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Investigation of the interaction between truck tyre waste rubber particulate and penetration grade and polymer modified bituminous binders

  • Authors: Mgangato, Siseko
  • Date: 2020
  • Subjects: Truck equipment industry
  • Language: English
  • Type: Thesis , Masters , MTech
  • Identifier: http://hdl.handle.net/10948/48500 , vital:40882
  • Description: Recent studies have investigated the waste tyre crumb rubber (TCR)-bitumen interaction by observing the swelling of waste TCR at elevated temperatures. It was found that the waste TCR-bitumen interaction alters the rigidity and shape of TCR, which causes the failure of asphalt mixtures. Consequently, the problem occurs when the waste TCR swells during waste TCR-bitumen interaction from mixing and transportation of the asphalt mixture. Extensive laboratory studies have shown that the rate of absorption of bitumen is correlated with the TCR rubber composition and particle size. However, it is possible that swelling of waste TCR can be prevented or reduced before waste TCR-bitumen interaction by means of pre-treating the rubber crumb as to prevent the alteration of bitumen properties. Therefore, this study seeks to investigate the interaction of truck tyre wastes rubber particulates (WRP)-bitumen with the pretreatment of truck tyre WRP with H2SO4, HNO3 and HCℓ. This treatment was done to make TCR suitable for the dry process asphalt mixtures, where TCR acts as a filler instead of altering bitumen binder properties. The investigation characterized truck tyre WRP-bituminous binder interaction by interacting a single truck tyre WRP with penetration grade (50/70 and 70/100) and industrial polymer modified binders (AE-2 and PolyMod). The interaction through kinetic study revealed that the swelling of truck tyre WRP is either a non-Fickian two-step swelling or anomalous diffusion mechanism of bituminous binders. In addition, the study showed that temperature has an effect on the diffusion, sorption and permeation coefficients; where coefficients increased as the temperature was increased. The characterization of which bituminous binder component was observed by the truck tyre WRP was studied using Fourier Transform Infra-Red Spectroscopy (FTIR), Carbon 13 Nuclear Magnetic Spectroscopy (13C NMR) and Thermalgravimetric Analysis (TGA). The study showed that by analysing the extracted bituminous binder from residual truck tyre WRP after the interaction, Polycyclic Aromatic Hydrocarbons (PAHs) consisting of molecular structure characteristics of bitumen constituent aromatics. So as to restricting the diffusion of bituminous binder into truck tyre WRP, the surface of truck tyre WRP was treated with H2SO4, HNO3 and HCℓ acids from concentrations of 1, 6 and 12 M. The H2SO4 and HCℓ treated WRP showed a change in molecular ii structure, toluene sorption coefficient, surface morphology and thermal characteristics (TGA and DSC). However, changes that were observed with the HNO3 treatment showed that the truck tyre WRP material was in fact being digested by the HNO3 acid. In all the respective acid treatments, the effects were distinct with 12 M acid concentration. This was observed with a decrease in toluene sorption coefficient with increasing acid concentration. From the treatment of the truck tyre WRP with H2SO4, HNO3 and HCℓ acids, the 6 M acid concentration showed desirable characteristics. Interaction of the respective acid treated truck tyre WRP-bituminous binder interaction was carried out following the drainage basket method. In this investigation, the 6 M acid (H2SO4, HNO3 and HCℓ) treated WRP was used and it was found that swelling followed a two-stage and anomalous non-Fickian diffusion patterns. Hence HNO3 absorbed the least binders and this was confirmed by the low sorption coefficients. Although the H2SO4 and HCℓ did not show a significant difference with 50/70 and 70/100 and a significant change with AE-2 and PolyMod binder absorption, the dynamic shear rheometre (DSR) measurements revealed that the residual binders (50/70, 70/100, AE2 and PolyMod) had a higher rutting temperature than respective original binder, where G*/sinδ is ≤ 1 kPa. These binders also had lower fatigue to cracking temperature through analysis of G*sinδ at 5 000 kPa. In addition, the measured phase angle at the respective rutting temperature showed to be between 45 ̊and 90 ̊which suggested that the binders were viscoelastic. Viscoelastic characteristics were therefore assessed using multiple stress creep recovery test (MSCR). The measured MSCR parameters, % recovery and non-recoverable compliance, showed that there was a slight gain in elasticity with 50/70 and 70/100 after the interaction. The AE-2 and PolyMod binders experienced a decrease in elasticity after the interaction. Despite unforeseen outcomes, the treatment of truck tyre WRP with H2SO4, HNO3 and HCℓ acids decreased the swelling phenomenon of truck tyre WRP in a bituminous binder.
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  • Date Issued: 2020

