UWCScholar :: Browsing by Author "Khotseng, Lindiwe"

Browsing by Author "Khotseng, Lindiwe"

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Acid mine drainage prediction techniques and geochemical modelling: case study on gold tailing dams, West Rand, Witwatersrand basin area, South Africa
(University of the Western Cape, 2021) Wu, Changhong; Khotseng, Lindiwe
Acid Mine Drainage (AMD) is identified as one of the contributors to environmental hazard in the gold mining region of South Africa, as caused by the mining operational activities performed by mining industries in South Africa. This effect motivates the development of AMD prediction techniques application and geochemistry modelling using gold tailing dams located in West Rand area, Witwatersrand Basin as a case study. Control strategies are devised to assess, understand and measure the acidic potential generation of waste materials in ensuring the right method required to analyse risks caused by AMD to environment. The method encompasses mineralogical and geochemical analysis of 93 samples collected, AMD prediction, test modification and geochemical modelling. This method was appropriately applied to understand the basic mechanisms involved in controlling acid generation, assessing prediction procedure and selecting the right prediction tools. Study objectives are attained by performing a series of experimental lab tests on the samples collected from the two major tailing dams (Mogale and Gold One_1 tailings). Results derived from the lab experiments (XRD and SEM-EDS) show presence of mineral phases characterised with the surface feature of samples, and unknown substances of samples were identified. Geochemical characterisation was performed by XRF and ICP-MS to determine the major oxides elements and trace elements, respectively. Leco test generate total sulphur and total carbon. Multistatistical analysis is used to interpret the data derived from geochemical characterisation process to explicate the metal and trace elements distribution and occurrence. Initial samples were screened and categorised based on paste pH and EC using kinetic tests to determine acid-forming and neutralising minerals in samples and static tests to determine acid generation potential in samples. Net Acid Producing (NAPP) was mathematically calculated from Acid Neutralising Capacity (ANC), Maximum Potential Acidity (MPA) and total Sulphur. Results obtained from the Paste pH demonstrate that samples collected from 1 meter downward the holes to 10 meters, with a few meters samples in hole T003 at Gold One_1 are non-acidic while the remaining tailing samples are acidic. ANC/MPA ratio was applied to assess the risk of acid generation from mine waste materials. Graphical illustrations of the Acid Base Account (ABA) are plotted to demonstrate the net acidic generation potential trends of samples, which were classified into non-acid forming, potential acid forming and uncertain categories. Results integration between ANC, Single Addition Net Acid Generation (NAG) test and NAPP were used to classify acid generation potential of the samples. Leachate collected from leaching column test were analysed for pH, EC and chemical element by ICP-MS. The leaching column test used to analyse samples (T004) and (T001) collected from the two major tailings was set up for a 4-month experiment. Study findings present environmental assessment report on the two investigated gold tailing dams in Witwatersrand Basin area. Other findings are improved understanding of the application and limitations of various existing AMD prediction methods for assessment of gold mine waste and conceptual geochemical modelling developed to test appropriate methodology for AMD potential at a given gold mine site.
Antibacterial and photodegradation of organic dyes using lamiaceae-mediated zno nanoparticles: A review
(MDPI, 2022) Mutukwa, Dorcas; Taziwa, Raymond T.; Khotseng, Lindiwe
The green synthesis of zinc oxide nanoparticles (ZnO NPs) using plant extracts has been receiving tremendous attention as an alternative to conventional physical and chemical methods. The Lamiaceae plant family is one of the largest herbal families in the world and is famous for its aromatic and polyphenolic biomolecules that can be utilised as reducing and stabilising agents during the synthesis of ZnO NPs. This review will go over the synthesis and how synthesis parameters affect the Lamiaceae-derived ZnO NPs. The Lamiaceae-mediated ZnO NPs have been utilised in a variety of applications, including photocatalysis, antimicrobial, anticancer, antioxidant, solar cells, and so on. Owing to their optical properties, ZnO NPs have emerged as potential catalysts for the photodegradation of organic dyes from wastewater. Furthermore, the low toxicity, biocompatibility, and antibacterial activity of ZnO against various bacteria have led to the application of ZnO NPs as antibacterial agents. Thus, this review will focus on the application of Lamiaceae-mediated ZnO NPs for the photodegradation of organic dyes and antibacterial applications.
