Thesis (M.Sc.(Chemistry)) -- University of Limpopo, 2022 / Water contamination caused by toxic elements has serious human health and ecological implications. The increasing quantity of toxic elements in surface and groundwater is currently an area of greater concern, especially since many industries are discharging their metal containing effluents into freshwater without any adequate treatment. The mineral dissolution in mining regions is highly enhanced by mining and smelting activities. The mine waste and drainage in areas surrounding mines have high levels of toxic element contamination above the permissible limits. Contamination of groundwater by toxic elements such as As, Fe, Mn, Al, Cr, Zn and Co due to operational activities of surrounding mines in the Sekhukhune district was reported by several researchers. Removal of toxic elements from contaminated water is a big challenge. The affected communities need to attain a safe water supply source for daily usage, hence there is an urgent need of technologies for the treatment of water supplies contaminated with these toxic elements to ensure the safety of potable water. The study was undertaken by modifying nitrogen-doped multi-walled carbon nanotubes (N-MWCNTs) and investigating the removal of chromium, nickel and lead from anthropogenic contaminated groundwater in the Sekhukhune area, in Limpopo. The as-prepared N-MWCNTs functionalised with metal oxide, thiol and amino functional groups are expected to increase the surface area of the nanocomposite, which can facilitate high adsorption of contaminants from water samples. The adsorption capabilities for the removal of these toxic elements by modified N MWCNTs nanocomposites were investigated in batch studies as a function of different parameters. The parameters studied included pH, contact time, adsorbent dosage, initial concentration, temperature, competing ions and reusability. The optimum condition was then acquired for removal of selected toxic elements from real water studies. The removal efficiencies of the as-prepared nanocomposites were pH dependent and the optimal pH values for adsorption was 5.5, 1.5, 11 and 6 at optimum contact time of 10, 80, 60 and 120 min and dosage of 0.30, 0.35, 0.05 and 0.6 g/L for Cr(III), Cr(VI), Ni(II) and Pb(II), respectively. The prepared nanocomposites were characterised using various techniques such as Fourier transform infrared (FTIR) spectroscopy, powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer-Emmet-Teller (BET) and thermogravimetric analysis (TGA). The FTIR analysis confirmed the presence of Fe3O4, -SH and -NH2 groups on the functionalised MWCNTs. The PXRD analysis further supported that the synthesized nanocomposites consisted of hexagonal graphite structure of MWCNTs. Furthermore, SEM and TEM results showed that the introduced functional groups were uniformly attached on the surface of the MWCNTs. The BET analysis indicated that the surface area of the modified MWCNTs nanocomposites increased significantly as compared to the acid treated MWCNTs. In addition, TGA showed that the M-MWCNTs (M = modified) nanocomposites possess high thermal stability. Raw N-MWCNTs showed higher stability as compared to oxidised N-MWCNTs, which decomposes at lower temperatures of 200 °C. No weight loss was observed below 800 °C for the hydrazine functionalised nanocomposites as compared to the triethylenetetramine (TETA)- substituted nanocomposites, which showed weight loss at 300 °C. Toxic elements in solutions before and after treatment were quantified using flame atomic absorption spectrometry (F-AAS). The adsorption isotherms of the as-prepared nanocomposites for chromium, nickel and lead removal fitted both the Langmuir and Freundlich model depending on the adsorbent used, which suggest that the adsorption process met both monolayer and heterogeneous adsorption. Thermodynamic analysis showed that the adsorption of Cr(III), Cr(VI), Ni(II) and Pb(II) ions are spontaneous and endothermic. The as-prepared nanocomposites showed an outstanding regeneration performance retaining over 50% toxic elements removal. Thus, the