Investigation of wild garlic plant extracts as potential devulcanizing agents

  • Authors: Mpuputla, Mooketsi
  • Date: 2020
  • Subjects: Plant products , Plant extracts Traditional medicine
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: http://hdl.handle.net/10948/49204 , vital:41610
  • Description: Commercially available chemical compounds used as devulcanizing agents have been found to be relatively expensive, and harmful to human health. These include compounds such as diallyl disulfide (DADS) and diphenyl disulfide (DPDS). However, compounds like DADS and other sulfides are found in the readily available natural resource material, T. violacea, which is rich in sulfur-derived compounds that may exhibit potential use as devulcanizing agents. Hence, this study is aimed at examining the efficacy of the extracted sulfur compounds of T. violacea as potential devulcanizing agents. The sulfides of T. violacea were successfully extracted by means of sequential extraction using chloroform (CHCl3), ethyl acetate (EtOAc), and methanol (MeOH). Identification of present sulfides was done by phytochemical analysis, using the TLC method. The commercially available HPLC grade DADS reference standard was used to quantify the amount of DADS in each extract. Reversed-phase high-performance liquid chromatography (RP-HPLC) was used for quantification. The HPLC results showed that only the EtOAc and MeOH extracts contained DADS, while insignificant amount of DADS was seen in the CHCl3 extracts. The EtOAc roots, bulbs and leaf extracts (18.8 × 10-3, 8.84 × 10-3, 7.2 × 10-3 mg/mL) showed greater DADS concentration compared to the MeOH roots, bulbs and leaf extracts (5.3 × 10-3, 8.07 × 10-3, 1.9 × 10-3 mg/mL), respectively. RP-HPLC and Gel Permeation Chromatography (GPC) were the methods used to monitor and identify crosslink formation and devulcanizing. The vulcanization and devulcanization studies were carried out using the model compound, squalene. All extracts showed a decrease in the molecular weight distribution of the devulcanized products. The leaf extract, CHCl3 and EtOAc, showed the highest devulcanization efficacy overall, while the MeOH extracts showed least devulcanization efficacy as devulcanization agents. Thermal analysis studies were performed to investigate the interactions of the curatives used in the vulcanization system(s). Isothermal analysis of the vulcanization system was evident in a vulcanization reaction at an optimal time of 20 min, and at onset temperature of 177.6 oC. Upon devulcanization, DSC analysis gave evidence of the glass transition of squalene products. This indicates that no main-chain scission or backbone breakage occurred in reacting the vulcanized products with the devulcanizing agents.
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  • Date Issued: 2020

Linking onshore and offshore crustal features, integrating seismic and borehole data in the Gamtoos basin

  • Authors: Makuzeni, Manyano
  • Date: 2020
  • Subjects: Submarine geology , Geology Geophysics
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: http://hdl.handle.net/10948/49137 , vital:41604
  • Description: The margin of the Southern Africa continent harbours the history about the fragmentation and separation of Gondwana in its basins. The integration of onshore and offshore geology is of primordial importance to understand the complete geological history and evolution of the southern African border. The study focuses on the Gamtoos Basin, where the sediment deposits on the onshore portion are generally unfossiliferous and therefore difficult to correlate with the offshore portion of the basin. In an attempt to do this, several datasets were integrated such as old 2-D seismic reflection data and borehole wells. This data, acquired by SOEKER in the 1970s was purchased from the Petroleum Agency of South Africa (PASA). Some data reprocessing involved digitization and conversion of the old seismic data from TIF format to SEG-Y format. Conventional seismic stratigraphic method (Mitchum, JR, et al., 1977) was used to identify seismic discontinuities and remarkable stratigraphic surfaces and units based on reflection configurations and facies characteristics, and ages of these surfaces were provided by well data. Seismic interpretation was first done on printed seismogram papers, and then integrated into the ‘Kingdom Suite’ software to ensure coherency at all crossing lines. Isochron and Isopach maps (using QGIS, Mirone and tools such as GMT) were created. The first results, allow us to estimate for the first time a precise age calibration of onshore deposit. Furthermore, the delimitation in 5 second-order seismic sequences along the Gamtoos Basin suggest a link between different basin filling dynamics and kinematic phases related to the opening of the Indian and Atlantic Oceans along the southern Africa margins. The study shows that the Gamtoos Basin is an essential area linking the geological histories of both East and Western parts of the Southern Africa continent.
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  • Date Issued: 2020

Occurrence of early stage fishes associated with Anaulus australis in a temperate South African surf zone, with notes on feeding ecology and incidental microplastic consumption in a dominant species

