In this thesis, the synthesis and characterization of nitrogen-doped graphene (NG) and NG-Co3O4 composites are described. Moreover, the effect of airborne contamination and nitrogen doping on the capacitance of graphene was investigated. Firstly, nitrogen-doped thermally expanded graphene oxide (NtGO) was prepared by a facile thermal expansion and hydrothermal doping process. The thermal expansion process plays a vital role in improving the electrochemical performance of N-doped graphene by preventing its aggregation and improving its conductivity. The specific capacitance of NtGO is 270 F g-1 at a discharge current density of 1 A g-1 and the capacitance retention is 97 % after 2000 cycles at this current density. Secondly, a hierarchical electrode structure, consisting of cobalt oxide and nitrogen-doped graphene foam (NGF), has been fabricated with the aim of achieving enhanced charge storage performance. The Co3O4/NGF electrode shows an enhanced charge-storage performance, attributed to the 3D hierarchical structure and the synergistic effect of Co3O4 and NGF. The present study shows that specific capacitances as high as 451 F g-1 can be obtained, indicating that high-performance electrochemical capacitors can be made using electrode materials with advanced structures. Thirdly, a study of the differences between the capacitance of freshly exfoliated highly ordered pyrolytic graphite (HOPG, sample denoted FEG), HOPG aged in air (denoted AAG) and aged in an inert atmosphere (hereafter IAG) is presented in this work. Electrochemical impedance spectroscopy shows the FEG possesses a higher intrinsic capacitance (6.0 µF cm-2 at the potential of minimum capacitance) than AAG (4.3 µF cm-2) and IAG (4.7 µF cm-2). This change in capacitance is correlated with other physical changes of the sample, and attributed to contamination due to airborne hydrocarbons. Finally, the effect of N-doping of graphene prepared by chemical vapour deposition is investigated. The differential capacitance of PG and NG was measured by a microinjection-micromanipulator system. The quantum capacitance of PG and NG was calculated and discussed. The increase in differential capacitance with nitrogen-doping and the growth of the quantum capacitance of NG suggest that the increased capacitance of many electrodes of electrochemical capacitors is primarily due to the modification of the electronic structure of the graphene by the N dopant.

This work describes, for the first time, the electrochemical and electrocatalytic properties of self-assembled layers of single-walled carbon nanotubes (SWCNTs) intergrated with selected organo-iron complexes and Cysteamine (Cys) forming a base on gold electrodes. The organo-iron complexes selected for this study were octa(hydroxyethylthio)phthalocyaninatoiron(II) (FeOHETPc), tetraaminophthalocyninatoiron(II) (FeTAPc), tetraaminophthalocyninatocobalt(II) (CoTAPc), ferrocene monocarboxylic acid (FMCA), ferrocene dicarboxylic acid (FDCA) or a mixture of SWCNT and FMCA or FDCA. The successful fabrication of these electrodes were established using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and electrochemical techniques such as cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), square wave voltammetry (SWV) and chronoamperometry (CA) The Au-Cys-SWCNT-FeOHETPc electrode exhibited strong dependence on the reaction of the head groups and the pH of the working electrolytes. The high electron transfer capability of the Au-Cys-SWCNT-FeOHETPc electrode over other electrodes as the Au-Cys-SWCNT or the Au-Cys-FeOHETPc or the Au-FeOHETPc suggests that SWCNT greatly improves the electronic communication between FeOHETPc and the bare gold electrode. The electron transfer rate constant (kapp) of Au-Cys-SWCNT-FeOHETPc in pH 4.8 conditions (~1.7 x 10-2 cm s-1) over that of the electrode obtained from SWCNT integrated with tetraaminophthalocyninatocobalt(II) (Au-Cys-SWCNT-CoTAPc) (5.1 x 10-3 cm s-1) is attributed to the possible effect of both the central metal on the phthalocyanine core and subsituents on the peripheral positions of the phthalocyanine rings. This work clearly proved that the aligned SWCNTs arrays exhibit much faster electron transfer kinetics to redox-active