Philosophiae Doctor - PhD (Chemistry)

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Advanced materials on the basis of nanostructured catalysed magnesium hydride for hydrogen storage
(University of the Western Cape, 2019) Goh, Jonathan Teik Ean; Lototskyy, Mykhaylo; Yartys, V; Khotseng, L.
Magnesium hydride has long been regarded as a promising candidate for lightweight hydrogen storage applications, owing to reasonably high theoretical capacity (7.6 wt. %). It is burdened by slow absorption/desorption kinetics which has been the target for improvement of many research groups over the years. Nanostructured MgH2 prepared by high energy reactive ball milling (HRBM) of Mg under hydrogen atmosphere with the addition of V or Ti results in modified MgH2 that demonstrates superior hydrogenation/dehydrogenation kinetics without a crippling compromise in storage capacity. Mg – FeV nanocomposites prepared via ball milling of Mg and FeV raw materials demonstrated up to 96.4% of the theoretical storage capacity and comparable kinetics to Mg - V prepared via the same method using pure refined V (which is far costlier than FeV). In both cases, the hydrogenation/dehydrogenation kinetics was much improved than pure Mg alone, as evidenced by faster hydrogenation times. In terms of cyclic stability, Mg – 10FeV demonstrated improvement over pure Mg with final absorption and desorption capacities of 4.93 ± 0.02 wt. % and 4.82 ± 0.02 wt. % respectively over 30 cycles. When compared against Mg – V, Mg – FeV showed slightly inferior improvements, attributed to incomplete hydrogenation of V in the presence of Fe. However, they share similar crystalline BCC, BCT – V2H and FCC - VH phases with the size of less than 10 nm and demonstrated the same behaviour at high temperatures; at temperatures approaching 400 °C, particle sintering became an issue for both nanocomposites resulting in a drop in absorption capacity even in the first cycle. The further inclusion of carbonaceous species showed several effects, one of which was an improvement in hydrogen uptake speed as well as kinetics for the addition of 5 wt. % activated carbon. For the sample with 5 wt. % graphite, the appearance of an initial incubation period of up to 60 minutes was noted, presumably corresponding to the duration of time when the carbon was sheared and crushed before hydrogenation commences.
Advanced oxidative water treatment process using an electrohydraulic discharge reactor and TiO2 immobilised on nanofibres
(University of Western Cape, 2013) Okolongo, Gauthier Nganda; Petrik, Leslie; Perold, Willem
The aim of this study was to design and build an electrohydraulic discharge reactor in such a way that the synthetic immobilized TiO2 nanophotocatalytic components could be integrated, for the production of active species such as OH radicals, ozone and hydrogen peroxide, as a cocktail to clean drinking water without the addition of chemicals. The research objectives include: • To design and construct the different AOP prototypes based on various electrode configurations and compare their operation. • To optimize the discharge parameters and conditions of the best AOP system. • To determine the effectiveness of the best prototype for the degradation of methylene blue as model pollutant. • To compare the designed AOP system with the Sodis method for the disinfection of contaminated river water. • To prepare supported TiO2 nanoparticles via electro spinning, followed by combustion and study the effect on the morphology of TiO2 nanoparticles. • To determine the stability and robustness of composite nano-crystalline TiO2 photocatalysts by sonication • To determine the enhanced effect of combining the composite TiO2 in the AOP system on degradation of methylene blue under the same conditions. • To detect the active species promoting disinfection.
Advanced Ti – based AB and AB2 hydride forming materials
(University of the Western Cape, 2011) Davids, Wafeeq; Linkov, V.M; Lototsky, M.V
Ti – based AB and AB₂ hydride forming materials have shown to be very promising hydrogen storage alloys due to their reasonable reversible hydrogen storage capacity at near ambient conditions, abundance and low cost. However, these materials are not used extensively due to their poor activation performances and poisoning tolerance, resulting insignificant impeding of hydrogen sorption. The overall goal of this project was to develop the knowledge base for solid-state hydrogen storage technology suitable for stationary and special vehicular applications focussing mainly on Ti – based metal hydrides. In order to accomplish this goal, the project had a dual focus which included the synthesis methodology of Ti – based AB and AB₂ materials and the development of new surface engineering solutions, based on electroless plating and chemical vapour deposition on the surface modification of Ti – based metal hydride forming materials using Pd-based catalytic layers. TiFe alloy was synthesised by sintering of the Ti and Fe powders and by arc-melting. Sintered samples revealed three phases: TiFe (major), Ti₄Fe₂O, and β-Ti. Hydrogen absorption showed that the sintered material was almost fully activated after the first vacuum heating (400 °C) when compared to the arc-melted sample requiring several activation cycles. The increase in the hydrogen absorption kinetics of the sintered sample