Chemistry

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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.
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.
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).
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.
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.
AB inito studies of a pentacyclo-undecane cage lactam.
(2011) Singh, Thishana; Bissety, K.; Kruger, Hendrik Gerhardus.
Abstract available in PDF.
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.
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.
Adsorption of pharmaceuticals by nano-molecularly imprinted polymers (nano-MIPs) from wastewater: kinetics, isotherms, and thermodynamics studies.
(2024) Nxumalo, Nonhlazeko Loveday.; Mahlambi, Precious Nokwethemba.; Mahlambi, Mphilisi.; Mngadi, Sihle.; Chokwe, Tlou.
It has been reported that pharmaceuticals are not entirely removed or broken down during the wastewater treatment process, allowing them to escape into effluent water. This stems from the pharmaceuticals widespread use and the inefficient wastewater treatment methods. Therefore, the objective of this study was to develop more effective methods for removing pharmaceuticals from wastewater systems. Adsorption-based pharmaceutical removal is one of the most promising approaches because it is easily incorporated into current water treatment systems. The first part of this work reports on literature studies for recent advancements in the adsorption process involving the incorporation of an artificial molecularly imprinted polymer (MIP), that is an effective molecular receptor that can selectively recognize and remove pollutants. In magnetic solid-phase extraction, dispersive solid-phase microextraction, and solid-phase extraction, MIPs can be used as a selective adsorbent for analyte cleanup and preconcentration. Moreover, MIPs can be produced by combining nanoparticles to develop composite nanomaterials (nanoMIPs). In comparison to conventional bulk adsorbents, the enhanced selective adsorption capacity and kinetics are attributed to the large surface area per unit volume and specific functionality of nanomaterials. Nonetheless, some significant barriers to the application of nanomaterials are their dispersive qualities, difficulty in cycling, and secondary pollution from the loss of adsorbent during treatment. Another way to use nanoparticles for detectability enhancement is to modify the molecularly imprinted polymers chemical or physical characteristics. The nanoparticles' embedding in the MIP enhances the material's surface area or gives the adsorbent new features. This study describes a method for creating reusable, economical, and effective polymer-based silver nanoparticles-adsorbents. Notably, silver nanoparticles have a wide range of applications due to their unique properties which include their large surface area, shape and size. Plant-mediated synthesis plays a significant role in their synthesis. Remarkably, the synthesis of silver nanoparticles from plant extracts is inexpensive, easily scalable, and harmless for the environment. Plant extracts can be used to produce nanoparticles with controlled sizes and shapes. The molecular imprinting technique was used to create species-specific functionalities like carboxylic acid (-COOH) on a polymer surface. MIPs offer several advantages, including large surface area, targeted functionalities for high reactivity, and the ability to minimise nanoparticles from leaking into the surrounding environment when MIP-based adsorbents are being handled. To further comprehend the behaviour of adsorbents and the adsorption process, kinetics, thermodynamics, and isotherm models were explored. The second part of the work involved synthesizing the MIPs for efficient and selective removal of pharmaceuticals from specific groups. All target compounds were employed as multiple templates in a bulk polymerization process carried out at 70 °C to synthesize MIPs. Additional reagents utilized in the synthesis included toluene as a porogenic solvent, ethylene glycol dimethacrylate as cross-linker, 1,1'-azobis-(cyclohexane carbonitrile) as an initiator and 2- vinyl pyridine as functional monomer, respectively. The synthesis of a non-imprinted polymer (NIP) was conducted without templates, using reaction conditions similar to those of MIP. Furthermore, following the synthesis, the polymers were characterized using X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry, Fourier transform infrared spectroscopy, and scanning electron microscopy. Liquid chromatography-mass spectrometry (LC-MS) was successfully used to develop an analytical method for detection and quantification of the target pharmaceuticals. The method yielded quantification limits of 0.42 to 0.75 mg L-1 