  • Authors: McGregor, Steven
  • Date: 2020
  • Subjects: Estuarine fishes -- Ecology
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: http://hdl.handle.net/10948/48489 , vital:40881
  • Description: Surf zones are important fish nursery areas, however, microhabitats and threats to fishes within them remain understudied. Diatom accumulations in surf zones are a worldwide phenomenon on certain beach types and discolour the water, offering refuge from visual predators and feeding opportunities for fishes, thus providing a microhabitat for early stage fishes. Surf diatom accumulations require long lasting rip current-entrained gyres to occur, which also entrap buoyant microplastics. These microplastics may then be consumed by filter feeding fishes such as the Southern mullet Chelon richardsonii. This work aimed to assess the extent of association of early stage fishes with diatom Anaulus australis accumulations and the feeding ecology and incidence of microplastic ingestion in the commercially important and dominant surf zone mugilid C. richardsonii. Early stage fishes were sampled within and outside of A. australis accumulations in the Sundays Beach surf zone on the southeast coast of South Africa, using a 4.5 x 1.5 m modified larval seine net with 500 µm mesh. Later developmental stage C. richardsonii were captured using a cast net. A total of 338 replicate larval fish seine hauls were done, capturing 1074 fishes including 33 taxa from 19 families. To assess ontogenetic shifts in diet of the dominant species C. richardsonii, stomach contents of 150 fish were categorised and assessed by prey abundance, frequency of occurrence, volume, index of relative importance and dietary niche breadth and compared across all developmental stages, excluding flexion and preflexion. Dominant families of early stage fishes were Sparidae, Soleidae, Mugilidae and Clupeidae that comprised 93 % of the catch, with dominant species including Heteromycteris capensis, Rhabdosargus holubi, Solea turbynei, Diplodus capensis and Chelon richardsonii. Species diversity and catch per unit effort (CPUE) were significantly higher within accumulations compared to outside, as was the CPUE of postflexion larvae and early juveniles. Generalized Linear Models showed that temperature, dissolved oxygen (mg l-1 ), turbidity and A. australis biomass (µg Chl a l -1 ) were the most significant factors affecting the overall CPUE and that of dominant species. It was suggested that after reaching the postflexion stage of development, fishes utilise diatom accumulations opportunistically when and where they are present. A diet study of the dominant species showed an ontogenetic dietary shift in C. richardsonii using A. australis accumulations as a feeding area, with postflexion larvae feeding mostly on copepods and microplastic fibres, while later developmental stages consumed predominantly A. australis cells and sand. Microplastic fibres were present in 40 % of fish sampled and microplastic fragments in 5 %, with both types found in all developmental stages assessed. It was suggested that C. richardsonii were unable to distinguish microplastics from their natural prey and incidentally ingested them. This presents a conservation concern, because chemicals associated with microplastics could bioaccumulate and biomagnify up the food chain if key baitfish species such as C. richardsonii are ingesting plastic. This study was the first to assess the association of early stage fishes with surf diatom accumulations, and the first to record microplastic ingestion in C. richardsonii. Understanding the function of microhabitats for early stage fishes and threats within them is needed to understand the life history strategies and survival of fishes in key coastal nursery and feeding areas.
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  • Date Issued: 2020

Ocean dynamics of the shelf and bays of the eastern Agulhas bank: a process-oriented numerical modelling study

  • Authors: Bailey, Dylan Francis
  • Date: 2020
  • Subjects: Oceanography -- Research , Marine biology , Marine meteorology , Hydrography
  • Language: English
  • Type: Thesis , Doctoral , DPhil
  • Identifier: http://hdl.handle.net/10948/49038 , vital:41595
  • Description: There is a general need for a broader base of information on the finer detail of ocean processes in the Eastern Agulhas Bank region. In this thesis, the Regional Ocean Modelling System (ROMS) was applied to resolve high resolution (~1km) bay and shelf scale ocean processes along the south eastern coastline of South Africa using an offline multi-nested approach. Experimental and reference ocean model runs were used with in situ instrument mooring data to investigate how currents and temperature in the bays and the adjacent shelf are affected by the bathymetry, Agulhas Current (AC), regional winds, and coastal trapped waves (CTW). Focus was given to temperature, circulation, and coastal trapped waves, given the abundance of hourly in situ mooring data for these variables, making them suitable for comparison with the ocean model. SST variability trends were seasonally and spatially predictable, being greatest in the summer months and smallest in the winter months. A region of high SST variability extended from Port Alfred toward the south-west, indicating entrainment of nearshore upwelled water and instabilities in the inshore front of the AC. Shelf bottom temperature variability had a more spatially diverse seasonal trend, with coastal variability the highest (lowest) and offshore variability the lowest (highest) during the summer (winter) months. A distinct asymmetry in mean seasonal shelf bottom temperatures evident to the south of Algoa Bay and St Francis Bay was shown to be dependent on the profile of the shelf margin in relation to the inshore front of the AC using an experimental model run. Bay-scale anti-cyclonic circulation patterns dominate the bays throughout the year, with regions of strong mean surface currents occurring south of Cape Recife and Cape St Francis. General circulation patterns over the shelf are strongly governed by regional wind regimes, with the strongest flows being south-westward occurring during north-easterly wind events. Shelf bottom flows typically follow the expected Ekman-veering response, apart from near coastal flows that are topographically steered. A region of consistently strong south-westward shelf bottom flow extends from the east of Port Alfred to the shelf margin south of Bird Island. This flow is predominantly driven by the AC, although its velocity is strongly governed by regional winds. Circulation patterns during powerful eastward moving wind systems are strongly governed by the passage of associated CTW. Comparisons with an experimental model run where surface winds were removed revealed that the shelf wave was responsible for 61% of water volume displacement during a CTW event, and that the coastal shear turbulence caused by this displacement has a direct effect on the mixed layer depth. The links made between the complex shelf and bay ocean processes indicate that subtle changes to the ocean state will have far reaching effects on the regional ocean environment and its biota. Given the challenges of climate change, this is of paramount importance if we are to quantify these effects and mitigate their impacts, particularly with respect to the socio-economic dependency of those who rely on the ocean for its living resources.
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  • Date Issued: 2020