species in solutions compared to the randomly dispersed (drop-dried) SWCNTs. The advantageous electron transfer properties of the aligned Au-Cys-SWCNT-FeOHETPc electrode, coupled with its ease of fabrication and electrochemical stability, could be found useful in electrochemical sensing and catalysis. Thiocyanate ion was used as an analytical probe to examine the electrocatalytic properties of these modified gold electrodes. This work shows that SWCNT-FeOHETPc hybrid exhibits excellent sensitivity towards the detection of thiocyanate compared to electrodes containing SWCNT or FeTAPc or FeOHETPc only, indicating the ability of the SWCNTs to function as effective conductive nanowires for the detection of this important analyte. The electrochemical response of the FeOHETPc based electrodes was greater than their FeTAPc-based electrode counterparts, indicative of the impact of peripheral substituents on the phthalocyanine core towards electrocatalytic behaviour of these types of hybrids. Nevertheless, the exchange of the central metal as seen with the case of CoTAPc (see chapter 3), provide useful comparative electrochemical activity of this complexes versus FeTAPc with the same chemical environment with an indication of iron being the best as metal centre. FMCA or FDCA were covalently attached to the base Cysteamine monolayer to form the Au-Cys-FMCA and Au-Cys-FDCA, respectively. The same covalent attachment strategy was used to form the mixed SWCNTs and ferrocene-terminated layers (i.e., Au-Cys-SWCNT/FMCA and Au-Cys-SWCNT/FDCA). The impact of neighbouring SWCNTs on the electron transfer dynamics of the ferrocene molecular assemblies in acidic medium (0.5 M H2SO4) and in a solution (pH 7.2) of an outer-sphere redox probe ([Fe(CN)6]4-/ [Fe(CN) 6]3-) was explored. The electron transfer rate constants in both solution media essentially decrease as Au-Cys-FMCA > Au-Cys-SWCNT/FDCA > Au-Cys-FDCA > Au-Cys-SWCNT/FMCA. This trend has been interpreted in terms of several factors such as the locations of the ferrocene species in a range of environments with a range of potentials, the proximity /interactions of the ferrocenes with one another, and electrostatic interaction or repulsion existing between the negatively-charged redox probe and the modified electrodes. Square wave voltammetry was used to examine the catalytic behaviour of the electrodes. Au-Cys-SWCNT/FDCA proved to be the best electrode, possibly due to the repulsive interactions between the negatively charged SCN- and high number of surface –COOH species at the SWCNT/FDCA. This novel study has provided some useful insights as to how CNTs co-assembled with ferrocene-terminated thiols could impact on the heterogeneous electron transfer kinetics as well as the electrocatalytic detection of the self-assembled ferrocene layers. / Thesis (PhD)--University of Pretoria, 2010. / Chemistry / unrestricted

LiCoO₂thin films have been grown by pulsed laser deposition on stainless steel and SiO₂/Si substrates. The film deposited at 600°C in an oxygen partial pressure of 100mTorr shows an excellent crystallinity, stoichiometry and no impurity phase present. Microstructure and surface morphology of thin films were examined using a scanning electron microscope. The electrochemical properties of the thin films were studied with cyclic voltammetry and galvanostatic charge-discharge techniques in the potential range 3.0-4.2 V. The initial discharge capacity of the LiCoO2 thin films deposited on the stainless steel and SiO₂/Si substrates reached 23 and 27 µAh/cm², respectively. / Singapore-MIT Alliance (SMA)

Made available in DSpace on 2014-06-11T19:35:45Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-02-28Bitstream added on 2014-06-13T20:26:51Z : No. of bitstreams: 1 tavares_ba_dr_bauru.pdf: 1248092 bytes, checksum: da6929f1575f2be1fe621cd06198cce0 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Dentre os compostos mais pesquisados atualmente encontram-se os eletrólitos sólidos com elevada condutividade iônica, pois estes apresentam potenciais aplicações em baterias de estado sólido, entretanto, na literatura, há poucos trabalhos que descrevam o processo de preparação e caracterização de pós com estrutura tipo perovskita