (4F9/2 → 6H15/2), which suggest the ligand HL2 is an effective organic antenna to absorb and transfer energy to the dysprosium ion. A series of mononuclear Nd(III) complexes with the Schiff base derivatives 2-methoxy-6-[(E)(phenylimino)methyl]phenol (HL2), 5-methoxy-2-[(E)-(phenylimino)methyl]phenol (HL3) and 2-methoxy-6-{(E)-[(2-methoxyphenyl)imino]methyl}phenol (HL4) yielded structurally diverse complexes defined by the formulae [Nd(HL2)2(NO3)3], [Nd(HL3)3(NO3)3] and [Nd(HL4)2(NO3)3]·CH3OH. Crystallographic analysis shows HL2 and HL4 coordinate bidentately via the phenolate and methoxy oxygen atoms, while HL3 is bound monodentately through the phenolate oxygen atom. Continuous shape measures depict that the decacoordinate complexes with HL2 and HL4 conform to the sphenocorona and tetradecahedron geometries, respectively, whilst the nona-coordinate Nd(III) complex with HL3 exhibits the muffin geometry. The effect of the ligand substituents and their positions (meta versus para) on the absorption and emission intensities of the complexes is demonstrated. Additionally, the electrochemical behaviour of the o-vanillin-derived Schiff base ligands and their complexes was also investigated, and the results illustrate ligand-based reductions and metal-centred redox potentials that are significantly shifted by the ligand substituents.
- Full Text:
- Date Issued: 2020
- Authors: Pikoli, Sibongile
- Date: 2020
- Subjects: Rare earths , Schiff bases
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/47050 , vital:39778
- Description: This research describes the coordination chemistry of lanthanide complexes with potentially multidentate nitrogen- and oxygen-donor Schiff base derivatives. The studies were performed using various physico-chemical techniques including melting point, IR and NMR spectroscopy, UV-Vis spectroscopy, elemental analyses, conductivity measurements, X-ray crystallography and cyclic voltammetry. The reaction of [Ln(NO3)3·xH2O] (Ln = Nd, Gd, Yb; x = 6 for Nd and Gd, x = 5 for Yb) with the flexible salen-type Schiff base ligand 1,3-bis(o-hydroxybenzylideneamino)propane (H2L1) produced three polynuclear complexes with the general formulae {[Nd(µH2L1)4(NO3)3]·2H2O}n and [Ln(µ-H2L1)2(NO3)6(H2L1)] (Ln = Gd and Yb). Single-crystal Xray crystallography revealed a ten-coordinate polymeric Nd(III) complex that crystallised in the monoclinic space group P21/c, and isostructural nine-coordinate binuclear Gd(III) and Yb(III) complexes (triclinic system, space group P-1). The lanthanide contraction effect is clear across the series. The flexible nature of HL2 results in the self-assembly of the Nd(III) complex in a 1D polymer chain by acting as the bridge between the metal ions. The Nd-Ophenolate bond distances are 2.403(18), 2.463(17), 2.379(17) and 2.367(19) Å and the average Nd-Onitrate bond length is 2.671 Å. Furthermore, the electronic absorption spectra displays 4f→4f transitions solely for the neodymium(III) compound. The syntheses and characterisation of the lanthanide complexes, [La(HL2)3(NO3)3], [Dy(HL2)2(NO3)3] and [Dy(HL2)2Cl3(H2O)]·2CH2Cl2 with the o-vanillin-derived Schiff base ligand 2-methoxy-6-[(E)-(phenylimino)methyl]phenol (HL2) are reported. The nitro-stabilised La(III) and Dy(III) compounds are ten-coordinate with metabidiminished icosahedron and sphenocorona geometries, respectively. Substitution of the nitrate with chloride ions in the starting metal compounds yielded an eight-coordinate Dy(III) complex that adopts the biaugmented trigonal prism geometry. For all three complexes, HL2 exists as a zwitterion that is bound to the metal centre in a mono- and bidentate fashion via the phenolate and methoxy oxygen atoms. The dysprosium(III) chloride complex is stabilised by both intramolecular N−H···O and intermolecular O−H···C1 hydrogen bonds, while the crystal packing of the Ln(III) nitrate complexes is ensured by mainly intramolecular N−H···O hydrogen bonds. Fluorescence studies displayed characteristic Dy(III) f→f transitions (4F9/2 → 6H15/2), which suggest the ligand HL2 is an effective organic antenna to absorb and transfer energy to the dysprosium ion. A series of mononuclear Nd(III) complexes with the Schiff base derivatives 2-methoxy-6-[(E)(phenylimino)methyl]phenol (HL2), 5-methoxy-2-[(E)-(phenylimino)methyl]phenol (HL3) and 2-methoxy-6-{(E)-[(2-methoxyphenyl)imino]methyl}phenol (HL4) yielded structurally diverse complexes defined by the formulae [Nd(HL2)2(NO3)3], [Nd(HL3)3(NO3)3] and [Nd(HL4)2(NO3)3]·CH3OH. Crystallographic analysis shows HL2 and HL4 coordinate bidentately via the phenolate and methoxy oxygen atoms, while HL3 is bound monodentately through the phenolate oxygen atom. Continuous shape measures depict that the decacoordinate complexes with HL2 and HL4 conform to the sphenocorona and tetradecahedron geometries, respectively, whilst the nona-coordinate Nd(III) complex with HL3 exhibits the muffin geometry. The effect of the ligand substituents and their positions (meta versus para) on the absorption and emission intensities of the complexes is demonstrated. Additionally, the electrochemical behaviour of the o-vanillin-derived Schiff base ligands and their complexes was also investigated, and the results illustrate ligand-based reductions and metal-centred redox potentials that are significantly shifted by the ligand substituents.
- Full Text:
- Date Issued: 2020
Synthesis and characterization of MXS (M = Mo & V) and carbon supported MXS nanocomposites as Pt-free counter electrodes for electrode for DSSC application
- Authors: Bede, Asanda
- Date: 2020
- Subjects: Voltammetry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10353/18599 , vital:42612
- Description: It has been reported that the morphology, crystalline phase composition and electrochemical properties of counter electrode materials such MxS (Mo, V) and carbon supported MxS (Mo, V) composite nanomaterials was of considerable importance because it governs the efficiency of many photon assisted chemical and physical reactions in dye sensitized solar cells (DSSCs). The efficiency of DSSCs with composite counter electrode materials is reliant on the stability of the photochemistry reactions which can be optimized by appropriate doping levels of the composite materials. Moreover, the microstructure such as surface area, distribution of the MxS (Mo, V) and carbon supported MxS (Mo, V) composite nanomaterials, and the stability of the electrostatic bonds between the MxS (Mo, V) with the carbon support also play a significant role in the performance of the DSSCs. This work evaluates the effect of different mole ratios of the MxS (Mo, V) and carbon supported MxS (Mo, V) composite nanomaterials on the morphological, structural and electrochemical properties of the composite materials. MoS2 nanoflakes nanostructures have been synthesized by hydrothermal technique using sodium orthovanadate (Na2MoO4) as precursor. In this work Carbon supported MoS2 NFs have been prepared by physically/chemically mixing different mole ratios of MoS2 NFs with multi-walled carbon nanotubes (MWCNTs) and polyvinylidene in N-methyl-2-pyrrolidinone. The morphological, structural and electrochemical properties of the composite counter electrode materials have been investigated using SEM, XRD FTIR, TEM, RS and CV. SEM analysis has revealed the presence of large MoS2 nanoflakes (NFs) as synthesized. SEM analysis has also revealed significant change in the surface morphology of carbon supported MoS2 composite nanostructures with the change in the mole ratio of the MoS2 NFs and carbon support multi-walled carbon nanotubes. Structural analysis through HRTEM analysis revealed a d-spacing of 0.65 nm with a corresponding (002) lattice plane belonging to a trigonal crystalline phase of MoS2. Also, HRTEM analysis has revealed d-spacing of 0.291 nm corresponding to 002 plane of MWCNTs. Raman spectroscopy has revealed Characteristic Raman vibration frequencies and symmetries at 264.6 cm-1(Eg), 354.2 cm-1 (Ag ) belonging trigonal phase of MoS2 (1T-MoS2). FTIR analysis has revealed a narrow peak at 457.6 cm-1 due Mo-S vibration bond. This observation confirms the success of synthesis of MoS2 nanostructures. Cyclic voltammetry (CV), charge-discharge (CD) and electrochemical impedance spectroscopy (EIS) measurements have revealed that the ratio 6:3:1 have shown to be optimum ratio due to its large reduction rate compared to pristine MoS2 NFs and other carbon supported MoS2 NFs. Calculated Rreduction for the carbon supported MoS2 NFs is the order 3:6:1>1:8:1>6:3:1>8:1:1 indicating the trend of ratio 3:6:1 appeared to have higher reduction rate than the rest of the material and it had far less ΔEpp than the rest of other ratios. All