and detection limits of 0.14 to 0.25 mg L-1 for the target pharmaceuticals. The synthesized polymer attained maximum matrix-matched adsorption capacities of 3.89, 4.97 and 3.40 mg g-1 for sulfamethoxazole, nevirapine and ibuprofen, respectively within 10 minutes. Competitive adsorption of the target pharmaceuticals demonstrated a link between adsorption and the pharmaceuticals pKa, log Kow, and molecular size. Studies on batch adsorption and kinetics revealed that the binding of pharmaceuticals to the MIP particles suited the pseudo-second order kinetics, leading to various interactions through chemisorption. The data also fitted well in Langmuir isotherm which meant that the target pharmaceuticals adsorption occurred on the homogeneous binding sites of the MIP. Furthermore, the thermodynamic data demonstrated the adsorption process's endothermic and spontaneous nature. Notably, the synthesized MIP was highly selective and its application in environmental studies led to the development of a less expensive analytical method. Moreover, the MIP particles that had been generated were recovered to be reusable up to five cycles with removal efficiency >90%. The third part involved incorporating silver nanoparticles (AgNPs) into MIPs using ibuprofen, nevirapine, and sulfamethoxazole as templates. In this part, starch (St) and macadamia nutshells (MCD) were employed in the synthesis of AgNPs as reducing and stabilizing agents. Following that, each of these AgNPs was incorporated with MIP, and the most effective combination was identified through comparison. The synthesized adsorbents were further optimized for the adsorptive removal of selected target pharmaceuticals. The % removal efficiencies were greater than 70%, indicating that the adsorbents are suitable for use in water treatment processes. The material's adsorption mechanisms and performance were examined through the application of various kinetics and isotherm models. Both the St and MCD-AgNPs experimental data fit to Freundlich and Langmuir adsorption isotherms. However, based on the somewhat higher correlation coefficients, the Langmuir isotherm model provided a better fit. The St/MCD nanoMIPs best suited the Freundlich model, indicating that the adsorption occurred on the multilayer heterogeneous surface. Further, both the St/MCD nanoMIP adsorbents underwent spontaneous, endothermic adsorption, as demonstrated by the thermodynamic data, whereas the behaviour of the kinetics was effectively anticipated by pseudo-second order model, which suggested adsorption through chemisorption. Accordingly, large internal surface area, greater loading capacity, thermal stability, and reusability were among the advantageous properties of the nanoMIPs adsorbent materials. Moreover, both adsorbents showed improved qualities and were highly selective and effective in removing the selected pharmaceuticals in wastewater. As a result, during the course of five adsorption/desorption cycles, the St/MCD nanoMIPs show a removal efficiency of more than 90%. As a result, they demonstrated proficiency in efficient application. The fourth part involved the incorporation of MIP with Platanus acerifolia and Moringa oleifera silver nanoparticles. Using plants to synthesize AgNPs is a more cost-effective and lowmaintenance method; in contrast, using other organisms requires a particular medium and a specific amount of time. Therefore, the leaves of both the platanus acerifolia (PL) and moringa oleifera (MO) served as stabilizing and reducing agents during the synthesis of AgNPs. Each optimized parameter that could influence the adsorption potential, such as temperature, adsorbate concentration, pH, adsorbent dose, and contact time, was examined in relation to the removal effectiveness of the MO/PL nanoMIP adsorbents. These evaluated parameters were optimum at pH 7, concentration of 0.2 mg/L and contact time of 10 minutes for both MO and PL-nanoMIPs, mass dosage of 30 mg and 20 mg, and temperature of 40 and 30 °C for MO and PL-nanoMIP, respectively. Further, the maximum removal efficiencies obtained at these optimum conditions were >97% for both MO-nanoMIP and PL-nanoMIP. The adsorption experimental data for both MO/PL-AgNPs and MO/PL-nanoMIPs nano-adsorbents fitted with the linear Langmuir model which suggests that the binding took place on the homogenous monolayer surface. Additionally, compared to MO/PL-AgNPs, the MO/PL-nanoMIPs adsorption capacities for the target pharmaceuticals were higher, suggesting that the nanoMIPs larger surface areas contribute to their enhanced adsorption capacity. The linear pseudo-second order kinetic model best fitted on MO/PL-nanoMIPs which implied adsorption through chemisorption, whereas the thermodynamic data demonstrated that the adsorption process was endothermic and spontaneous. Moreover, the