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Research Articles (Chemistry)

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    Chelated N^N and N^O Donor Nickel(II) complexes as ethylene oligomerization catalysts.
    (2016) Ngcobo, Makhosonke.; Ojwach, Stephen Otieno.
    Abstract available in PDF file.
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    An evaluation of chromatographic modes for the determination of rare earth elements in geological materials by HPLC-ICP-MS.
    (2016) Bagwandin, Risa.; Pillay, Letitia.
    Scandium, Y and 15 lanthanides, commonly classified as rare earth elements (REE) are indispensable to modern technology and constitute integral components for the manufacture of advanced technological materials. Their determination in geological materials by ICP-MS are susceptible to numerous spectroscopic and matrix interferences that inhibit accurate quantification. The chromatographic separation of individual REE from interferents prior to detection by ICP-MS has been established as an effective approach for overcoming these interferences. However, application of this approach in literature does not address both mutual REE and matrix induced spectroscopic interferences. Furthermore it requires extensive sample pre-treatment, introducing errors in analysis. This study investigates established chromatographic modes of REE separation (ion pair and ion exchange chromatography) on their capability to separate individual REE and sample matrix components without sample pre-treatment. It further aims to evaluate the potential of these chromatographic methods to be integrated to a hyphenated HPLC-ICP-MS technique for elimination of interferences which affect ICP-MS REE quantification. Ion pair and ion exchange methods were optimised using HPLC with post-column derivatisation and UV-Vis detection (as a preliminary detection method). These methods were compared on the basis of their REE separation efficiency and capability to address ICP-MS spectroscopic interferences that affect REE determination. The potential integration of the preferred chromatographic method (ion pair chromatography) prior to ICP-MS detection was evaluated by analysis of CRMs before and after separation. The influence of mobile phase composition on analytical performance of ICP-MS for REE determination was assessed. This study has shown that ion pair chromatography has the potential to achieve complete separation of individual REE without interference from sample matrix components and avoiding sample pre-treatment procedures. However, the surfactant properties of the ion pair reagent and organic and sodium content of its mobile phase composition can impair ICP-MS sensitivity. This study also provides insight to challenges that will be encountered during application of ion pair chromatography with ICP-MS detection (HPLC-ICP-MS) and presents appropriate suggestions and improvements. These will enhance the potential application of ion pair chromatography with HPLC-ICP-MS such that a more effective means for accurate and precise determination of REE in geological materials can be achieved.
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    Experimental optimization of nanostructured nickel oxide deposited by spray pyrolysis for solar cells application.
    (Research India Publications., 2018) Ukoba, Kingsley Ogheneovo.; Inambao, Freddie Liswaniso.; Eloka-Eboka, Andrew Chukwudum.
    This study focused on the experimental optimization of nanostructured nickel oxide (NiO) for solar cell applications. The optimization procedure involved the variation of the precursor concentrations of nickel acetate with attendant measurement of the properties of nickel oxide films. The films were spray deposited on glass substrate. Nickel acetate precursor was used at a substrate temperature of 350 oC. Precursor concentrations were: 0.025 M, 0.05 M, 0.075 M and 0.1 M respectively. The surface morphology revealed nanostructured film with particles densely distributed across the substrate’s surface. The films are homogeneous, smooth, well adherent and devoid of pinholes and cracks. The morphology became grainier as the precursor solution increased. Elemental composition exposes the presence of Ni and O elements in NiO film. Oxygen concentration decreases as precursor solution increases. The film structural property reveals that deposited NiO film has an amorphous structure at 0.025 M while the other concentrations are polycrystalline in nature with cubic structure. X-ray diffractometry (XRD) further reveals that the intensity of NiO films increases with increased molarity. Preferred orientation was along the (1 1 1) peak with minor intensity along the (2 0 0) peak. XRD patterns have peak diffraction at (2θ = 37 o and 43 o) for the (1 1 1) and (2 0 0) planes respectively, and 64 o for the (2 2 0) plane for 0.1 M. Crystallite size was obtained at 63.77 nm maximum. Film thickness increased with increasing precursor concentration from 6.277 μm to 11.57 μm. Film micro strain was observed to have compression for all precursor solutions. Optical studies showed that transmittance decreased with increasing concentration from 80 % to 71 %. Optical band gap energy was between 3.94 eV to 3.38 eV as precursor concentration increased, revealing the effect of varied concentrations on NiO film properties. Optimized results obtained are precursors in the development of low cost, efficient, durable solar cell fabrication for developing countries.