On the association of graphs to rings

  • Authors: Mzulwini, Sboniso
  • Date: 2020
  • Subjects: Categories (Mathematics)
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: http://hdl.handle.net/10948/47060 , vital:39779
  • Description: Let R be a commutative ring with nonzero identity, and let Z (R) be the set of its zerodivisors. There exists an association between a simple graph (R) and the set Z(R) of nonzero zero-divisors of R. In this dissertation we investigate how the properties of R a⁄ect the properties of (R) and vice versa. There are other graphs that are associated with R. Some of these are shown to be special cases of the congruence-based zero-divisor graph.
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  • Date Issued: 2020

Patterns and Pattern Languages for Mobile Augmented Reality

  • Authors: Munro, Donald
  • Date: 2020
  • Subjects: Augmented reality , Educational technology
  • Language: English
  • Type: Thesis , Doctoral , PhD
  • Identifier: http://hdl.handle.net/10948/48510 , vital:40883
  • Description: Mixed Reality is a relatively new field in computer science which uses technology as a medium to provide modified or enhanced views of reality or to virtually generate a new reality. Augmented Reality is a branch of Mixed Reality which blends the real-world as viewed through a computer interface with virtual objects generated by a computer. The 21st century commodification of mobile devices with multi-core Central Processing Units, Graphics Processing Units, high definition displays and multiple sensors controlled by capable Operating Systems such as Android and iOS means that Mobile Augmented Reality applications have become increasingly feasible. Mobile Augmented Reality is a multi-disciplinary field requiring a synthesis of many technologies such as computer graphics, computer vision, machine learning and mobile device programming while also requiring theoretical knowledge of diverse fields such as Linear Algebra, Projective and Differential Geometry, Probability and Optimisation. This multi-disciplinary nature has led to a fragmentation of knowledge into various specialisations, making it difficult to integrate different solution components into a coherent architecture. Software design patterns provide a solution space of tried and tested best practices for a specified problem within a given context. The solution space is non-prescriptive and is described in terms of relationships between roles that can be assigned to software components. Architectural patterns are used to specify high level designs of complete systems, as opposed to domain or tactical level patterns that address specific lower level problem areas. Pattern Languages comprise multiple software patterns combining in multiple possible sequences to form a language with the individual patterns forming the language vocabulary while the valid sequences through the patterns define the grammar. Pattern Languages provide flexible generalised solutions within a particular domain that can be customised to solve problems of differing characteristics and levels of iii complexity within the domain. The specification of one or more Pattern Languages tailored to the Mobile Augmented Reality domain can therefore provide a generalised guide for the design and architecture of Mobile Augmented Reality applications from an architectural level down to the ”nuts-and-bolts” implementation level. While there is a large body of research into the technical specialisations pertaining to Mobile Augmented Reality, there is a dearth of up-to-date literature covering Mobile Augmented Reality design. This thesis fills this vacuum by: 1. Providing architectural patterns that provide the spine on which the design of Mobile Augmented Reality artefacts can be based; 2. Documenting existing patterns within the context of Mobile Augmented Reality; 3. Identifying new patterns specific to Mobile Augmented Reality; and 4. Combining the patterns into Pattern Languages for Detection & Tracking, Rendering & Interaction and Data Access for Mobile Augmented Reality. The resulting Pattern Languages support design at multiple levels of complexity from an object-oriented framework down to specific one-off Augmented Reality applications. The practical contribution of this thesis is the specification of architectural patterns and Pattern Language that provide a unified design approach for both the overall architecture and the detailed design of Mobile Augmented Reality artefacts. The theoretical contribution is a design theory for Mobile Augmented Reality gleaned from the extraction of patterns and creation of a pattern language or languages.
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  • Date Issued: 2020

