School of Chemistry (ETDs)
Permanent URI for this communityhttps://hdl.handle.net/10539/38001
Browse
70 results
Search Results
Item Method development for the quantification of rare earth elements in South African monazite by various spectroscopic techniques(University of the Witwatersrand, Johannesburg, 2025-03) Rangata, Mmantheka Patricia; Tshilongo, James; Mkhohlakali, Andile; Chimuka, LukeThe rare earth elements are critical, and their various applications include electronics, the defence sector, manufacturing, renewable energy, technology and the medical sciences. The increasing demand for these critical elements will strain the existing supply chain. There is a major concern that any disruption to the supply chain will negatively impact innovation. Countries worldwide are seeking to secure new reserves, find the material substitutes, and boost the research in recycling electronics that have reached the end of life. Monazite contains critical rare-earth-elements responsible for green energy transition. The bottleneck associated with analysing rare-earth elements in monazite is its refractory nature and associated heavy minerals that do not decompose completely in the sulphuric acid fuming procedure. Furthermore, rare-earth elements have been successfully measured in geological materials employing the sensitive inductively coupled plasma mass spectrometry techniques. Nevertheless, it suffers from a low tolerance of total dissolved solids in matrices such as monazite. While, inductively coupled plasma optical emission spectroscopy suffers from poor sensitivity and matrix removal is often required for accurate rare-earth elements determinations. Extensive research has been conducted on sensitive procedures and efficient sample preparation for trace elements determinations including rare-earth elements. This study aims to develop a method for direct determination of rare-earth elements in monazite. The monazite ore samples were collected from the extractive metallurgy within Mintek for method development for quantification of REEs. Three preparation methods for sample digestion techniques were evaluated. The methods involved the flux fusion method using the lithium metaborate and sodium peroxide respectively and the multi acids digestion with hotplate as the source of heat followed by rare earth elements quantification using both the inductively coupled plasma mass spectrometry and inductively coupled plasma optical emission spectroscopy. Moreover, the complete sample dissolution was achieved with the flux fusion method while the partial sample dissolution was observed via multiple (repetitive) treatment steps by multi acids digestion method. The total dissolved solids were mitigated, and the matrix effect was eliminated when glass beads were treated (dissolved) in a mixture containing nitric and hydrofluoric acids. The analyte spectrum was often completely obscured by wing overlap and direct overlap of emission lines from interfering elements during-inductively coupled plasma optical emission spectroscopy analysis. In addition, the recoveries for some rare earth elements were suppressed with enhanced spikes for rare earth elements concentration were observed from inductively coupled plasma optical emission analysis particularly from the solution samples digested in alkaline fusion. The inductively coupled plasma optical emission spectroscopy results for the rare earth elements suggest that the sample matrix significantly affects the sensitivity. The method’s validity was tested using a monazite ore-certified reference material. In contrast to the optical emission spectroscopy, the accurate analysis of rare earths from all the digested samples was obtained using the inductively coupled plasma mass spectrometry. The results of the rare earth elements obtained for all digested samples analysed using the mass spectrometry strongly agree with the certified values. The excellent accuracy of the method was realised with the rare earth elements data obtained from quality control samples, and recoveries yield within the range of 90-110%, and the relative standard deviation of 0.2-5.4%. The selectivity and sensitivity of the method were realised with individual rare earths accurately measured in the presence of other interfering elements, as indicated by lower detection of limit ~ (0.0004-0.016 ppm) and limit of quantification ~ (0.0001-0.0290 ppmn). Calibration curve linearity for individual rare earth elements is demonstrated by the correlation coefficient in the range of 0.99 to 1.0. Moreover, multi fusion methods followed by mass spectrometry are futuristic analytical approaches for determining rare earth elements in monazite associated minerals and they can be used interchangeably. In South African context, South Africa