Development of adsorptive materials for selective removal of toxic metals in wastewater: A review
(MDPI, 2022) Motitswe, Moeng Geluk; Badmus, Kassim Olasunkanmi; Khotseng, Lindiwe
Removal of toxic metals is essential to achieving sustainability in wastewater purification. The achievement of efficient treatment at a low cost can be seriously challenging. Adsorption methods have been successfully demonstrated for possession of capability in the achievement of the desirable sustainable wastewater treatment. This review provides insights into important conventional and unconventional materials for toxic metal removal from wastewater through the adsorption process. The importance of the role due to the application of nanomaterials such as metal oxides nanoparticle, carbon nanomaterials, and associated nanocomposite were presented. Besides, the principles of adsorption, classes of the adsorbent materials, as well as the mechanisms involved in the adsorption phenomena were discussed.
Development of Anode Materials Using Electrochemical Atomic Layer Deposition (E-ALD) for Energy Applications
(University of the Western Cape, 2018) Xaba, Nqobile; Khotseng, Lindiwe
Nanomaterials have been found to undeniably possess superior properties than bulk structures across many fields of study including natural science, medicine, materials science, electronics etc. The study of nano-sized structures has the ability to address the current world crisis in energy demand and climate change. The development of materials that have various applications will allow for quick and cost effective solutions. Nanomaterials of Sn and Bi are the core of the electronic industry for their use in micro packaging components. These nanomaterials are also used as electrocatalysts in fuel cells and carbon dioxide conversion, and as electrodes for rechargeable sodium ion batteries. There are various methods used to make these nanostructures including solid state methods, hydrothermal methods, sputtering, and vacuum deposition techniques. These methods lack the ability to control the structure of material at an atomic level to fine tune the properties of the final product. This study aims to use E-ALD technique to synthesis thin films of Sn and Bi for various energy applications, and reports the use of E-ALD in battery applications for the first time. Thin films were synthesised by developing a deposition sequence and optimising this deposition sequence by varying deposition parameters. These parameters include deposition potential, and concentration of precursor solution. The thin films were characterised using cyclic voltammetry, linear sweep voltammetry, chronoamperometry for electrochemical activity. These were also characterised using scanning electron microscope for morphology, x-ray diffraction for crystal phases, energy dispersive spectroscopy for elemental mapping, and focused ion beam scanning electron microscope for thickness. The elemental content was analysed using electron probe micro analysis and inductively coupled plasma mass spectrometry. The electrochemical impedance charge and discharge profile were used for electrochemical battery tests.
Development of modified TiO2 nanostructures for photocatalysis
(University of the Western Cape, 2019) Mashiya, Nzaliseko; Khotseng, Lindiwe; Iwuoha, Emmanuel
TiO2 has been broadly used as a standard photocatalyst due to its high stability, low cost, relatively low toxicity, and excellent photocatalytic performance in comparison to other semiconductor materials. However, the large band gap of TiO2 limits its use as a photocalyst due to the high energy required for excitation of the electrons in the UV region. Research on the reduction of TiO2 band gap to the visible region of the spectrum has been explored with little success. Therefore, this study focusses on shifting the band gap of TiO2 catalyst from the UV region to the visible region by doping with graphene and nitrogen-doped graphene to form TiO2-G and TiO2-NG nanocomposites, respectively. The N-doped graphene support was prepared by doping the graphene oxide with nitrogen through Hydrothermal process, followed by the reduction of the materials. Fourier Tranform Infrared (FTIR) spectroscopy confirmed the successful doping of graphene to N-graphene by the appearance of C-N and N-H vibrational modes on the spectra. The XRD results show the fingerprint patterns of TiO2 and N-graphene, which confirms the successful preparation of the nanocomposites. Morphological studies of the nanocomposites using transmission electron microscopy (TEM) show the TiO2 nanowires dispersed on graphene related supports. The optical band gap of TiO2 from UV-Vis spectroscopy was found to be 3.2eV, which decreased to 2.7eV and 2.5eV upon incorporation of grapheme and N-graphene, respectively. These results prove the success in the achievement of the aim in this study. When electrochemical studies were further conducted on the materials, TiO2-NG was found to possess better electrochemical properties with fast electron kinetics observed on the impendance spectroscopy results. The results obtained justified use of TiO2-NG photocatalyst the optimal material for organic mineralisation in Advanced Oxidation Processes (AOPs).