was associated with the influence of the formed hydrogen transfer catalyst, viz. oxygen containing Ti₄Fe₂O₁₋ₓ and β-Ti, which was confirmed by the XRD data from the samples before and after hydrogenation. The introduction of oxygen impurity into TiFe alloy observed in the sintered sample significantly influenced on its PCT performances, due to formation of stable hydrides of the impurity phases, as well as destabilisation of both β-TiFeH and, especially, γ-TiFeH₂. This finally resulted in the decrease of the reversible hydrogen storage capacity of the oxygen-contaminated sample. TiFe alloy was also prepared via induction melting using graphite and alumo-silica crucibles. It was shown that the samples prepared via the graphite crucible produced TiFe alloy as the major phase, whereas the alumo-silica crucible produced Ti₄Fe₂O₁-x and TiFe₂ as the major phases, and TiFe alloy as the minor one. A new method for the production of TiFe – based materials by two-stage reduction of ilmenite (FeTiO₃) using H₂ and CaH₂ as reducing agents was developed. The reversible hydrogen absorption performance of the TiFe – based material prepared via reduction of ilmenite was 0.5 wt. % H, although hydrogen absorption capacity of TiFe reported in the literature should be about 1.8 wt. %. The main reason for this low hydrogen capacity is due to large amount of oxygen present in the as prepared TiFe alloy. Thus to improve the hydrogen absorption of the raw TiFe alloy, it was melted with Zr, Cr, Mn, Ni and Cu to yield an AB₂ alloy. For the as prepared AB₂ alloy, the reversible hydrogen sorption capacity was about 1.3 wt. % H at P=40 bar and >1.8 wt.% at P=150 bar, which is acceptable for stationary applications. Finally, the material was found to be superior as compared to known AB₂-type alloys, as regards to its poisoning tolerance: 10-minutes long exposure of the dehydrogenated material to air results in a slight decrease of the hydrogen absorption capacity, but almost does not reduce the rate of the hydrogenation. Hydrogen storage performance of the TiFe-based materials suffers from difficulties with hydrogenation and sensitivity towards impurities in hydrogen gas, reducing hydrogen uptake rates and decreasing the cycle stability. An efficient solution to this problem is in modification of the material surface by the deposition of metals (including Palladium) capable of catalysing the dissociative chemisorption of hydrogen molecules. In this work, the surface modification of TiFe alloy was performed using autocatalytic deposition using PdCl₂ as the Pd precursor and metal-organic chemical vapour deposition technique (MO CVD), by thermal decomposition of palladium (II) acetylacetonate (Pd[acac]₂) mixed with the powder of the parent alloy. After surface modification of TiFe – based metal hydride materials with Pd, the alloy activation performance improved resulting in the alloy absorbing hydrogen without any activation process. The material also showed to absorb hydrogen after exposure to air, which otherwise proved detrimental.
Aluminium and gold functionalized graphene quantum dots as electron acceptors for inverted Schottky junction type rainbow solar cells
(University of Western Cape, 2020) Mathumba, Penny; Iwuoha, Emmanuel
The main aim of this study was to prepare band gap-engineered graphene quantum dot (GQD) structures which match the different energies of the visible region in the solar spectrum. These band gap-engineered graphene quantum dot structures were used as donor materials in rainbow Schottky junction solar cells, targeting all the energies in the visible region of the solar spectrum for improved solar-to-electricity power conversion efficiency. Structural characterisation of the prepared nanomaterials under solid-state nuclear magnetic resonance spectroscopy (SS-NMR) showed appearance of bands at 40 ppm due to the presence of sp3 hybridised carbon atoms from the peripheral region of the GQD structures. Other bands were observed at 130 ppm due to the presence of polycyclic aromatic carbon atoms from the benzene rings of the GQD backbone, and around 180 ppm due to the presence of carboxylic acid carbons from oxidation due to moisture. Fourier-transform infrared resonance (FTIR) spectroscopy further confirmed the presence of aromatic carbon atoms and oxidised carbons due to the presence of C=O, C=C and -OH functional groups, concurrent with SS-NMR results.
The catalytic membrane reactor for the conversion of methane to methanol and formaldehyde under mild conditions
(University of the Western Cape, 2005) Modibedi, Remegia Mmalewane; Linkov, Vladimir M; Dept. of Chemistry; Faculty of Science
This thesis described the development of new catalytic system for the conversion of natural gas (methane) to liquid products such as methanol and formaldehyde. This technology can allow the exploitation of small and medium size gas fields without the need to build an expensive gas to liquid plants or long pipelines. The technology is based on a concept of non-separating membrane reactor where an inorganic membrane paper serves as a catalyst support through which a reaction mixture is flowing under mild conditions and short residence times.
The chemical and biological characterization of South African helichrysum species
(University of the Western Cape, 2015) Popoola, Olugbenga Kayode; Mohammed, Ahmed; Marnewick, Jeanine L.