CV curves for both pristine MoS2 NFs and carbon supported MoS2 NFs confirmed a distinct Faradic characteristic. The VS2 nanosheets (NSs) and carbon supported VS2 NSs were also effectively synthesized via hydrothermal method. The SEM micrographs for VS2 NSs and carbon supported VS2 NSs samples reveals level increased. Furthermore, SEM-EDX analysis have confirmed the presence of V and S as well as C and O on carbon supported VS2 nanocomposites, and it clearly shown a gradually blending as the ratios increases. The structural studies through XRD analysis have revealed peaks at 2θ angles of 15.4◦, 28.2◦, 34.2◦, 36.2◦, 43.3◦,48.3◦, 54.4◦, 57.7◦ and 66.2◦ which correspond to the lattice planes (001), (002), (100), (011), (102), (003), (110), (103) and (201) belonging to hexagonal VS2 (H-VS2) crystalline phase as per JCPDS card 36-1139. The HRTEM have revealed that the VS2 NSs have an edge to edge length of ~ 0.294 – 1.248 µm. Also, HRTEM micrographs of VS2 NSs have revealed interplanar d spacing of 0.571 nm belonging to the (001) lattice plane of hexagonal VS2 (H-VS2) structure. FTIR analysis have shown a peak at 558 cm-1 attributed to V-S which is evident that sulfur has bonded with the metal (V) and is in agreement with EDS. CV, CD and EIS measurements have shown that the ratio 1:8:1 is more superior to VS2 NSs and other carbon supported VS2 NSs. Based on Rreduction for the carbon supported nanosheets VS2 nanosheets are ordered as 1:8:1>3:6:1>6:3:1>8:1:1. Carbon supported VS2 NSs of the mole ratio 1:8:1 showed a small resistance of 0.32 Ω. This is further evidence that the carbon supported VS2 NSs of the mole ratio 1:8:1 in addition to revealing excellent catalytic behaviour is also more chemically stable and has good conductivity properties._________
- Full Text:
- Date Issued: 2020
- Authors: Bede, Asanda
- Date: 2020
- Subjects: Voltammetry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10353/18599 , vital:42612
- Description: It has been reported that the morphology, crystalline phase composition and electrochemical properties of counter electrode materials such MxS (Mo, V) and carbon supported MxS (Mo, V) composite nanomaterials was of considerable importance because it governs the efficiency of many photon assisted chemical and physical reactions in dye sensitized solar cells (DSSCs). The efficiency of DSSCs with composite counter electrode materials is reliant on the stability of the photochemistry reactions which can be optimized by appropriate doping levels of the composite materials. Moreover, the microstructure such as surface area, distribution of the MxS (Mo, V) and carbon supported MxS (Mo, V) composite nanomaterials, and the stability of the electrostatic bonds between the MxS (Mo, V) with the carbon support also play a significant role in the performance of the DSSCs. This work evaluates the effect of different mole ratios of the MxS (Mo, V) and carbon supported MxS (Mo, V) composite nanomaterials on the morphological, structural and electrochemical properties of the composite materials. MoS2 nanoflakes nanostructures have been synthesized by hydrothermal technique using sodium orthovanadate (Na2MoO4) as precursor. In this work Carbon supported MoS2 NFs have been prepared by physically/chemically mixing different mole ratios of MoS2 NFs with multi-walled carbon nanotubes (MWCNTs) and polyvinylidene in N-methyl-2-pyrrolidinone. The morphological, structural and electrochemical properties of the composite counter electrode materials have been investigated using SEM, XRD FTIR, TEM, RS and CV. SEM analysis has revealed the presence of large MoS2 nanoflakes (NFs) as synthesized. SEM analysis has also revealed significant change in the surface morphology of carbon supported MoS2 composite nanostructures with the change in the mole ratio of the MoS2 NFs and carbon support multi-walled carbon nanotubes. Structural analysis through HRTEM analysis revealed a d-spacing of 0.65 nm with a corresponding (002) lattice plane belonging to a trigonal crystalline phase of MoS2. Also, HRTEM analysis has revealed d-spacing of 0.291 nm corresponding to 002 plane of MWCNTs. Raman spectroscopy has revealed Characteristic Raman vibration frequencies and symmetries at 264.6 cm-1(Eg), 354.2 cm-1 (Ag ) belonging trigonal phase of MoS2 (1T-MoS2). FTIR analysis has revealed a narrow peak at 457.6 cm-1 due