as prepared nanocomposites are promising for practical application in toxic element treatment. Analysis of the collected river and borehole water in Sekhukhune indicated that the concentration of total chromium, nickel and lead before treatment varied from (0.207 to 0.286 mg/L), (0.226 to 0.380 mg/L) and (3.301 to 8.017 mg/L), respectively which were above acceptable levels recommended by the South African National Standards (SANS), United States Environmental Protection Agency (USEPA) and World Health Organisation (WHO), i.e., 0.05 mg/L, 0.07 mg/L and 0.01 mg/L. After treatment, the nanocomposites were able to remove 100% of the metal ions from the water. TETA-functionalised nanocomposites showed greater removal efficiencies in comparison to the hydrazine-functionalised nanocomposites for all the studies done. / Water Research Commission (WRC)

M. Tech. (Department of Chemistry, Faculty of Applied and Computer Sciences), Vaal University of Technology. / The presence of organic and inorganic pollutants in aqueous environments is one of the major challenges confronting man. It is therefore important to develop sensitive, versatile and cheap techniques for their detection. Arsenic (III), 2-chlorophenol (2-CP) and sulfamethoxazole (SMX) are priority pollutants that pose health threats to humans and animals. This study was thus aimed at exploring two promising carbon nanomaterials as electrode modifiers for the electrochemical sensing of arsenic (III), 2-CP and SMX in water. Glassy carbon electrode (GCE) was modified with a nanocomposite of carbon dots (CDs) and graphitic carbon nitride (g-C3N4) and used as a sensor for the analytes in aqueous media. The CDs was prepared by a facile one-pot hydrothermal method using pine cone as the carbon source; g-C3N4 and g-C3N4/CDs nanocomposite were prepared via the microwave irradiation heating method. CDs, g-C3N4 and g-C3N4/CDs were dropped-dried on the surface of bare GCE. Transmission electron microscopy (TEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) were used to characterize the prepared materials. GCE, g-C3N4/GCE, CDs/GCE and g-C3N4/CDs/GCE electrodes were electrochemically investigated by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) using a ferrocyanide [Fe (CN) 6]3-/4- redox probe. The current and the reversibility of the redox probes were enhanced in the presence of modifiers. The electrochemical behavior of arsenic (III), 2-CP and SMX on different electrodes (GCE, CDs/GCE, g-C3N4/GCE and g-C3N4/CDs/GCE) were investigated by differential pulse voltammetry (DPV) under optimized conditions in a phosphate buffer solution (pH 7.6, 6 and 5 for 2-CP, As (III) and SMX respectively). The results demonstrated that the g-C3N4/CDs/GCE electrode significantly enhanced the oxidation peak current of all three analytes. The detection sensitivity of the analytes was greatly improved, suggesting that this new modified electrode has great potential in the determination of trace level of arsenic (III), 2-CP and SMX in water. The oxidation peak currents displayed a linear relationship to concentrations for 2-CP (0.5 - 2.5 μM, R2=0.958, n=5), arsenic (III) (2 - 10 μM R2=0.978, n=5) and SMX (0.3 - 1.3 μM R2=0.9906, n=5). The detection limits of 0.62 μM, 1.64 μM and 0.10 μM were obtained for 2-CP, arsenic and SMX, respectively. Phenol and 4-chloro-3-methyl-phenol were found to interfere with the detection of 2-CP, while, Cu2+, Zn2+, Pb2+ and Cd2+ were the only significant ions that interfered with the electrochemical detection of arsenic (III). EDTA was used as a ligand to mask the interference effects of copper, cadmium, lead and zinc on arsenic sensing. The modified electrode (g-C3N4/CDs/GCE) was used to determine arsenic, 2-CP and SMX in spiked tap and effluent water samples by the standard addition method and the results showed percentage recoveries varying from 93-118% for 2-CP, 98-100% for arsenic and 80-105% for SMX. The outcomes of this study established that the nanocomposite material represents an easy and sensitive sensing platform for the monitoring of arsenic (III), 2-CP and SMX in aqueous media.