Development of nanostructured electrocatalysts using electrochemical atomic layer deposition technique for the direct liquid fuel cells By
(University of Western Cape, 2020) Mkhohlakali, Andile Cyril; Khotseng, Lindiwe; Fuku, Xolile; MmalewaneModibedi, Remegia
The depletion of fossil fuel resources such as coal and the concern of climatic change arising from the emission of greenhouse gases (GHG) and global warming [1] lead to the identification of the 'hydrogen economy' as one of the renewable energy sources and possible futuristic energy conversion solution. Sources of hydrogen as fuel such as water through electrolysis and liquid organic fuel (Hydrogen carriers) have been found as potential game-changers and received increased attention, due to its low-carbon emission.
Development of palladium nickel/tin metal oxide catalysts on carbon nanotube supports for direct alcohol fuel cells
(University of Western Cape, 2020) Juqu, Thando; Khotseng, Lindiwe; Modibedi, Mmalewane
Palladium can be used as an anodic catalyst for the alkaline direct alcohol fuel cells (ADAFCs). Palladium has displayed high tolerance towards carbon monoxide (CO) poisoning and high catalytic activity for alcohol oxidation reaction in alkaline medium. Palladium-based catalysts have arisen as an alternative to performing alcohol oxidation reaction, especially when combined with other transition metals and multi walled carbon nanotubes (MWCNT) as a support, which induces changes in the palladium electronic structure, and thus, increasing its activity. This research is focused on the development of palladium catalysts incorporated with nickel and tin (transitional metals) on multi walled carbon nanotubes for alkaline direct glycerol fuel cells.
Effects of heat treatment on the catalytic activity and methanol tolerance of carbon-supported platinum alloys
(Springer, 2012) Valisi, Andiswa; Maiyalagan, Thandavarayan; Khotseng, Lindiwe; Linkov, Vladimir; Pasupathi, Sivakumar
This work studies the effect of heat treatment of carbon-dispersed platinum and platinum alloys on its methanol tolerance and catalytic activity as gas diffusion electrodes for oxygen reduction reaction (ORR) in acid medium. The catalyst powders were subjected to heat treatments at three different temperatures for a fixed period at controlled atmospheres. Differences in catalyst morphology were characterized using X-ray diffraction, energy dispersive X-ray analysis and transmission electron microscope techniques. The electrochemical characteristics and activity of the electro-catalysts were evaluated for ORR and methanol tolerance using cyclic voltammetry, in the form of gas diffusion electrodes. The optimum heat-treatment temperature is found to be strongly dependent on the individual catalyst. The maximum ORR activity and better methanol tolerance for the oxygen reduction reaction (ORR) was observed in Pt-Fe/C and Pt-Cu/C catalysts subjected to heat treatment at 350 °C.A trend of catalytic activity for oxygen reduction reaction (ORR) was obtained: Pt-Cu/C (350°C)>Pt-Fe/C (350°C) > Pt-Ni/C (350°C) > Pt-Co/C (250°C) > Pt/C (350°C), showing that Pt-Cu/C-type catalysts had a higher catalytic activity with reasonable methanol tolerance.