should prioritise the development of Rare Earth Elements (REE) extraction and recycling technologies in order to maximise yield, purity, and environmental sustainability, notably through enhanced procedures for monazite-rich deposits. Investing in a circular economy paradigm, such as boosting REE recovery from electronic trash, can minimise dependency on virgin resources and help to create a more sustainable future. To further help the country's green energy transition, the government should fund research into REE-based technologies critical to renewable energy systems such as wind turbines, solar panels, and electric cars. Furthermore, developing regulatory frameworks that ensure responsible mining techniques and monitor the entire REE supply chain will assist to mitigate environmental and social consequences. Additionally, South Africa can enhance its role in the global REE market by collaborating with international partners, leveraging external expertise, and promoting sustainable technologies, thereby contributing to a low-carbon economy.Item Antimicrobial activity of silver and copper nanoparticles incorporated with biodegradable polymeric scaffolds for wound healing application(University of the Witwatersrand, Johannesburg, 2022) Shumbula, Ndivhuwo Prince; Moloto, NosiphoThere has been a significant increase in the prevalence of chronic diseases such as diabetes and cancer which cause wounds like diabetic foot ulcers and pressure ulcers. This usually causes infection(s), leading to the amputation of limbs or even death. Chronic wounds do not follow the typical stages of wound healing and thus either take a very long time to heal or do not heal at all. Therefore, the need for developing advanced and novel wound treatment products that offer infection control and sharp debridement is vital. To combat this issue, this project focussed on fabricating bioactive nanomaterials to design an advanced wound dressing in the form of 3D scaffolds. The scaffolds were made of nanocomposites containing biocompatible and biodegradable polymers decorated with antimicrobial active Cu and Ag NPs. Prior to designing the scaffolds, pristine Ag and Cu NPs were fabricated and their antimicrobial activity and cytotoxicity were tested. The antimicrobial activity of these NPs was tested against E. coli and S. aureus bacterial strains, while their cytotoxicity was evaluated using baby hamster kidney fibroblasts (BHK-21) cells. Ag NPs with various sizes and spherical shapes were synthesized using dopamine (DA) as a reducing agent. Ag NPs with the smallest diameter exhibited the most antimicrobial activity compared to those with big diameters. The cytotoxicity of Ag NPs was very low, with cell viability of over 70% between 2 μg/mL and 32 μg/mL. At concentrations above 32 μg/mL, a decrease in cell viability was observed, indicating increasing toxicity, especially for small NPs. Cu-based NPs were also synthesized using hydrazine and DA as reducing and capping agents, respectively. Pure metallic Cu, Cu 2 O and the mixture of Cu and Cu 2 O (Cu/Cu2 O) NPs were separately prepared. Cu and Cu2 O NPs exhibited promising antimicrobial activity against E. coli and S. aureus. An improved antimicrobial activity was observed for Cu/Cu2 O NPs, compared to the Cu and Cu2O NPs, and this was attributed to the synergistic effect. The cytotoxicity of Cu2 O NPs was higher compared to that of Cu and Cu/Cu 2 O NPs. The antimicrobial activity and cytotoxicity of both Ag and Cu NPs incorporated with polydopamine (PDA) were also studied. Cu and Ag NPs were either embedded within the matrix of PDA (Cu-PDA or Ag-PDA) or incorporated on the surface of PDA (Cu@PDA or Ag@PDA). Cu@PDA and Ag@PDA showed stronger antimicrobial activity than Cu-PDA and Ag-PDA due to the NPs exposure to the bacteria. These nanocomposites showed very iii low cytotoxicity with cell viability of over 80 % at concentrations as high as 250 μg/mL. However, a drastic decrease in cell viability was observed when the concentrations of Cu@PDA and Ag@PDA were increased above 250 μg/mL. Taking advantage of the strong biological activity exhibited by Cu and Ag NPs, bimetallic nanoalloys of these two metals were prepared. Nanoalloys with a fibrous shape were obtained as bimetallic nanofibres (BNF). The mole ratio of Cu:Ag was found to have an effect the antimicrobial activity of the BNFs. The BNFs prepared with a mole ratio of 1:2 (BNF-2) exhibited a strong antimicrobial activity compared to 1:1 (BNF-1) and 2:1 (BNF-3). Furthermore, the BNFs showed minimal cytotoxicity towards the BHK-21 cells at low concentrations (7.8 μg/mL), with the cell viability ranging between 75-90 %. Compared to BNF-1 and BNF-2, BNF-3 was found to have a negative impact on cell viability when the concentrations were increasing. The