Philosophiae Doctor - PhD (Chemistry)

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The synthesis of Ventiloquinones J and F
(University of Western Cape, 2002) van Eeden, Nestor; Green, lvan R
In chapter 2 the synthesis of ventiloquinone J is described, starting from vanillin, the key intermediate cis-3,4-dihydro-5,7-dimethoxy-10- methoxymethyleneoxy-1,3-dimethyl-1H-naphtho[2.3-c]pyran-6,9-dione was prepared in 19 steps by using inter alia Diels-Alder adduct formation, mild acetylation, oxymercuration and finally converted to ventiloquinone J in an overall yield of 0.5%. Protection of the C-10 position of the ventiloquinone J precursor was eventually effectively provided by the methoxymethyleneoxy (MOM) group which upon removal with acid treatment provided the hydroxy group in this position unambiguously in the final product. Attempts to effect this same protection using a benzyl group proved ineffective due to the extreme difficulty in separation of the cyclised stereoisomers; cis and trans 10- benzyloxy-3,4-dihydro -5,6,7,9-tetramethoxy-1,3-dimethyl-lH-naphthol2,3- c]pyrans In addition decomposition of the molecule occurred during the subsequent oxidation step affording low yields of the quinones and finally the unwanted isomer viz., the trans 1,3-dimethylpyran was the major product of the cyclisation. Protection of C-10 of the precursor to ventiloquinone J usingthe 2'-methoxyethoxymethyleneoxy (MEM) group proved problematic in that it was sensitive to the acidity of the silica gel stationary phase used for column chromatography, and that cyclisation of the intermediate alcohol, 2-(l'- hydroxyethyl)-4,5,6,8-tetramethoxy-l-(2'-methoxyethoxymethyleneoxy)-3- prop-2'-enylnaphthalene, Ied to a mixture of the corresponding cis and trans l,3-dimethyl pyrans in which the MEM protecting group had been lost in a combined crude yield of only 25%o. In addition all the MEM compounds showed considerable decomposition on standing. The synthesis of one of the initial target molecules, 6-hydroxy-7- methoxyeleutherin was not completed due to premature displacement of the required C-5 protecting groups employed in the naphthalene precursors upon acylations under Lewis acid Ventiloquinone F was successfully synthesised from 3,4,6- trimethoxybenzaldehyde in 12 steps making use of a Stobbe Condensation with methyl succinate to construct the desired oxygenated naphthalene nucleus. An overall yield of 9.5oh was obtained and its stereoisomer, isoventiloquinone F was also obtained in an overall yield of 10%.trans- 5-benzyloxy-3,4-dihydro-6,7,9'ttimethoxy-1,3-dimethyl-1I/- naphtho[2,3-c]pyran led to the formation of four pyranquinones which were successfully separated and purified. These were cis- and trans-5-benzyloxy- 3,4-dihydro-7-methoxy-1,3-dimethyl-lF/-naphthol2,3-clpytarr-6,9-diones as well as the corresponding cis and trans ortho quinone isomers.
An investigation into the synthesis, characterisation and some applications of novel metal-containing polymers and dendrimers of transition metals
(University of the Western Cape, 2003) Smith, Gregory Stuart; Mapolie, S.F.; Dept. of Chemistry; Faculty of Science
metal-containing complexes, that exhibit enhanced chemical and physical properties. This thesis describes the synthesis of new metal-containing linear polymers and dendritic molecules. Chapter 1 presents an overview of the field of metal-containing polymers, with particular attention to the synthesis of polymers via condensation polymerisation. This review includes the various types of metal-containing condensation polymers and the applications of these materials, where available. This discussion is followed by a brief summary of metal-containing dendrimers, which includes a concise description of their structure and applications in general. There are two routes to preparing metal-containing polymers. Chapter 2 describes the synthesis of three bifunctional organometallic monomers, of the general type [M]-O-{2,6-(CH2OH)2-4-CH3-C6H2}, where [M] represents the various metal-containing moieties, (η5-C5H5)(CO)2 Fe(CH2)3 (25), (η5-C5H4-CH2CH2CH2-)Re(CO)3 (26) and Fpdendr (27). These monomers were prepared using 2,6-bis(hydroxymethyl)-p-cresol as the key reagent. The monomers were used in classical polycondensation reactions with terephthaloyl chloride using ambient temperature solution techniques. This yielded new low molecular weight oligomeric polyesters, that were characterised using FTIR and 1HNMR spectroscopy, differential scanning calorimetry, thermogravimetric analysis and sizeexclusion chromatography. In Chapter 3, an alternate route to metal-containing polymers is described. In this case, bifunctional organic monomers were polymerised to give preformed organic