South Africa has immensely rich natural flora diversity with more than 20 000 species of higherplants. Asteraceae is one of the biggest families of flowering plants with about 246 genera and 2,300 species in southern Africa. South Africa being home to more than 35 % of the world's Helichrysum species (c.a. 244) of which many are used in traditional medicine, and can be considered as a potential resource for new bioactive chemical entities. Chemical studies on the total extract of the South African Helichrysum species viz: H. teretifolium, H. niveum and H. rutilans resulted in the isolation of twenty eight [14 flavonoids (C1-C10; C22- C25), 10 phloroglucinols (C11-C20) and 4 terpenoids (C21, C26-C28)] pure compounds. The chemical structures of the newly isolated compounds were elucidated on the basis of their 1D and 2D-NMR, HRMS, IR and UV spectroscopic data as heliteretifolin (C1), 1-benzoyl-3-(3-methyl- 2-butenylacetate)-phloroglucinol (helinivene A, C11), 1-benzoyl-3-(2-hydroxyl-3-methyl-3- butene-1-yl)-phloroglucinol (helinivene B, C12) and 8-(2-methyl-1-propanone)-3,5,7- trihydroxyl-2,2-dimethoxychromone (helinivene C, C13), while occurrence of 7- methoxyisoglabranin (C6), 4-methoxyquercetin (C8), 4`-methoxykaempferol (C9), mosloflavone (C10), 3β-24-dihydroxyterexer-14-ene (C21), 5,7,8-trihydroxy-3,6-dimethoxyflavone-8-O-2- methyl-2-butanoate (C22) and 15--hydroxy-(-)-kaur-16-en-19-oic acid (C28), from Helichrysum genus were reported for the first time. In vitro inhibition of oxidative stress by the isolated compounds were measured as total antioxidant capacity using the FRAP, TEAC, ORAC (hydroxyl and peroxyl radicals) as well as Fe2+-induced microsomal lipid peroxidation assays. Inhibitory activities against skin-diseases related enzymeswere evaluated in a tyrosinase and elastase non-biological system, while In vitro prooxidant behavior of the compounds was also investigated in the presence of copper (II). Compounds C7, C8, C11 and C12 in comparison with the commercial antioxidant EGCG demonstrated TEAC (4529.01 ± 2.44; 4170.66 ± 6.72; 19545.00 ± 10.25; 43615.73 ± 6.66; vs 11545.40 ± 17.28) μM TE/g respectively, and ORAChydroxyl radical (7.265 ± 0.71; 6.779 ± 3.40; 64.85± 10.95; 94.97 ± 5.80; vs 3.91 ± 4.65) X106 μM TE/g capacities, respectively. Inhibition of Fe2+- induced microsomal lipid peroxidation demonstrated by C7, C8, C11 and C12 expressed as IC50 values included: 2.931 ± 0.64; 6.449 ± 3.16; 5.115 ± 0.90; 3.553 ± 1.92 µg/mL respectively. Additionally, the total antioxidant capacities measured as FRAP (4816.31 ± 7.42; 3584.17 ± 0.54)µMAAE/g, and ORACperoxyl radical (17.836 ± 2.90; 12.545 ± 5.07) X 103 µMTE/g were also observed for compounds C7 & C8, respectively. Compound C7 demonstrated potent anti-tyrosinase activity with IC50 8.092 ± 7.14, while mild anti-tyrosinase activities were demonstrated by compounds C8, C11, C12, C22 and C23 and expressed as IC50 values (IC50 = 27.573 ± 3.11; 35.625 ± 4.67; 26.719 ± 5.05; 25.735 ± 9.62;24.062 ± 0.61) µg/mL respectively. Anti-elastase activity with IC50 values of 25.313 ± 7.85 µg/mL was observed for C13. This is the first scientific report to be carried out on the chemical and biological profiles of H. teretifolium.H. niveum and H. rutilans. The results suggest that these isolated compounds might become natural agents to inhibit oxidative stress and skin disease-related enzymes, with the prospect of being utilized in cosmetic products formulation upon further biological and clinicalinvestigations.
Chemical and biological investigation into some selected African indigenous medicinal plants
(University of the Western Cape, 2009) Babajide, Jelili Olalekan; Mabusela, Wilfred Thozamile; Green, Ivan R.; Dept. of Chemistry; Faculty of Science
African medicinal plants are commonly used throughout Africa to treat a variety of ailments including wounds and ulcers, cough and chest complaints, gingivitis, fever and gonorrhoea, indication all related to infection and inflammation. In screening several plant species from an inventory of common medicinal plants from both South and West Africa for diverse medicinal purposes, 6 plants were selected because of their interesting and useful ethnomedicinal values.
Chemical interactions and mobility of species infly ash-brine co-disposal systems
(University of the Western Cape, 2010) Fatoba, Ojo Olanrewaju; Petrik, Leslie; Dept. of Chemistry; Faculty of Science
The primary aim of these coal fired industries for co-disposing fly ash and brine was to use the fly ash as a sustainable salt sink. It is therefore important to study the interaction chemistry of the fly ash-brine systems to fully understand the leaching and mobility of the contaminant species, and to determine the possibility of capturing the salts from the brine solution when fly ash and brine are co-disposed. In order to achieve the aims and objectives of this study, several leaching procedures such as batch reaction tests, long-term fly ash-brine interaction tests, acid neutralization capacity (ANC) tests, up-flow percolation tests and sequential extraction tests were employed. The geochemical modeling software was applied to predict the formation of secondary mineral phases controlling the release of species in the fly ash-brine systems. Several analytical techniques such as x-ray diffraction (XRD), x-ray fluorescence (XRF), scanning electron microscopy-energy dispersion spectroscopy (SEM-EDS), inductively coupled plasma-mass spectroscopy (ICP-MS) and ion chromatography (IC) were applied to characterize the fresh fly ashes, solid residues recovered from the fly ash-brine interaction tests, the brine sample used in this study and the leachate samples in order to determine the chemical and mineralogical compositions and speciation of the waste materials.
