Browsing by Author "Makame, Yahya M. M."

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    Cadmium Sulfide Quantum Dots Stabilized By Castor Oil and Ricinoleic Acid
    (Elsevier, 2016) Kyobe, Joseph W.; Mubofu, Egid B.; Makame, Yahya M. M.; Mlowe, Sixberth; Revaprasadu, Neerish
    Castor oil and ricinoleic acid (an isolate of castor oil) are environmentally friendly bio-based organic surfactants that have been used as capping agents to prepare nearly spherical cadmium sulfide quantum dots (QDs) at 230, 250 and 280 °C. The prepared quantum dots were characterized by Ultra violet–visible (UV–vis), Photoluminescence (PL), Transmission Electron Microscopy (TEM), High Resolution Transmission Electron Microscopy (HRTEM) and X-ray diffraction (XRD) giving an overall CdS QDs average size of 5.14±0.39 nm. The broad XRD pattern and crystal lattice fringes in the HRTEM images showed a hexagonal phase composition of the CdS QDs. The calculated/estimated average size of the prepared castor oil capped CdS QDs for various techniques were 4.64 nm (TEM), 4.65 nm (EMA), 5.35 nm (UV–vis) and 6.46 nm (XRD). For ricinoleic acid capped CdS QDs, the average sizes were 5.56 nm (TEM), 4.78 nm (EMA), 5.52 nm (UV–vis) and 8.21 nm (XRD). Optical properties of CdS QDs showed a change of band gap energy from its bulk band gap of 2.42–2.82 eV due to quantum size confinement effect for temperature range of 230–280 °C. Similarly, a blue shift was observed in the photoluminescence spectra. Scanning electron microscope (SEM) observations show that the as-synthesized CdS QDs structures are spherical in shape. Fourier transform infra-red (FTIR) studies confirms the formation of castor oil and ricinoleic acid capped CdS QDs.
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    Wet Oxidation of Maleic Acid By Copper(II) Schiff Base Catalysts Prepared Using Cashew Nut Shell Liquid Templates
    (2011-05) Hamad, Fatma; Mubofu, Egid B.; Makame, Yahya M. M.
    Novel heterogeneous copper(II)Schiff basecatalysts have been successfully prepared using a Cashew Nut Shell Liquid (CNSL) templating agent. The preparation of catalyst supports was via a one-pot route and afforded aminopropyl-functionalized Micelle Templated Silica (MTS-AMP). The MTS-AMP support was then condensed with pyridine-2-carboxyaldehyde, 2-hydroxybenzaldehyde, 2-hydroxynaphthaldehyde to produce the corresponding Schiff bases. In each case, the Schiff base was complexed with copper(II) acetate solution at room temperature. The supports and heterogeneous catalysts were porous with pore diameters of up to 25 nm and grain sizes of up to 1.0 μm as revealed by Nitrogen Physisorption Study and Scanning Electron Microscopy (SEM) respectively. The maximum copper loading was about 3% w/w for heterogeneous catalysts supported on CNSL based supports whereas the maximum loading of about 2% w/w was obtained for coppercatalysts prepared using commercially available dodecylamine and hexadecylamine templates. The catalysts were tested on the oxidation of maleic acid at room temperature using H2O2 as an oxidant and the catalysts had an excellent catalytic efficiency with a yield of up to 90% and turn over number of about 1000 in ten minutes. The performance of catalysts depended on the type of ligands, the template used to prepare the catalyst support and on the method of catalyst preparation. Catalysts prepared using CNSL templates were more efficient than those prepared using the commercially available templates. The catalysts prepared by a stepwise approach were robust and gave good results while those prepared by an imprinting approach leached out after one reaction cycle.