novel and porous 3D scaffolds were prepared by coating chitosan/gelatine (CS/Gel) scaffolds with PDA using the freeze-drying method. This was followed by decorating the surface of the scaffolds with either Ag or Cu NPs, in situ. The presence of the catechol functional group inherent from PDA facilitated the reduction of Ag ions to form pure zerovalent Ag NPs on the surface of the scaffolds. However, to reduce Cu ions to form Cu NPs, an access reducing agent (hydrazine) was added. The scaffolds showed reasonably high fluid uptake (FU) with time-dependent biodegradability, a property that would be advantageous in controlling wound exudates. These scaffolds also showed excellent antimicrobial activity against E. coli and S. aureus with low cytotoxicity towards human fibroblast cells. Taken together, the designed scaffolds could act as a barrier from the external environment, help prevent bacterial infections and further accelerate skin cells regeneration. The most important feature of these scaffolds is their potential ability to penetrate deep wounds and provide a conducive environment for skin cells to regenerate without any difficulties from bacterial colonization.Item Synthesis and evaluation of flexible pyrimethamine analogues as antifolates against drug-resistant malaria(University of the Witwatersrand, Johannesburg, 2025-03) Maree, Matthew; Ngwira, Kennedy; Rousseau, AmandaIn many parts of the world today, malaria still represents a major health crisis, with millions of cases and hundreds of thousands of deaths reported each year. The major malaria causing parasite is Plasmodium falciparum, which accounts for the majority of cases and deaths worldwide. This parasite has shown a remarkable ability to rapidly mutate and develop resistance against initially effective drug molecules. The continued threat of malaria today motivates the development of new molecules which can remain active despite point mutations that arise in the active site of the targeted enzymes. Previous work done by A. Rousseau and colleagues showed that modifying existing class II antifolates, which target the bifunctional parasite enzyme dihydrofolate reductase – thymidylate synthase (DHFR-TS), by adding a flexible four-atom linker allowed for high levels of antiplasmodial activity to be maintained against drug-resistant forms of the parasite. In the present work, molecular modelling techniques were used to optimize the structural elements of flexible pyrimethamine analogues for binding ability against mutant enzymes. The effects of various functional groups around a conserved structure were evaluated, and a library of compounds was selected for synthesis. Numerous flexible pyrimethamine analogues were successfully synthesized making use of partially established experimental procedures, and were submitted for various antiplasmodial assessments. The synthesized compounds showed excellent activity in single enzyme assays, inhibiting drug-resistant PfDHFR enzymes at low nanomolar concentrations. Whole cell assays were also conducted, where a significant decrease in activity was observed, with the most active compounds inhibiting the parasite cells at low micromolar concentrations. These results suggested that while the compounds were effective binders of the target enzyme, they had some pharmacokinetic limitations which prevented them from effectively exhibiting their mode of action inside the cell. A second-generation of analogues was then envisaged, taking inspiration from existing antifolate compounds which are known to have favourable pharmacokinetic properties. Methods for the synthesis of the devised second-generation analogues were developed as part of this work, and the binding ability of the compounds was validated with further molecular modelling studies. We are currently awaiting the results for the biological assessments of the second-generation analogues.Item The preparation of pyridylimine Mn(I) and Ru(II) complexes as catalyst precursors in formic acid dehydrogenation(University of the Witwatersrand, Johannesburg, 2024-11) Mphuti, Thabiso Isaac; Swarts, Andrew JohnA series of known and new pyridylimine ligands L1 – L9 were synthesized in high yields (79 –96%) from the condensation reaction between the appropriate pyridine-2-carboxaldehyde and amine derivatives. All the ligands were fully characterized by a range of analytical techniques. Reactions of ligands L1 – L9 with MnBr(CO)5 yielded the new neutral manganese(I) complexes C1 – C9 in moderate to good yields (50 – 84%). The complexes were characterized by NMR and FT-IR spectroscopy, mass spectrometry, and elemental analysis. Single-crystal X-ray diffraction analysis confirmed the molecular connectivity for the targeted ligands and Mn(I) complexes. Evidence of light-induced