Chemical isolation and electro-chemical characterization of antidiabetic compounds from selected South African lamiaceae plant species
(University of the Western Cape, 2020) Etsassala, Ninon Geornest Eudes Ronauld; Iwuoha, Emmanuel
Diabetes mellitus (DM), being one of the most common metabolic disorders with an elevated morbidity and mortality rate around the world. It is characterised by deficiency in insulin secretion or degradation of secreted insulin. Many internal and external factors such as oxidative stress, obesity and sedentary lifestyle among others have been suggested as the major causes of these cell alterations. Diabetes I and II are the most common types of diabetes. Treatment of type I requires insulin injection, while type II can be managed using different synthetic antidiabetic agents. However, their effectiveness is limited as a result of low bioavailability, high cost of drug production, and unfavourable side effects. There is a great need to develop alternative and more active antidiabetic drugs from natural sources. Natural products are a well-known source for the discovery of new scaffold for drugs discovery, and South Africa is one of the most important megaflora with high percentage of endemism.
Chemistry and speciation of potentially toxic and radioactive elements during mine water treatment
(University of the Western Cape, 2012) Madzivire, Godfrey; Petrik, Leslie; Gitari, W. M.; Vadapalli, Viswanath R. K.
Mine water poses a serious environmental challenge and contains elements such as Fe, Al, and Mn in potentially toxic concentrations. The major anion in mine water is sulphate. The complexity and diversity of mine water composition makes its treatment very expensive, and there is no “one-fits-all” treatment option available for mine water. Active treatment of mine water produces water with good quality but the processes are not sustainable because of the costs. Previous studies have shown that acid mine drainage can be treated with coal FA to produce better quality water. The use of coal FA, a waste material from coal fired power station and mine water would go a long way in achievement of sustainable treatment of mine water as per previous studies. In this study mine water and coal FA were characterized to determine their physiochemical properties. This study linked the modelling results obtained by using the Geochemist’s workbench (GWB) software to the results obtained during the actual treatment of Matla mine water and Rand Uranium mine water using coal FA and lime. The chemistry involved when Matla mine water and Rand Uranium mine water were treated with flocculants was also investigated. Lastly the chemistry and kinetics involved was investigated when mine water was treated with various ameliorants such as Matla coal FA, lime and/or Al(OH)3 using jet loop mixing or overhead stirring. Mine water from Matla coal mine had a pH of 8 and therefore was classified as neutral mine drainage (NMD). Rand Uranium mine water had a pH of less than 3 and therefore was classified as acid mine drainage (AMD). The concentration of sulphate, Na, Ca, Mg, B, Hg, Se and Cd ions in Matla mine water was 1475, 956, 70, 40, 15, 2.43, 1.12 and 0.005 mg/L respectively. The concentration of sulphate, Fe, Ca, Mn, Mg, Al, B, Cr, Pb, U, Cd, Se and As ions in Rand Uranium mine water was 4126, 896, 376, 282, 155, 27, 5.43, 3.15, 0.51, 0.29, 0.007, 0.06 and 0.006 mg/L respectively . These concentrations were above the target water quality range (TWQR) for potable water set by the Department of Water Affairs (DWA) and World Health Organization (WHO). The gross alpha radioactivity was 6.01 Bq/L and gross beta radioactivity was 6.05 Bq/L in Rand Uranium mine water.
Chromium and Titanium based Stannum Nanocomposites materials as electron acceptors for next generation bulk Heterojunction photovoltaic cells
(University of the Western Cape, 2018) Raleie, Naledi; Iwuoha, Emmanuel
Renewable energy has become the centrepiece of research in resolving the energy crisis. One of the forms of renewable energy is solar energy. This form of energy is costly to develop. Organic molecules are promising materials for the construction of next generation photovoltaic cells considering their advantage of lower cost compared to crystalline silicon that is currently used in solar cells. This forms the basis of this research, which focused on the synthesis and characterisation of poly(3- hexylthiophene) P3HT, stannum (Sn) nanoparticles and stannum-based bimetallic stannum-titanium (SnTi), stannum-chromium (SnCr) and stannum-vanadium (SnV) nanoparticles for the application in the construction of heterojunction photovoltaic cells (PVCs).
