M. Tech. (Department of Biotechnology, Faculty of Applied and Computer Sciences) Vaal University of Technology. / Chemical precipitation method is the most widely used of all methods for preparing good quality semiconductor nanoparticles. Several conditions are optimized for producing the desired size and shape of particles. The parameters such as capping molecule, precursor concentration, time and temperature were investigated using the colloidal hot injection method. The effect of capping agent was the first parameter investigated in the synthesis of copper selenide, copper sulphide and copper oxide nanoparticles. The capping agents of interest in this study were oleylamine (OLA) and trioctylphosphine (TOP), due to their ability to act as reducing agents, surfactant, solvent and enhancement of colloidal stabilization. The use of oleylamine and trioctylphosphine were carried out at 220 °C for 30 minutes. The optical and structural properties of the yielded nanoparticles were characterize using UV/Vis spectroscopy, TEM and XRD and showed dependence on the type capping interactions from the two agents. Nanoparticles synthesized using TOP produced two phases whereas a single phase was observed from OLA as confirmed by XRD. OLA produced bigger particle sizes compared to TOP but with a wider variety of shapes. The wide variety of particle structures of OLA capped nanoparticles was advantageous since different types of bacteria were targeted in this work. Therefore, other synthetic parameters were investigated using OLA as both solvent and capping molecule. Precursor concentration ratio showed bigger effect in the size, and shape of the yielded nanoparticles. For copper selenide and copper sulphide (Cu: Se/ S), 1:1 concentration ratio gave the best optical and structural properties while copper oxide (CuO) nanoparticles demonstrated its best optical and structural properties in 2:1 ratio (Cu: O). Nonetheless, 1:1 precursor concentration ratio was used to optimise other parameters. Since reaction time has a profound effect on the nanocrystals size and shapes, the effect of reaction time in OLA was also investigated. The reaction time showed no effect on the phase composition of the synthesized copper sulphide, copper oxide and copper selenide nanoparticles. Reaction time of 30 minutes gave the best optical (the shape of the absorption band edge and emission maxima values) and structural (size distribution of particles) properties for CuSe and CuS compared to other reaction times (15 min, 45 and 60 min). 15 min reaction time gave the best optical and structural properties for copper oxide but nonetheless, 30 min was used as the optimum reaction time for further optimization. Temperature showed an effect in size, shape and the stoichiometry of the reaction. These effects were confirmed by the optical and structural properties of the synthesized nanoparticles. XRD patterns revealed some differences with the temperature change, indicating an effect on the phase composition of CuS and CuO but not on CuSe nanoparticles. CuSe and CuS nanoparticles synthesized at 220 °C gave the ideal optical and morphological features compared to other temperatures that were selected (160 ºC, 190 ºC and 240 ºC). Nonetheless, CuO revealed its best optical and structural properties at 160 ºC. 220 ºC was deduced to be the optimum temperature for the synthesis of these three materials under the synthetic conditions. The optimum parameter (220 ºC, 30 min and 1:1 ratio) were used to synthesize the three copper chalcogenides which were then tested against Gram-negative (E. coli and P. aeruginosa), Gram-positive (S. aureus and E. faecalis), and fungi (C. albicans). The plant species, Combretum molle and Acacia mearnsii were phytochemical screened for the presence of active organic compounds and the content of total phenols, flavonoids and antioxidants using different solvents. Both C. molle and A. mearnsii revealed the highest phenolic content in acetone extracts. C. molle revealed its highest flavonoid content in methanol extract and its highest free radical scavenging activity in acetone extract. Acetone extracts demonstrated the highest flavonoid content as well as the highest free radical scavenging activity of A. meansii. The solubility of copper chalcogenides and plant extract was tested in four different solvents and the solvent that demonstrated highest solubility was used for the coordination of the plant extract and copper chalcogenides. The plant extract coordinated nanoparticles were tested for their antibacterial and antifungal activity. Their results were compared to those of the active ingredient in their respective solvents from the medicinal plants as well as those of copper chalcogenides nanoparticles without plant extracts using diffusion disk and MICs methods. The synthesized nanoparticles showed better performance than plant extracts with copper oxide performing the best, followed by copper selenide and lastly by copper sulfide. The performance of plants extracts highly dependent on the solvent of extract with acetone showing the best performance for both C. molle and A. Mearnsii followed by ethanol. The addition of active ingredients from C. molle and A. mearnsii to the synthesized nanoparticles did not enhance the performance of these nanoparticles.