para aplicações como catodos em baterias de lítio. Assim, este projeto teve como objetivo o desenvolvimento do processo de preparação do pó de La0.50Li0.50TiO3 pelo método de precursores poliméricos. O comportamento térmico do pó obtido a 350ºC foi avaliado através das técnicas de Análise Termogravimétrica (TGA) e Análise Térmica Diferencial (DTA); já a evolução térmica do pó obtido a 350 e 700ºC foi analisada por meio das técnicas espectroscópicas de Infravermelho (IR) e Raman. O processo de cristalização do pó foi realizado por Difração de Raios X (DRX), em conjunto com o Método de Rietveld que identificou uma fase pervskita altamente cristalina durante o processo de cristalização, no entanto, uma fase secundária, LiTi2O4, também foi detectada. A morfologia do pó foi observada por Microscopia Eletrônica de Varredura (MEV-FEG), que revelou uma microestrutura de grãos esféricos e homogêneos. Quanto às medidas eletroquímicas, foram utilizadas as técnicas de Titulação Galvanostática Intermitente (GITT), Cronopotenciometria e Voltametria Cíclica que evidenciaram a presença de dois processos cinéticos diferentes / Among the most researched compounds currently are the solid electrolytes with high ionic conductivity, because of their potential applications in solid state batteries, however, in the literature there are few studies that describe the preparation and characterization of powders with perovskite structure for applications such as cathodes in lithium batteries. Thus this project aimed to develop the process of preparing the powder La 0.50Li0.50TiO3 by the polymeric precursor method. The thermal behavior of the power obtained at 350ºC was evaluated using the techniques of Thermogravimetric analysis (TGA) and Differential Thermal Analysis (DTA), whereas the thermal evolution of the power obtained at 350 and 700ºC was analyzed by spectroscopic techiniques IR and Raman. The crystallization process was analyzed by X-ray powder diffraction together with the Rietveld Method that identified a highly crystalline perovskite phase during the crystallization process; however, a secondary phase LiTi2O4 was also detected. The morphology of the powder was observed by field emission gun scanning electron microscopy (FEG-SEM), which revealed a microstructure of spherical and homogeneous grains. As for the eletrochemical measurements, we have used the Galvanostatic Intermittent Intermittent Titration Technique (GITT), Chronopotenciometry and Cyclic Voltammetry demonstrating the presence of two different kinetic processes

This dissertation investigates the heterogeneous electron transfer dynamics and electrocatalytic behaviour of the following molecules immobilized on gold electrode: (a) 2-dimethylaminoethanethiol (DMAET), with and without integration with poly (m-aminobenzenesulfonic acid) functionalised single-walled carbon nanotubes (SWCNT-PABS); (b) SWCNT-PABS and iron (II) phthalocyanine nanoparticles (nanoFePc); (c) Colloidal gold / Gold nanoparticles (AuNP) and nanoFePc (d) ; water-soluble iron (II) tetrasulfophtalocyanine (FeTSPc) and SWCNT-PABS, and (e) novel monolayer protected gold nanoparticles (MPCAuNPs) by means of either (i) layer-by-layer (LBL) self-assembly or (ii) self-assembled monolayer (SAM) fabrication strategy. Atomic force microscopy and electrochemical studies (cyclic voltammetry, and electrochemical impedance spectroscopic) were used to monitor the substrate build-up, via strong electrostatic interaction. The surface pKa of DMAET was estimated at 7.6, smaller than its solution pKa of 10.8. It is also shown that SWCNT-PABS is irreversibly attached to the DMAET SAM. For layered films involving SWCNT-PABS and nanoFePc (Au-DMAET- SWCNT-PABS-nanoFePc) n (n=1-5 layers) as the number of bilayers increase, the electron transfer kinetics of the [Fe(CN) 6]3-/4 redox probe decreases. On the contrary, LBL assembly involving AuNP and nanoFePc (Au-DMAET-AuNP-nanoFePc) n (n=1-4 layers) shows an increase followed by a decrease in electron transfer kinetics subsequent to the adsorption of nanoFePc and AuNP layers, respectively. For SAMs involving FeTSPc and SWCNT-PABS, the mixed hybrid (Au-DMAET-SWCNT-PABS/FeTSPc) exhibited fastest charge transport compared to other