Extraction and synthesis of silicon nanoparticles (sinps) from sugarcane bagasse ash: A mini-review
(MDPI, 2022) Seroka, Ntalane Sello; Taziwa, Raymond T.; Khotseng, Lindiwe
This current study reviews the utilization of the traditional extraction methods and latest findings in extraction of silica from agricultural wastes, in particular, sugarcane bagasse, using inorganic acids to produce nano-silicon. The three key processes discussed in detail include elec-trochemical, ball milling, and sol–gel processes. The sugarcane bagasse has been identified as the cheapest source of producing silica from the potential raw material for the preparation of nano-silicon. The acid-base extraction and precipitation methodology involves the use of bases like sodium hydrox-ide (NaOH) and potassium hydroxide (KOH), and acids such as hydrofluoric acid (HF), sulphuric acid (H2SO4 ), nitric acid (HNO3 ), and hydrochloric acid (HCl) for the treatment of the ash.
Fabrication of metal-organic frameworks with application-specific properties for hydrogen storage application
(University of Western Cape, 2019) Bambalaza, Sonwabo Elvis; Khotseng, Lindiwe; Langmi, H.W.; Musyoka, N.M.
The application of porous materials into industrial hydrogen (H2) storage systems is based on their use in combination with high-pressure cylinders. The processing of metal-organic frameworks (MOF) powders into shaped forms is therefore imperative in order to counteract the adverse effects of poor packing of powders in cylinders. The fabrication of shaped MOFs has, however, been shown to be accompanied by compromised properties such as surface areas, gravimetric and volumetric H2 capacities, and also the working/deliverable H2 capacities in comparison to MOF powders.
Fabrication of polyoxometalate-modified palladium–nickel/reduced graphene oxide alloy catalysts for enhanced oxygen reduction reaction activity
(Royal Society of Chemistry, 2021) Sanij, Fereshteh Dehghani; Balakrishnan, Prabhuraj; Khotseng, Lindiwe
Designing advanced nanocatalysts for effectively catalyzing the oxygen reduction reaction (ORR) is of great importance for practical applications of direct methanol fuel cells (DMFCs). In this work, the reduced graphene oxide (rGO)-supported palladium–nickel (Pd–Ni/rGO) alloy modified by the novel polyoxometalate (POM) with Keggin structure (Pd–Ni/rGO-POM) is efficiently fabricated via an impregnation technique. The physical characterizations such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, inductively coupled plasma optical emission spectroscopy (ICP-OES), field emission scanning electron microscopy coupled with energy dispersive Xray spectroscopy (FESEM-EDX), and transmission electron microscopy (TEM) are utilized to confirm the structure, morphology, and chemical composition of the fabricated samples. The XRD results verify the formation of the POM-modified Pd8Ni2/rGO alloy electro-catalyst with the face-centered-cubic (fcc) structure and average crystallite size of 5.54 nm.
Green synthesis of crystalline silica from sugarcane bagasse ash: Physico-chemical properties
(MDPI, 2022) Seroka, Ntalane S.; Taziwa, Raymond; Khotseng, Lindiwe
Sugarcane bagasse South Africa is an agricultural waste that poses many environmental and human health problems. Sugarcane bagasse dumps attract many insects that harm the health of the population and cause many diseases. Sugarcane ash is a naturally renewable source of silica. This study presents for the first time the extraction of nanosilica from sugar cane bagasse ash using L-cysteine hydrochloride monohydrate acid and Tetrapropylammonium Hydroxide. The structural, morphological, and chemical properties of the extracted silica nanoparticles was cross examined using XRD, FTIR, SEM, and TGA. SEM analysis presents agglomerates of irregular sizes. It is possible to observe the structure of nanosilica formed by the presence of agglomerates of irregular shapes, as well as the presence of some spherical particles distributed in the structure. XRD analysis has revealed 2 angles at 20, 26, 36, 39, 50, and 59 which shows that each peak on the xrd pattern is indicative of certain crystalline cubic phases of nanosilica, similar to results reported in the literature by Jagadesh et al. in 2015.