values of ΔH° for the MO/AgNPs were less than 40 kJ/mol and more than 40 kJ/mol for the MO/PL-nanoMIPs. This therefore confirmed that the MO/AgNPs was dominated by physical adsorption whereas the MP/PL-nanoMIPs was dominated by chemical adsorption. The MO/PL-nanoMIPs confirmed the high efficiency for the removal of target pharmaceuticals in wastewater. Upon recycling the adsorbents for five cycles, it was noted that the MO-nanoMIP adsorbent was effective continued to remove 86.7- 88.8% and 97-98% for PL-nanoMIP even in the fifth cycle. Indeed, the removal of sulfamethoxazole, nevirapine, and ibuprofen by nanoMIP adsorbents has demonstrated the importance of the surface area, structural stability, pore size and the electrostatic interactions brought about by the charges on the nanoMIPs surface. Consequently, among the investigated nanoMIP adsorbents, PL-nanoMIP demonstrated strong adsorption capacities for the targeted pharmaceuticals due to it large surface area and narrow size distribution as compared to the other nanoMIP adsorbents. The usability of plant leaves as a reducing and capping agent for nanoparticles as well as the recycling of nanoMIPs has the potential to transform waste that is no longer useful into valuable pollutants adsorbents. This would solve the problem of waste disposal and have beneficial impacts on the environment pollution and the economy. Notably, the nanoMIPs synthesized in this study are highly selective, reusable adsorbents that are cost effective and environmentally friendly. In contrast, as a substitute for more costly synthetic materials, these nanoMIPs are a promising material for the removal of different classes of pharmaceuticals in wastewater treatment plants and they can possibly be applied on a large scale.
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.
The alkaloids of the Amaryllidaceae : the isolation and structures of two new alkaloids from Haemanthus natalensis and Nerine krigeii and contributions to the chemistry of coccinine : the absolute configuration of alkaloids based on the 5:10b-Ethanophenanthridine nucleus.
(1960) Jeffs, P. W.; Warren, Frank Louis.
No abstract available.
The alkaloids of the Amaryllidaceae : the isolation of the alkaloids of Boophone disticha Herb., the structure of buphanitine and contributions to the chemistry of buphanidrine.
(1959) Goosen, Andre.
No abstract available.
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.
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.
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.
The analysis of organometallic compounds using SFC-ICPMS.
(1994) Blake, Earl.; Raynor, Mark W.; Cornell, David H.; Ross, Graham.
Supercritical fluid chromatography has recently been coupled to an ICPMS detector. The method has been shown to be suitable for the speciation and analysis of organometallic compounds at trace levels. This study has attempted to further the research initiated by other groups in this field by developing a new interface for coupling these two instruments. The new interface makes use of a modified join between the nebuliser and the torch in the ICP unit. The effect of the mobile phase on the plasma with time has been investigated and little spectral background interference has been observed. The chromatographic conditions were optimised using a flame ionisation detector and a series of tin, arsenic, iron, and mercury compounds were analysed using SFC-ICPMS. Mter focusing the ICP-MS on the element of interest, each compound was evaluated in terms of the change in peak intensity with change in concentration and the theoretical detection limits were compared to the practical detection limit. The restrictor temperature was determined using a rough calibration procedure with bench top experiments. The effect of the restrictor temperature on the peak intensity of each compound was then studied. All results were plotted and a theory for the observed trends and observations is proposed. The results obtained and the interface used have been compared to the results and interfaces of other groups and differences have been explained. Attempts to extract relevant compounds from topsoil using supercritical fluid extraction were made. Finally, sediment samples were collected from relevant points in Durban Bay and an attempt was made to extract these samples using supercritical fluid extraction. The extracted samples were analysed using SFC-ICPMS although little success was obtained. Reasons for the failure of this method on the real samples have been proposed. In the concluding section of this study SFC~ICPMS has been evaluated in terms of its future applicability and use as a viable analytical method.
An analysis of Sappi Saiccor's effluent streams.
(2003) Ismail, Fathima.; Marsh, Jeremy J.; Mulholland, Dulcie Aca.