Coal fly ash and acid mine drainage based heterogeneous Fe catalysts Friedel-Crafts alkylation reaction
(University of Western Cape, 2020) Hlatywayo, Tapiwa; Petrik, Leslie
The catalytic support materials used in the present study are zeolite HBEA and MCM-41. These high silica zeolites were synthesised from coal fly ash (CFA) waste via a novel approach that involved a fusion step, acid assisted silica extraction and removal of Al, Ca and Na from the silica by treatment with oxalic acid. The generated silica was converted to HBEA and MCM-41 via conventional hydrothermal treatment. The metal incorporation onto HBEA was done via two approaches namely; liquid phase ion exchange (LIE) and wet impregnation (WI) while the loading on MCM-41 was only done via WI since the material does not possess exchange sites. The metal solution precursors were AMD and Fe extracted from CFA (FeAsh) via acid leaching followed by pH regulation by concentrated NaOH. This is the first time these solutions were tested as possible metal precursors in catalyst synthesis.
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.
Complexation and Bioavailability of Dissolved Mercury Evaluation by Hplc and a Novel Au-Hydrogel Analytical Sensor Protocol.
(University of the Western Cape, 2017) Le Roux, Shirley Theodora Rose; Baker, P.G.; Crouch, A.M.
Anthropogenic sources as well as natural contributions (e.g. volcanic activity and evaporation from the oceans) have increased mercury levels in the environment. Mercury deposits mainly in sediments, and it finally ends up in aquatic systems. Sediments are capable of immobilising toxic metals but this does not guarantee that the metals are safely removed from aquatic systems.
Composite poly(dimethoxyaniline) electrochemical nanobiosensor for glufosinate and glyphosate herbicides
(University of the Western Cape, 2008) Songa, Everlyne Apiyo; Iwuoha, Emmanuel; Baker, Priscilla G.L.; Dept. of Chemistry; Faculty of Science
In this thesis, I present a simple, sensitive and low cost electrochemical nanobiosensor for quantitative determination of the herbicides glufosinate, glyphosate and its metabolite aminomethylphosphonic acid (AMPA). Firstly, the nanostructured poly(2,5-dimethoxyaniline) (PDMA) materials were synthesized on gold electrode by the electrochemical "template"method using poly(4-styrenesulfonic acid) (PSS) as the dopant and structure-directing molecule. Fourier transform infrared (FTIR) spectroscopy, UV-Vis Spectroscopy, Transmission electron microscopy (TEM) and Scanning electron microscopy (SEM) studies inferred successful doping of the nanostructured PDMA film by PSS and that the template PSS directed the synthesis of both nanotubes and nanoparticles of PDMA with diameters less than 100 nm.
Degradation of bisphenol-a and 2-Nitrophenol by combined advanced oxidation technologies
(University of the Western Cape, 2015) Tijani, Jimoh Oladejo; Petrik, Leslie F.; Perold, Willem J.; Fatoba, Ojo.O.
Emerging micropollutants such as bisphenol-A and 2-nitrophenol present a great threat in drinking water due to their adverse effects. Most conventional technologies in water and wastewater treatment are not designed to eliminate these xenobiotics; instead pollutants are merely transferred from one phase to another. Advanced oxidation technologies (AOTs) however, have been identified as suitable routes for the degradation of these potential damaging substances based on free radical mechanisms and use of less expensive chemicals. Moreover, due to the structural complexity of wastewater and the existence of pollutants as mixtures, no single advanced oxidation technology can convincingly remove all forms of contaminants and then most often than not, a combination of treatment processes is required for an effective purification process. Besides, the problem of adequate degradation of emerging contaminants in the environment, when AOT(s) are used individually, they present inherent problems. For instance, powder TiO₂ photocatalysts obstruct light penetration, thus prevent effective interaction of UV light with the target pollutants, and particulates present problems of post-filtration and recovery of catalyst particles after treatment. Additionally, TiO₂ has a high band gap energy, high electron-hole recombination rate, and is prone to aggregation of the suspended particles. Similarly, the dielectric barrier discharge (DBD) system produces ultra violet light and hydrogen peroxide within the plasma zone which is not fully maximised for the mineralization of persistent organic pollutants. Rapid oxidation and aggregation of nano zero valent iron particles in photo-Fentons process reduce the particles mobility and affect its performance. In the same vein, the jet loop reactor (JLR) system is characterised by low impingement yield, which is responsible for low mineralization rate. In light of this background, this research investigated the degradation of bisphenol-A and 2- nitrophenol in aqueous solution using the following combined advanced oxidation methods: DBD/supported TiO₂ or Ag doped TiO₂ photocatalysts, DBD/photo-Fenton induced process and JLR/UV/H₂O₂. The target was to assess the performance of each single system and then identify the best combined AOTs capable of significantly mineralizing the target compounds. Firstly, two materials were developed namely supported TiO₂ and stabilized nano zero valent Fe. The TiO₂ photocatalyst supported on a stainless steel mesh was