electrodes. For the novel MPCAuNPs, the protecting or stabilizing ligands investigated were the (1-sulfanylundec-11-yl) tetraethylene glycol (PEG-OH) and the (1-sulfanylundec-11-yl) polyethylene glycolic acid (PEG-COOH). Three different mass percent ratios (PEG-COOH : PEG-OH), viz. 1:99 (MPCAuNP-COOH1%), 50:50 (MPCAuNP-COOH50%) and 99:1 (MPCAuNP-COOH99%) were used to protect the gold nanoparticles. The impact of these different ratios on the electron transfer dynamics in organic and aqueous media was explored. The average electron transfer rate constants (ket / s-1) in organic medium decreased as the concentration of the surface-exposed –COOH group in the protecting monolayer ligand increased: MPCAuNP-COOH1% (~ 10 s-1) > MPCAuNP-COOH50% (~ 9 s-1) > MPCAuNP-COOH99% (~ 1 s-1). In aqueous medium, the trend is reversed. This behaviour has been interpreted in terms of the hydrophobicity (quasi-solid nature) and hydrophilicity (quasi-liquid nature) of the terminal –OH and –COOH head groups, respectively. The ionization constants of the terminal groups (i.e., surface pKa) was estimated as ~ 8.2 for the MPCAuNP-COOH1%, while both MPCAuNP-COOH50% and MPCAuNP-COOH99% showed two pKa values of about 5.0 and ~ 8.0, further confirming the hydrophilicity / hydrophobicity of these surface functional groups. Hydrogen peroxide (H2O2), epinephrine (EP) and ascorbic acid (AA) were used as model analytes to examine electrocatalytic ability of these nanostructured assemblies. The electrochemical reduction of H2O2 at a constant concentration was amplified upon increasing bilayer formation of SWCNT-PABS and nanoFePc, while SWCNT-PABS/FeTSPc showed the best response towards the detection of epinephrine. MPCAuNP-COOH99% showed an excellent suppression of the voltammetric response of the AA and an enhanced electrocatalytic activity towards the detection of EP compared to the other MPCAuNPs. / Thesis (PhD)--University of Pretoria, 2010. / Chemistry / unrestricted

For the first time, new metallophthalocyanine (MPc) complexes: (i) nanostructured MPc (nanoMPc, where M = iron or cobalt); (ii) octabutylsulphonylphthalocyanine (MOBSPc, where M = iron or cobalt); and (iii) iron (II) tetrakis(diaquaplatinum)octacarboxyphthalocyanine (PtFeOCPc) were synthesized and characterized using advanced microscopic and spectroscopic techniques such as MS, AFM, HRTEM, FESEM, and EDX. Electrochemical techniques such as cyclic voltammetry, square wave voltammetry, chronoamperometry, rotating disk electrode, and electrochemical impedance spectroscopy, were used to explore the redox chemistry, heterogeneous electron transfer kinetics (HET), and electrocatalytic properties of these MPc complexes towards oxygen reduction reaction (ORR), oxidation of formic acid, thiocyanate and nitrite on a edge plane pyrolytic graphite electrode (EPPGE) platform pre-modified with or without acid functionalized multi-walled carbon nanotubes (MWCNTs). The MWCNT-MPc platforms exhibit enhanced electrochemical response in terms of (i) HET towards an outer-sphere redox probe ([Fe(CN)6]3-/[Fe(CN) 6]4-), and (ii) catalytic activities towards the investigated analytes. The MWCNTnanoMPc electrode exhibits faster HET constant (kapp ≈ 30 – 56 x 10-2 cms-1 compared to their bulk MPc counterparts (≈ 4 – 25 x 10-2 cms-1). The MWCNT-nanoMPc exhibited enhanced electrocatalytic properties (in terms of sensitivity and limit of detection, LoD) towards the detection of thiocyanate and nitrite in aqueous solutions. ORR was a 4- electron process with very low onset potential (-5 mV vs. Ag|AgCl saturated KCl). HET and ORR at MOBSPc complexes supported on MWCNTs showed that the MWCNT–MOBSPc exhibited larger Faradaic current responses than the electrodes without MWCNTs. The rate constant at the MWCNT-MOBSPc electrodes (kapp ≈ (22 – 37) x 10-2 cms-1) is about a magnitude higher than the electrodes without MWCNT (kapp ≈ (0.2 – 93) x 10-3 cms-1). The MWCNT–FeOBSPc electrode gave the best ORR activity involving a direct 4-electron mechanism with low onset potential (0.0 mV vs. Ag|AgCl saturated KCl). The onset potential is comparable and even much lower than recent reports. The HET and electrocatalytic properties of PtFeOCPc supported on a MWCNT platform (MWCNT-PtFeOCPc) gave