Mo-S vibration bond. This observation confirms the success of synthesis of MoS2 nanostructures. Cyclic voltammetry (CV), charge-discharge (CD) and electrochemical impedance spectroscopy (EIS) measurements have revealed that the ratio 6:3:1 have shown to be optimum ratio due to its large reduction rate compared to pristine MoS2 NFs and other carbon supported MoS2 NFs. Calculated Rreduction for the carbon supported MoS2 NFs is the order 3:6:1>1:8:1>6:3:1>8:1:1 indicating the trend of ratio 3:6:1 appeared to have higher reduction rate than the rest of the material and it had far less ΔEpp than the rest of other ratios. All CV curves for both pristine MoS2 NFs and carbon supported MoS2 NFs confirmed a distinct Faradic characteristic. The VS2 nanosheets (NSs) and carbon supported VS2 NSs were also effectively synthesized via hydrothermal method. The SEM micrographs for VS2 NSs and carbon supported VS2 NSs samples reveals level increased. Furthermore, SEM-EDX analysis have confirmed the presence of V and S as well as C and O on carbon supported VS2 nanocomposites, and it clearly shown a gradually blending as the ratios increases. The structural studies through XRD analysis have revealed peaks at 2θ angles of 15.4◦, 28.2◦, 34.2◦, 36.2◦, 43.3◦,48.3◦, 54.4◦, 57.7◦ and 66.2◦ which correspond to the lattice planes (001), (002), (100), (011), (102), (003), (110), (103) and (201) belonging to hexagonal VS2 (H-VS2) crystalline phase as per JCPDS card 36-1139. The HRTEM have revealed that the VS2 NSs have an edge to edge length of ~ 0.294 – 1.248 µm. Also, HRTEM micrographs of VS2 NSs have revealed interplanar d spacing of 0.571 nm belonging to the (001) lattice plane of hexagonal VS2 (H-VS2) structure. FTIR analysis have shown a peak at 558 cm-1 attributed to V-S which is evident that sulfur has bonded with the metal (V) and is in agreement with EDS. CV, CD and EIS measurements have shown that the ratio 1:8:1 is more superior to VS2 NSs and other carbon supported VS2 NSs. Based on Rreduction for the carbon supported nanosheets VS2 nanosheets are ordered as 1:8:1>3:6:1>6:3:1>8:1:1. Carbon supported VS2 NSs of the mole ratio 1:8:1 showed a small resistance of 0.32 Ω. This is further evidence that the carbon supported VS2 NSs of the mole ratio 1:8:1 in addition to revealing excellent catalytic behaviour is also more chemically stable and has good conductivity properties._________
- Full Text:
- Date Issued: 2020
Synthesis of 2,4-Xylidine in continuous flow systems
- Authors: Sagandira, Mellisa Brenda
- Date: 2020
- Subjects: Chemistry, Physical and theoretical -- Research , Chemistry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/49270 , vital:41616
- Description: The continuous flow synthesis of 2,4-xylidine, an important compound in the fine chemical, pharmaceutical as well as the dyes and pigments industries was investigated in this study utilizing 1,3-dimethylbenzene as starting material. The first step involves the highly exothermic nitration of 1,3-dimethylbenzene with mixed acid to afford two nitro isomers, namely 1,3-dimethyl-2-nitrobenzene and 2,4-dimethyl-1-nitrobenzene. Since 2,4-xylidine is the targeted isomer, it is important to get a higher proportion of its nitration precursor 2,4-dimethyl-1-nitrobenzene. A safe and efficient synthesis of 2,4-dimethyl-1-nitrobenzene was therefore developed in continuous flow. This was aided by the micro reactor’s large surface area-to-volume ratio, one of the many features of continuous flow synthesis that enable rapid dissipation of heat allowing exothermic reactions to be conducted safely at ambient or higher temperatures. Two nitration protocols were developed using different micro reactors, a sonicated 1 ml PTFE tube reactor and 2 ml Uniqsis chip reactor. Using a sonicated PTFE tube reactor at room temperature and 15 min residence time, 2,4-dimethyl-1-nitrobenzene was afforded in 100 % conversion and 80 % selectivity. An increase in selectivity to 95 % and 90 % conversion towards 2,4-dimethyl-1-nitrobenzene was achieved using a 2 ml Uniqsis chip reactor at room temperature in 6 min residence time. This was accounted for due to efficient mixing of the two phases brought about by the reactor’s mixing structures, which are designed to create turbulent mixing. Scale-up synthesis of 2,4-dimethyl-1-nitrobenzene was conducted in a 4.5 ml LTF-XXL-ST-04 reactor