synthesised using sol-gel solution of 8 % PAN/DMF/TiCl₄. The influence of calcination temperature and holding time on the formation of nanocrystals was investigated. Afterwards, various amounts of metallic silver were deposited on the (optimum) supported TiO₂ photocatalyst using thermal evaporation. The catalysts were characterized by several analytical methods; HRSEM, HRTEM, EDS, SAED, FTIR, TGA-DSC, UV-vis/diffuse reflectance spectroscopy, XRD, BET, and XPS. The photocatalytic activity of the prepared catalysts was determined using methylene blue as a model pollutant under ultra-violet light irradiation. Secondly, the TiO2 photocatalyst and 2.4 % Ag doped TiO₂ nanocomposites obtained as optimums (in section 1) were combined with the DBD to decompose BPA or 2-NP in aqueous solution. Moreover, the photo-Fenton process was applied for degradation of the model pollutants, and different dosages of stabilized nZVI (in the range of 0.02 -1.00 g) were added to the DBD system to induce the photo-Fenton process and improve BPA or 2-NP degradation efficiency. Finally, a jet loop reactor (JLR) presenting advanced mixing by the “impinging effect” was explored to decompose BPA or 2-NP in aqueous solution as a function of inlet applied pressure, solution pH, and initial concentration of BPA or 2-NP. Subsequently, different concentrations of hydrogen peroxide (H₂O₂) were added to the JLR to enhance the mineralization process. Furthermore, a combination of JLR with in-line UV light and H₂O₂ were further utilised to decompose BPA or 2-NP in aqueous solution. The residual concentration of the model compounds and intermediates were analysed using high performance liquid chromatography (HPLC) and liquid chromatography mass spectrometry (LCMS). The concentration of the ozone, hydrogen peroxide and hydroxyl radicals generated by the DBD in the presence or absence of a catalyst was monitored using Ultraviolet-visible spectroscopy and Photoluminescence spectroscopy. The results revealed that the optimal thermal conditions to obtain well supported uniformly grown, highly active crystalline TiO₂ catalysts with high specific surface area was 350 ºC at a 3 h holding time in N2 atmosphere with a flow rate of 20 mL/min. Pyrolysis temperature and holding time played an important role on the crystalline nature and photocatalytic activity of the catalyst. Moreover, 2.4 % Ag doped TiO₂ nanocomposites exhibited higher photocatalytic activity for methylene blue degradation than the undoped supported TiO₂ nanocrystals. The results indicated that combining DBD with 2.4 % Ag doped TiO₂ nanocomposites achieved 89 % and 81 % removal efficiency for BPA or 2-NP compared to 67.22 % or 56.8 % obtain when using the DBD system alone. The 2.4 % Ag doped TiO₂ nanocomposites demonstrated excellent activity and offered photochemical stability after four repeated applications.In the case of the photo-Fenton induced process, nano zero valent iron particles (nZVI) stabilized with polyethylene glycol were synthesised using a modified borohydride reduction method. The HRSEM, BET, XRD, and XPS analysis confirmed the formation of filamentous, high surface area iron nanoparticles in the zero valent state. Unlike combined DBD/Ag doped TiO2 nanocomposites, 100 % or complete removal of BPA or 2-NP in aqueous solution was achieved with DBD/nZVI system within 30 minutes compared to 67.9 % (BPA) or 56.8 % (2-NP) with DBD alone after 80 minutes. The removal efficiency was attributable to the production of an increased concentration of OH radicals as well as existence of a synergetic effect in the combined DBD/nZVI system. Five new transformation products namely: 4-nitrophenol (C₆H₅NO₃), 4-nitrosophenolate (C₆H₄NO₂), 4-(prop-1-en-2-yl) cyclohexa-3,5-diene-1,2-dione, (C₉H₈O₂), 4-(2- hydroxylpropan-2-yl)cyclohexane-3,5-diene-1,2-dione (C₉H₁₀O₃), and 1,2-dimethyl-4-(2- nitropropan-2-yl)benzene (C₉H₁₀NO₄) were identified during the degradation of BPA. While, three aromatic intermediate compounds such as 2-nitro-1,3,5-benzenetriolate (C₆H₂NO₅), 2- nitro-1,4-benzoquinone (C₆H₃NO₄), and 2,5-dihydroxyl-1,4-benzoquinone (C₆H₄O₄) respectively were identified during the degradation of 2-NP for the first time in the DBD with JT14 or JT17 using LC-MS. These intermediate compounds have never been reported in the literature, thereby expanding the number of BPA or 2-NP intermediates in the data base in the DBD/JT14 or DBD/nZVI system. BPA degradation proceeded via ozonation, hydroxylation, dimerization, and decarboxylation and nitration step, while 2-NP proceeded via hydroxylation, nitration and denitration respectively. Furthermore, maximum removal efficiency of BPA or 2-NP in aqueous solution using JLR alone under the optimum solution pH (3), inlet pressure (4 bar), flow rate (0.0007 m3/s) was 14.0 % and 13.2 % respectively after 80 minutes. A removal efficiency of 34.9 % was recorded for BPA while 33.2 % was achieved for 2-NP using combined JLR/UV under the same conditions as JLR alone. For the combined JLR/H₂O₂ under optimum conditions of inlet pressure (4 bar), solution pH (3) and peroxide dosage (0.34 g/L), a 51.3 % and 50.1 % removal efficiency was achieved for BPA and 2-NP respectively under same conditions relative to JLR alone. Combination of JLR/UV/H₂O₂ achieved 77.7 % (BPA) or 76.6 % (2- NP) removal efficiency under the same conditions. The combined JLR/UV/H₂O₂ process was found to be most effective combination under the optimized operating parameters