polymers. Two types of organic polymers were prepared, viz. polyesters (with pendant vinyl moieties) and polyimines (with α-diimine units along the polymer backbone). Functionalisation of these preformed organic polymers with various metal sources was attempted. Hydrozirconation reactions of the vinyl polyesters with Schwartz’s reagent, Cp2Zr(H)Cl, were attempted and were largely unsuccessful. Competing reactions with the ester functionality prevailed, preventing the desired reaction. Reaction of the polyimines with PdCl2(COD) yielded insoluble, intractable metal-containing oligomers. Partial characterisation of the complexes is described. The synthesis of new poly(propylene imine) iminopyridyl metallodendrimers is described in Chapter 4. Schiff-base condensation reaction of the commercially available DAB dendrimers with 2-pyridinecarboxaldehyde, gave the dendrimers 51, 52, and 53, with four, eight and sixteen pyridylimine functionalities respectively on the periphery. Successful complexation reactions with PdCl2(COD), PtCl2(COD) and CuCl2 produced the corresponding metal-containing dendrimers, with either PdCl2 (54, 55, 56), PtCl2 (57) or CuCl2 (58) moieties bound on the periphery. The metallodendrimers were insoluble in the more common organic solvents, and were characterised by IR and 1H-NMR spectroscopy and microanalysis where possible. Dendrimers with salicylaldiminato ligands on the periphery were prepared by reacting the DAB dendrimers with salicylaldehyde. These ligands were reacted with various metal acetates in an attempt to prepare new metalcontaining salicylaldimine dendrimers. This work yielded either paramagnetic metal complexes or insoluble, intractable compounds. Chapter 5 describes the applications of the catalyst precursors (54, 55, 56, 57, 58), discussed in Chapter 4, in the polymerisation of ethylene and the use of complexes 54 and 55 as Heck cross-coupling catalyst precursors. The complexes all showed catalytic activity toward ethylene polymerisation. A discussion of their activity, the polyethylene molecular weight and microstructure is presented in this chapter. The precursors 54 and 55 are also effective catalysts in the Heck reactions, coupling iodobenzene with methyl acrylate, styrene and 1-octene in high conversions.
Thiolato schiff base complexes of nickel and palladium as mesogens and molecular wires
(University of the Western Cape, 2003) Moutloali, R.M; Darkwa, J
Thermal analysis data of compounds A, C, F and I established that they were nonmesogenic while E and G were found to be mesogenic. The lack of mesogenic behaviour of A could be attributed to hydrogen bonding. The non-mesogenic behaviour of C and F is due to reduced molecular anisotropy as a result of large lateral substituents. Complexes I decomposed at high temperatures and before melting and hence no liquid crystalline behaviour was found. It is likely that the high decomposition temperature is the result of increased molecular interactions. We found that removing the phosphine ligands and increasing molecular length induced liquid crystalline behaviour in complexes E. The more planar complexes G were also found to be liquid crystalline
The development of inorganic and organic/inorganic membranes for DMFC application
(University of the Western Cape, 2004) Mokrani, Touhami; Linkov, V.M; Dept. of Chemistry; Faculty of Science
A fuel cell is an energy device that converts chemical energy to electrical energy. Low temperature fuel cells, namely the hydrogen fuel cell and the direct methanol fuel cell are preferred amongst other fuel cell types for stationary and vehicular applications, due to their small size and their low operating temperature. The direct methanol fuel cell has several advantages over the hydrogen fuel cell including ease of transport and storage since methanol is a liquid. Since methanol is used directly in the cell there is no need for a reforming process, which results in a less complicated system. However, direct methanol fuel cell are in their infancy and many problems need to be overcome before reaching commercialization. The direct methanol fuel cell has several disadvantages, namely, the sluggish methanol oxidation reaction, the high cost of state-of-the-art proton exchange membranes, the high methanol permeability from anode to cathode and the dependence on the conductivity on membrane water content, which limits their use to temperatures below the boiling point of water, while the need is to work at high temperatures. Attempts to overcome the disadvantages of the state-of-the-art membrane were made in this study, including the development on novel proton exchange membranes and also the modification of existing state-of-the-art membranes.
