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    1-D particle-in-cell simulations of plasmas with kappa velocity distributions.
    (2013) Abdul, Reginald Francis.; Mace, Richard Lester.
    The main aim of this project was the development of a particle-in-cell (PIC) plasma simulation code. While particle-in-cell simulations are not new, they have largely focused on using an initial Maxwellian particle loading. The new feature the code implemented for this project is the use of kappa distributions as an initial loading. This specialises the code for the investigation of waves and instabilities in space plasmas having kappa-type velocity distributions. The kappa distribution has been found to provide a better fit to space plasma particle velocity distributions than the Maxwellian in a wide variety of situations. In particular, it possesses a power law tail which is a frequent feature of charged particle velocity distributions in space plasmas. Traditionally, the treatment of such out-of-equilibrium velocity distributions has been via a summation over several Maxwellians with different temperatures and average number densities. Instead, the approach used in this work is guided by recent advances in non-extensive statistical mechanics, which provide a rigorous underpinning for the existence of kappa distributions. As case studies, the simulation code was used to investigate the ion-acoustic instability as well as electrostatic Bernstein waves in both Maxwellian and kappa plasmas. Results were compared to kinetic theory and the differences in the Maxwellian and kappa plasma behaviours are discussed. To analyse the instabilities various diagnostics were used, including Fourier analysis of the wave fields to determine the dispersion relation, and particle binning to determine the particle velocity distributions. Both the Maxwellian and kappa particle loading algorithms were found to agree well with the theoretical velocity distributions and the dispersion relations were found to agree with kinetic theory for both kappa and Maxwellian plasmas. The code was developed in the C programming language using an incremental approach that enabled careful testing after each new level of sophistication was added. A version of the code was parallelised using Message Passing Interface (MPI) to take advantage of the distributed supercomputing environment provided by the CHPC.
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    2,4,6-Trichloro-1,3,5-triazine as a triorthogonal chemoselective linker.
    (2019) Rotimi, Sheyi Ebenezer.; Albericio, Fernando.; Garcia de la Torre, Beatriz.
    Abstract available in PDF.
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    2D3V electromagnetic particle-in-cell simulations of plasmas having kappa velocity distributions.
    (2018) Abdul, Reginald Francis.; Mace, Richard Lester.
    It is now well established that the kappa distribution is a more appropriate kinetic model for space plasmas than the Maxwellian distribution. In particular it possesses a power-law tail, frequently observed in space plasmas. The research presented in this thesis outlines the development of a two-dimensional electromagnetic particle-in-cell (PIC) simulation code, designed to run on general purpose graphics processing units (GPGPUs), and presents results from simulations of waves and instabilities obtained using it. While PIC simulations are not new, the majority have focussed on the old paradigm of initial particle loadings with a Maxwellian velocity distribution, or one of its variants. Distinguishing this research from previous PIC simulations is the use of the kappa distribution for the initial particle loading. To achieve this, a fast and e cient algorithm for generating multi-dimensional kappa distributed deviates was developed. The code is rst applied to the study of waves in an electron-ion plasma, in a stable equilibrium con guration with a constant background magnetic eld. Both species are modelled by isotropic (a) kappa and (b) Maxwellian velocity distributions. In each case, spectral analysis of the eld uctuations is performed, allowing mode identi cation. For parallel propagation, the maximum uctuation intensities follow the dispersion relations for the L and R modes, respectively, while those at perpendicular propagation follow the dispersion relations for the X, O and electromagnetic electron and ion Bernstein waves. The variation of wave intensity for the oblique angles is also investigated. For the kappa case, this yields new and important information presently unavailable by analysis alone. The e ects of the kappa distribution on wave intensity, as well as its e ect on the dispersion relations of the modes is discussed in detail. The second application is to the simulation of the electron temperature anisotropy driven whistler instability in an electron-ion plasma, where the electron species is modelled by the (a) bi-kappa and (b) bi-Maxwellian velocity distribution. For parallel propagation, the maximum eld uctuation intensities agree well with the dispersion relation for the whistler instability in a kappa plasma. While most of the wave intensity is in the parallel whistler mode, the oblique modes also contribute signi cantly to the overall uctuation spectrum, but their intensities vary with angle of propagation relative to the magnetic eld. The dependence of the growth rate on the index e of the electron kappa distribution is discussed in detail and compared with the well known Maxwellian results. Saturation of the instability via pitch angle scattering, reducing the electron temperature anisotropy, is observed.
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    57 Fe Mössbauer studies of 57 Mn* implanted III-V semiconductors InP and InAs.
    (2011) Dlamini, Wendy Bonakele.; Naidoo, D.; Bharuth-Ram, Krishanlal.