due to existence of a synergetic index value of 6.42 or 6.84. This implies that JLR should be coupled with UV and H₂O₂ to achieve greater mineralization efficiency instead of using the system individually. The obtained experimental data of these combined treatment processes fitted the pseudo-first order kinetic models. The combination of the JLR/UV/H₂O₂ was found to be energy efficient and could effectively degrade BPA or 2-NP in aqueous solution to a greater extent than the JLR, JLR/UV or JLR/H₂O₂ system. However, the total organic carbon (TOC) reduction value by all combined DBD and JLR system recorded was not completely achieved due to the formation of recalcitrant intermediate compounds under the applied conditions. In conclusion, this study is reporting for the first time a combination of supported 2.4 % Ag doped TiO₂ nanocomposites with dielectric barrier discharge system for BPA/2-NP degradation in aqueous solution; a combination jet loop reactor based on impingement with in-line UV lamp and H2O2 for successfully decomposing BPA or 2-NP in aqueous solution; as well as a combination of dielectric barrier discharge system and stabilised nano zero valent iron particles, which induced a photo-Fenton process for highly effective removal of BPA or 2-NP in aqueous solution. This study conclusively supports the hypothesis that combined advanced oxidation technologies offer a sustainable and highly efficient means of achieving partial or complete removal of BPA or 2-NP in aqueous solutions. Considering all the combinations of AOTs investigated in this study, the novel DBD/photo-Fenton-induced process under optimised operating parameters was found to be the most efficient in the elimination of BPA or 2-NP in aqueous solutions. The combination of DBD with photo- Fenton like process offers a promising advanced waste water purification technology in the immediate future. Based on these findings, it is recommended that DBD should be redesigned to prevent loss of ozone and JLR system reconfigured to increase impingement and cavitational yield in order to have an effective combination treatment strategy for waste water purification especially in large scale waste water management.
Degradation of persistent organic pollutants (pharmaceuticals & dyes) by combined dielectric barrier electrohydraulic discharge system and photo catalysts
(University of the Western Cape, 2019) Mouele, Emile Salomon Massima; Petrik, Leslie; Fatoba, Olanrewaju Ojo
Water pollution problems have continued to increase not only in South Africa but worldwide due to human activities. The presence of organic toxins and bacteria in water sources is mostly due to population growth, industrial development and agricultural run-off. The accumulation of persistent organic pollutants (POPs) in water and wastewater sources has raised various questions on the safety of potable water used for drinking, households and other activities. Traditional mechanical, biological, physical, and chemical methods such as flocculation, coagulation, reverse osmosis, filtration, ultrafiltration, adsorption and active sludge treatment methods have failed to remove these new xenobiotic from aquatic media. This is due to the fact that instead of degrading the toxins, the methods listed above often transform organic contaminants from one form another. Also, the post treatment of by-products resulting from these methods is costly. In addition, this new generation of contaminants, often referred to as compounds of emerging concern (CECs), exist in tiny concentrations (ng) and conventional techniques have not been designed for these low levels of pollutants which consequently pass through during treatment processes and end up in the treated effluents at minute concentrations (ug/L to ng/L). However, complete remediation of chemical toxins in wastewater treatment plants has not been achieved. A better option involves the direct oxidation of the pollutants in the effluent but so far their complete mineralisation has not been achieved. Advanced oxidation processes (AOPs) have emerged in recent years as adequate techniques for the complete removal of POPs. AOPs focus more on the production of non-selective hydroxyl radicals (OH.) which have been considered as the most powerful oxidants (2.8 V) that directly or indirectly mineralise the organic pollutant into dissolved CO2, H2O and harmless end-products. However, the use of excessive chemicals, corrosion of catalyst supports, wasted UV, ozone escapes and the cost associated with AOPs often limit their application for the removal of POPs from water and wastewater treatment facilities. The principal aim of this study was to optimise a double cylindrical barrier discharge (DBD) system for the removal of low concentration persistent organic pollutants (POPs). The efficiency of the DBD system was initially confirmed by quantification of three main reactive oxygen species including ozone (O3), hydrogen peroxide (H2O2) and hydroxyl radicals (.OH) among others. These three active species were successfully detected and quantified using indigo, per titanyl sulphate and terephthallic acid (TA) spectroscopy methods, respectively. Thereafter, the DBD reactor was optimised by assessing the effect of electrophysico-chemical parameters on the removal efficiencies of two selected pollutants including orange II sodium salt dye (O.II) and sulfamethoxazole (SMX), a pharmaceutical, as model persistent organic pollutants.