Ph. D. (Department of Chemistry, Faculty of Applied and Computer Sciences), Vaal University of Technology. / Aromatic organic contaminants are difficult to biodegrade, and thus effective green technologies are required to remove these pollutants from the ecosystem. Tetracycline antibiotic, an organic water pollutant, can be degraded by heterogeneous photocatalysis using an appropriate catalyst, with capability in converting the visible light energy into active species. The thesis focused on silver nanoparticles anchored on silver bromide (Ag/AgBr) as a plasmonic catalyst dispersed on activated carbon (ACK), were used as a photocatalyst (AABR-ACK) in tetracycline removal. The aim is to develop a catalyst that is active in low intensity visible light, whilst the addition of activated carbon will increase the light absorption and separate the charge pairs, after the photocatalyst has been excited by the visible light. The activated carbons were derived from pinecone pyrolyzed in a microwave. The pinecone mass to potassium hydroxide impregnation ratio and microwave pyrolysis time influenced the activated carbon properties. An impregnation ratio of 2.24 and microwave pyrolysis time of 16 minutes at constant microwave power of 400 W yielded the activated carbon with the best-developed porous structure and electrochemical properties. This activated carbon was used during the optimisation of the Ag/AgBr activated carbon (AABR-ACK) catalysts preparation using a thermal polyol precipitation method and response surface methodology. The most active catalyst was the AABR-ACK 11 obtained by a preparation temperature of 140 ºC, time (17.50 minutes), mass of surfactant and activated carbon (0.26 g and 0.03 g) respectively. This catalyst had an ordered nanospheres morphology, reduced electron-hole recombination rate, better electrochemical properties and exhibited enhanced activity on the tetracycline antibiotic removal in comparison to other Ag/AgBr activated carbon catalysts. A percentage degradation of 92% was obtained in 180 minutes were obtained with the AABR-ACK 11 catalyst. The photocatalyst prepared using the best activated carbon derived from pinecone developed in this study was compared to photocatalysts prepared using commercial activated carbon and biochar. The Ag/AgBr activated carbon catalysts using pinecone-derived activated carbon degraded the tetracycline to 92%, which is significantly higher than the percentage degradations (80% and 74%) for the catalyst prepared using commercial activated carbon and biochar catalysts respectively. The higher activity of the Ag/AgBr activated carbon catalysts using pinecone-derived activated carbon was due to the conductive attributes of the catalyst support for accelerated transfer of photo-induced electrons. The Ag/AgBr activated carbon catalysts using pinecone- derived activated carbon also exhibited better performance on tetracycline removal when compared to photocatalysts reported in literature. Two catalyst preparation methods, thermal polyol and deposition precipitation, were compared. The thermal polyol method yielded a more active catalyst for the degradation of the tetracycline in comparison to the deposition precipitation method. The degradation reaction conditions such as pH, light intensity and degradation temperature influenced the rate of the reaction. The highest rate of degradation was obtained at a pH of seven, white light and 40 ºC temperature. The intermediate products formed because of hydroxylation, deamination, demethylation and dehydration during the photocatalytic degradation of tetracycline antibiotics were identified using liquid chromatography mass spectrometer. Quenching experiments with hydroxyl, hole, and superoxide anion species showed that the most important radical responsible for the tetracycline degradation was the superoxide anion radical.

Although products of coal combustion (PCCs) such as coal ash are currently exempted from classification as a hazardous waste in the United States under the 1976 Resource Conservation and Recovery Act (RCRA), the U.S. Environmental Protection Agency (EPA) is now revising a proposed rule to modify disposal practices for these materials in order to prevent contamination of ground- and surface water sources by leached trace elements. This paper analyzes several aspects of EPA’s scientific reasoning for instating the rule, with the intent of answering the following questions: 1) Are EPA’s cited values for PCC production and disposal accurate estimates of annual totals?; 2) In what ways can EPA’s leaching risk modeling assessment be improved?; 3) What is the total quantity of