The catalytic membrane reactor for the conversion of methane to methanol and formaldehyde under mild conditions
(University of the Western Cape, 2005) Modibedi, Remegia Mmalewane; Linkov, Vladimir M; Dept. of Chemistry; Faculty of Science
This thesis described the development of new catalytic system for the conversion of natural gas (methane) to liquid products such as methanol and formaldehyde. This technology can allow the exploitation of small and medium size gas fields without the need to build an expensive gas to liquid plants or long pipelines. The technology is based on a concept of non-separating membrane reactor where an inorganic membrane paper serves as a catalyst support through which a reaction mixture is flowing under mild conditions and short residence times.
Preparation and physico-chemical properties of nickel nanostructured materials deposited in etched ion-track membrane
(University of the Western Cape, 2005) Nkosi, Mlungisi Moses; Linkov, V.M.; Nechaev, A.; Theron, C.C.; Dept. of Chemistry; Faculty of Science
The development of finely dispersed powders and superfine-grained materials intended for application in various areas of science and engineering is one of the challenges facing modern nanotechnology. Thus, specific fundamental and applied research was required in order to consolidate advancement made in preparing nano- and submicron crystalline composite materials. Useful templates for electrochemical deposition of nanowires include porous alumina films formed by anodic oxidation of aluminium, nuclear track-etched porous membranes, nanochannel array-glass and mesoporous channel hosts. The properties of the nanowires are directly related to the properties of the nanoporous templates such as, the relative pore orientations in the assembly, the pore size distribution, and the surface roughness of the pores. The template synthesis method, based on the use of porous polymeric and inorganic matrixes, is now actively used for synthesis of such composite materials. The method allows the chemical and/or electrochemical synthesis of nano- and microstructured tubes and wires consisting of conducting polymers, metals and semiconductors.In this study various technological challenges relating to template synthesis and development of nickel nano- and microstructures on adequately strong and durable substrates were investigated. The two methods used were the electrochemical and chemical deposition. “Hard nickel” bath solution was used for optimal nickel deposition. This optimization included investigating variables such as the template structure, type of electrolyte and form of electrolytic deposition. Scanning Electron Microscopy was used to investigate the structures of template matrixes and the resultant materials. The cyclic voltammetry method was applied for the analysis of electrochemical properties and hydrogen evaluation reaction of nano- and microstructured nickel based electrodes. The activity of composite nano- and microstructured materials in various configurations resulting from pore filling of template matrices by nickel was explored. Studies of the physical structure and chemical properties of the nanostructured materials included investigating the necessary parameters of template matrices. The optimum conditions of synthesis, which allowed development of materials with the highest catalytic activity, were determined. The effect of the template structure on microcrystallinity of the catalyst particles was established using the XRD method. Different new types of non-commercial asymmetric ion track membranes has been tested for nanostructure preparation. The catalytic activity of the new developed nanomaterials is higher as compared to materials using commercial templates. The procedures to modify the newly developed nickel catalyst with Pt, Pd and Pt-Pd alloy have been developed. The Pt and Pt-Pd alloy containing catalyst showed the best performance in water electrolysis. In this work, the promising role for specific application of the new materials in hydrogen economy has been demonstrated.
Synthesis and characterization of nanofluids for cooling applications
(University of the Western Cape, 2006) Botha, Subelia Senara; Linkov, V.M.; Bladergroen, B.J.; Dept. of Chemistry; Faculty of Science
Low thermal conductivity is a primary limitation in the development of energy-efficient heat transfer fluids that are required in numerous industrial sectors. Recently submicron and high aspect ratio particles (nanoparticles and nanotubes) were introduced into the heat transfer fluids to enhance the thermal conductivity of the resulting nanofluids. The aim of this project was to investigate the physico-chemical properties of nanofluids synthesized using submicron and high aspect ratio particles suspended in heat transfer fluids.