Dehydrogenation of alkanes using sulfided metal catalysts
(University of Western Cape, 2021) Tahier, Tayyibah; Mdleleni, Masikana
Light olefins are some of the main raw materials for the petrochemical industry. With the rise in oil prices and increasing demand for olefins, there is an increasing interest in finding cheaper alternatives for processes in the petrochemical industry (PETROSA 2017). Research into the dehydrogenation of light alkanes has received significant attention. This dehydrogenation process represents a route to obtain olefins from inexpensive hydrocarbon feedstocks. The use of inexpensive hydrocarbons as a feedstock in the petrochemical industry could reduce the dependence on oil. Commercially used catalysts based on chromium or platinum have major disadvantages, including the harmful effects of chromium and the high cost of platinum, which limit their application to a certain extent. Therefore, research into developing efficient dehydrogenation systems using environmentally friendly and inexpensive metals have become highly desirable. Sulfide-containing metal catalysts have gained significant research interest for use in the dehydrogenation process and display interesting catalytic activity.
Dendritic poly(3-hexylthiophene) star copolymer systems for next generation bulk heterojunction organic photovoltaic cells
(University of the Western Cape, 2018) Yonkeu, Anne Lutgarde Djoumessi; Iwuoha, Emmanuel; Cimrova, Vera
The continuous increase in energy consumption and decrease in fossil fuels reserves are a primary concern worldwide; especially for South Africa. Therefore, there is an urgent need for alternative energy resources that will be sustainable, and environmentally friendly in order to tackle the ecological degradation generated by the use of fossil fuels. Among many energy ‘niches’, solar energy appears to be one of the most promising and reliable for the African continent because of the constant availability of sun light. Organic conjugated polymers have been identified as suitable materials to ensure proper design and fabrication of flexible, easy to process and cost-effective solar cells. Their tendency to exhibit good semiconducting properties and their capability to absorb photons from the sunlight and convert it into electrical energy are important features that justify their use in organic photovoltaic cells. Many different polymers have been investigated as either electron donating or electron accepting materials. Among them, poly(3-hexylthiophene) is one of the best electron donor materials that have been used in organic photovoltaic cells. It is a good light absorber and its Highest Occupied Molecular Orbital (HOMO) energy level is suitable to allow electron transfer into an appropriate electron acceptor. On the other hand, the molecular ordering found in dendrimers attracted some interest in the field of photovoltaics as this feature can ensure a constant flow of charges. In this work, I hereby report for the first time, the chemical synthesis of a highly crystalline dendritic star copolymer generation 1 poly(propylene thiophenoimine)-co-poly(3-hexylthiophene) (G1PPT-co-P3HT) with high molecular weight and investigate its application as donating material in bulk heterojunction organic photovoltaics.
The design of ultrasensitive immunosensors based on a new multi-signal amplification gold nanoparticles-dotted 4-nitrophenylazo functionalised graphene sensing platform for the determination of deoxynivalenol
(University of Western Cape, 2014) Sunday, Christopher Edozie; Iwuoha, Emmanuel; Baker, Priscilla G. L.
A highly dispersive gold nanoparticle-dotted 4-nitrophenylazo functionalised graphene nanocomposite (AuNp/G/PhNO2) was successfully synthesised and applied in enhancing sensing platform signals. Three label-free electrochemical immunosensors for the detection of deoxynivalenol mycotoxin (DON) based on the systematic modification of glassy carbon electrodes (GCE) with AuNp/G/PhNO2 was effectively achieved. General electrochemical impedance method was employed for the sensitive and selective detection of DON in standard solutions and reference material samples. A significant increase in charge transfer resistance (Rct) of the sensing interface was observed due to the formation of insulating immune-complexes by the binding of deoxynivalenol antibody (DONab) and deoxynivalenol antigen (DONag). Further attachments of DONab and DONag resulted in increases in the obtained Rct values, and the increases were linearly proportional to the concentration of DONag. The three immunosensors denoted as GCE/PDMA/AuNp/G/PhNH2/DONab, GCE/Nafion/[Ru(bpy)3]2+/AuNp/G/PhNH2/DONab and GCE/Nafion/[Ru(bpy)3]2+/G/PhNH2/DONab have detection range of 6 – 30 ng/mL for DONag in standard samples. Their sensitivity and detection limits were 43.45 ΩL/ng and 1.1 pg/L; 32.14ΩL/ng and 0.3 pg/L; 9.412 ΩL/ng and 1.1 pg/L respectively. This result was better than those reported in the literature and compares reasonably with Enzyme Linked Immunosorbent Assay (ELISA) results. The present sensing methodology represents an attractive alternative to the existing methods for the detection of deoxynivalenol mycotoxin and other big biomolecules of interest due to its simplicity, stability, sensitivity, reproducibility, selectivity, and inexpensive instrumentation. And they could be used to develop high-performance, ultra-sensitive electrochemiluminescence, voltammetric or amperometric sensors as well.

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