    III-V compound semiconductors such as Gallium Arsenide, Indium Phosphide as well as Indium Arsenide have recently demonstrated the capability of applications in high speed semiconductor devices compared to those made from Silicon. As a result, III-V compound semiconductors have drawn attention of material researchers, in particular in understanding the effects that may occur during manufacturing of these devices. Optical and electrical properties of a device may alter when a foreign atom is introduced during the manufacturing of the device. However, the foreign atom may also lead to the formation of lattice disorder (defects). A convenient way of introducing impurity atoms into a substrate and tailoring their functionality for particular applications is by ion implantation. Mössbauer spectroscopy is a useful technique usually utilized for understanding site location of the impurity atoms in a lattice and the formation of defect complexes. The focus of this dissertation is the study of lattice location of ion implanted ⁵⁷Mn/⁵⁷Fe ions in the III-V semiconductors InP, n-type InAs and p type InAs, and the annealing of implantation induced lattice damage in these samples. ⁵⁷Fe Mössbauer spectroscopy studies have been conducted on III-V semiconductors InP, n-type InAs and p-type InAs with the 57Fe Mössbauer state being populated following the implantation of radioactive ⁵⁷Mn⁺ ions which has the advantage that extremely low fluence implantations are sufficient to give data with good statistics. The ⁵⁷Mn⁺ ions were accelerated to 60 keV at the ISOLDE/CERN facility and implanted with fluences of up to 2x10¹² ions/cm² into single crystal samples which were held at 300 –700 K in an implantation chamber. βdecay of the Mn⁺ imparts an average recoil energy of 40 keV to the daughter ⁵⁷*Fe which are then re-distributed onto interstitial and/or substitutional sites, or trapped in defect complexes and damage sites. The Mössbauer spectra were collected with a light-weight parallel plate avalanche counter, with ⁵⁷Fe enriched stainless steel electrodes, mounted on a conventional drive unit outside the implantation chamber. The spectra were analyzed with the Mössbauer fitting code VINDA which allowed for simultaneous fits of the set of spectra for each sample collected at different temperatures. Acceptable fits to the Mössbauer spectra of the InP, n-type InAs and p-type InAs samples required three components: an asymmetric doublet attributed to Fe atoms in implantation induced damaged environments, a single line assigned to Fe on substitutional In sites, and a weak symmetric doublet assigned to impurity-vacancy complexes. In InP there is already an appreciable substitutional Fe (Feѕ) fraction on implantation at room temperature; while in the InAs samples FeS only becomes significant above 400 K. In all samples, the asymmetric doublet dominates the spectra below 400 K. Implantation damage, however, anneals quite rapidly and at high temperatures (above 400 K), the single line due to Feѕ dominates the spectra while the Fe-defect complex dissociates at 500 K. The implantation induced damage is observed to anneal fast in the arsenide samples compared to the phosphide sample. The slow annealing of the damage in InP was supported by the higher Debye temperature (290 K) extracted from the temperature dependence of the site population for the damage site in InP compared with InAs (194 K and 200 K for n-type and p-type, respectively). Variations in the isomer shift and quadrupole splitting for the damage site in InP at high temperatures (above 400 K) suggest structural changes in the neighborhood of the ⁵⁷Fe probe. Furthermore, the isomer shifts of the spectral components were consistent with near trivalent state and fully trivalent state i.e., Fe³⁺ with d⁵ electron configuration for Fe ions in the damage site and at the substitutional (In) site, respectively. The impurity Fe atoms associated with vacancies are identified to be in the Fe²⁺ state with a d⁶ electron configuration.
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    A highly efficient, low-cost, and sustainable method of water purification and desalination using solar-driven interfacial evaporation.
    (2024) Nnaeme, Esther Uchechukwu.; Van Zyl, Werner Ewald.; Bissessur, Ajay Bissessur.
    Water scarcity has become one of the most daunting global challenges, and as a result, a continuous supply of potable water has become a bane to most societies. Techniques such as distillation and reverse osmosis have been adopted in the production of potable water but these processes are energy-consuming and highly expensive making them less attractive to many households. A viable economical technique is the removal of salt from seawater or brackish water through a solar distiller. This research was based on the design of a low-cost and new improved solar distiller which was made up of a wooden basin and an inclined glass cover. In the basin is contained sea or brackish water and photothermal materials which include recycled materials that act as an insulation material, an evaporation structure, and a solar absorber. These photothermal materials were designed and fabricated to meet with the current state-of-the-art method of evaporation which is solar interfacial evaporation. The fabricated materials were characterized using scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). The solar distiller and photo thermal materials were evaluated for their efficiencies via real-time outdoor experiments using solar energy. The rate of evaporation was calculated, while parameters such as pH, conductivity, Total dissolved solids (TDS) and salinity were analyzed on the freshwater collected and compared with the standard of drinking water by the World Health Organisation (WHO) and South African National Standard (SANS241). Heavy metal concentration in the water samples and remediated water collected were analyzed using inductively coupled plasma optical emission spectroscopy (ICP-OES) and compared with the WHO and SANS241 standards as well. The findings could provide adequate and affordable potable water to all households irrespective of societal status and it will reduce the cost of health management, as many diseases associated with consumption of untreated water can be drastically reduced. This is in-line with South Africa’s National Development Plan (NDP) 2030 and the United Nations’ Sustainable Development Goals (SDGs).
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    A phytochemical and elemental analysis of senecio serratuloides DC, and its antidiabetic potential.
    (2024) Gumede, Andile.; Koorbanally, Neil Anthony.; Moodley, Roshila.; Mshengu, Bongiwe Pridesworth.
