Philosophiae Doctor - PhD (Chemistry)

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Investigation of ternary catalysts as anode catalysts for direct methanol fuel cell
(University of the Western Cape, 2023) Adebare, Nurudeen Adewunmi; Khotseng, Lindiwe E
This chapter reports on various catalyst synthesis methods (impregnation, polyol, modified polyol and microwave-assisted modified polyol methods) to determine which method would result in the most electrochemically active platinum–ruthenium (PtRu) electrocatalyst supported on multi-walled carbon nanotubes (MWCNTs) for methanol oxidation reaction in an acidic medium. Different techniques were used to characterise the synthesised catalysts, including the high-resolution transmission electron microscope used for morphology and calculating particle sizes, and X-ray diffraction for determining crystalline sizes while Energy dispersive analysis Spectroscopy, EDS was used to determine elemental compositions. The electroactive catalyst surface area, ECSA of the electrocatalysts was determined using cyclic voltammetry (CV), while the electroactivity, electron kinetics and stability of the electrocatalysts towards methanol oxidation were evaluated using CV, electrochemical impedance spectroscopy and chronoamperometry, respectively. The microwave-assisted modified polyol method produced the PtRu/MWCNT electrocatalyst with the most enhanced electrocatalytic activity compared to other PtRu/MWCNT catalysts produced by the impregnation, polyol and modified polyol methods.
Quantum dots for multiplexed biological imaging
(University of the Western Cape, 2023) Mtotywa, Alungile; Onani, M.O
Over the past two decades, indium phosphide (InP) colloidal quantum dots (QDs) have attracted substantial interest as a possibly less hazardous alternative to cadmium-based QDs. The improvements in their colloidal synthesis techniques have made it possible to synthesize a wide range of compositions, and ligands with perfect quantum yields close to unity, spectrum tunability from blue to near-infrared, and narrow emission linewidths. Additionally, InP QDs have better optical stability than cadmium chalcogenides due to their higher covalency. Modern InP QDs have demonstrated superior performance in a wide range of applications, including solar cells with strong commercial potential, luminescent solar concentrators (LSCs), and light-emitting diodes. The use of non-cadmium-based quantum dots (QDs) as highly effective, non-toxic optical probes for bioimaging is discussed in this study. Core/ shell InP/ZnS and InP/ZnSe QDs were synthesized using tris (dialkylamino) phosphines via one-pot synthesis. Water compatibility was achieved through ligand exchange with 3- mercaptopropionic acid. Chitosan was further added to make the QDs more stable and less toxic. All the synthesized QDs were characterized with UV-Vis, PL, FTIR, and HRTEM.
Thiolato schiff base complexes of nickel and palladium as mesogens and molecular wires
(University of the Western Cape, 2003) Moutloali, R.M; Darkwa, J
Thermal analysis data of compounds A, C, F and I established that they were nonmesogenic while E and G were found to be mesogenic. The lack of mesogenic behaviour of A could be attributed to hydrogen bonding. The non-mesogenic behaviour of C and F is due to reduced molecular anisotropy as a result of large lateral substituents. Complexes I decomposed at high temperatures and before melting and hence no liquid crystalline behaviour was found. It is likely that the high decomposition temperature is the result of increased molecular interactions. We found that removing the phosphine ligands and increasing molecular length induced liquid crystalline behaviour in complexes E. The more planar complexes G were also found to be liquid crystalline
Palladium surface-modified rare earth metal-based ab5 type hydride-forming materials
(University of the Western Cape, 2008) Williams, Mario; Linkov, V.M.; Nechaev, A.N.