Evaluation of the leachate chemistry and contaminants attenuation in acid mine drainage by fly ash and its derivatives
(University of the Western Cape, 2006) Gitari, Wilson Mugera; Key, David; Dept. of Chemistry; Faculty of Science
The mining industry in South Africa has a huge potential to impact negatively on the environment. Negative impacts include generation of reactive tailings and acid mine drainage (AMD). AMD is highly acidic (pH 2-4), sulphate-rich and frequently carries a heavy metal burden. South Africa uses more than 100 million tonnes of low grade bituminous coal annually to produce cheap electricity. The associated mining operations result in millions of tonnes of polluted water and in turn coal burning power stations produce vast amounts of waste ash such as fly ash. The highly soluble CaO occurring as sub-micron fragments on the fly ash particles is highly reactive and can be utilized in the neutralization of acid mine drainage. Acid mine drainage (AMD) was reacted with two different South African fly ashes in a batch setup in an attempt to evaluate their neutralization and inorganic contaminants removal capacity. The concentrations of major constituents in the AMD were found to determine the final pH attained in the reaction mixture and the reaction time of breakthrough to circum-neutral and alkaline pH. Efficiency of elemental removal in the AMD by the FA was directly linked to the amount of FA in the reaction mixture and to the final pH attained. Most elements attained ≈ 100 % removal only when the pH of minimum solubility of their hydroxides was achieved. In the second part of the study, Acid mine drainage (AMD) was reacted with coal fly ash in a 24 hour equilibration time using 1:3 and 1:1.5 FA: AMD ratios by weight to produce neutral and alkaline process waters. The capacity of the fly ash to remove the major inorganic contaminants from AMD was examined with time. The geochemical computer software PHREEQC and WATEQ4 database were used for geochemical modeling of the process water chemistry at selected reaction times. The collected solid residues were analyzed by X-ray diffraction, scanning electron microscopy (SEM) and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX). At both ratios the reaction mixture was at saturation or oversaturated with alunite, basaluminite, jurbanite, boehmite, gibbsite, diaspore, gypsum, barite, K, Na-jarosites, ettringite, amorphous Fe (OH)3 and goethite at specific contact times. The precipitation of the many inorganic contaminants was established in terms of the mineral phases at saturation or over-saturation. Sequential extraction revealed the amorphous fraction to be the most important in retention of the major and minor inorganic contaminants at pH > 6.32 which implies that the concentration of total Fe and Al in the AMD being treated has a direct effect on the clean-up efficiency of the process. In the third part of the study, a column leaching of the solid residues (SR) blended with varying amounts of fly ash (5 %, 25 %, 40 %) and 6 % Ordinary Portland Cement (OPC) was carried out to assess the contaminant attenuation with time. The columns were drained with synthetic acid mine drainage (SAMD) over a period of 165 days. In addition the solid residues were modified with 1-6% OPC and their strength development monitored over a period of 365 days. The column solid cores were observed to acidify in a stepwise fashion, exhibiting three buffer zones. The SR alone and SR blended with fly ash exhibited strong buffering capacity at pH (7.5-9) for an extended period of time (97-110 days). Encapsulation of solid residue particles by the calcium silicate hydrate gels (CSH) in OPC blended solid residues obscured the appearance of the sustained buffering at pH 7-9.5. The fly ash and OPC blend solid residues exhibited decontamination efficiencies of (82-99 %) for Al, Fe, Mn and SO4 2- over the study period. However the OPC blend SR exhibited high attenuation efficiency even as the pH dropped to below 4. SR + 6 % OPC core was observed to be the most efficient interms of retention of highly mobile elements such as B and Mo. pH was observed to be the main determining factor in contaminants attenuation. Geochemical modeling results revealed that pH and SO42- concentrations in the leachate had a significant impact on the mineral phases controlling Fe and Al concentration in the leachates. In the SR + 6 % OPC solid cores, EDX analysis revealed that CSH gels and calcium aluminate hydrate gels were being precipitated. These gels were either incorporating Fe, Mg, Mn in their matrix or encapsulating the solid residue particles that were rich in these elements. Sequential extractions of the leached solid cores revealed the amorphous fraction to be the most important in retention of the major contaminants and were most enhanced in the OPC blend solid residues. The OPC blend solid residue slurries developed unconfined compressive strength (UCS) (2-3 Mpa) comparable to paste formulated from sulphidic rich mine tailings confirming that the solid residues can be used for backfilling. Therefore the solid residues (SR) can successively be applied for a dual purpose in mined out areas namely, to remediate acid mine drainage waters and also provide support for the overburden. Keywords: Acid Mine Drainage; Fly Ash; Neutralization; Sulphates; Metal ions; Solid Residues (SR); Column Leaching; Geochemical Modeling; Sequential Extraction; Buffering.