    Senecio serratuloides DC, from the Asteraceae, has been widely used in South African traditional medicine for the treatment of various conditions such as swollen gums, chest pains, sores, cuts, burns and ulcers. This study was conducted to determine a chemical profile of the plant, both in terms of the secondary metabolites and essential and toxic elements contained in the plant. The plant extracts were further tested for their antibacterial (minimal inhibitory concentrations) and antidiabetic potential (α-amylase and α-glucosidase inhibitory activity). The phytochemical analysis of the leaves and stems resulted in the isolation of the sterols, β- sitosterol (S1) from the stems, and stigmasterol (S2) and stigmasterol glucoside (S3) from the leaves. A further rare sterol, 18α-ursa-12,20(30)-dien-3β-ol (S4) was also isolated from the leaves. Three flavonoids, quercetin (S5), quercetin-3-O-glucoside (S6) and hesperidine (S7) were also isolated from the leaves, along with an aromatic acid, caffeic acid (S8). Extracts of the plant showed good in vitro antidiabetic activity, with the methanol extract from the leaves exhibiting the highest activity against α-glucosidase and α-amylase. However, the extracts did not exhibit any significant antibacterial activity in the assays carried out. The elemental analysis of the plant indicated a decreasing order of Ca > Mg > Zn > Fe > Co > Cu > Cr > Mn > Ni > As > Se. The leaves also showed good quantities of vitamin C, with an appreciable amount being extracted during the cooking phase. The results also show that moderate consumption of the leaves pose no probable threats of metal poisoning. The extracts obtained from S. serratuloides DC were found to have no antibacterial activity. This is surprising, since some of the isolated compounds were reported to have shown some antibacterial properties, however, these may have been too low to have any significant effect in the crude extracts.
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    A study on the atmospheric and environmental impacts of aerosol, cloud and precipitation interaction.
    (2022) Yakubu, Abdulaziz Tunde.; Chetty, Naven.
    Understanding the mechanisms and processes of aerosol-cloud-precipitation interactions (ACPI) is essential in the determination of the specific role of aerosols in modulating extreme weather events and climate change in the long run. Atmospheric aerosols are mainly of various types and are emitted from differing sources. Considering they commonly exist in the heterogeneous forms in most environments, they significantly influence the incoming solar energy and the general perturbation of the clouds depending on their constituents. Thus, a systemic identification and characterisation of these particles are essential for proper representation in climate models. To better understand the process of climate change, this research explores the climate diversity of South Africa to examine aerosol sources and types concerning the atmospheric aerosol suspension over the region and their role in clouds and precipitation formation. The study further provided answers to the cause of extreme precipitation events, including drought and occasional flooding experienced over the region. Also, an insightful explanation of the process of ACPI is provided in the context of climate change. Furthermore, the research found that the effective radiative forcing (RF) over South Africa as monitored in Cape Town and Pretoria is negative (i.e., cooling effect) and provided an analysis of the cause. Similarly, the validation of some satellite datasets from MISR (Multiangle Imaging Spectroradiometer) and MODIS (Moderate Resolution Imaging Spectroradiometer) instruments against AERONET (Aerosol Robotic Network) is conducted over the region. Although a significant level of agreement is observed for the two instruments, intense improvements are needed, especially regarding measurements over water surfaces. Finally, the study demonstrated the proficiency of effective rainfall prediction from satellite instrument cloud datasets using machine learning algorithms.
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    An ab initio molecular orbital study of some binary complexes of water.
    (1996) Tshehla, Tankiso Michael.; Ford, Thomas Anthony.
    Ab initio molecular orbital theory has been successful in predicting the stabilities of many weak complexes; typical of these are the complexes formed between water and various small molecules. To account for the correlation effect, Moller-Plesset perturbation theory truncated at the second order level was employed. In order to account for the hydrogen bonding, the 6-3lG** basis set was used. The geometry optimisations of the complexes were carried out using the Gaussian-92 suite of programs installed on a Hewlett-Packard 720 computer operating under UNIX. The interaction energies of the complexes were subjected to further analysis by applying the Morokuma decomposition scheme. The electrostatic interaction component accounts for over 40% of the total stabilisation energy in all the typical hydrogen bonded complexes. Gas phase enthalpies were computed and compared with the experimental values of similar systems. For the systems studied here, the prediction is that all complexes are stable at 25° C. A second program, Vibra, was used for carrying out a normal coordinate analysis. A third computer program for the graphical representation of molecular and crystallographic models, Schakal-92, was employed to illustrate the predicted equilibrium geometries and the fundamental vibrational modes. The predicted geometries, interaction energies, charge redistributions, vibrational wave numbers, infrared intensities and force constants are listed and compared with those in the literature, where applicable. Correlations between the various predicted properties show some interesting chemistry.
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    AB inito studies of a pentacyclo-undecane cage lactam.
    (2011) Singh, Thishana; Bissety, K.; Kruger, Hendrik Gerhardus.
    Abstract available in PDF.
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    Activation of n-hexane using vanadium-exchanged zeolites.
    (2010) Naicker, Thirusha.; Friedrich, Holger Bernhard.