at room temperature and 6 min residence time affording 90 % conversion and 95 % selectivity with a throughput of 16.6 g/h. Subsequently, reduction of 2,4-dimethyl-1-nitrobenzene to afford 2,4-xylidine was investigated in a 1 ml PTFE tube reactor (0.8 mm ID) using hydrazine in the presence of iron (III) 2,4-pentanedionate catalyst. Maximum conversion of 75 % was achieved at 170 °C in 15 min residence time. A more efficient reduction protocol was developed in a 2.7 ml packed column reactor (10 mm ID) using hydrazine in the presence of Pd/C at 50 °C and 2.5 min residence time affording 94 % conversion towards 2,4-xylidine. Lastly, multistep synthesis of 2,4-xylidine was performed using optimum conditions found using the 2 ml Uniqsis chip reactor and 2.7 ml packed column reactor with the incorporation of a phase separator. Joining the two reactors into a single continuous step afforded 100 % conversion and 95 % selectivity towards 2,4-xylidine with 8 min total residence time. Nitration of other organic compounds followed by reduction of the resultant nitro products was also investigated under respective optimum conditions determined for nitration of 1,3-dimethylbenzene and reduction of 2,4-dimethyl-1-nitrobenzene.
- Full Text:
- Date Issued: 2020
- Authors: Sagandira, Mellisa Brenda
- Date: 2020
- Subjects: Chemistry, Physical and theoretical -- Research , Chemistry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/49270 , vital:41616
- Description: The continuous flow synthesis of 2,4-xylidine, an important compound in the fine chemical, pharmaceutical as well as the dyes and pigments industries was investigated in this study utilizing 1,3-dimethylbenzene as starting material. The first step involves the highly exothermic nitration of 1,3-dimethylbenzene with mixed acid to afford two nitro isomers, namely 1,3-dimethyl-2-nitrobenzene and 2,4-dimethyl-1-nitrobenzene. Since 2,4-xylidine is the targeted isomer, it is important to get a higher proportion of its nitration precursor 2,4-dimethyl-1-nitrobenzene. A safe and efficient synthesis of 2,4-dimethyl-1-nitrobenzene was therefore developed in continuous flow. This was aided by the micro reactor’s large surface area-to-volume ratio, one of the many features of continuous flow synthesis that enable rapid dissipation of heat allowing exothermic reactions to be conducted safely at ambient or higher temperatures. Two nitration protocols were developed using different micro reactors, a sonicated 1 ml PTFE tube reactor and 2 ml Uniqsis chip reactor. Using a sonicated PTFE tube reactor at room temperature and 15 min residence time, 2,4-dimethyl-1-nitrobenzene was afforded in 100 % conversion and 80 % selectivity. An increase in selectivity to 95 % and 90 % conversion towards 2,4-dimethyl-1-nitrobenzene was achieved using a 2 ml Uniqsis chip reactor at room temperature in 6 min residence time. This was accounted for due to efficient mixing of the two phases brought about by the reactor’s mixing structures, which are designed to create turbulent mixing. Scale-up synthesis of 2,4-dimethyl-1-nitrobenzene was conducted in a 4.5 ml LTF-XXL-ST-04 reactor at room temperature and 6 min residence time affording 90 % conversion and 95 % selectivity with a throughput of 16.6 g/h. Subsequently, reduction of 2,4-dimethyl-1-nitrobenzene to afford 2,4-xylidine was investigated in a 1 ml PTFE tube reactor (0.8 mm ID) using hydrazine in the presence of iron (III) 2,4-pentanedionate catalyst. Maximum conversion of 75 % was achieved at 170 °C in 15 min residence time. A more efficient reduction protocol was developed in a 2.7 ml packed column reactor (10 mm ID) using hydrazine in the presence of Pd/C at 50 °C and 2.5 min residence time affording 94 % conversion towards 2,4-xylidine. Lastly, multistep synthesis of 2,4-xylidine was performed using optimum conditions found using the 2 ml Uniqsis chip reactor and 2.7 ml packed column reactor with the incorporation of a phase separator. Joining the two reactors into a single continuous step afforded 100 % conversion and 95 % selectivity towards 2,4-xylidine with 8 min total residence time. Nitration of other organic compounds followed by reduction of the resultant nitro products was also investigated under respective optimum conditions determined for nitration of 1,3-dimethylbenzene and reduction of 2,4-dimethyl-1-nitrobenzene.