Hydrothermal conversion of agricultural and food waste
(University of Western Cape, 2022) Makhado, Tshimangadzo; Khotseng, Lindiwe
The global dependence on non-renewable fossil fuels to meet energy needs cannot be sustained for a long time and it is already evident in the escalation of fuel prices over the past decade. This research was performed towards renewable energy production from agricultural and food waste. The use of agricultural and food waste has benefits such as being grown in a land that is not in competition with food crops protein, all year round availability, and having high lipid content. The produced bio-crude oil can be upgraded to remove moisture and acidity level, and can be used as a substitute for heavy oils such as diesel to power static appliances or can be used as petrol distillate fuel alternative. Hydrothermal liquefaction (HTL) process is one of the commonly used technologies for converting agricultural and food waste into liquid biofuels.
Materials, components, assembly and performance of flexible polymer electrolyte membrane fuel cell: A review
(Elsevier, 2023) Duan, Yuan; Liu, Huiyuan; Khotseng, Lindiwe
With emerging demand of potable and wearable electronic devices, reliable and flexible energy suppliers are inevitable. Polymer electrolyte membrane fuel cells (PEMFCs) attract great attention due to high energy density and sustainability. However, non-bendability limits their application in flexible electronic devices. To make PEMFCs adaptable and flexible, considerable efforts have been devoted to developing various bendable com- ponents or advanced techniques. This review, therefore, focuses on the advancement of components and relative techniques of flexible PEMFCs, which determine the performance and durability, while achieved little concern in other reviews. The components and techniques include membrane, flexible catalytic layer, flexible gas diffusion layer, flexible bipolar plates, assembly of single cell or stack, store or supply of fuel and oxidant. In each section, the materials or techniques commonly used in conventional PEMFCs are summarized firstly, followed by the reasons why they aren’t appliable to flexible PEMFCs and then proceeding to the development of flexible components and relevant techniques of flexible PEMFCs. Subsequently, the flexible PEMFCs’ performance and durability are presented, reaching to 100–200 mW cm and dozens of hours, respectively, still far lower than those of conventional PEMFCs. Finally, a brief perspective on remaining challenges and future development of flexible PEMFCs are provided
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.
Nanostructured silicon derived from an agricultural residue bagasse ash via magnesiothermic reduction method
(MDPI, 2023) Seroka, Ntalane S.; Taziwa, Raymond; Khotseng, Lindiwe
This study presents the magnesiothermic reduction of silica into silicon. This reduction process occurs at a lower reaction temperature than its carbothermal counterpart. Furthermore, silica was extracted from sugarcane bagasse ash via a thermo-chemical treatment method using, for the first time, L-cysteine chloride monohydrate and used as a precursor in the production of silicon using magnesiothermic reduction. The as-synthesized nanocrystalline silicon’s physicochemical properties were investigated using XRD, Raman, FTIR, BET, and SEM. A peak at 2 of 28.2 with a crystallite size of 32 nm was discovered using X-ray diffraction spectroscopy. The pronounced peak around 518 cm􀀀1 was observed from the Raman spectrum, characteristic of crystalline silicon. The FTIR analysis showed two sharp peaks at 446 cm􀀀1 and 1056 cm􀀀1, indicative of the Si-O rocking mode and Si-O-Si stretching mode functional groups present.
Polydopamine coated platinum catalysts to improve fuel cells durability
(University of Western Cape, 2022) Mugeni, Ange Mireille; Khotseng, Lindiwe
Polymer electrolyte membrane fuel cells (PEMFC) are in the forefront of energy production and have drawn a great deal of attention in both fundamental and application in recent years. It is a promising energy system used in commercialized electric vehicles presenting with the following advantages: low-temperature operation, high power density (40%–60%), nearly zero pollutants compared to conventional internal combustion gasoline vehicles, simple structure, and so on. There are, however, two major obstacles which obstruct PMFCs pathway to commercialization— durability and cost. Recent advances in PEMFC systems showed the most common fuel cell catalysts to be Platinum (Pt) (or platinum alloys) supported by high surface carbon in both the cathode and anode. However, carbon is very susceptible to corrosion and results in lower durability of Pt supported catalysts.