    The influence of the form of the ZSM-5 zeolite, vanadium content and the elimination of the exterior surface acidity on the activity and selectivity of n-hexane oxidation was studied using a fixed bed reactor. Blank reactor studies (carborundum packed reactor) showed no conversion below 450°C with the highest conversion (8%) at 500°C. The dominant products were found to be carbon oxides (Sel./% = 90) with minor selectivities to the hexene isomers (7%) and the remainder being cracked products, THF and benzene. H-ZSM-5 with different SiO2/Al2O3 ratios (100 and 320) and Na-ZSM-5 (SiO2/Al2O3 ratio of 100) were tested under non-oxidative and oxidative conditions. Under oxidative conditions as the ratio of the SiO2/Al2O3 increased, the aluminium content decreased and so too did the cracking ability of the zeolite (i.e. yield of cracked products dropped from 36% to 8%). However, the use of the Na- form of ZSM-5 completely eliminated acid cracking. Under oxidative conditions H-ZSM-5 (100) was found to be more active and resulted in higher formation of cyclic and aromatic compounds. With increasing time on-stream and higher temperatures the catalyst was found to deactivate. Evidence of this was seen by a decrease in surface area and pore volumes of the spent catalyst. The Na-ZSM-5 (100) showed lower activity, but deactivation was shown to be lower. These findings led to the investigation of vanadium ion-exchanged Na-ZSM-5 catalyst for n-hexane activation. Catalysts with different vanadium loadings were prepared using the solid state ion-exchange method. Catalysts were characterised using various methods. These techniques showed that vanadium was successful loaded onto the catalyst and that the highest vanadium loading that could be achieved was 2.5%. The lower loadings were not found to alter the catalyst structure while the highest loading of 2.5% was found to show some pore blockage and to possibly alter the structural environment of the zeolite. Time on stream experiments were conducted and temperature (350, 400 and 450°C), contact time (0.5, 0.8, 1.1 and 1.5 s) and fuel-air ratios (0.7, 1.3 and 2) were varied. The optimum conditions (Conv./% = 39) for terminally activated products were found using the Na-V-ZSM-5 (0.9%) at a temperature of 400°C, a contact time of 1.1 s and fuel-air ratio of 1.3. With the lower fuel-air ratio of 0.7 (oxygen rich conditions), hexanal formation was favoured. The Na-V-ZSM-5 catalyst could be regenerated with initial activity and selectivity being regained. Silanisation was found to be possible, however, the extent and degree of silanisation was difficult to control. Pore blockage was possibly responsible for the lower activity and selectivity obtained using the silanised Na-V-ZSM-5.
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    Activation of n-octane and cyclohexane to oxygenates using modified zeolites.
    (2014) Cele, Mduduzi N.; Friedrich, Holger Bernhard.; Bala, Muhammad Dabai.
    Three types of zeolites namely ZSM-5, Faujasite Y and MOF-5 were synthesized. The synthesis of Na-Fe-silicalite-1(34), H-Fe-silicalite-1(34), Na-Fe-silicalite-1(41), Na-Fe-silicalite-1(68), Na-Fe-silicalite-1(80), Fe-silicalite-1(128), Na-Fe-ZSM-5(66) and Na-Fe-ZSM-5(114) was conducted using a solid gel method. Further to this, Na-Fe-silicalite-1(41), Na-Fe-silicalite-1(80), Fe-silicalite-1(128), Na-Fe-ZSM-5(66) and Na-Fe-ZSM-5(114) were modified by silanisation using tetraethoxysilane (TEOS) as the silanisation agent to produce Na-Fe-silicalite-1(41:Sil), Na-Fe-silicalite-1(80:Sil), Na-Fe-silicalite-1(128:Sil), Na-Fe-ZSM-5(66:Sil), Na-Fe-ZSM-5(114:Sil). The numbers in brackets represent Si/Fe molar ratio while Sil represent silanisation. Powder XRD results showed that only the ZSM-5 phase was obtained. The second type was synthesized by encapsulation of Fe-TPP (tetraphenylporphyrin) inside faujasite Y to produce Fe-TPP-NaY. Powder XRD results confirmed the faujasite structure after encapsulation. Finally, Fe-MOF-5(1), Fe-Zn-MOF-5(0.5) and Fe-Zn-MOF-5(0.2) were synthesized using conventional methods with the numbers in brackets representing the Fe wt%. Also, XRD results showed that the MOF-5 phase was obtained with a sharp peak at 2θ below 10° which is characteristic of a highly crystalline material. All synthesized catalysts were tested in the oxidation of n-octane to oxygenates with H2O2 as the oxidant in MeCN. Furthermore, Fe-TPP-NaY was also used to activate 1-octene, 4-octene and cyclohexane while Fe-MOF-5 was used to activate cyclohexane. Na-Fe-silicalite-1(34), H-Fe-silicalite-1(34) and Na-Fe-silicalite-1(68) produced selectivities of 24, 2 and 27% respectively to terminal products at 80 °C in 13 mL MeCN. Furthermore, Na-Fe-silicalite-1(41), Na-Fe-silicalite-1(80), Fe-silicalite-1(128), Na-Fe-ZSM-5(66) and Na-Fe-ZSM-5(114) achieved selectivities to terminal products of 20.2, 28.1, 17.6, 24.5 and 21.3 respectively while Na-Fe-silicalite-1(41:Sil), Na-Fe-silicalite-1(80:Sil), Na-Fe-silicalite-1(128:Sil), Na-Fe-ZSM-5(66:Sil) and Na-Fe-ZSM-5(114:Sil) showed selectivities to terminal products of 20.7, 14.3, 12.3, 25.7 and 27.3 % respectively at 80 °C in 80 mL MeCN. Fe-TPP-NaY showed 13% selectivity to terminal products in oxidation of n-octane at 80 C in 13 mL MeCN. In the oxidation of n-octane using Fe-MOF-5 catalysts, selectivity to terminal products was found to increase with a decrease in the wt% of Fe. Hence, selectivities of 9.5, 12.9 and 20.7% were recorded for Fe-MOF-5(1), Fe-Zn-MOF-5(0.5) and Fe-Zn-MOF-5(0.2) respectively.