Driven by mounting standards of living and a growing population, South African energy consumption is expected to increase dramatically within the next decade. The increased demand for more energy will require enormous growth in the capacity for energy generation, more secure and diversified energy sources, and a successful strategy to reduce greenhouse gas emissions. The wellbeing of the South African economy depends on reliable and affordable supplies of energy; whilst environmental wellbeing, from improving urban air quality to abating the risk of global warming, requires energy resources that emit less greenhouse gases compared to petrochemicals. Amongst the various alternative energy strategies, building an energy infrastructure that utilises hydrogen as the primary energy carrier may enable a non-polluting energy security in the future, when it is produce using renewable energy sources (e.g. water electrolysis). Hydrogen has been acknowledged as a key element in the future generation of energy and will be essential in increasing and maintaining economic growth. The significance of hydrogen as a future energy source is due to its large abundance and an energy density that is three times greater than that of an average hydrocarbon fuel. Roughly 80% of hydrogen is produced by natural gas reforming, partial oxidation of light alcohols, and autothermal reforming. In addition, a number of alternative technologies exist in which hydrogen can be generated from starting materials such as coal; biomass; and water, including electrolysis, fossil fuel processing, and coal gasification. However, most of these technologies produce a hydrogen product which is of poor purity. Purification is achievable considering equipment costs are extremely high and the process is therefore mostly economically unfeasible.
The synthesis of Ventiloquinones J and F
(University of Western Cape, 2002) van Eeden, Nestor; Green, lvan R
In chapter 2 the synthesis of ventiloquinone J is described, starting from vanillin, the key intermediate cis-3,4-dihydro-5,7-dimethoxy-10- methoxymethyleneoxy-1,3-dimethyl-1H-naphtho[2.3-c]pyran-6,9-dione was prepared in 19 steps by using inter alia Diels-Alder adduct formation, mild acetylation, oxymercuration and finally converted to ventiloquinone J in an overall yield of 0.5%. Protection of the C-10 position of the ventiloquinone J precursor was eventually effectively provided by the methoxymethyleneoxy (MOM) group which upon removal with acid treatment provided the hydroxy group in this position unambiguously in the final product. Attempts to effect this same protection using a benzyl group proved ineffective due to the extreme difficulty in separation of the cyclised stereoisomers; cis and trans 10- benzyloxy-3,4-dihydro -5,6,7,9-tetramethoxy-1,3-dimethyl-lH-naphthol2,3- c]pyrans In addition decomposition of the molecule occurred during the subsequent oxidation step affording low yields of the quinones and finally the unwanted isomer viz., the trans 1,3-dimethylpyran was the major product of the cyclisation. Protection of C-10 of the precursor to ventiloquinone J usingthe 2'-methoxyethoxymethyleneoxy (MEM) group proved problematic in that it was sensitive to the acidity of the silica gel stationary phase used for column chromatography, and that cyclisation of the intermediate alcohol, 2-(l'- hydroxyethyl)-4,5,6,8-tetramethoxy-l-(2'-methoxyethoxymethyleneoxy)-3- prop-2'-enylnaphthalene, Ied to a mixture of the corresponding cis and trans l,3-dimethyl pyrans in which the MEM protecting group had been lost in a combined crude yield of only 25%o. In addition all the MEM compounds showed considerable decomposition on standing. The synthesis of one of the initial target molecules, 6-hydroxy-7- methoxyeleutherin was not completed due to premature displacement of the required C-5 protecting groups employed in the naphthalene precursors upon acylations under Lewis acid Ventiloquinone F was successfully synthesised from 3,4,6- trimethoxybenzaldehyde in 12 steps making use of a Stobbe Condensation with methyl succinate to construct the desired oxygenated naphthalene nucleus. An overall yield of 9.5oh was obtained and its stereoisomer, isoventiloquinone F was also obtained in an overall yield of 10%.trans- 5-benzyloxy-3,4-dihydro-6,7,9'ttimethoxy-1,3-dimethyl-1I/- naphtho[2,3-c]pyran led to the formation of four pyranquinones which were successfully separated and purified. These were cis- and trans-5-benzyloxy- 3,4-dihydro-7-methoxy-1,3-dimethyl-lF/-naphthol2,3-clpytarr-6,9-diones as well as the corresponding cis and trans ortho quinone isomers.