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.
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  • 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.
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  • Date Issued: 2020

Phytoplankton of the Southern Agulhas Large Marine Ecosystem (sACLME)

  • Authors: Sonnekus, Martinus Jakobus
  • Date: 2020
  • Subjects: Botanical chemistry
  • Language: English
  • Type: Thesis , Doctoral , PhD
  • Identifier: http://hdl.handle.net/10948/47646 , vital:40261
  • Description: The southern Agulhas Large Marine Ecosystem (sACLME) consists of the greater Agulhas Current system, including the areas influenced by the Agulhas Current, the Agulhas Shelf, Agulhas Bank, Agulhas Retroflection as well as the Agulhas Return Current. Four biogeographical regions were identified within the sACLME and the composition of the phytoplankton communities and the associated physico-chemical variables in each were investigated. Water temperature and nitrate concentration were found to be the main drivers of the sACLME phytoplankton community. A total of 215 phytoplankton taxa were identified that were separated into two groups: the Agulhas Current group and the Southwest Indian Ocean Ridge group. The structure of the phytoplankton community was consistently homogeneous throughout the sACLME. Nutrient concentrations of the water varied, but nitrate was the most abundant source of nitrogen, especially in regions that were subjected to the upwelling of cold nutrient-rich water. The phytoplankton communities were significantly influenced by the availability and stoichiometry of the macronutrients nitrogen; phosphorus and silicon. The low mean N:P ratio of 5.5 is an indication that the waters of the sACLME are generally nitrogen limited, as is typical of oceanic systems. There is a change in phytoplankton cell size and functional groups within in the various water masses that are specific to certain biogeographical regions within the Agulhas Current system. It is clear that frontal systems may form barriers between phytoplankton communities.
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  • Date Issued: 2020

Plankton dynamics in response to algal blooms in a highly eutrophic estuary in South Africa

  • Authors: Smit, Taryn
  • Date: 2020
  • Subjects: Algal blooms -- South Africa , Estuaries -- South Africa
  • Language: English
  • Type: Thesis , Doctoral , DPhil
  • Identifier: http://hdl.handle.net/10948/49303 , vital:41619
  • Description: The global rise in the incidence of harmful algal blooms in estuaries is a major concern given their importance as a nursery area for a variety of invertebrates and fishes. On the warm-temperate, south-east coast of South Africa, the Sundays Estuary experiences persistent, seasonal HABs due to stable eutrophic conditions. Spring blooms of the dinoflagellate, Heterosigma akashiwo, were recorded for several years in the estuary. This Raphidophyte is known for its consequences in fish and shellfish aquaculture and exhibits harmful properties such as mucilage and reactive oxygen species production. Subsequently, the dissertation investigated larval fish assemblage dynamics, larval prey and predator dynamics and body condition in association with H. akashiwo blooms. HABs mainly altered the water quality within the mesohaline zone in terms of microalgal biomass and dissolved oxygen. Hypereutrophic blooms of H. akashiwo reached 24 996 cells∙mL-1 during the study period. Supersaturated dissolved oxygen concentrations (up to ~13 mg∙L-1 at night and ~21 mg∙L-1 during the day) were recorded during hypereutrophic blooms (> 80 μg∙L-1, ≥ 2781 H. akashiwo cells∙mL-1). Dissolved oxygen differed significantly by bloom state, with the highest dissolved oxygen concentrations. Larval fish density, diversity and community structure variability were lower during hypereutrophic blooms compared to standard blooms and bloom absence, albeit statistically insignificant. Estuarine resident larval density was negatively correlated with dissolved oxygen concentration (P < 0.001). Dominant prey copepod of G. aestuaria larvae, P. hessei, was less abundant and variable during hypereutrophic blooms (mean: 664, range: 4-4301 individuals per m3) compared to standard blooms (mean: 950, range: 2-5237 individuals per m3) and bloom absence (mean: 1182, range: 23-7259 individuals per m3). Although HABs did not appear to drive a mismatch between prey and G. aestuaria larvae, early juvenile larvae made only a small contribution to the assemblage (0.2-1.8%). In terms of predator effects, yolk sac larvae were negatively related to R. terranatalis (P < 0.05). A significant positive relationship was found between prey, P. hessei and G. aestuaria preflexion (P < 0.001), flexion (P < 0.001) and postflexion (P < 0.05) larvae. In a world first, the effects of HABs were investigated on a larval fish species, Gilchristella aestuaria, using biochemical body condition analyses. During severe bloom conditions, G. aestuaria larvae were smaller and the assemblage consisted of mainly early developmental stages (stats). Body condition (RNA per dry weight) was poorest in the presence of hypereutrophic blooms (P < 0.001). A bell-curved relationship between RNA/DW and dissolved oxygen concentration was also produced in a 3-day time-lagged GAM (P < 0.001). In conclusion, hypereutrophic bloom conditions appeared to trigger adult G. aestuaria spawning in the upper mesohaline zone of the estuary in response to heightened primary productivity which occurs during the early bloom stage. However, reductions in copepod abundance (P. hessei) and unfavourable oxygen concentrations interfered with grow-out of G. aestuaria larvae. This research showed that HABs can alter nursery properties to the detriment of G. aestuaria larvae can have serious knock-on effects up the food chain. The loss in abundance of adult, juvenile and larval G. aestuaria, a key forage fish in South African estuaries, has major implications for estuarine food webs, especially in reduced prey availability to juvenile fishes and birds. There is still much to learn about the effects of HABs on the physiological and behavioural aspects on plankton communities worldwide.
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  • 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.
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  • 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