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    Adsorption of selected pollutants from aqueous solutions onto modified carbon nanotubes.
    (2015) Oyetade, Oluwaseun Akinwole.; Martincigh, Bice Susan.; Nyamori, Vincent Onserio.; Jonnalagadda, Sreekantha Babu.
    The significance of wastewater remediation before its discharge into the aquatic environment cannot be overemphasized. Adsorption has been proven to be effective for the removal of toxic pollutants from industrial effluents and/or wastewater, due to its simplicity in operation and the possibility of regenerating sorbents for reuse. This concept was exploited to achieve the effective removal of toxic contaminants from simulated wastewater. Carbon nanotubes, a fascinating member of the carbon family, possessing unique physical and chemical properties, have been reported as superior adsorbents for wastewater remediation purposes. Their large specific surface areas and porosity, hollow and layered structures, and great mechanical and thermal stability, makes them good candidates as sorbents for wastewater treatment and contamination control. This thesis interrogates the efficacy of carbon-structured nanomaterials containing multiwalled carbon nanotubes (MWCNTs) as the backbone, for the removal of divalent metal ions and organic contaminants from aqueous solutions. In this work, a novel adsorbent was successfully synthesized by incorporating a nitrogen-donor ligand (4-phenyl-2, 2':6', 2''-terpyridine) onto MWCNTs to afford nitrogen-functionalized MWCNTs (MWCNT-ttpy). The effectiveness of this sorbent towards the removal of divalent metal ions (Pb2+, Cd2+, Zn2+, Hg2+ and Cu2+), and organic contaminants (bisphenol A and ibuprofen) from aqueous solutions was investigated. The adsorption uptake of these pollutants onto MWCNT-ttpy was compared with that of acid-functionalized MWCNTs (MWCNT-COOH) to determine the sorbent with best removal efficiencies. Further, magnetic nanocomposites containing cobalt ferrite nanoparticles and MWCNT-COOH were synthesized in varying ratios to investigate their effectiveness for the removal of rhodamine B from aqueous solutions. All nanomaterials synthesized were characterized by means of TEM, SEM, TGA, BET, FTIR and Raman spectroscopy before application. Batch adsorption experiments were conducted to determine the effects of pH, contact time, adsorbent dose, initial adsorbate concentration and temperature for each sorption process in order to evaluate the best experimental conditions necessary for pollutant removal. The experimental data were fitted into the pseudo-first order, pseudo-second order, intraparticle diffusion and Elovich models to determine the dynamics and rate-determining step of the adsorption processes. The mechanism of the process was investigated by fitting the experimental data into various two- and three-parameter isotherms. iii The application of MWCNT-ttpy for the removal of both heavy metal ions and organic pollutants demonstrated much enhanced uptakes than MWCNT-COOH. The incorporation of nitrogen onto MWCNT-COOH significantly improved the affinity towards the removal of metal ions, forming strong electrostatic and coordination interactions between the active sites on the adsorbent and metal ion cations. Increasing hydrophobicity of MWCNT-ttpy over MWCNT-COOH accounted for the enhanced removal of bisphenol A and ibuprofen, since their uptake is primarily decided on by the hydrophobic nature of sorbates. Further, the application of both MWCNT-COOH and magnetic carbon nanotube-cobalt ferrites nanocomposites showed good removal efficiencies for rhodamine B from aqueous solution, with the best uptake achieved by using MWCNT-COOH. However, the magnetic nanocomposites give an advantage of separation under magnetic influence, hence, limiting inconveniences encountered during separation. The kinetics of adsorption were mostly described by the pseudo-second order and the Elovich models, while the equilibrium data were best described by the Langmuir and the Sips isotherm models. The thermodynamic parameters of adsorption, namely, the change in Gibbs energy (ΔGº), change in enthalpy (ΔHº) and change in entropy (ΔSº) were estimated for each adsorption process. The adsorption of all adsorbates were endothermic in nature except in the case of ibuprofen and Cd2+ which exhibited an exothermic process. All adsorption processes described in this study were spontaneous, implying the feasibility of the sorbents for the removal of targeted pollutants from wastewater. Desorption studies aimed at regenerating the adsorbents for reuse were successful. High recovery efficiencies between 60-95% were achieved by using eluents such as 0.1 mol dm-3 HCl for metal ions, and ethanol and acetone/acetic acid for organic contaminants. This process averts the production of secondary pollutants, supporting the reutilization of both the adsorbents and the adsorbates. Thus, all adsorbents used in this study were efficiently regenerated by using simple conventional chemicals and can be reused for the removal of targeted pollutants from aqueous solutions. The competitive adsorption of Pb2+, Cd2+, Zn2+ and Cu2+ and the binary adsorption of bisphenol A and ibuprofen onto MWCNT-ttpy was also investigated in both single-solute and multi-component adsorption systems. The sorption of metal ions onto MWCNT-ttpy was in the sequence Cd > Pb > Cu > Zn and Pb > Cu > Cd > Zn in single-solute and multicomponent systems, respectively, while the removal of ibuprofen was higher than that of bisphenol A in a typical binary adsorption system. For the first time, the competitive sorption of organic contaminants (bisphenol A and ibuprofen) in the presence of metal ions (Cd2+ and Pb2+) onto nitrogen-functionalized MWCNT was investigated. The iv study revealed a cooperative mechanism of adsorption between metal ions and organic pollutants in a multicomponent system. Thus, the novel adsorbent proved effective for the removal of metal ions, bisphenol A and ibuprofen in both single-solute and multicomponent adsorption systems. MWCNT-ttpy also proved remarkably effective for removing three heavy metal ions, Pb2+, Cu2+ and Zn2+, in three different real-life water samples, obtained from the Umgeni River. Removal efficiencies greater than 95% were achieved for all three metal ions. The modification of MWCNTs to afford both nitrogen-functionalized MWCNTs and cobalt-ferrite/MWCNT nanocomposites was successful. These sorbents exhibited excellent pollutant removal abilities, attributed to improved textural characteristics of the nanomaterials synthesized. The application of these sorbents for wastewater and industrial effluent remediation should be further explored for prudent management of water resources.