enhanced electrochemical response in terms of (i) HET (kapp ≈ 78 x 10-2 cms-1), (ii) catalytic rate constant (kcat ≈ 41 cm3mol-1s-1) and (iii) tolerance towards CO poisoning during formic acid oxidation. The ORR activity is a direct 4-electron transfer process at a rate constant of 2.78 x 10-2 cms-1; with a very low onset potential approximately 0.0 mV vs. Ag|AgCl saturated KCl. The electrooxidation of formic acid at MWCNT-PtFeOCPc follows the preferred ‘direct pathway’. This work clearly proves that the MWCNT-MPcs hybrid exhibit enhanced electrochemical and electrocatalytic activities towards the selected analytes compared to the MPcs alone. Considering the ease of fabrication of these electrodes (drop-dry method), these nanocomposite materials are promising platform for potential application in sensing and cataly. / Thesis (PhD)--University of Pretoria, 2011. / Chemistry / unrestricted

This work describes metal (M) and metal oxides (MO) films (where M = Ni, Co and Fe) obtained by electrosynthesis and chemical synthesis, and modified with carbon nanotubes (CNTs) on edged plane pyrolytic graphite electrode (EPPGE). The MO nanoparticles investigated are nickel oxide (NiO), cobalt oxide Co3O4) and iron oxide (Fe2O3). Successful modification of the electrodes with the M or MO/CNT nanocomposite was confirmed by field emission scanning electron microscopy (FESEM), high resolution scanning electron microscopy (HRSEM), high resolution transmission electron microscopy (HRTEM), atomic force microscopy (AFM), x-ray diffraction spectroscopy (XRD), x-ray photoelectron spectroscopy (XPS), electron dispersive x-ray spectroscopy (EDX), fourier transformed infra-red spectroscopy (FTIR) and ultraviolet-visible (UV-vis) spectroscopy. Electron transport (ET) properties of the modified electrodes was explored using cyclic voltammetry (CV) and electrochemical impedance spectroscopic techniques (EIS) with ferricyanide/ferrocyanide ([Fe(CN) 6]3-/4-) as the redox probe. The electron transfer constant (k0) differs in terms of materials, method of synthesis and electrical equivalent circuits used in the fitting or modelling process. Generally, the k0 values are in the 10-3 – 10-2 cms-1 with Ni nanoparticles having the highest k0 or fastest electron transport. The presence of CNTs also enhances the ET compared with electrodes without CNTs. The electrocatalytic properties of the modified electrodes were explored using the following analytical probes: diethylaminoethanethiol (DEAET), hydrazine, nitrite and dopamine. The study showed that the electrocatalytic oxidation of DEAET and hydrazine was favoured on electrode modified with Ni nanoparticles; nitrite and dopamine were best catalysed by the Co and Fe2O3 nanoparticles, respectively. Electroanalysis results (using chronoamperometry, square wave voltammetry and linear sweep voltammetry) indicated some level of adsorption of DEAET, hydrazine and nitrite on the modified electrode, while dopamine electrocatalytic oxidation and detection followed a simple diffusion controlled process. The adsorption process was found to be physically induced and could be eliminated by repetitive cycling of the electrode in the aqueous electrolyte solution. Electrodes modified with chemically-synthesised material (particularly nickel) were less adsorptive towards DEAET and hydrazine detection, and gave sensitivity and limit of detection values that compared with data obtained using electrochemical deposition / synthesis. The chemical stability and reproducibility of the modified electrodes were determined and discussed. Finally, electrochemical properties were studied to help screen these electrode materials in supercapacitors. CNT-NiO nanocomposites exhibit remarkable super capacitive behaviour in neutral and acidic media compared to the other CNT-MO nanocomposites investigated. Interestingly, the capacitive behaviour of the CNT-NiO was more enhanced in H2SO4 solution than in Na2SO4, possibly due to the high conductivity of the former. The CNT-NiO electrode maintained good stability with only about 5% loss of its specific capacitance after 1000 cycle life. / Thesis (PhD)--University of Pretoria, 2011. / Chemistry / unrestricted

No description available.