- Full Text:
- Date Issued: 2020
Synthesis, crystal structures and characterization of metal–organic framework architectures involving dinuclear copper(ii) benzoic acid derivative complexes
- Authors: Ndima, Lubabalo
- Date: 2020
- Subjects: Supramolecular chemistry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/46783 , vital:39657
- Description: Structural copper(II) complexes with aromatic carboxylic acids show a wide spectrum of coordination schemes. Studies of dicopper(II) carboxylates have been associated with a variety of interests for their catalytic, biological and magnetic applications [1]. Various novel dinuclear copper(II) complexes [Cu2(X-benzoate)4L2] with varying substituents (X = CH3, F, Cl, Br, I, NO2 & OCH3) with a desired octahedral geometry have been synthesized. The various complexes were characterized by single crystal X-ray diffraction studies, spectroscopic and thermal methods (UV/Vis, FTIR and TGA, DSC). In most cases, the structures consists of centrosymmetric dimers in which the Cu atoms show a square pyramidal CuO5 coordination. In all cases, dimeric paddle wheel complexes where two copper(II) ions are held together by four benzoates (forming syn– syn bridges between the copper atoms) and the apical coordination site occupied by a solvent ligand (L) or supramolecular linker were obtained. The dimers are extended into 1D chains that result from hydrogen bonding between the coordinated methanol (solvent ligand) on one Cu(II) and the carboxylate group on an adjacent Cu(II) dimer, including interactions arising from various substituents. π–π Stacking interactions are found to be present in the various crystal structures forming 3D supramolecular array. FTIR and UV/Vis spectra of each complex have shown how the resonance and inductive effect of each substituent affects spectral data of each complex.
- Full Text:
- Date Issued: 2020
- Authors: Ndima, Lubabalo
- Date: 2020
- Subjects: Supramolecular chemistry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/46783 , vital:39657
- Description: Structural copper(II) complexes with aromatic carboxylic acids show a wide spectrum of coordination schemes. Studies of dicopper(II) carboxylates have been associated with a variety of interests for their catalytic, biological and magnetic applications [1]. Various novel dinuclear copper(II) complexes [Cu2(X-benzoate)4L2] with varying substituents (X = CH3, F, Cl, Br, I, NO2 & OCH3) with a desired octahedral geometry have been synthesized. The various complexes were characterized by single crystal X-ray diffraction studies, spectroscopic and thermal methods (UV/Vis, FTIR and TGA, DSC). In most cases, the structures consists of centrosymmetric dimers in which the Cu atoms show a square pyramidal CuO5 coordination. In all cases, dimeric paddle wheel complexes where two copper(II) ions are held together by four benzoates (forming syn– syn bridges between the copper atoms) and the apical coordination site occupied by a solvent ligand (L) or supramolecular linker were obtained. The dimers are extended into 1D chains that result from hydrogen bonding between the coordinated methanol (solvent ligand) on one Cu(II) and the carboxylate group on an adjacent Cu(II) dimer, including interactions arising from various substituents. π–π Stacking interactions are found to be present in the various crystal structures forming 3D supramolecular array. FTIR and UV/Vis spectra of each complex have shown how the resonance and inductive effect of each substituent affects spectral data of each complex.