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..
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  • 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.
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  • 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.
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  • Date Issued: 2020

Synthesis, characterisation and antitumour activities of lanthanide complexes with hydrazones and carboxylic acid ligands

  • Authors: Madanhire, Tatenda
  • Date: 2020
  • Subjects: Organic acids
  • Language: English
  • Type: Thesis , Doctoral , PhD
  • Identifier: http://hdl.handle.net/10948/48456 , vital:40878
  • Description: The tridentate hydrazone ligands, (E)-N'-(2-hydroxybenzylidene)benzohydrazide (H2phen) and (E)-N'-(2-hydroxybenzylidene)nicotinohydrazide (H2Nic), were synthesised and complexed to Ln(III) acetates. The centrosymmetric, acetato-bridged dinuclear coordination compounds with the formulae, [La2(Hphen)2(OAc)4(H2O)2]·DMF·H2O (1), [Ln2(HNic)2(OAc)4(H2O)2]·DMF·H2O (Ln = La (2) and Nd (3)) and [Ln2(HNic)2(OAc)4(H2O)2]·DMF (Ln = Er (4) and Yb (5)) were isolated and characterised by elemental analyses, IR spectroscopy, UV-Vis spectroscopy, X-ray diffraction studies and SHAPE 2.1. The nine-coordinate complexes 1–3 crystallise in the triclinic space group P-1, with the metal centres having the distorted spherical capped square antiprism geometry (C4v), while the eight-coordinate Er(III) and Yb(III) complexes (monoclinic system, space group P21/c) display the geometry of distorted triangular dodecahedron (D2d). Geometry optimisation of the monoanionic forms of the hydrazone ligands (Hphen– and HNic– ) were performed using Density Functional Theory (DFT) with Becke’s three parameter hybrid method and correlation functional of Lee, Yang and Parr (B3LYP) with augcc-pVTZ basis set. Natural population analysis (NPA) and molecular electrostatic potential (MEP) maps indicated that the most preferred sites for electrophilic attack in the anionic ligands are the phenolate and carbonyl oxygens, and the azomethine nitrogens. The evaluation of the cytotoxic activity of the compounds on breast cancer (MCF-7), the endometrial carcinoma (HEC-1A) and the human monocytic (THP-1) cell lines using the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl tetrazolium bromide (MTT) assay revealed that the hydrazone ligands and complexes 1–4 are partially cytotoxic against MCF-7 cells, while the Schiff bases and complexes 3–5 significantly inhibit cell growth in HEC-1A cells. The complexation reactions of Ce(III), Nd(III), Gd(III) and Er(III) with the chelating/ bridging monoanionic ligand N-(2,6-dimethylphenyl)oxamate (Hpma– ) in basic media were performed in view of the potential applications of oxamate derivatives as cytotoxic agents. The coordination compounds were characterised by different Abstract T. Madanhire Nelson Mandela University xxvi physico-chemical techniques: elemental analysis, conductivity measurements, IR, 1 H NMR and UV-Vis-NIR spectroscopy. The anionic Hpma– was obtained through conversion of the proligand ethyl (2,6-dimethylphenylcarbamoyl)formate (Hdmp). The reactions afforded lanthanide(III)–oxamate coordination polymers of formulae: {[Ln(Hpma)3(MeOH)(H2O)]∙2MeOH}n (Ln = Ce (1) and Nd (2)), {[Gd2(Hpma)6(MeOH)4]∙6MeOH}n (3), {[Er2(Hpma)6(MeOH)(H2O)3]∙2MeOH}n (4) and [Ln2Na2(Hpma)8(EtOH)(H2O)6]n (Ln = Nd (5) and Gd (6)). The polymeric complexes feature Ln-Hpma moieties bridged by μ2-η 1 :η 1 :η 1 Hpma– , giving onedimensional zig-zag chains of the –Ln–O–C–O–Ln– type. Atomic charge analysis and the MEP map of the Hpma– moiety done using the DFT/B3LYP method were found to be consistent with the chelating and bridging modes of the anionic ligand through all the oxygen atoms. The evaluation of the cytotoxic activities of the metal salts, the proligand and the novel lanthanide complexes on MCF-7, HEC-1A and THP-1 cell lines revealed that only the rare-earth metal salts [Ce(NO3)3∙6H2O] and [Nd(NO3)3∙6H2O] showed modest cytotoxicity against MCF-7 and HEC-1A cells, respectively.
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  • 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.
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  • Date Issued: 2020