In response to more stringent global CO2 emissions, automotive manufacturers have increased the use of advanced high strength steels (AHSS). Ultra-high strength steels are often used within the body-in-white (BIW) for safety critical parts and structural reinforcements, such as roof rails and side impact beams. Currently, the most commonly used press hardened steel (PHS) grade for these applications is 22MnB5, with a typical composition of 0.22C 1.2Mn 0.25Si 0.005B (wt%). Automotive OEMs have expressed a desire to use Zn-based coatings as they are compatible with the current painting system and have the potential to provide robust cathodic protection. The steel blanks generally undergo direct hot press forming (DHPF) to achieve the necessary martensitic microstructure and target mechanical properties, but this presents challenges for Zn-coated 22MnB5. The adoption of Zn-based coatings within the automotive industry has been inhibited by the prospect of liquid metal embrittlement (LME) resulting from DHPF, as well as the desire to provide robust cathodic protection. Previous literature has reported that a zinc ferrite (α-Fe(Zn)) coating with a global Zn content of at least 30 wt% will provide cathodic protection to the underlying substrate. The main goal of this work was to determine the microstructural evolution and electrochemical properties of galvanized (GI70 – 70 g/m2/side) 22MnB5 substrates as a function of the annealing time at a typical austenization temperature of 900°C. It was found that the Zn-based coatings annealed at 700°C consisted to a mixture of small volume fraction of α-Fe(Zn) and Г-Fe3Zn10. After heating to 900°C, the coating comprised varying volume fractions of α-Fe(Zn) and Zn(Fe) liquid, which transformed to Г-Fe3Zn10 after solidification. The relative fraction of Г Fe3Zn10 was found to decrease with increasing annealing time until the coating completely transformed to α-Fe(Zn) after annealing at 900°C for 240 s. GDOES results found that, when the sample was annealed at 900°C for 240 s, the global Zn content of the coating was less than 30 wt%. Coatings comprising varying fractions of Г-Fe3Zn10 were subjected to uniaxial tensile tests to determine how the coating microstructure affected the mechanical properties in comparison to the uncoated substrate material. It was found that the uncoated substrate material met the mechanical property requirements of σ(UTS)min ≥ 1500 MPa regardless of annealing time. However, σ(UTS) was found to decrease with increasing annealing times for the GI70 coated samples until the target mechanical properties were not met when the sample was annealed at 900°C for 180 s. This was attributed to increased coating thicknesses leading to a decrease in the martensitic cross-sectional area to support the load. Furthermore, the coatings were subjected to a variety of electrochemical characterization techniques, including potentiodynamic and galvanostatic polarization scans, potentiostatic scans, and electrochemical noise tests. Potentiodynamic polarization scans indicated a higher driving force for cathodic protection when the coating contained some fraction of Г-Fe3Zn10. Furthermore, a limiting current density for these samples was observed, demonstrating that Г-Fe3Zn10 corrodes at a slower rate in comparison to α Fe(Zn). Galvanostatic polarization measurements indicated that, when the fraction of Г Fe3Zn10 within the coating was below 15 vol%, the protective properties of the phase were not exhibited. XRD and TEM analysis revealed the formation of three corrosion products on the surface: simonkolleite, hydrozincite, and akaganeite. It was found that, when samples contained greater than 15 vol% Г-Fe3Zn10 in the coating, the predominant corrosion products were a combination of simonkolleite and hydrozincite. When the Г Fe3Zn10 content was below this value, the dominant corrosion product was found to be akaganeite. Furthermore, substrate attack was observed on a sample annealed at 900°C for 420 s when the coating layer was intact, indicating that the α-Fe(Zn) only containing coating obtained at this time does not provide cathodic protection. Based upon the current results, it was determined that a minimum volume fraction of 15 vol% Г-Fe3Zn10 must be present within the coating layer to obtain robust cathodic protection. Furthermore, it was determined that the processing window to develop cathodically protective Zn based coatings while mitigating LME is extremely narrow. This is a result of the fact that it is necessary for at least 15 vol% Г-Fe3Zn10 to be present within the coating microstructure at room temperature, which is liquid at the forming temperatures of 900°C. From the current findings, it was found that it is unlikely that a cathodically protective Zn-based coating can be obtained for DHPF steel parts using 22MnB5 as a substrate material. This is due to the high forming temperature resulting in liquefication of the coating and the rapid cooling rates necessary to achieve the target mechanical properties of σ(UTS)min ≥ 1500 MPa. Thus, it is recommended that the current substrate material be altered such that the part may be formed below the peritectic temperature of 782°C. / Thesis / Master of Applied Science (MASc)