Mn-CO bond dissociation accompanied by an increase in the Mn metal center's oxidation state (+1 to +2) was shown using FT-IR and SCXRD. The pyridylimine Mn(I) complexes C1 – C9 were evaluated and found to exhibit poor to no activity toward the dehydrogenation of FA. Varying several reaction parameters such as solvent, base, temperature, and catalyst loading, was futile. The poor activity of these complexes was attributed to their light-sensitive nature in solution and the generation of unproductive Mn(II) catalytic species during the reaction. The reaction of ligands L1 – L9 with [RuCl2(p-cymene)]2 generated cationic, half-sandwich ruthenium complexes C10 – C20 in good yields (73 – 87%). The complexes were characterized by FT-IR and NMR spectroscopy, mass spectrometry, elemental analysis, and single-crystal X-ray diffraction analysis. The cationic Ru(II) complexes were found to be active precatalysts for the base/additive-assisted dehydrogenation of FA. The performance of C10 – C18 was largely influenced by the pyridylimine ligand framework, as shown by catalyst screening studies. Varying the nature of the counterion on the cationic complexes did not affect FA dehydrogenation in DMSO. Complex C1 displayed solvent-dependent catalytic activities in DMSO and water. The activation energies were estimated to be 84 and 108 kJ/mol for reactions performed in DMSO and water, respectively. The key Ru-monohydride species (d = -11 ppm) in the catalytic cycle was identified using 1 H NMR spectroscopy. KIE experiments indicated decarboxylation as the rate-determining step in both DMSO and water. Based on the kinetic and spectroscopic investigations, plausible pathways for the dehydrogenation of FA over C10 in DMSO and water were proposed. Catalyst recyclability studies indicated increased reusability of C10 in water with TON = 6748 after six FA addition cycles compared to DMSO (TON ~ 3000).Item The structure study of low-temperature rhombohedral bismuth oxide-based electrolytes(University of the Witwatersrand, Johannesburg, 2025-06) Morrison, Caitlin Audrey; Billing, Caren; Erasmus, Rudolph; Billing, DaveSolid oxide fuel cells (SOFCS) are high-temperature devices, that operate from 800 to 1000 °C. In this work, stabilized bismuth oxide (Bi2O3) is investigated as a potential solid electrolyte for SOFCs. When doping Bi2O3 with suitable metals, an unnatural phase known as the rhombohedral phase can form at intermediate temperatures between 450 and 650 °C. The overall aim of this study was to investigate the formation and conductive properties of the rhombohedral phase of doped Bi2O3. The dopants included lanthanum (La), samarium (Sm) and gadolinium (Gd) at concentrations between 15 mol and 25 mol%. The citric sol-gel method was used for synthesis of materials that were characterized using laboratory and synchrotron powder X-ray diffraction, Raman spectroscopy and Electrochemical impedance spectroscopy. Substitution of Bi2O3 with 25 mol% La, Sm or Gd confirmed that all three substituents predominantly formed the rhombohedral phase at this concentration. However, La has distinct conductive behaviour compared to the other two substituents with a significant conductivity jump at 700 °C. Varying the substituent concentration in Bi(1−𝑥)Sm𝑥O1.5 from 15 to 25 mol% revealed that the least substituted material had the highest conductivity, but was not stable and underwent a phase change at 550 °C. Annealing duration of Bi0.75Sm0.25O1.5 was varied between 5 and 15 hours at 750 °C, which revealed that the time-length of annealing does not have a significant influence on phase or conductivity behaviour. Annealing this same material at two different temperatures, 610 °C and 750 °C, formed different phase compositions at room temperature and had different conductive behaviour. This work provides further insight on how to leverage synthetic and structural conditions to successfully form the rhombohedral phase and improve its conductive behaviour.Item Development of a quantitative method for the analysis of zinc in various ores by spectroscopy(University of the Witwatersrand, Johannesburg, 2025-03) Mokgosi, Dimakatso Rachael; Tshilongo, James; Mabowa, Happy; Chimuka, LukeZinc is the most used non-ferrous metal in modern society and it has the major ability to prevent steel from corrosion which has significant positive effects on the economy and environment. Given the vital role of zinc in such applications, the inconsistent results produced necessitated further investigation on the zinc analysis. Inductively coupled plasma optical emission spectroscopy and X-ray fluorescence spectroscopy were used in this study to investigate sample preparation and develop a comparative approach for determining zinc concentrations in various ores. This study emphasised