Synthesis, crystal structures and molecular modelling of rare earth complexes with bis(2-pyridylmethyl)amine and its derivatives : a quantum chemical investigation of ligand conformational space, complex intramolecular rearrangement and stability

  • Authors: Matthews, Cameron
  • Date: 2020
  • Subjects: Rare earths , Complex compounds , Ligands
  • Language: English
  • Type: Thesis , Doctoral , PhD
  • Identifier: http://hdl.handle.net/10948/46229 , vital:39517
  • Description: Limited research has been performed on the coordination behaviour of hybrid aliphatic and heterocyclic polyamines with trivalent rare earth elements. The rare earth coordination properties of several Nalkylated derivatives of the tridentate ligand bis(2-pyridylmethyl)amine (DPA, HL1) backbone - involving the rare earth elements Y, La-Nd, Sm, Eu and Tb-Lu - have been investigated in this study However, the structural and energetic characteristics of DPA coordination with rare earth elements (REE) have not been studied thus far. Potential applications of DPA-based rare earth complexes are primarily dependent on their electronic and magnetic characteristics, which are affected weakly by the coordination environment, where potential applications may include use as Lanthanide Shift Reagents (LSR), Luminescence probes and small-molecule magnets (SMM). A systematic conformational search of DPA was carried out in this study in order to identify the global minimum conformer and for comparison of the free and coordinated geometries, using the M06(D3) functional belonging to the Density Functional Theory (DFT) family of model chemistries. An understanding of the aforementioned would play an important role in analysis of bulk characterization and the prediction of the reactivity of DPA. Final geometries and electronic energies were obtained from the ‘domain based local pair natural orbital’ (DLPNO)-Møller-Plesset and -coupled cluster theoretical methods, as follows: DLPNO-CCSD(T0)/aug-cc-pVQZ//DLPNO-MP2/aug-cc-pVTZ. Fifteen Single-crystal X-ray diffractometer (SC-XRD) crystal structures of mononuclear rare earth chloride coordination complexes with DPA (RE = La-Nd, Sm, Eu, Tb-Lu and Y) were obtained and geometrically analysed in this study. Three isostructural series of constitutional isomers were identified, consisting of one series of nine-coordinate molecule (M1) and two series of eight-coordinate ion pairs (M2 and M3). This conformational diversity is most likely due the flexible nature of the DPA backbone, as well as the additional stability gained from reduced coordination spheres as a function of decreasing rare earth ionic radii across the lanthanide series (Lanthanide contraction). A Quantum Theory of Atoms-in-Molecules (QTAIM) topological analysis was performed in order to identify and characterise potential hydrogen bonding interactions in H-optimised crystal structures. The crystal structures of five dinuclear (RE = Tb-Tm) and two tetranuclear (RE = Yb and Lu) rare earth chloride complexes with DPA have also been structurally analysed. Furthermore, one mononuclear (RE = Dy), two dinuclear complexes (RE = Dy and Lu) with EtDPA, and one mononuclear complex with the DPA-derivative HL4 (RE = Dy) were structurally characterised. A DFT study of the theoretical interconversion of one real- and two hypothetical- mononuclear lanthanum containing isostructural series (cf. aforementioned crystal structures) was undertaken in order to gain a deeper understanding of the processes involved, in terms of the participating minimum energy paths (MEPs), intermediates and transition states – as determined via the Nudged-Elastic Band (NEB) procedure. This hypothesis is supported by the well-known conformational lability of rare earth complexes, due to the weak/minor covalency of their coordination bonds. An attempt was made to determine the respective energies of one real- and two hypothetical diamagnetic or ‘closed-shell’ constitutional isomers containing the rare earth ions La3+(M1), Y3+(M2) and Lu3+ (M3). It was assumed that the most stable isomers have a greater probability of being observed as the asymmetric unit of the complex crystal structure – assuming weak contributions of lattice or intermolecular interactions towards the geometry of the asymmetric unit.
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  • Date Issued: 2020

