Browsing by Author "Kyobe, Joseph W."

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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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    Cdse Quantum Dots Capped with Naturally Occurring Biobased Oils
    (2015) Kyobe, Joseph W.; Mubofu, Egid B.; Makirita, Yahya M. M.; Mlowe, Sixberth; Revaprasadu, Neerish
    We report a green synthesis of CdSe quantum dots (QDs) using bio-based materials (castor oil and ricinoleic acid) as capping agents. The absorption spectra of the as-synthesized CdSe QDs showed typical features of quantum confinement. The particle sizes of QDs were determined using the absorption band edges and found to be 3.81 to 6.80 nm and 5.91 to 8.31 nm for the entire range of reaction temperatures for QD-capped with castor oil (CSTO) and ricinoleic acid (RA), respectively. The photoluminescence spectra showed narrow emission peaks. The transmission electron microscopy (TEM) images showed spherical particles with sizes comparable to those determined from the absorption spectra. Comparatively, large particles were observed for RA capped CdSe QDs than those stabilized by CSTO. X-ray diffraction patterns revealed that the synthesized CdSe quantum dots have cubic structure. The particle sizes of CdSe deduced from X-ray diffraction measurements were in excellent agreement with those deduced from absorption spectra and TEM images. The d-spacings from the HRTEM images were consistent with those reported in literature. The surface area and the agglomeration number for as-synthesized CdSe QDs of different sizes are also reported.