- Full Text:
- Date Issued: 2020
Synthesis, photophysicochemical properties and photodynamic therapy activities of indium and zinc phthalocyanines when incorporated into Pluronic polymer micelles
- Authors: Motloung, Banele Mike
- Date: 2020
- Subjects: Indium , Zinc , Phthalocyanines , Polymers , Photochemotherapy , Micelles
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/167529 , vital:41489
- Description: This thesis reports on the syntheses, photophysicochemical properties and photodynamic therapy activities of symmetrical metallophthalocyanines (MPcs) when alone or when incorporated into Pluronic polymer micelles. The Pcs contain either zinc or indium as central metals and have phenyldiazenylphenoxy, pyridine-2-yloxy and benzo[d]thiazol-2-ylthio as ring substituents. Spectroscopic and microscopic techniques were used to confirm the formation MPcs with micelles. The photophysics and photochemistry of the Pcs were assessed when alone and with micelles. All the studied Pcs showed good photophysicochemical behavior with relatively high triplet and singlet oxygen quantum yields corresponding to their low fluorescence quantum yields. The Pcs with indium in their central cavity exhibited higher triplet and singlet oxygen quantum yields in comparison to their zinc counterparts due to the heavy atom effect obtained from the former. The in vitro dark cytotoxicity and photodynamic therapy of the Pc complexes and conjugates against MCF7 cells was tested. All studied Pc complexes alone and with micelles showed minimum dark toxicity making them applicable for PDT. All complexes displayed good phototoxicity < 50% cell viability (except for complex 2 > 50% cell viability) at concentrations ≤100 μg/mL, however the conjugates showed < 45% cell viability at concentrations ≤ 100 μg/mL, probably due to the small micellar size and EPR effect. The findings from this work show the importance of incorporating photosensitizers such as phthalocyanines into Pluronic polymers micelles and making them water soluble and ultimately improving their photodynamic effect.
- Full Text:
- Date Issued: 2020
- Authors: Motloung, Banele Mike
- Date: 2020
- Subjects: Indium , Zinc , Phthalocyanines , Polymers , Photochemotherapy , Micelles
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/167529 , vital:41489
- Description: This thesis reports on the syntheses, photophysicochemical properties and photodynamic therapy activities of symmetrical metallophthalocyanines (MPcs) when alone or when incorporated into Pluronic polymer micelles. The Pcs contain either zinc or indium as central metals and have phenyldiazenylphenoxy, pyridine-2-yloxy and benzo[d]thiazol-2-ylthio as ring substituents. Spectroscopic and microscopic techniques were used to confirm the formation MPcs with micelles. The photophysics and photochemistry of the Pcs were assessed when alone and with micelles. All the studied Pcs showed good photophysicochemical behavior with relatively high triplet and singlet oxygen quantum yields corresponding to their low fluorescence quantum yields. The Pcs with indium in their central cavity exhibited higher triplet and singlet oxygen quantum yields in comparison to their zinc counterparts due to the heavy atom effect obtained from the former. The in vitro dark cytotoxicity and photodynamic therapy of the Pc complexes and conjugates against MCF7 cells was tested. All studied Pc complexes alone and with micelles showed minimum dark toxicity making them applicable for PDT. All complexes displayed good phototoxicity < 50% cell viability (except for complex 2 > 50% cell viability) at concentrations ≤100 μg/mL, however the conjugates showed < 45% cell viability at concentrations ≤ 100 μg/mL, probably due to the small micellar size and EPR effect. The findings from this work show the importance of incorporating photosensitizers such as phthalocyanines into Pluronic polymers micelles and making them water soluble and ultimately improving their photodynamic effect.
- Full Text:
- Date Issued: 2020
System analysis of fatigue in pilots and co-pilots executing short-hall flight operations
- Authors: Bennett, Cleo Taylor
- Date: 2020
- Subjects: Air pilots -- Health and hygiene , Fatigue , Work environment -- Psychological aspects , Work environment -- Physiological aspects
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/146622 , vital:38543
- Description: Background: This study was conducted as part of Denel’s South African Regional Aircraft (SARA) development project. Regional aircraft have a maximum flight time of 60 minutes. Hence, the study focuses on matters pertaining to the short-haul flight context. Pilot fatigue has been recognised as a safety concern in the aviation industry. It impacts on pilot performance across the board, not least in the short-haul context. However, the specific factors that lead to pilot fatigue in short-haul operations have not been well researched. Research Aim: To identify and examine the factors which influence pilot/co-pilot fatigue in short-haul aviation contexts. Method: Fatigue is multifaceted, and has multiple definitions and descriptions. It is acknowledged as a complex phenomenon, the development of which is dynamically influenced by various factors. Thus, a systems approach based on the work system model by Smith and Carayon-Sainfort (1989) was adopted for this study. A systems analysis was conducted in two parts: 1) a literature analysis, and 2) expert interviews. Results: Both the literature analysis and the interviews indicated that pilot fatigue in short-haul flight operations represent composite system outcomes influenced by various factors. The factors identified were structured (systematised) into categories, namely organizational factors, task-related factors, environmental factors, factors linked to technology and tools, and non-work-related factors specific to the individual pilot. An