Effluent water treatment utilising a combination of hydrodynamic shear and flotation technology for the specific application of wastewater from the oil and gas industry
(University of the Western Cape, 2022) Cerff, Bradley Robert; Bladergroen, Bernard
Water plays an important role in the petrochemical production and refining processes. The wastewaters released by these processes are often rich in petroleum pollutants, that requires significant treatment prior to disposal. Of particular importance is the processing of oil in water (o/w) emulsions. The processing and treatment of oil emulsions is focussed on breaking the emulsion and separation into the aqueous and oil phases for further appropriate disposal. The general approach is to optimise the processing to achieve relatively clean water, that can be recycled or discharged into the environment, whereas the oil is disposed of or recycled appropriately. The use of chemical coagulants and flocculants results in the degradation of the oil phase forming sludges as well as toxicity issues when using aluminium based coagulants.
Green synthesis of novel nanostructured silicon semiconductor thin film material from sugarcane bagasse ash for solar energy materials
(University of the Western Cape, 2022) Seroka, Ntalane Sello; Khotseng, Lindiwe. E.
The sun is considered the most abundant source of renewable and clean energy. With silicon being the most common element used for the direct conversion of solar energy into electrical energy, solar cells have, over the years, been the corresponding technology to the problem of energy on our planet. This technology is most common in aerospace applications. Nonetheless, the application in terrestrial areas is currently hampered by the high cost of photovoltaic modules. Therefore, the study focuses on the extraction and synthesis of silicon nanostructures from sugarcane bagasse ash. Notably, silicon is found in this feedstock in the form of silicic acid and predominantly as silica. The study's main goal could be achieved through the sustainable extraction of silica from sugarcane bagasse ash and subsequent transformation into nanostructured silicon.
Kesterite-amplified aptameric nanobiosensors for interferon gamma Tuberculosis biomarker
(University of the Western Cape, 2022) Uhuo, Onyinyechi Vivian; Iwuoha, Emmanuel I.
Tuberculosis (TB) disease has continued to plague the world, infecting and killing thousands of men, women, and children yearly. Developing countries with limited access to power supply, standard laboratory facilities with special biosafety conditions, and trained medical personnel required for the current diagnostic techniques, experience high TB incidence and deaths yearly. The urgent need to eradicate TB globally can be met with improvement in TB diagnosis. Aptasensor approach to TB diagnosis offers a rapid, user-friendly, robust, highly sensitive, and selective means of detecting biomarkers of TB disease.
Modification of nanostructured carbon based supports for direct methanol fuel cells
(University of the Western Cape, 2022) Sabejeje, Akindeji Jerome; Khotseng, Lindiwe
Palladium (Pd) and Palladium-Ruthenium (Pd-Ru) nanoparticles supported by various carbon nanomaterials which include graphene oxide (GO), reduced graphene oxide (rGO) and multiwalled carbon nanotubes (MWCNTs) with their hybrids were prepared in this work. The synthesized nanoparticles were used as electrocatalysts for direct methanol fuel cell. The graphene was synthesized by modified Hummer’s method and subsequently, the support materials were doped with nitrogen using melamine. The electrocatalysts were synthesized using modified polyol method. The synthesis method of the electrocatalyst was also modified by adjusting the pH of the electrocatalyst. The structural characterization of all the support materials was carried out using Fourier Transform Infrared (FT-IR) Spectroscopy and Brunauer-Emmett-Teller (BET) Technique.
The Synthesis of Biaxial Naphthoquinones and an Initial Investigation regarding their Potential as anti- Mycobacterium tuberculosis and Apoptotic Agents
(University of the Western Cape, 2009) Swigelaar, Wendell Peter; Green, Ivan R.