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    Aerosol characteristics over different regions of southern Africa : using sunphotometer and satellite measurements.
    (2015) Adesina, Joseph Ayodele.; Venkataraman, Sivakumar.
    Aerosols and cloud play a major role in understanding and interpreting the varying earth’s energy budget. It is necessary to characterize these atmospheric particles by their sizes, chemical composition, water content etc. Aerosols can both cause heating and cooling depending on what they are made of; dust will generally tend to scatter leading to cooling effect while some species of black carbon will absorb sunlight thereby causing a heating effect. In order to assess their impact on global climate, a multiple measurement approach is necessary and specifically, we need long and short term ground-based measurements in clean and polluted environment and long term satellite measurements. In this thesis, we have used aerosol measurements from CIMEL Sunphotometer (part of the world-wide network; Aerosol Robotic Network: AERONET) over, Pretoria (25.75º S, 28.28º E) and Skukuza (24.9º S, 31.5º E) in South Africa, and satellite data from Moderate Resolution Imaging Spectroradiometer (MODIS) and Multiangle Imaging Spectroradiometer (MISR). Pretoria is situated in industrial region with adequate influence of urban/industrial aerosols while Skukuza is an agricultural based region with frequent burning of agricultural waste to clear the harvest during the late winter, spring and summer seasons. Thus, the study over industrial and agricultural regions explores more understanding about the regional radiative forcing in relation to aerosol loading and meteorology. MODIS satellite data was utilized for addressing long term trend in aerosol loading and cloud interaction studies over different locations of South Africa where no ground based sunphotometer data are available. Using six months sunphotometer data (July–December 2012), aerosol characteristics over Gorongosa were studied with particular attention to how aerosol loading evolves during the biomass burning season (spring) including pre- and post-months. The results revealed that the monthly mean aerosol optical depth (AOD₅₀₀) was at maximum in September and minimum in November. The study also investigated biomass burning and forest fire occurrences in Mozambique using MODIS active fire data. Using a year sunphotometer data (January – December 2012) obtained from Pretoria’s (CSIR_DPPS) AERONET site, aerosol was characterized by its optical, microphysical and radiative properties. The study explored meteorological effects on aerosol loading and aerosol direct radiative forcing over Pretoria. Maximum value of aerosol optical depth (AOD₅₀₀) was found during February (summer) and August (winter) while the atmospheric forcing was found to be independent of seasonal variation in AOD. Besides, AOD, Angstrom exponent (AE; α440-870), columnar water vapor (CWV), volume size distribution (VSD), single scattering albedo (SSA) and aerosol radiative forcing (ARF) were computed and their variations with their climatic implications were studied. Using the ground-based instrument of AERONET at Skukuza, we performed validation of MISR and MODIS (Terra and Aqua) level 3 AOD products using the data retrieved for the year 2010. We also carried out regression analysis on these satellite products using 10 years of dataset (2004-2013) to evaluate their performance at a hinterland and coastland stations with two distinct environments in SA. The validation showed that MISR was better correlated with sunphotometer having a coefficient of determination (R²=0.94), Aqua MODIS (R²=0.77) and Terra MODIS (R²=0.68). The long term regression analysis at the two selected locations showed MODIS products underestimating MISR. At the hinterland, MISR showed an increasing trend while MODIS products showed a decreasing trend over the study period but at the coastland MISR and Terra MODIS showed a negative trend while Aqua MODIS showed a positive trend. When the two MODIS products were compared, they were better correlated at the coastland (R²=0.66) than hinterland (R²=0.59) and when compared based on seasonal variation, they were better correlated in the winter season in both locations than any other season. The Ozone Monitoring Instrument (OMI) Ultra-Violet Aerosol Index (UVAI) which was used to monitor the absorption aerosol index showed an increasing trend over the two locations with 0.0089/yr hinterland and 0.0022/yr at coastland. In the present thesis, we also used data obtained from the Terra satellite onboard of the MODIS to investigate the spatial and temporal relationship between AOD and cloud parameters namely, water vapor (WV), cloud optical depth (COD), cloud fraction (CF), cloud top pressure (CTP) and cloud top temperature (CTT) based on 5 years (January 2008 -December 2012) of dataset over six locations in South Africa. AOD has high values during spring (September to November) but low values in winter (June to August) in all locations. In terms of temporal variation AOD was lowest at Bloemfontein 0.06±0.04 followed by Cape Town 0.08±0.02, then Potchefstroom 0.09±0.05, Pretoria and Skukuza had 0.11±0.05 each and Durban 0.13±0.05. The mean AE values for each location show a general prevalence of fine particles for most parts of the year. Our analysis of AOD and WV showed both quantities only co-vary at the beginning of the year but later in the year they tend to have opposite trend over all the locations. AOD and CF showed negative correlation for most of the locations while AOD and COD were positive over three of the locations. AOD and CTT, CTP showed similar variations in almost all the locations. The co-variation of CTT and CTP may be due to large scale meteorological variation.