Polypyrrole supports for direct alcohol fuel cells.
(University of Western Cape, 2021) Mseleku, Zicabangele; Khotseng, Lindiwe
Anode catalysts are one of the key components of direct alcohol fuel cells (DAFCs). They play a huge role in the alcohol oxidation reaction (AOR) that occurs on the anode side. Palladium (Pd) supported on carbon material has been reported to have good catalytic activity towards alcohol oxidation reactions. Better stability and activity has been reported for catalysts supported on conductive polymers like polypyrrole (PPy) when compared to traditional carbon support material. This study investigated the effect of support materials on Pd and PdCo electro-catalysts while concurrently determining the support material that can improve the activity and stability of Pd and PdCo electro-catalysts used as direct alcohol fuel cells catalysts. All Pd and PdCo catalysts supported onPPy (prepared using oxidative polymerization method), reduced graphene oxide (rGO) and prepared using modified Hammers method and multi-walled carbon nanotubes and pre-treated by acid. All the catalysts were synthesized using the modified polyol method.
Solar energy materials-evolution and niche applications: A literature review
(MDPI, 2022) Seroka, Ntalane S.; Taziwa, Raymond; Khotseng, Lindiwe
The demand for energy has been a global concern over the years due to the ever increasing population which still generate electricity from non-renewable energy sources. Presently, energy produced worldwide is mostly from fossil fuels, which are non-renewable sources and release harmful by-products that are greenhouses gases. The sun is considered a source of clean, renewable energy, and the most abundant. With silicon being the element most used for the direct conversion of solar energy into electrical energy, solar cells are the technology corresponding to the solution of the problem of energy on our planet. Solar cell fabrication has undergone extensive study over the past several decades and improvement from one generation to another.
Synthesis and characterization of binary Palladium based electrocatalysts towards alcohol oxidation for fuel cell application
(University of the Western Cape, 2018) Klaas, Lutho Attwell; Khotseng, Lindiwe
The anode catalyst is one of the important parts of the direct alcohol fuel cell (DAFC); it is responsible for the alcohol oxidation reaction (AOR) takes place at the anode side. Pd has been reported to have good alcohol oxidation reactions and good stability in alkaline solution. Better stability and activity has been reported for Pd alloyed catalysts when compared to Pd. Choosing a suitable alcohol also has an effect on the activity and stability of the catalyst. This study investigates the best catalyst with better AOR and the best stability and also looks at the better alcohol to use between glycerol and ethanol for the five in-house catalysts (20% Pd, PdNi, PdNiO, PdMn3O4 and PdMn3O4NiO on multi walled carbon nanotubes) using cyclic voltammetry (CV), linear sweep voltammetry (LSV), electrochemical impedance spectrometry (EIS) and chronoamperometry. HR-TEM and XRD techniques were used to determine the particle size and average particle size, respectively while EDS used to determine elemental composition and ICP was used to determine catalyst loading. It was observed from LSV that PdNiO was the most active catalyst for both ethanol and glycerol oxidation, and it was the most stable in ethanol while PdMn3O4 proved to be the most stable catalyst in glycerol observed using chronoamperometry. The best alcohol in this study was reported to be glycerol having given the highest current densities for all the inhouse catalysts compared to ethanol observed using LSV. From XRD and HR-TEM studies, particle sizes were in the range of 0.97 and 2.69 nm for XRD 3.44 and 7.20 nm for HR-TEM with a little agglomeration for PdMn3O4 and PdMn3O4NiO.

Browsing by Author "Khotseng, Lindiwe"

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