Preparation and characterization of highly active nano pt/c electrocatalyst for proton exchange membrane fuel cell
(University of the Western Cape, 2006) Ying, Qiling; Petrik, Leslie; Nechaev, A.N.; Dept. of Chemistry; Faculty of Science
Catalysts play an essential role in nearly every chemical production process. Platinum supported on high surface area carbon substrates (Pt/C) is one of the promising candidates as an electrocatalyst in low temperature polymer electrolyte fuel cells. Developing the activity of the Pt/C catalyst with narrow Pt particle size distribution and good dispersion has been a main concern in current research. In this study, the main objective was the development and characterization of inexpensive and effective nanophase Pt/C electrocatalysts. A set of modified Pt/C electrocatalysts with high electrochemical activity and low loading of noble metal was prepared by the impregnation-reduction method in this research. The four home-made catalysts synthesized by different treatments conditions were characterized by several techniques such as EDS, TEM, XRD, AAS, TGA, BET and CV.Pt electrocatalysts supported on acid treatment Vulcan XC-72 electrocatalysts were produced successfully. The results showed that Pt particle sizes of Pt/C (PrOH)x catalysts between 2.45 and 2.81nm were obtained with homogeneous dispersion, which were more uniform than the commercial Pt/C (JM) catalyst. In the electrochemical activity tests, ORR was confirmed as a structure-sensitive reaction. The Pt/C (PrOH/pH2.5) showed promising results during chemically-active surface area investigation, which compared well with that of the commercial standard Johnson Matthey Pt/C catalyst. The active surface area of Pt/C (PrOH/pH2.5) at 17.98m2/g, was higher than that of the commercial catalyst (17.22 m2/g ) under the conditions applied. In a CV electrochemical activity test of Pt/C catalysts using a Fe2+/Fe3+ mediator system study, Pt/C (PrOH/pH2.5) (67mA/cm2) also showed promise as a catalyst as the current density is comparable to that of the commercial Pt/C (JM) (62mA/cm2).A remarkable achievement was attained in this study: the electrocatalyst Pt supported on CNTs was synthesized effectively. This method resulted in the smallest Pt particle size 2.15nm. In the electrochemically-active surface area study, the Pt/CNT exhibited a significantly greater active surface area (27.03 m2/g) and higher current density (100 mA/cm2) in the Fe2+/Fe3+ electrochemical mediator system than the other home-made Pt/C catalysts, as well as being significantly higher than the commercial Pt/C (JM) catalysts. Pt/CNT catalyst produced the best electrochemical activities in both H2SO4 and K4[Fe(CN)6] electrolytes. As a result of the characteristics of Pt/CNT, it can be deduced that the Pt/CNT is the best electrocatalyst prepared in this study and has great potential for use in fuel cell applications.
Development of polyaniline nanotube electrocatalysts and sesor devices for phenolic-pollutants
(University of the Western Cape, 2007) Klink, Michael John; Iwuoha, Emmanuel; Baker, P.G.L.; Dept. of Chemistry; Faculty of Science
As a source of life, water is one of the most precious commodities for all living organisms. Water resources are reported to be declining in numbers or the amount of water present and the existing onses are being polluted as a result of negligent human activities and intense industrialisation. thus, there is an ever increasing demand to monitor the quality of portable and waste water in our surroundings in real time. This study has been directed towards the prepaparation of polyanilines.
The synthesis and evaluation of potential anti-Mycobacterium tuberculosis and apoptotic agents
(University of the Western Cape, 2007) Sagar, Sunil.; Green, Ivan R.; Ameer, F.; Dept. of Chemistry; Faculty of Science
Tuberculosis (TB) and Cancer are among the most devastating and therapeutically challenging diseases that need to be addressed in South Africa today. The development of muti-drug resistance in TB causing bacteria, Mycobacterium tuberculosis and cancerous cells has prompted the search for effective novel compounds. The present study focused on the synthesis and the evaluation of different analogues of diospyrin, a proven anti-TB and anti-cancer agent.