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    Amino-, amido- and oxy-bipyridyl complexes of copper, ruthenium, molybdenum and rhodium.
    (1996) Bernardis, Francesco Luigi.; Haines, Raymond John.
    The work described in this thesis concerns the synthesis and study of the coordination behaviour of the 6-anilino-2,2'-bipyridyl (Habipy), 6-N-methylanilino-2,2'-bipyridyl (mabipy), 6-piperidyl2,2'.- bipyridyl (pipbipy) and 2,2'-bipyridin-6-one (Hobipy) ligands. Chapter one reviews the coordination chemistry of the 2-aminopyridyl (Rap), 2-hydroxypyridyl (Hhp) and the 2-(2-pyridyl)-I,8-naphthyridine (pynp) ligands. These ligands are closely related to Habipy, mabipy, pipbipy and Hobipy in that they share a common NCN or NCO fragment. Thus the review of their coordination behaviour provides insight into the expected coordination of the Habipy, mabipy, pipbipy and Hobipy ligands. The synthesis and characteristaion of the novel Habipy, mabipy and pipbipy ligands are reported in Chapter two. X-ray crystal structure determinations of mabipy and pipbipy reveal that the geometry about the exocyclic nitrogen atom in both ligands is nearly planer, suggesting substantial overlap of the nitrogen lone pair orbital with the 1t electron system of the bipyridyl rings. In both mabipy and pipbipy the N3-C 10 bond lengths are shorter then normal N-C single bonds. In Chapter three -the synthesis and characterisation of copper(I) complexes containing mabipy, pipbipy and Habipy, and a copper(II) complex containing mabipy are reported. The copper(I) complexes have the general formula [Cu(l12-L)2r, where L= mabipy 1, pipbipy 2 or Habipy 3. The structures of complexes 1 and 2 are determined by X-ray crystallography. In complexes 1- 3 the bipyridyl fragments of mabipy, pipbipy and Habipy chelate while the exocyclic nitrogen atoms remain free. The crystal structures of 1 and 2 reveal that the exocyclic nitrogens have a planar geometry as was the case in the uncoordinated ligand. The crystal structure of [Cu(1l2-mabipY)2f+ (4) is determined by X-ray crystallography and is very similar to that of the copper(I) species. Coordination of the mabipy ligand in 4 is the same as that in 1 and the exocyclic nitrogen in 4 is also planar. The redox couple 4/1 is shown to be electrochemically reversible with EV2= 0.45 V. In Chapter four the synthesis and chararcterisation of dinuclear complexes containing the Ru2 2+, Ru/+, Mo24+and ~4+ cores are reported in which the abipy ligand bridges two metal centres. The complexes [Rulll-L)lCO)4], where L= abipy 5 or obipy 6, were synthesised by the r~action of the free ligands with [{RuiCO)102CCH3)2}n] in toluene. The structures of5 and 6 are determined by X-ray crystallography and show the ligands bridging the Ru(I) atoms in a head to tail fashion and occupy mutually cis positions about the octahedral Ru(I) atoms. The Ru-Ru separations in 5 and 6 are 2.668(1) and 2.671(1) A respectively. The reaction of Habipy with [Rui02CCH3)4CI]n was found to afford the mixed valence species [Ruill-abipy)(02CCH3)3CI] (7), the structure of which is determined by X-ray diffraction methods. The structure of7 reveals one abipy ligand bridging the two ruthenium atoms as in 5. The Ru-Ru separation in 7 is 2.294(2) A. The reaction of [Moi02CCH3)4] with habipy in methanol affords (Moill-abipy)(02CCH3)3] (8). The structure of 8 is determined by X-ray diffraction methods and reveals one abipy ligand bridging two quadruply bonded molybdenum atoms which have a Mo-Mo separation of 2.094(2) A. The [Rhlll~abipy)(02CCH3)iH20)] (9) is formed from the reaction of [Rh i02CCH3)4] with Habipy in methanol. The structure of [Rh2(Il-abipy)(02CCH3)iNCPh)] is determined by X-ray diffraction methods and shows the abipy ligand bridging two Rh(II) atoms which are separated by 2.399(1) A. This chapter is concluded with a discussion of the possiblity of substitution of more than one acetate ligand by the abipy ligand in terms of 'hard' and' soft' acid-base theory and synthetic methods.