the determination of Zinc from different zinc ores by the conventional and new technology methods, which include X-ray fluorescence spectroscopy, inductively coupled plasma optical emission spectroscopy and X-ray diffractometer techniques. Mineral abundance was shown by analytical data from the x-ray diffractometer including sphalerite, pyrite, dolomite, chalcopyrite and calcite. The X-ray fluorescence spectroscopy data indicated that the elemental compositions had high concentrations ranging from 50 to 0.07% for (Zn, S, Fe, Ca, Cu, Mg and Si) as major elements. Certified reference materials were used to validate the methods and compare the results produced by the two techniques. The instrumental analysis results demonstrated that inductively coupled plasma emission spectroscopy by microwave acid digestion performed better than the X-ray fluorescence spectroscopy pressed pellet approach. The results showed that inductively coupled plasma optical emission spectroscopy is more efficient method for obtaining zinc ore samples. Both techniques achieved good recovery rates ranging from 80 to 120%. Inductively coupled plasma optical emission spectroscopy revealed a higher concentration of zinc ore in the samples investigated than X-ray fluorescence spectroscopy. Microwave acid digestion with inductively coupled plasma optical emission spectroscopy acquired 99.64 and 100.4% whereas the pressed pellet approach with X-ray fluorescence technique obtained 98.89 and 99.22% recoveries. The results of the two techniques were in good agreement; however, the inductively coupled plasma optical emission spectroscopy outperforms the X-ray fluorescence spectroscopy. Overall performance of the methods was satisfactory, demonstrating consistency and reliability in achieving accurate zinc recoveries.Item Conversion of Limonene to Carvone by Oxidative Biocatalysis(University of the Witwatersrand, Johannesburg, 2025-03) Govender, Otisha; Ngwira, Kennedy; Brady, DeanFlavour and fragrances play an important role in our daily lives. R-(−)-carvone, an oxygen containing monoterpene, is the characteristic odour found in spearmint. It is commercially important and used in the baking, cosmetic and pharmaceutical industries. However, demand greatly exceeds the natural supply, and the bulk of carvone is produced synthetically. Unfortunately, the chemical synthesis of carvone from the sustainable natural compound limonene produces harmful by-products such as nitrosyl-chloride. Hence, we aimed to use biocatalysis to convert limonene to carvone in an environmentally friendly manner. We used lipoxygenase (LOX) rich soybean meal to facilitate the conversion of limonene to carvone. Two soybean preparations were compared for efficiency, ground soybean (GSB) and milled defatted soybean (MDS). GSB unfortunately produced excessive emulsions that trapped our product and made the reaction workup difficult. Since both GSB and MDS provided similar conversions, we opted to use MDS throughout going forward for ease of product extraction. Our study sought to characterise the enzyme activity and thereby confirm that LOX was indeed responsible for conversion of limonene to carvone. We found that the maximum enzyme activity occurred at the pH 8.5, using a 0.1 M sodium borate buffer. A temperature study was also conducted, and it was found that the enzyme activity was highest at 50°C and temperatures higher than this causes the enzyme to denature. Reactions excluding oxygen did not proceed, therefore we can confirm that they involve an oxidative biocatalyst that utilises molecular oxygen. The conversion was also demonstrated to require the intermediate peroxidation of fatty acids. These results are consistent with LOX activity. We decided to investigate which isozyme of LOX is responsible for the conversion. Calcium is a known inhibitor of LOX-3 activity but increases the activity of LOX-1 and LOX-2. After adding calcium salts to the reaction, the conversion rate increased. This result, and the optimal pH of 8.5, are consistent with the activity of LOX-1. It was determined that the optimal MDS to substrate ratio was 10:1. The highest conversion obtained for the reaction was at 58% when adding FeSO4.7H2O to the reaction, implying a synergistic Fenton reaction. Finally, carvone was successfully isolated and purified using column chromatography and the chemical identity confirmed using GC-MS and NMR.Item Synthesis and characterization of marula nut derived carbon and modified manganese fluorophosphates for electrochemical energy storage applications(University of the Witwatersrand, Johannesburg, 2023-11) Shaku, Bokome; Maubane-Nkadimeng, Manoko S.; Coville, Neil J.; Ozoemena, Kenneth IkechukwuIn this thesis, six (6) different electrode materials for supercapacitor applications