example of a task-related factor would be the performance by pilots of multiple take-offs and landings; organizational factors include work time arrangements and duty scheduling (e.g. unpredictable schedule, early starts/late finishes, number of flight sectors in a shift, extended working hours, numerous consecutive work days, standby duties, flight, duty and rest limitations (regulations and guidelines); and short turnaround periods); environmental factors might include the small pressurised cockpit environment, movement restriction, very low humidity, low air pressure, vibrations, high noise levels, low light intensity light, and inclement weather); there are many examples of how tools and technology utilized by pilots might affect their fatigue levels; and finally, pilot-specific non-work-related factors would include things like the pilot’s age, health (lifestyle), family stress, work experience and sleep environment. All of these factors were identified during the literature analysis and have a significant bearing on how fatigue could present in short-haul pilots/co-pilots. Other important fatigue-related factors revealed during the expert interviews included, organizational culture, time management, health implications of fatigue, and management of fatigue. Conclusions: Pilot fatigue is a complex and multi-factorial physiological condition. There are many interacting components which contribute to pilot fatigue in short-haul operations. These should be viewed from an integrated perspective and holistic, systems-based approaches should be taken to manage these issues, particularly in the context of short-haul operations. This would optimize pilot performance and well-being and, most importantly, improve the safety of the work environment to enhance overall operation safety. Limitations: The study does not quantify the contributions made to pilot fatigue by the various factors explored. Therefore, care needs to be taken when designing and implementing interventions based on this research.
- Full Text:
- Date Issued: 2020
- Authors: Bennett, Cleo Taylor
- Date: 2020
- Subjects: Air pilots -- Health and hygiene , Fatigue , Work environment -- Psychological aspects , Work environment -- Physiological aspects
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/146622 , vital:38543
- Description: Background: This study was conducted as part of Denel’s South African Regional Aircraft (SARA) development project. Regional aircraft have a maximum flight time of 60 minutes. Hence, the study focuses on matters pertaining to the short-haul flight context. Pilot fatigue has been recognised as a safety concern in the aviation industry. It impacts on pilot performance across the board, not least in the short-haul context. However, the specific factors that lead to pilot fatigue in short-haul operations have not been well researched. Research Aim: To identify and examine the factors which influence pilot/co-pilot fatigue in short-haul aviation contexts. Method: Fatigue is multifaceted, and has multiple definitions and descriptions. It is acknowledged as a complex phenomenon, the development of which is dynamically influenced by various factors. Thus, a systems approach based on the work system model by Smith and Carayon-Sainfort (1989) was adopted for this study. A systems analysis was conducted in two parts: 1) a literature analysis, and 2) expert interviews. Results: Both the literature analysis and the interviews indicated that pilot fatigue in short-haul flight operations represent composite system outcomes influenced by various factors. The factors identified were structured (systematised) into categories, namely organizational factors, task-related factors, environmental factors, factors linked to technology and tools, and non-work-related factors specific to the individual pilot. An example of a task-related factor would be the performance by pilots of multiple take-offs and landings; organizational factors include work time arrangements and duty scheduling (e.g. unpredictable schedule, early starts/late finishes, number of flight sectors in a shift, extended working hours, numerous consecutive work days, standby duties, flight, duty and rest limitations (regulations and guidelines); and short turnaround periods); environmental factors might include the small pressurised cockpit environment, movement restriction, very low humidity, low air pressure, vibrations, high noise levels, low light intensity light, and inclement weather); there are many examples of how tools and technology utilized by pilots might affect their fatigue levels; and finally, pilot-specific non-work-related factors would include things like the pilot’s age, health (lifestyle), family stress, work experience and sleep environment. All of these factors were identified during the literature analysis and have a significant bearing on how fatigue could present in short-haul pilots/co-pilots. Other important fatigue-related factors revealed during the expert interviews included, organizational culture, time management, health implications of fatigue, and management of fatigue. Conclusions: Pilot fatigue is a complex and multi-factorial physiological condition. There are many interacting components which contribute to pilot fatigue in short-haul operations. These should be viewed from an integrated perspective and holistic, systems-based approaches should be taken to manage these issues, particularly in the context of short-haul operations. This would optimize pilot performance and well-being and, most importantly, improve the safety of the work environment to enhance overall operation safety. Limitations: The study does not quantify the contributions made to pilot fatigue by the various factors explored. Therefore, care needs to be taken when designing and implementing interventions based on this research.
- Full Text:
- Date Issued: 2020