M. Tech. (Department of Chemistry, Faculty of Applied and Computer Sciences), Vaal University of Technology. / The ligand 2, 2-dithiobisbenzothiazole and it metal complexes have been a subject of interest in various fields but they have found to exhibit remarkable and prevalent biological and pharmacological activities. The ligand tends to coordinate to complexes through the sulfur atom and hence the metal-sulphide bond are good precursor to generate metal sulfide nanoparticles using single-source precursor route. The complexes are generally prepared by reflux for 1 to 2 hours depending on the solvent used to produce very stable solid products and some form in crystalline form. All the prepared nickel and cadmium complexes were characterized using techniques such as elemental analyzer, IR, 13C NMR spectroscopy and thermogravimatric analysis. The data obtained from the spectroscopic analysis was consistent of the coordination of the ligand with the metal ions through the sulphur atoms of the 2,2-dithiobisbenzothiazole moiety. The thermal analysis of the prepared complexes gave a final residue of metal sulphide for both metal complexes. Characterization techniques showed the formation of bidentate complexes for both nickel complex and cadmium complex. The prepared complexes were then used to synthesize metal sulphide nanoparticles .The nanoparticles were prepared by thermal decomposition method of the single source precursor in a solution of oleylamine (OLA). Two different parameters were investigated temperature and time to study their effect on the size and shape of the nanoparticles. The synthesized nanoparticles were characterized using techniques such as UV-Vis spectroscopy, photoluminescence spectroscopy, and X-ray diffraction analysis and transmission electron microscopy. The temperatures of the reaction have a significant effect on the rate of the reaction that will affect the size and shape of the nanoparticles. This effect was confirmed by the optical properties of the synthesized nanoparticles prepared at different reaction temperatures. The spectra shows that absorption maximum and band edge shift to lower wavelength as the temperature of reaction was progressively increased. This trend is associated to the decrease in particles size of the prepared nanoparticles. TEM images further confirmed that the particles size of the prepared nanoparticles was progressively decreased as the temperature was increased. The time of the reaction is one of the most significant factors in the synthesis of the nanoparticles. The investigation of the time of the reaction yield results that depicted that with increase in time of the reaction, the band edge increases, but relatively at short wavelength to the bulk. Hence, the band edges of the nanoparticles were blue shifted significantly to the bulk. The results show that with an increase in the time of the reaction, the nanoparticles increases in their size due to Ostwald ripening. The optimum complexes and optimum nanoparticles were used to further study their electrochemical properties using cyclic voltammetry and electrochemical impedance spectroscopy (EIS) graphs were fitted using the randles circuit and they confirm that the NiS nanoparticles GCE greatly increase the electron transfer rate, probably due to the nanostructured surface property of the NiS nanoparticles. Differential pulse voltammetry (DPV) was used to study the electrochemical behavior and the DPV showed that the current response of Rhb was higher for the optimum temperature NiS nanoparticles compared to all the materials used. There was an increase in the Rhb current response with an increase in pH and pH 7 was used as the optimum pH when Ni- complex was used as a modifier and pH 8 was used as optimum when NiS nanoparticles were used as a modifier. Effect of concentration showed that the NiS nanoparticles for the optimum temperature had a wide linear range and a low detection limit. The method has good accuracy, acceptable precision, and reproducibility. This method provides a novel electrochemical method for determination of RhB.