M. Tech. (Department of Chemistry, Faculty of Applied and Computer Science): Vaal University of Technology / Here, we report the synthesis and characterization of silver (Ag) and silver selenide (Ag2Se) nanoparticles using the metal-organic route method. This method involves the reduction of selenium powder and silver nitrate in the presence of trioctylphosphine as a solvent. Tri-n-octylphosphine oxide (TOPO) and hexadecylamine (HDA) were used in the study as capping molecules. The optical properties of the as-prepared nanoparticles were studied using UV-Visible and photoluminescence spectroscopy (PL). Transmission electron microscopy (TEM) and X-ray powder diffraction (XRD) were used to study the structural properties. The effect of capping molecules and temperature were investigated on the growth of the nanoparticles. The prepared nanoparticles seem to depend on the reaction temperature were the increase in temperature led to an increase in particle sizes. The growth of the as-prepared TOPO-capped Ag2Se nanoparticles was influenced by temperature, this was evident when the temperature was increased, the nanoparticles evolved from sphere to hexagonal shape. TOPO-capped nanoparticles showed the tendency of agglomeration with increase in temperature compared to HDA-capped nanoparticles. The X-ray diffraction results showed peaks which were identified as due to α-Ag2Se body centered cubic compound for both TOPO/HDA-capped Ag2Se nanoparticles. Some evidence of impurities were observed in the XRD analysis and indexed to metallic silver. HDA-capped Ag nanoparticles were found to be affected by temperature variation. The prepared nanoparticles were characterized with UV-Vis spectroscopy and transmission electron microscopy. XRD analysis was not performed due to small yield obtained. The absorption spectra of HDA-capped Ag nanoparticles at different temperatures show a surface Plasmon resonance (SPR) band in the regions 418 - 428 nm. Uniform spherical shapes were obtained for both 130 and 190 °C and fewer particles were obtained at 160 °C. The synthesis of TOPO–capped Ag nanoparticles was unsuccessful since none of the particles were isolated from the solution due to its lower capping ability or it may be that TOPO is binding too strongly to Ag. The polymer nanofibres were electrospun using electrospinning technique. Parameters such as concentration and voltage were investigated. These parameters significantly affect the formation of fibre morphology. PVP and PMMA polymers were used for this study. The electrospun composite fibres were characterized using UV-Visible spectroscopy, scanning electron microscopy (SEM), Thermal gravimetric analysis (TGA), X-ray diffraction (XRD) and Fourier transformer infrared (FTIR) spectroscopy. The SEM results show that increasing the polymer concentration resulted in increased fibre diameters. Hence increasing the voltage decreases the fibre diameters. Ag2Se nanoparticles were incorporated into PVP and PMMA and electrospun using electrospinning to produce composite fibres. Their addition into PVP polymer fibres improved the fibre’s uniformity and further decreased their diameters. The SEM of composite fibres for PMMA is not shown. The absorption bands for PVP composites fibres show a blue shift from the pure Ag2Se nanoparticles, whereas the one for PMMA show a red shift from the pure Ag2Se nanoparticles. Both the composite fibres for PVP and PMMA show a blue shift from the bulk of Ag2Se. The XRD analysis of the composite fibres shows no significant effect upon addition of Ag2Se nanoparticles on the amorphous peak of the PVP polymer, whereas on the PMMA, it shows peaks which were due to the face centered cubic phase of Ag. The FTIR spectra of the composite fibres and pure polymers (PVP and PMMA) gave almost identical features. TGA curves show no significant effect on the thermal properties of the PVP polymer and its composites, however, on the PMMA composite fibres it show an increase in the thermal stability of the polymers upon addition of Ag2Se nanoparticles. The study was based on silver nanoparicles and its antibacterial activities. One of the synthetic challenges for silver nanoparticles is their solubility and yield. Selenide was introduced in the study to improve such shortcomings of silver nanoparticles and also for possible improved properties, chemical stability and increased activity against bacteria. The selenide group on the metal also provides stronger chemical interaction between the nanoparticles and the polymer. Therefore, the intension was to use these nanoparticles into polymer fibres for potential use in wound dressing.