Browsing by Author "Gumbi, Bhekumuzi Prince."

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Comparison of metachromatic titration versus a novel nano-gold tagging technique for the detection and quantification of polydiallyldimethylammonium chloride in water samples.
(2013) Gumbi, Bhekumuzi Prince.; Ndungu, Patrick Gathura.; Ngila, Jane Catherine.
Abstract available in PDF file.
Detection and quantification of emerging contaminants in Mgeni and Msunduzi rivers by gas chromatography-mass spectrometry in KwaZulu-Natal, South Africa.
(2018) Gumbi, Bhekumuzi Prince.; Ndungu, Patrick Gathura.; Moodley, Brenda.; Birungi, Grace.
This work concerns the development, optimization and validation of simple and affordable analytical methods for determination of different classes of emerging contaminants in environmental waters and solids. Occurrence of emerging contaminants in the African environment has received much attention recently. However, there is paucity of detailed analytical methods for determination and regulation of emerging contaminants in the environment and wastewater effluents in South Africa today some parts of the world. The developed methods included, extraction with solid phase (clean-up), ultrasound-centrifuge assisted extraction (sediments), detection with gas chromatography-mass spectrometry (after derivatization of polar analytes) and ecological risk assessment technique associated with emerging contaminants. For all developed methods, recoveries (60% - 130%), R2 (> 0.99) and precisions (< 25%) within acceptable limits were achieved. This study was undertaken to determine the occurrence and concentration of major classes of emerging contaminants (pharmaceuticals, personal care products and stimulants) between 2014 and 2016 in Mgeni and Msunduzi Rivers, KwaZulu-Natal, South Africa. Surface water, wastewater (influent and effluent), sediment and biosolid samples were collected from these rivers and wastewater treatment plants along both rivers. The developed methods were combined and applied to qualitative and quantitative analysis of pharmaceuticals (acidic/ non-steroidal antiinflammatory drugs, antibiotic and hormones), stimulants (caffeine) and personal care products (paraben and triclosan). Approximately 50 emerging contaminants of different classes were detected and only 15 were quantified. Environmental concentration of contaminants were found to range from 0.02 μg L-1 to 68 μg L-1 and 0.12 to 220 ng g-1 in water and sediments respectively. Acidic drugs, antibiotic and hormones were detected in all samples analysed in both water and sediments, however, stimulant and PPC were not detected in some of the samples. Wastewater treatment plants were recognised as one of the main routes of emerging contaminants into the aquatic environment. The developed methods can be used to monitor emerging contaminants in the environment.
The influence of metal oxide transport layer and annealing temperature on perovskite solar cells (PSCs)
(2021) Lekesi, Lehlohonolo Petrus.; Malevu, Thembinkosi Donald.; Motaung, Tshwafo Elias.; Gumbi, Bhekumuzi Prince.
Organic-inorganic halide Perovskite Solar Cells (PSCs) are the leading third-generation solar cells with the possibility to provide a fraction of green and affordable energy in the next technological era of solar energy. This type of photovoltaic cell is still new and has recently gained interest due to its low production cost, easy fabrication and rapidly improving power conversion efficiency (PCE). The performance of PSCs depends on the metal oxide/perovskite interface. This work focuses on improving the intermediate contact between the light-active perovskite layer and the electron transport layer (ETL) in a fully ambient PSC by annealing titanium dioxide (TiO2) ETL at extreme temperatures. The TiO2 semiconducting material was successfully synthesized using the hydrothermal method due to the method’s ability to produce pure and crystalline nanoparticles at low temperatures. With the future application of TiO2 projected to flexible conductive substrates, the as-synthesized TiO2 nanopowders were preheated from 200 to 1200 ℃ temperature range prior to deposition to avoid substrate deformation. To investigate the effect of annealing on the synthesized TiO2 nanopowders X-ray diffraction (XRD), transmission electron microscopy (TEM), Scanning electron microscopy (SEM), Energy dispersive x-ray (EDX) spectroscopy, Fourier transform infrared spectroscopy (FT-IR), and Ultraviolet-visible spectroscopy (UV-Vis) techniques were employed to study the structural, morphological, and opto-chemical property changes according to the temperature range described. From the crystal and morphology analysis, the as-synthesized TiO2 nanomaterial appears to be a crystalline multiphase material showing coexistence of anatase and rutile phases. Annealing increases the metal oxide crystallinity, porosity, and particle dispersion. The optical analysis of TiO2 material reveals successful bandgap tuning of the metal oxide wide-bandgap structure. The perovskite active layer was formed through the two-step spin coating of lead iodide (PbI2) and methylammonium iodide (CH3NH3I) respectively. To investigate the morphological structure, thermal and optical properties of TiO2/CH3NH3PbI3 SEM, Thermogravimetric analysis (TGA), Photoluminescence spectroscopy (PL), and UV-Vis techniques were used. Finally, perovskite solar cells of device structure ITO/c-TiO2/m-TiO2/MAPbI3/Spiro-MeoTAD/Conductive Ag ink/ITO were fabricated and their performance was evaluated using the Keithley solar simulator.