Development of new dendritic ligands for copper mediated Atom Transfer Radical Polymerization (ATRP) of methyl methacrylate
(University of the Western Cape, 2007) Moni, Lucky; Mapolie, S.F.; Faculty of Science
A variety of nitrogen based dendritic ligands have been synthesized and used in copper mediated Atom Transfer Radical Polymerization (ATRP) of MMA. These ligands were derived from the commercially available Generation 1 polypropyleneimine dendrimer DAB-(NH2)4. The first set of ligands was synthesized by reacting DAB-(NH2)4 with aromatic aldehydes such as 2-pyridinecarboxyaldhyde and 4-t-butyl benzaldehyde to form imine functionalized dendrimers. Analogous secondary amine functionalized dendrimers were also synthesized by reducing the abovementioned imine functionalized dendrimers using sodium borohydride. The ligands produced were characterized by 13C / 1H NMR, and infra-red spectroscopy as well as elemental analysis to confirm its structure. The ligands were then used in copper mediated ATRP of MMA. The resulting polymer solutions were analyzed by Gas Chromatography (GC) to monitor the monomer conversion while the isolated polymers were analyzed by gel permeation chromatography (GPC) for molecular weight determination. Results showed that the primary and secondary amine and imine dendritic ligands were not efficient in promoting ATRP reactions. This led to the modification of DAB-(NH2)4 using methyl methacrylate to replace the peripheral amino groups of the DAB-(NH2)4 with tertiary amine groups. A second generation tertiary amine dendrimer was also synthesized in a similar fashion. The ligands obtained were then characterized using 13C and 1H NMR spectroscopy. The tertiary amine dendrimers were used in copper mediated ATRP of MMA. The polymerization medium was analyzed over time using GC to monitor monomer conversion while GPC was used for molecular weight determination of the resulting polymers. The results obtained using the methyl methacrylate modified ligands indicated that in the case of MMA polymerization, these ligands essentially conformed to the requirements of a good ATRP system. However in the preliminary studies, when employed in copper mediated ATRP of styrene, these ligands did not perform well. Further investigation is needed to improve the performance of these ligands in styrene polymerization under ATRP conditions.
Mercaptobenzothiazole-on-Gold Biosensor Systems for Organophosphate and Carbamate Pesticide Compounds
(University of the Western Cape, 2007) Somerse, Vernon Sydwill; Iwuoha, Emmanuel; Baker, P.G.L.; Dept. of Chemistry; Faculty of Science
This study firstly reports the development, characterisation, and application of thick-film acetylcholinesterase (AChE) biosensors based on a gold electrode modified with a mercaptobenzothiazole (MBT) self-assembled monolayer and either poly(omethoxyaniline) (POMA) or poly(2,5-dimethoxyaniline) (PDMA) in the presence of polystyrene(4-sulphonic acid) (PSSA). The Au/MBT/POMA-PSSA/AChE and Au/MBT/PDMA-PSSA/AChE biosensors were then applied to successfully detect standard organophosphorous and carbamate pesticides in a 0.1 M phosphate buffer, 0.1 M KCl (pH 7.2) solution. Secondly, it reports the construction of the Au/MBT/PANI/AChE/PVAc thick-film biosensor for the determination of certain organophosphate and carbamate pesticide solutions in selected aqueous organic solvent solutions.
Nanostructured polypyrrole impedimetric sensors for anthropogenic organic pollutants
(University of the Western Cape, 2007) Akinyeye, Richard Odunayo; Baker, Priscilla; Iwuoha, Emmanuel; Dept. of Chemistry; Faculty of Science
Polypyrrole composites of polyaromatic hydrocarbon sulphonic acids (β–naphthalene sulphonic acid (NSA) and 1, 2-napthaquinone-4-sulphonic acid (NQS)), as well as those of transition metal oxides (tungsten (VI) oxide (WO3) and zirconium (IV) oxide (ZrO2)), were prepared and characterised for use as electrocatalytic sensors. The polymerization of pyrrole in β–naphthalene sulphonic acid (NSA) gave rise to nanotubules, nanomicelles or nanosheets polypyrrole (PPy) morphologies depending on the amount of NSA in the polymer and the polymerisation temperature. Scanning electron microscopy (SEM) measurements showed that the diameters of the nanostructured polypyrrole-β-naphthalene sulphonic acid (PPyNSA) composites were 150-3000 nm for the tubules, 100-150 nm for the micelles and 20 nm for the sheets. A red shift in the UV-Vis absorption spectra of PPy was observed for PPyNSA which is indicative of the involvement of bulky β-naphthalene sulphonate ion in the polymerization process. The