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    Amperometric determination of selected persistent organic pollutants and heavy metals using horseradish peroxidase biosensor.
    (2010) Nomngongo, Philiswa Nosizo.; Ngila, Jane Catherine.
    Persistent organic pollutants and heavy metals are released into the environment through different anthropogenic processes. They are of concern because they tend to bioaccumulate in the food chain and show adverse health effects ranging from acute to chronic toxicity. These pollutants need therefore to be monitored to conserve the environment. Conventionally, samples are sent to a laboratory for analysis by standard techniques such as chromatography and spectroscopy. Although these conventional techniques display high accuracy and low detection limits, they are expensive, require the use of highly trained personnel and tedious sample preparation. In comparison, electrochemical methods such as biosensors are sensitive, low cost and simple to operate. In this thesis, the determination of selected persistent organic pollutants (polybrominated diphenyl ethers, polybrominated biphenyls and polychlorinated biphenyls) and heavy metals (Cd, Pb and Cu) was achieved by the use of amperometric inhibition biosensor based on horseradish peroxidase (HRP) immobilized on the surface of platinum-polyaniline modified electrode. Polyaniline (PANI) film was electrochemically deposited on the platinum electrode surface. The film was characterized by cyclic voltammetry and spectrometric techniques. The CV results proved that the PANI was electroactive and exhibited a fast reversible electrochemistry. Characteristic Ultraviolet–Visible and Fourier Transform Infrared features of the polymer film were identified. They revealed that PANI film synthesized in this study is the conductive emeraldine salt. Horseradish peroxidase based biosensor was constructed by electrostatic attachment of the enzyme onto Pt-PANI electrode surface. Spectrometric and cyclic voltammetric results indicated that the immobilized HRP retained its bioelectrocatalytic activity towards the reduction of hydrogen peroxide. The Pt/PANI/HRP biosensor showed a linear response over a concentration range of 0.05 to 3.17 mM with a detection limit of 36.8 nM. Apparent Michaelis- Menten constant ( app M K ) was calculated as 1.04 mM. This implied that the HRP biosensor had a high affinity for H2O2. Furthermore, the fabricated biosensor showed high sensitivity, good reproducibility, repeatability and long-term stability. The Pt/PANI/HRP biosensor was applied to the determination of selected persistent organic pollutants and heavy metals. The latter was found to inhibit the HRP enzyme’s activity. The percentage inhibition of the investigated persistent organic pollutants decreases in the following order: 2,2´4,4´,6-pentabrominated diphenyl ether> 2-brominated biphenyl> 2-chlorinated biphenyl> 2,2´,4,5,5´-pentachlorinated biphenyl> 2,4,4´-trichlorinated biphenyl. In the case of heavy metals, the degree of inhibition of heavy metals was highest for Cd2+, followed by Cu2+ and then Pb2+. Kinetic study for the amperometric response to H2O2, recorded in the absence and presence of persistent organic pollutants and heavy metals revealed that for polybrominated diphenyl ethers, the inhibition process corresponded to a competitive type whereas for polybrominated biphenyls, polychlorinated biphenyls and heavy metals, it corresponded to the on-competitive type. The biosensor exhibited high sensitivity towards the determination of the metals and persistent organic pollutants as pollutants in real water samples, namely tap water and landfill leachate samples.
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    Analysing transient effects in the ionosphere using narrowband VLF data.
    (2009) Bremner, Sherry.; Collier, Andrew Blaine.
    Very Low Frequency (VLF) radio waves propagate within the Earth-ionosphere waveguide with very little attenuation. Modifications of the waveguide geometry affect the propagation conditions, and hence, the amplitude and phase of VLF signals. Changes in the ionosphere, such as the presence of the D-region during the day, or the precipitation of energetic particles, are the main causes of this modification. Using narrowband receivers monitoring remote VLF transmitters, the amplitude and phase of these signals are recorded. A multivariate data analysis technique, Principal Component Analysis (PCA), is applied to the data in order to determine parameters such as seasonal and diurnal changes which affect the variation of these signals. Data was then analysed for effects from extragalactic gamma ray bursts, terrestrial gamma ray flashes and solar flares. Only X-rays from solar flares were shown to have an appreciable affect on ionospheric propagation.
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    Analysis and monitoring of persistent organic pollutants in the Umgeni River, KwaZulu-Natal, South Africa.
    (2016) Gakuba, Emmanuel.; Moodley, Brenda.
    Abstract available in PDF file.
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    The analysis and optimization of electrostatic electron optical lenses with rotational symmetry, through use of orthogonal functions.
    (1978) Van der Merwe, Johannes Petrus.; Walker, Anthony David Mortimer.; Spalding, Dennis Raymond.
    No abstract available.