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    Fabrication of affordable and sustainable solar cells using NiO/TiO2 P-N heterojunction.
    (Hindawi., 2018) Ukoba, Kingsley Ogheneovo.; Inambao, Freddie Liswaniso.; Eloka-Eboka, Andrew Chukwudum.
    The need for affordable, clean, efficient, and sustainable solar cells informed this study. Metal oxide TiO²/NiO heterojunction solar cells were fabricated using the spray pyrolysis technique. The optoelectronic properties of the heterojunction were determined. The fabricated solar cells exhibit a short-circuit current of 16.8 mA, open-circuit voltage of 350 mV, fill factor of 0.39, and conversion efficiency of 2.30% under 100mW/cm² illumination. This study will help advance the course for the development of low-cost, environmentally friendly, and sustainable solar cell materials from metal oxides.
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    Influence of concentration on properties of spray deposited nickel oxide films for solar cells.
    (Elsevier., 2017) Ukoba, Kingsley Ogheneovo.; Eloka-Eboka, Andrew Chukwudum.; Inambao, Freddie Liswaniso.
    Spray pyrolysis technique was used to deposit various concentration of nickel oxide films on glass substrate. The Effect of varying precursor concentration on elemental, morphological and structural properties was investigated on the deposited NiO films. Nickel (II) acetate tetrahydrate precursor was used at substrate temperature of 350 oC. Precursor concentrations were 0.025, 0.05, 0.075 and 0.1 M. Scanning Electron Microscope (SEM) surface morphology revealed nanostructured films with particles densely distributed across substrates surface. Increased in surface grains was observed as the precursor solution increased. Elemental composition of NiO films revealed presence of Ni and O element. There was reduction in oxygen concentration as precursor solution increases. Amorphous structure was observed at concentration of 0.025 M while polycrystalline with cubic structure was observed at higher concentrations. Preferred orientation was along (1 1 1) peak with small intensity along (2 0 0) peak. XRD patterns have peak diffraction at (2θ = 37 o and 43 o) for (1 1 1) and (2 0 0) planes respectively and 64 o for (2 2 0) plane for 0.1 M. Film thickness grew with increase in precursor concentration. Film micro strain was observed to have compression for all precursor solution conspicuously revealing the effect of varied concentration on NiO films properties
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    Modeling of fabricated NiO/TiO2 P-N heterojunction solar cells.
    (Research India Publications., 2018) Ukoba, Kingsley Ogheneovo.; Inambao, Freddie Liswaniso.
    This paper reports modelling and theoretical validation of a fabricated NiO/TiO2 P-N heterojunction solar cell. The solar cell equations were modelled and thereafter theoretical validation of the fabricated solar cells was performed. Modelling tools were used to validate the influence of NiO material features such as deposition temperature, voltage and defect densities on the performances of an ITO/TiO2/NiO heterojunction solar cell structure. The working points used included a temperature of 350 oC, illumination of 1000 W/m2 using an AM1.5 lamp, with voltage range of 0 to 1.5 volts. The output gave Voc of 0.1445 V, Jsc of 247.959195E-6 mA/cm2 and FF of 37.87 % and Voc 0.7056 and Jsc 28.366911 mA/cm2 when both contacts were added. This opens a new frontier for modelling of metal oxide based thin film solar cells especially NiO thin film solar cells. These findings enhance the quest to develop affordable and sustainable energy and encourage further research in solar cell technologies in low-income countries.
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    Solar cells and global warming reduction.
    (Research India Publications., 2018) Ukoba, Kingsley Ogheneovo.; Inambao, Freddie Liswaniso.
    This study proposes one way of addressing the issue of climate change and pollution using solar cells. The quality of life in developing and low-income countries is on the decline because of air pollution. Energy has a role to play in the quality of life and reduction of air pollution especially in those countries. A reduction in the usage of fossil fuels and biomass in these countries will help decrease the air pollution and emissions generated by such energy sources. About 1 million solar lanterns are capable of reducing greenhouse gas emissions by over 30 000 tons. The role of eco-friendly solar cells in elimination of air pollution cannot be overstated.