UV-Vis also showed the existence of polaron and bipolaron in the polymer which may be responsible for the improved solubility of PPyNSA compared to PPy. All the characteristic IR bands of polypyrrole were observed in the FTIR spectra of PPyNSA, with slight variation in the absolute values. However, the absence of N–H stretching at 3400 cm-1 and 1450 cm-1 usually associated with neutral polypyrrole confirms that the polymer is not in the aromatic state but in the excited polaron and bipolaron defect state. Electrochemical analysis of PPyNSA reveals two redox couples: a/a′ - partly oxidized polypyrrole-naphthalene sulphonate radical cation/neutral polypyrrole naphthalene sulphonate; b/b′ - fully oxidized naphthalene sulphonate radical cation/partly reduced polypyrrole-naphthalene sulphonate radical anion. The corresponding formal potentials measured at 5 mV/s, Eº'(5 mV/s), are 181 mV and 291 mV, respectively. Analysis of the amperometric response of GCE/PPyNSA film to phenol gave sensitivities of 3.1 mA/mole dm-3 with a linear correlation coefficient of 0.982 for phenol concentrations of 19.8 μM to 139.5 μM. The apparent Michaelis-Menten constant (Km′) was estimated as 160 μM. Novel polypyrrole thin film microelectrodes prepared from an aqueous solution of the sodium salt of 1, 2- apthaquinone-4-sulphonic acid and pyrrole in hydrochloric acid as the supporting electrolyte was characterized electrochemically for the first time and found to exhibit good electronic and spectroscopic properties. The modified PPyNQS consisted of nano micelles with diameters of 50–100 nm. It also exhibited more pronounced voltammetric redox responses, improved solubility and stronger UV-Vis absorptions at wavelengths for polarons (380 nm), bipolarons (750 nm) and overlapped bi-polarons (820 nm) compared to conventional PPy. Voltammetric investigations showed that the polymer exhibited quasi-reversible kinetics in a potential window of - 400 mV to +700 mV, with a formal potential of 322 mV vs. Ag/AgCl. The diffusion coefficient was calculated to be 1.02 x 10-6 cm2/s for a thin film with a surface concentration of 1.83 x 10-7 mol/cm2 and a standard rate constant of 2.20 x 10-3 cm/s at 5 mV/s. Substractively normalised in situ Fourier transform infrared spectroscopy (SNIFTIR) confirmed the incorporation of the surfactant into the polypyrrole film, and for the first time structural changes within the polymer were observed and used to explain the electrochemistry of the polymer. Electrochemical impedance spectroscopy (EIS) results validated the quasi-reversible kinetics observed in the voltammetric experiment. The changes in electrical properties of the polymer during electrochemical p-doping and n-doping were quantified by equivalent electrical circuit fitting. Impedimetric nanosensor systems for the determination of two anthropogenic organic pollutants, namely benzidine and naphthalene, were constructed with smart Pt/PPyNQS nanomaterials. Analysis of sensor systems containing tungsten oxide or zirconium oxide-modified polypyrrole showed that nanohybrids of the polypyrrole were generated by the in-situ polymerisation of pyrrole in acidic solutions. Results from morphological and spectroscopic investigation confirmed the pattern of metal distribution within the nanohybrid polymers matrix. However, this class of polymers were devoid of charge carriers characteristics required for electrocatalytic sensor applications. The thesis provided justification for the preparation of nanostructured conducting polypyrrole for use as anodes for the determination of phenol, benzidine and naphthalene.
Synthesis, electrodynamics and biosensor applications of novel sulphonated polyaniline nanocomposites
(University of the Western Cape, 2007) Michira, Immaculate Nyambura; Iwuoha, Emmanuel; Baker, Priscilla; Dept. of Chemistry; Faculty of Science
The overall aim of this thesis was to prepare nanostructured more processable heteronuclear sulphonated polyanyline nanocomposites with electroconductive properties suitable for applications in biosensors. The sulphonated self-assembled polyaniline and derivatised polyaniline nanocomposites (SPAHs) were prepared by chemical oxidative polymerisation or electrical decomposition. The SPAHs prepared include those of polyaniline (PANi), poly-o-methoxyaniline (POMA) and poly-2.5 dimethoxyaniline (PDMA). Two types of sulphonic acids of heteronuclear aromatic hydrocarbons were used in the production of sulphonated SPAH composites. These were anthracene sulphonic acid (ASA) and naphthalene sulphonic acids (NSA) wich played both doping and surfactant roles.