trace elements contained within all PCCs disposed annually?; and 4) What would be the potential costs and feasibility of reclassifying PCCs not under RCRA, but under existing NRC regulations as low-level radioactive waste (LLRW)? Among the results of my calculations, I found that although EPA estimates for annual PCC disposal are 20% larger than industry statistics, these latter values appear to be closer to reality. Second, EPA appears to have significantly underestimated historical PCC disposal: my projections indicate that EPA’s maximum estimate for the quantity of fly ash landfilled within the past 90 years was likely met by production in the last 30 years alone, if not less. Finally, my analysis indicates that while PCCs may potentially meet the criteria for reclassification as low-level radioactive waste by NRC, the cost of such regulation would be many times that of the EPA June proposed disposal rule ($220-302 billion for PCCs disposed in 2008 alone, versus $1.47 billion per year for the Subtitle C option and $236-587 million for Subtitle D regulatory options). / text

This research focused on evaluating and comparing the perceptions, water-use behaviour, water conservation awareness and overall water stewardship of participants residing in Hammanskraal and Atteridgeville who have experienced intermittent water supply in their domestic households – due to either water contamination incidents caused by dilapidated infrastructure or water restrictions implemented by the City of Tshwane Metropolitan Municipality during the 2016–2017 drought in the Gauteng Province. The research concluded that the municipality needs to implement proactive water conservation awareness initiatives on an ongoing basis to reduce high water demands and to create a culture of water stewardship, especially in Atteridgeville. Transparent communication is also required from the municipality to instil the necessary trust among the public. It is recommended that the municipality attends to water leaks and ongoing complaints from the public timeously to reduce the current apathy from the public against reporting water-related issues and to ultimately ensure compliance to water restrictions. / Hierdie navorsing fokus op die evaluering en vergelyking van deelnemers wat in Hammanskraal en Atteridgeville woon se persepsies, waterverbruiksgedrag, waterbewaringsbewustheid en algehele waterrentmeesterskap, wat onderbroke watervoorsiening in hulle huishoudings ervaar het – as gevolg van waterbesoedelingsvoorvalle wat deur vervalle infrastruktuur veroorsaak is en waterbeperkings wat deur die Stad Tshwane Metropolitaanse Munisipaliteit gedurende die 2016 tot 2017-droogte in Gauteng ingestel is. Die navorsing het tot die gevolgtrekking gekom dat die munisipaliteit proaktiewe waterbewaringsbewustheidsinisiatiewe op ’n deurlopende grondslag moet implementeer om hoë wateraanvraag te verminder en ’n kultuur van waterrentmeesterskap, veral in Atteridgeville, te skep. Deursigtige kommunikasie word ook van die munisipaliteit vereis om die nodige vertroue by die publiek te kweek. Daar word aanbeveel dat die munisipaliteit betyds aandag aan waterlekkasies en deurlopende klagtes van die publiek sal gee om die huidige onverskilligheid van die publiek by die aanmeld van waterverwante aangeleenthede te verminder en om uiteindelik te verseker dat die publiek die waterbeperkings eerbiedig. / Patlisiso ena e ne e tsepame hodima ho lekola le ho bapisa maikutlo, boitshwaro ba tshebediso ya metsi, tsebo ka poloko ya metsi le tlhokomelo e akaretsang ya metsi ke bankakarolo ba dulang Hammanskraal le Atteridgeville ba bileng le phepelo ya metsi e kgaohang malapeng a bona – e ka ba ka lebaka la diketsahalo tsa tshilafatso ya metsi e bakilweng ke dipeipi tse senyehileng kapa ho kgaolwa ha metsi ho kentsweng tshebetsong ke Masepala wa Motsemoholo wa Metropolitan wa Tshwane nakong ya komello ya 2016–2017 porofenseng ya Gauteng. Patlisiso e fumane hore masepala o hloka ho kenya tshebetsong matsholo a ho atisa tsebo ka poloko ya metsi ka mokgwa o tswellang e le ho fokotsa tlhokeho e phahameng ya metsi le ho theha ditlwaelo tsa tlhokomelo ya metsi, haholo ho la Atteridgeville. Ho boetse ho hlokeha puisano e hlakileng e nang le ponaletso ho tswa ho masepala e le hore setjhaba se be le tshepo ho ona. Ho kgothaletswa hore masepala a sebetsane le diketsahalo tsa ho dutla ha metsi le ditletlebo tse tswellang tse tswang ho setjhaba ka potlako e le ho fokotsa maikutlo a ho tsotelle a tswang ho setjhaba mabapi le ho tlaleha mathata a amanang le metsi le ho netefatsa hore batho ba latela melawana ya phokotso ya metsi. / Geography / M. Sc. (Geography)