were created and studied. Electrode materials are one of the most important components in supercapacitors. The increase in energy density requires require electrode materials that have high surface area, conductivity, redox properties. Hence, in this study, the electrochemical characteristics of nitrogen doped activated carbons (N-ACs) material made from marula nuts as a carbon source and melamine as a nitrogen source were studied in both symmetric and asymmetric capacitors. Again, potassium and lithium intercalation in manganese fluorophosphate (MFP) were studied in asymmetric capacitor. Ceria oxide (CeO2) was used to form a composite with MFP and the electrode material was studied in asymmetric capacitor. All of the synthetic materials' morphology, crystallinity, defects, elemental composition, and structural porosity were examined. Additionally, electrochemical analysis of all materials in different electrolytes were ran to obtain current response, charge and discharge time and charge transfer resistance using two (2) and three (3) electrode systems respectively. Firstly, marula nutshell waste, was used as a source of carbon to form activated carbons (ACs) doped with nitrogen. The high surface area and nitrogen present on the material resulted in energy density that is high (17.2 Wh/kg). Secondly, a novel chemical intercalation synthesis method based on potassium hydroxide-induced hydrothermal process was used to create alkali ion-containing triplite MFP. Research findings in the study indicate that d-spacing increase when intercalating potassium into the triplite structure. An asymmetric supercapacitor was fabricated using potassium intercalated material (K+/MFP) as a cathode and N-ACs as anode in alkaline and neutral electrolytes. Higher energy density (26.9 Wh/kg) was observed in 1 M KNO3 than 6 M KOH with 25.2 Wh/kg. Thirdly, assembly of asymmetric supercapacitor of N-ACs and Li+/MFP was done. The electrode material exhibited energy of 18.8 Wh/kg in 1 M LiFSTI with capacitance retention of 69.5% after 15 000 cycles. N-ACs and MFP-CeO2 was assembled in 1 M K2SO4. The material gave energy of 23.8 Wh/kg with specific power of 525.6 Wh/kg. The MFP-CeO2//N ACs had a good cycling stability of 69.8% after 15 000 cycles.Item Photodegradation of synthetic organic dyes in water using tungsten disulfide and bismuth-based metal halide perovskite composite materials(University of the Witwatersrand, Johannesburg, 2024-06) Mabilane, Tshegofatso; Mubiayi, Kalenga P.; Moloto, Nosipho; Gqoba, Siziwe S.Synthetic organic dyes (SODs) are extensively used in the textile, paint, and printing industries. However, these dyes pose significant threats to the ecosystem. The degradation of SODs through photocatalysis has garnered considerable attention from researchers as a promising approach for wastewater treatment and environmental remediation. This research project aims to investigate the photodegradation of methyl red and rhodamine B as anionic and cationic types of SODs respectively, using a metal halide perovskite (MHP), Cs3Bi2Br9. Then, the photodegradation efficacy of Cs3Bi2Br9 was compared to that of a heterostructure, composed of Cs3Bi2Br9 and a transition metal dichalcogenide (TMDC), WS2. Cs3Bi2Br9 and WS2 were synthesized using hotinjection, and colloidal synthesis methods, respectively. The synthesized materials were characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), elemental mapping, ultraviolet-visible (UV-Vis) spectroscopy, Brunauer-Emmett-Teller (BET) analysis, zeta potential, powder X-ray diffraction (PXRD), and thermogravimetric analysis (TGA). Degradation experiments were conducted under controlled conditions, including varying catalyst loading (0.8 mg/mL, 1.6 mg/mL, and 2.4 mg/mL), initial dye concentrations (20, 40, and 60 ppm), and pH levels (pH 2, 7, and 12) to find the optimum dye photodegradation conditions. Photolysis studies were also carried out to assess the photolytic stability of the dyes. The oxidizing effect of adding 0.3519 M hydrogen peroxide to the photolysis and heterogeneous photocatalytic reactions was also investigated. When compared to Cs3Bi2Br9, the heterostructure, Cs3Bi2Br9/WS2, offered the advantages of improved dye degradation efficiency and stability due to enhanced charge separation. This is because WS2 is a layered material that has pockets that increase catalytic active sites thus making it a good co-catalyst. This project's findings shed light on the photocatalytic degradation of anionic and cationic dyes using a MHP and a heterostructure comprised of a MHP and TMDC. These findings contribute to the development of efficient and environmentally friendly approaches for SOD removal in wastewater.Item Source Apportionment, transport and fate of pollutants in the paper