Electrochemical impedance modelling of the reactivities of dendrimeric poly(propylene imine) DNA nanobiosensors
(University of the Western Cape, 2008) Arotiba, Omotayo Ademola; Baker, Priscilla; Dept. of Chemistry; Faculty of Science
In this thesis, I present the electrochemical studies of three dendrimeric polypropylene imine (PPI) nanomaterials and their applications as a platform in the development of a novel label free DNA nanobiosensor based on electrochemical impedance spectroscopy. Cyclic voltammetry (CV), differentia pulse voltammetry (DPV), square wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS) techniques were used to study and model the electrochemical reactivities of the nanomaterials on glassy carbon electrode (GCE) as the working electrode.
Palladium surface-modified rare earth metal-based ab5 type hydride-forming materials
(University of the Western Cape, 2008) Williams, Mario; Linkov, V.M.; Nechaev, A.N.
Driven by mounting standards of living and a growing population, South African energy consumption is expected to increase dramatically within the next decade. The increased demand for more energy will require enormous growth in the capacity for energy generation, more secure and diversified energy sources, and a successful strategy to reduce greenhouse gas emissions. The wellbeing of the South African economy depends on reliable and affordable supplies of energy; whilst environmental wellbeing, from improving urban air quality to abating the risk of global warming, requires energy resources that emit less greenhouse gases compared to petrochemicals. Amongst the various alternative energy strategies, building an energy infrastructure that utilises hydrogen as the primary energy carrier may enable a non-polluting energy security in the future, when it is produce using renewable energy sources (e.g. water electrolysis). Hydrogen has been acknowledged as a key element in the future generation of energy and will be essential in increasing and maintaining economic growth. The significance of hydrogen as a future energy source is due to its large abundance and an energy density that is three times greater than that of an average hydrocarbon fuel. Roughly 80% of hydrogen is produced by natural gas reforming, partial oxidation of light alcohols, and autothermal reforming. In addition, a number of alternative technologies exist in which hydrogen can be generated from starting materials such as coal; biomass; and water, including electrolysis, fossil fuel processing, and coal gasification. However, most of these technologies produce a hydrogen product which is of poor purity. Purification is achievable considering equipment costs are extremely high and the process is therefore mostly economically unfeasible.
Pt Nanophase supported catalysts and electrode systems for water electrolysis
(University of the Western Cape, 2008) Petrik, Leslie F.; Iwuoha, Emmanuel I.; Dept. of Chemistry; Faculty of Science
In this study novel composite electrodes were developed, in which the catalytic components were deposited in nanoparticulate form. The efficiency of the nanophase catalysts and membrane electrodes were tested in an important electrocatalytic process, namely hydrogen production by water electrolysis, for renewable energy systems. The activity of electrocatalytic nanostructured electrodes for hydrogen production by water electrolysis were compared with that of more conventional electrodes. Development of the methodology of preparing nanophase materials in a rapid, efficient and simple manner was investigated for potential application at industrial scale. Comparisons with industry standards were performed and electrodes with incorporated nanophases were characterized and evaluated for activity and durability.
Proton conducting polymer composite membrane development for Direct Methanol Fuel Cell applications
(University of Western Cape, 2008) Luo, Hongze; Vaivars, Guntars
The objective of this study was thus to prepare highly proton condictivity membranes that are cheap to manufacture and have low methanol permeability.
Composite poly(dimethoxyaniline) electrochemical nanobiosensor for glufosinate and glyphosate herbicides
(University of the Western Cape, 2008) Songa, Everlyne Apiyo; Iwuoha, Emmanuel; Baker, Priscilla G.L.; Dept. of Chemistry; Faculty of Science
In this thesis, I present a simple, sensitive and low cost electrochemical nanobiosensor for quantitative determination of the herbicides glufosinate, glyphosate and its metabolite aminomethylphosphonic acid (AMPA). Firstly, the nanostructured poly(2,5-dimethoxyaniline) (PDMA) materials were synthesized on gold electrode by the electrochemical "template"method using poly(4-styrenesulfonic acid) (PSS) as the dopant and structure-directing molecule. Fourier transform infrared (FTIR) spectroscopy, UV-Vis Spectroscopy, Transmission electron microscopy (TEM) and Scanning electron microscopy (SEM) studies inferred successful doping of the nanostructured PDMA film by PSS and that the template PSS directed the synthesis of both nanotubes and nanoparticles of PDMA with diameters less than 100 nm.

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