The application value and most appropriate mapping scales for site classification and evaluation in the South African forest industry

  • Authors: Sibhakabhaka, Thembisa
  • Date: 2020
  • Subjects: Forests and forestry -- South Africa , Forest products industry -- South Africa Geographic information systems
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: http://hdl.handle.net/10948/49281 , vital:41617
  • Description: The South African forest industry is challenged with aspects related to socio-political developments, conflicts with biodiversity values, uncertainties related to climate change, several biotic and abiotic risks, and a limited potential for expansion. For this reason, efficient and optimal land-use is essential, which requires sustainable forest management practices and accurate information and decision support systems. Tree growth patterns, productivity and risks vary according to changes in geology, topography, climate and soil conditions. It is therefore required that forest managers, planners and researchers have a conceptual understanding of the concept of forest site classification and evaluation. This is essential not only for improved levels resilience, but also to maintain a competitive industry in terms of socio-economic and environmental performance. The first chapter of the study aimed to investigate the perceptions and interpretations of a range of representative stakeholders from the forestry industry regarding the value, shortcomings, requirements and design of forest site classification and evaluation systems in use in the local industry. A questionnaire with 16 questions was used for this purpose, and data was analysed using quantitative and qualitative techniques. Results indicated variable levels of understanding amongst respondents of terminology and the nature of systems used in industry. Trends in responses were influenced by the background of stakeholders, the role of individuals in the value chain of forestry as well as past experiences. The perceived importance and value of potential site evaluation applications varied substantially amongst different stakeholders. Results point towards a narrow-focus application for site classification and evaluation systems for site-specific forestry, with a lesser regard with aspects of risk management and environmental performance. Several technical aspects related to site variables, data resolution and scale of presentation were also questioned by participants. Listed priorities for research and development include the integration of site classification and evaluation systems into corporate information systems, modernizing technology, more appropriate site evaluation models, advanced climatic modelling and the development of indices of water and nutrient availability related to forest productivity. There is general agreement for the development of a national forest site classification system. The value of this part of the study lies in the contribution it makes towards our knowledge of stakeholder perceptions regarding site classification and evaluation, as well as the valuable comments made by participants for the refinement of such systems that can serve as indicators for entities involved in education, governance and strategic forest management. The second data chapter of the study involved the development of high-resolution site classification systems in the form of Site Types for two selected study areas in South Africa, one located in Mpumalanga, and the other in the southern Cape. This enabled a comparative analysis with existing low-resolution Land Type classifications that were developed by different authors for the same two study areas, in terms of its reliability, accuracy and general usefulness for applications in the plantation forestry value chain. The comparison of the two types of classification systems revealed that the climate data forming part of the database were of equal accuracy and resolution. However, an obvious difference was detected in the information pertaining to soil in terms of descriptive and spatial data. In the case of both study areas, the Site Type classification systems revealed many soil and geological features that were not indicated by the lower-resolution Land Type systems. Variation in characteristics related to parent material, soil classification, soil depth, intensity of subsoil wetness and soil organic matter were not adequately reflected in these systems. This can potentially have important implications for applications such as species choice, predictions of yield, nutrient optimization, ratings of soil resilience, biodiversity management and evaluations for carbon sequestration potential. The data forming part of this study indicate that although Land Type classification systems can provide valuable support at strategic levels of planning and management, there are several limitations for use at finer scales of resolution. The final chapter of the study includes an investigation and qualitative comparison of the usefulness of Site Type vs. Land Type classification systems, based on existing knowledge in the industry. The two systems are compared in terms of its input towards the following applications: site-species matching, timber yield prediction, site amelioration / site preparation requirements, nutrient management requirements, vegetation management / weed control, management of pests and diseases, determination of risk for soil compaction, soil erosion and nutrient loss, decision making regarding forest engineering operations, prediction of wood / fibre properties, biodiversity management and lastly planning of research activities / priorities. This analysis indicated that applications that require data on only climate and general soil patterns can be supported with equal success by both types of site classification systems. On the other hand, in cases where high-resolution data on site factors are required, Land Type classification systems had numerous shortcomings and received a much lower rating of suitability. The outcome of the study can provide guidance on the development and design of future site classification and evaluation systems for the South African forest industry. High-resolution databases of key site factors should receive priority, together with the development of decision support systems based on causal relationships. This will contribute to the resilience and sustainability of an industry that is increasingly confronted with questions related to the placement, design and management of forest plantations.
  • Full Text:
  • Date Issued: 2020
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