recycling chain - An analytical exploration of the South African context(University of the Witwatersrand, Johannesburg, 2024-08) Mofokeng, Nondumiso Nomonde Radebe; Chimuka, Luke; Madikizela, Lawrence M.This thesis presents the analytical exploration of pollutants in the South African paper recycling chain. Recycled paper is a valuable commodity that forms an intrinsic part of actualising a circular economy. In South Africa, the recycled paper value chain includes largely unsorted waste paper recovered from household waste, businesses, retail, schools, industry as well as paper collected from public areas, solid waste disposal sites and landfills by informal waste pickers. Extensive research has been undertaken in Europe, America, and Asia on the implications of using recycled paper; specifically, in packaging intended for food, toys, and electric equipment. In South Africa, however, research on pollutants in recycled paper does not exist. As the global impetus towards sustainability increases, it is imperative to determine the type of pollutants that may arise from the recycled paper value chain as these may negatively affect humans and the surrounding biota. This study extended beyond typical food packaging migration studies and investigated the holistic extraction of both food and non-food paper-based materials. The stages of paper recycling that were investigated were pre-consumer, retail and post-consumer. In Paper 1, liquid and gas chromatography, both in tandem with mass-spectrometry, were used for the chemical characterisation of various paper recycling grades prepared by accelerated solvent extraction and ultrasonic assisted extraction, respectively. The findings indicated that polymer-associated chemicals such as plasticizers, antioxidants, flame retardants, and polymer degradants have infiltrated the paper recycling chain. Multi-residue quantification of 11 pollutants in recycling paper grades in South Africa using GC-MS after accelerated solvent extraction was the main focus of Paper 2. The target analytes included BBP, DEP, DBP, DEHP, DIBP, DIDP, DIPN, NBBS, BHT, AO168, and AO168O. A plot of the VIPscores showed that DEHP and DBP were the most prominent pollutants, whilst AO168 and BHT were the least significant pollutants in the examined samples. Paper 3 explored the previously unexplored contamination of paper by pharmaceuticals, emerging contaminants that have been historically detected in South African environmental matrices. The analyses were achieved by ultrasonic-assisted extraction of paper samples before targeted and suspect screening by UHPLC-Q Orbitrap. This study was able to uncover the presence of dexamethasone, ketoprofen, and 17β-estradiol in paper-based samples. In addition, suspect screening was able to tentatively identify additional pharmaceuticals through spectral database matches. Papers 4 and 5 studied PFAS prevalence in recycling paper grades used for the manufacture of recycled paperboard. In Paper 4, targeted analysis of per- and polyfluoralkyl carboxylic and sulphonic acids was undertaken. The possible propagation and amplification of PFAS was explored by comparing the concentrations detected in pre-consumer samples to those detected in retail and post-consumer samples. Suspect screening in Paper 5 tentatively identified additional PFAS present in the samples through the development of a study-specific suspect screening protocol reported with its associated confidence level. The samples were prepared using two extraction techniques; accelerated solvent extraction with solid-phase extraction and ultrasonic-assisted extraction. The different functional groups identified indicated the importance of both selective and non-selective extraction in understanding PFAS occurrence. It further demonstrated an urgent global need to understand the different PFAS that can occur in the paper recycling chain. In these Papers, manufacturing additives and retail activities were identified as possible exposure sources. Post-consumer usage, collection, sorting, and comingling of various waste materials were also identified factors that influence the prevalence of pollutants. The presence of certain pollutants in pre-consumer showed that certain compounds may potentially remain within the paper recycling chain, propagate and accumulate along with those from the retail and postconsumer stages. The lower abundance in comparison to retail and post-consumer samples indicated that other pollutants may likely be removed during the reprocessing of recycled fibre. This study thus showed that it is imperative that South Africa develop and implement legislation and guidelines that address the use, risk, and standardised waste management strategies that ensure a safe circular economy in the paper recycling chain.