Tuberculosis and cancer are amongst the most devastating diseases affecting the world today, especially Africa and other less developed countries. Both diseases have the ability to develop resistance against drugs being used as treatment regimes and therefore the search for effective novel drugs remains an ongoing challenge. Diospyrin and its monomer 7-methyljuglone, both naturally occurring quinones, and their synthetic derivatives have been shown to exhibit significant antimycobacterial and anti-tumour activity. The present study focuses on the synthesis of new compounds of similar structures to that of the lead compounds diospyrin and 7-methyljuglone, and their evaluation as potential antimycobacterial and anti-cancer agents via apoptosis. Three methoxynaphthoquinones were synthesized and coupled to several commercially available boronic acids using the Suzuki methodology. Eight compounds were evaluated against a drug susceptible strain, H37Rv of Mycobacterium tuberculosis, using the BACTEC method. Results indicate that the presence of an hydroxyl group peri to the quinone carbonyl moiety is crucial for these quinonoidal compounds to be effective as anti-TB agents, since their methyl ether analogues had little effect on the growth rate of the bacteria. Substituents, capable of donating electrons through a resonance electron effect to the carbonyl group, peri to the methoxy group, also enhance activity of these molecules. Several of the synthesized compounds were screened for their ability to induce apoptosis in five human cancer cell lines viz.,Hl57,Hek239T, HeLa, Jurkat, MCF-7 and two non cancerous cell lines viz., CHO (animal) and KMST-6 (human). The methods employed to assess the pro-apoptotic potential of the compounds were APOPercentagerM and DNA fragmentation. The APOPercentagerM assay showed that the activity of the compounds is concentration dependent and also revealed that in addition to the redox ability of the quinone carbonyl groups, the peri methoxy or hydroxyl group also plays a role in the apoptotic activity. An independent evaluation, the DNA fragmentation test, confirmed both a degree of selectivity viz, being not too active against non-cancerous cell lines on the one hand whereas on the other having a high apoptotic potential against all five of the cancer cell lines evaluated.
Synthesis of new biguanide derivatives as potential antidiabetic drugs
(University of the Western Cape, 2022) Salubi, Christiana Abimbola; Titinchi, Salam
The main purpose of this study was to synthesize biguanide compounds with potential as antidiabetic drugs. All biguanide compounds possess antidiabetic properties by decreasing the blood glucose level. Hence, we embarked on the synthesis of a series of biguanides in a threestep reaction which involves synthesis of a Schiff base, reduction of the Schiff base to a secondary amine using sodium borohydride and lastly formation of substituted biguanide derivatives with amines (primary or secondary) and dicyandiamide.
A comparative energy storage efficiency study of multiple cation doped LiMxMn2-xO4/MWCNT cathodes for advanced Li-ion batteries
(University of the Western Cape, 2022) Willenberg, Shane Clayton; Ross, Natasha
The current lithium-ion battery which is used in most technological applications is the LiCoO2 (LCO) battery. This battery offers a high theoretical capacity of 274 mAh.g-1. Scientists have however deemed this battery material as hazardous due to the toxicity of Cobalt and its explosive nature at high temperatures. LiMn2O4 (LMO) is considered to be substantially less toxic, cheaper than the LCO, and is also readily available in South Africa.
Phytochemical studies on extracts of selected South African indigenous medicinal plants
(University of the Western Cape, 2022) Yalo, Masande Nicholas; Mabusela, Wilfred T.
Nature has been identified as a rich source of potentially useful chemicals. Throughout the years, phytochemical studies have led to the unearthing of a huge number of natural products, their chemical diversity is unique and many of them possess various biological activities. South Africa is blessed with a rich plant biodiversity of +24,000 indigenous plants, representing about 10% of all higher plants on earth and with more than 50 % of such plant species found nowhere else in the world but in South Africa. However, only a few of the South African medicinal plants have been exploited to their full potential. Screening of more medicinal plants for biological activities and phytochemicals is important for finding potential new compounds for therapeutic uses.