SAPPI SAICCOR is a pulp and paper mill situated in Umkomaas, 50 kms south of the port of Durban in South Africa. It was the first company to produce high grade dissolving pulp from the Eucalyptus tree and is currently the world's largest manufacturer of chemical cellulose. SAICCOR is one of the few pulp and paper mills that produces its dissolving pulp by the acid sulphite process using both calcium and magnesium as bases in the form of calcium bisulphite and magnesium bisulphite. Four streams of effluent are produced during their process, namely, the calcium spent liquor, the magnesium pulp condensate and two streams from the bleaching stages. An acid hydrolysis of the effluent streams yielded a range of organic compounds such as lignans and lignin - type precursors as well as a triterpenoid. Column chromatography and thin layer chromatography, using various ratios of hexane, dichloromethane, ethyl acetate and methanol, were carried out in isolating and purifying the compounds. The structures of these compounds were determined using NMR spectroscopic and mass spectrometric techniques.
Analysis of skin preparations.
(2015) Navondo, Funani Thelma.; Martincigh, Bice Susan.
Abstract available in PDF file.
Analysis of targeted pharmaceuticals and metabolites at a wastewater treatment plant in KwaZulu-Natal, South Africa.
(2022) Inarmal, Nikitha.; Moodley, Brenda.
Globally, surface water bodies are shown to be severely contaminated by chemical compounds as a result of human activity. Some of these compounds are inclusive of pharmaceuticals and their metabolites which are classified as emerging contaminants (ECs). A major contributor to this pollution event is treated wastewater effluent. This is an area of growing concern, particularly for emerging economies, due to an increase in demand for clean and potable water arising from rapid urbanisation and significant population growth. In South Africa, there is limited information outlining concentrations of various pharmaceuticals in treated wastewater effluent and surface water bodies and there is currently no legislation indicating maximum concentrations to be allowed in wastewater effluent. This research study aimed to identify and quantify concentrations of selected pharmaceuticals and metabolites present at various stages within the Wastewater Treatment Plant (WWTP). Additionally, the study aimed to determine seasonal pharmaceutical trends in relation to SARS-CoV-2 (COVID-19) and influenza infections, removal efficiencies and undertake an environmental risk assessment (ERA). The pharmaceuticals that were analysed included metformin, caffeine, sulfamethoxazole hydroxylamine, sulfamethoxazole, nevirapine, prednisolone, valsartan, rifampicin, 17α ethinylestradiol (EE2) and ivermectin, all of which being pharmaceuticals that are commonly prescribed for the treatment of medical conditions that are prevalent in South Africa and for the treatment and prevention of COVID-19. Analyte concentrations were assessed in wastewater samples taken from the inlet, balancing tank, secondary effluent, and maturation river over three sampling seasons. Analytes were extracted using a solid phase extraction (SPE) method and extracts were analysed using liquid chromatography – mass spectrometry (LC – MS). Method percentage recoveries ranged from 73.53 – 100.70% while limit of detection (LOD) and limit of quantification (LOQ) overall ranged from 0.0330 – 0.886 mg L-1 and 0.0990 – 2.68 mg L-1, respectively. Analyte concentrations quantified in inlet samples ranged from 0.007587 – 1.243 mg L-1 while balancing tank concentrations ranged from 0.007599 – 1.042 mg L-1. Secondary effluent and maturation river concentrations ranged from 0.0005244 – 0.9483 mg L-1 and 0.0002507 – 0.9286 mg L-1, respectively. Non-detection of certain analytes in some samples could imply the possibility that the pharmaceutical converted into transformation products and thus evaded detection. Influent pharmaceutical concentrations showed distinct seasonal variation, and this was statistically shown using a one-way ANOVA analysis. P-values were recorded as < 0.05 for caffeine, sulfamethoxazole hydroxylamine, sulfamethoxazole, EE2 and ivermectin, thus implying that significant differences were observed between seasonal levels of pharmaceutical compounds and in relation to the COVID-19 and influenza infection peaks. Analyte removal efficiencies based on the plant treatment processes ranged from 7.70 – > 99.99 %. The ERA performed indicated ratios within the range of 0.0863 and 10.5x 108, which is of significant concern as values greater than 1 would severely impact the health of aquatic organisms and ecosystems within the receiving surface water body.
Analytical and biochemical studies of selected seaweeds obtained from the eastern coast of South Africa`s Indian Ocean in KwaZulu-Natal.
(2015) Magura, Judie.; Jonnalagadda, Sreekantha Babu.; Moodley, Roshila.
Abstract available in PDF file.

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