Phytochemical and biological studies of extracts from selected South African indigenous medicinal plants: Bulbine and helichrysum species
(University of the Western Cape, 2022) Makhaba, Masixole; Mabusela, Wilfred
Medicinal plants from the Asteraceae and Asphodelaceae families are among the most widely recognized in South African traditional medicine for managing diabetes mellitus. Diabetes mellitus is a universal epidemic, yet there are no permanent treatments for this disease. Three South African indigenous medicinal plants, namely Helichrysum petiolare (Asteraceae), H. splendidum (Asteraceae), and Bulbine frutescens (Asphodelaceae) which have reported ethnobotanical usage in the management of diabetes were investigated in this study. Despite the increasing scientific evidence using the extracts that supports the ethnobotanical claims of these medicinal plants, the active metabolites, or their mechanism of action is not considered.
Identification, separation and quantification of persistent organic pollutants using capillary electrophoresis
(University of the Western Cape, 2022) Omoniyi, Emmanuel Oluseyi; Petrik, Leslie F.
Water quality deterioration and scarcity can be attributed to natural causes and anthropogenic activities which include climate change and an incessant industrialisation, yet with lack of functional and reliable wastewater treatment facilities. As a consequence of these activities, many chemicals have found their way into water bodies and subsequently compromise the quality of water systems. Among these chemicals are persistent organic pollutants (POPs), including pharmaceuticals, endocrine disrupting compounds (EDCs), etc. In order to separate, identify and quantify persistent and emerging contaminants in the water samples, this study considered the pre-concentration and separation steps followed by quantification using capillary electrophoresis.
Electro-analytical protocols for quantitative assessment of phenols in South African rooibos, green and black tea samples
(University of Western Cape, 2022) Abrahams, Dhielnawaaz; Baker, Priscilla
The worldwide tea market was estimated at almost 200 billion U.S. dollars in 2020. It is perceived to rise to 318 billion dollars by 2025. Tea has a long history of prominence around the world. Increases in tea production in Africa over the past decade have aggravated the pressure the industry exerts on natural resources such as water, soil, and vegetation. The increasing numbers of tea production factories coupled with the increased global demand for tea are adding to the growing problem. The growing conflicts over water resources are set to worsen in the context of climate change. This increase has occurred at a time when regional and national legislation is becoming increasingly stringent. These controls have been taken to offset environmental damage. Tea has probably the most elevated substance of polyphenols among food and refreshment items.
Microwave synthesized ruthenium antimony oxide-graphene nanocomposite materials for asymmetric supercapacitors
(University of the Western Cape, 2022) Ekwere, Precious Idinma; Iwuoha, Emmanuel
With the rapid rise in energy demand and ever-escalating environmental hazards, the need for transition from fossil fuel to renewable energy sources is of paramount importance, requiring better and efficient energy storage devices such as supercapacitors. Supercapacitors are energy storage devices with high power density and long cycle life, but relatively low energy density when compared to batteries. New and advanced electrode materials are required to improve the energy density requirements of next-generation supercapacitors. However, the search for new types of active materials to be used as supercapacitors' electrodes continues to be a tough challenge. Herein, ruthenium antimony oxide (RuSbO) and ruthenium antimony oxide graphene (RuSbO-G) were synthesized via the microwave-assisted method for the first time and tested as a possible electrode material for an asymmetric supercapacitor. Graphene oxide prepared by modified Hummer’s method was exfoliated at low temperature and used for the synthesis of RuSbO-G.
Extraction, fractionation, nanoparticles formulation, and antimicrobial activity of lipids from black soldier fly larvae
(University of Western Cape, 2021) Omores, Raissa Andong; Petrik, Leslie F.
Hermetia illucens (Diptera: Stratiomyidae) known as the black soldier fly (BSF) is an efficient ecological organic waste decomposer. Its larvae grow through six larval instars on a variety of decomposing organic substrates inhabited by a variety of microorganisms, including pathogenic ones. Survival in these environments requires a good functioning immune system to protect them from pathogen invasion, hence it can be expected that the BSF larvae possess antimicrobial substances. BSF larvae farming has recently gained popularity as a new source of protein and lipid. The lipid is highly sourced due to its applications in a variety of areas which span across food and pharmaceutical industries. Different extraction methods have been used to extract lipid from different sources.
Method development for selective recovery of rare earths elements from phosphogypsum waste
(University of Western Cape, 2021) Muvumbu, Jean-Luc Mukaba; Petrik, Leslie
The need for rare earth elements (REEs) in current technologies has motivated countries with high imports dependency to search for alternatives sources. Several studies have been carried out to investigate the feasibility for REE extraction and recovery through the recycling of low value waste streams. Amongst these waste streams, phosphogypsum (PG) which is a major by-product from phosphoric acid processing has drawn research attention as it contains up to an average of 0.4 wt % of REEs. To date, a number of approaches have been reported on REE extraction from PG leaches after a total or partial dissolution. Amongst all the approaches, adsorption was found as one of the most promising due to its high efficiency, availability and simplicity.
Development of Impedimetric Immunosensor for Fumonisin on Polyanilino-Carbon Nanotubes Doped with Palladium Telluride Nanocrystals
(University of the Western Cape, 2013) Masikini, Milua; lwuoha, Emmanuel
Immunosensors are affinity ligand-based biosensor solid-state devices in which the immunochemical reaction is coupled to a transducer. The specificity of the molecular recognition of antigens by antibodies to form a stable complex is the basis of the immunosensor on the electrode. The development of such a sensor requires a better design and preparation of an optimum interface between the biomolecules and the detector material. The immunosensors were developed based on Polyaniline derivative composite. Novel water soluble PdTe quantum dots (QD) was synthesized and characterized by different physical techniques such as UV-Visible (UV-VIS), Fluorescence Spectroscopy (PL), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and X-Ray Diffraction (XRD). The electroactivity of such synthesized quantum dots was studied by cyclic voltammetry in aqueous media. The synthesis of poly(2,5- dimethoxyaniline)-multi wall 'carbon nanotubes nanocomposite was carried out by electropolymerization in situ of 2,5-dimethoxyaniline - multi wall carbon nanotubes (PDMA-MWCNT) from aqueous dispersion containing acid-treated multi wall carbon nanotubes (MWCNT) and 2,5-dimethoxyaniline subsequently modifying a glassy carbon electrode in acid media. An undoped PDMA was also prepared for control. The composite for this work, consists of layer-by-layer method to form a multilayer film of QDs and PDMA-MWCNT. The method used was as follows; the drop coating of quantum dots followed by electrodeposition of poly(2,5- dimethoxyaniline )-carbon nanotubes onto surface of glassy carbon. The PDMA-CNT was characterized by UV-Visible (UV-Vis), Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM). The electrochemical characterisation of PDMA-CNT was carried out using cyclic voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS). The composite (QDs-PDMA-MWCNT) was also characterized using above mentioned techniques. The electrochemical immunosensor for fumonisin a mycotoxin was prepared by dropcoating of mycotoxins antibody onto the composite modified glassy carbon electrode. The response profiles of fumonisins sensors system were obtained from electrochemical impedance spectroscopy (EIS) measurements. The fumonisin immunosensor was used for the detection of fumonisins in certified com reference materials. For comparison reasons, analysis of such mycotoxins was carried out by using conventional analytical method enzyme-linked immunosorbent assay (ELISA). The EIS response of FBI immunosensor (GCEIPT-PDMA-MWCNT/anti-Fms-BSA) gave a linear range of 7 to 49 ng L-I and the corresponding sensitivity and detection limits were 0.0162 ka L ng-I and 0.46 pg L-I, respectively. Hence the limit of detection of GCEIPT-PDMA-MWCNT immunosensor for fumonisins in com certified material was calculated to 0.014 and 0.011 ppm for FBI, and FB2 and FB3, respectively. These results are lower than those obtained by ELISA, a provisional maximum tolerable daily intake (PMTDI) for fumonisins (the sum of FBI, FB2, and FB3) established by the Joint FAO / WHO expert committee on food additives and contaminants of 2 ug kg" and the maximum level recommended by the U.S. Food and Drug Administration (FDA) for protection of human consumption (2-4 mg L-I).

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