Browsing by Author "Muya, Francis Ntumba"

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    Box-behnken design optimization of photocatalytic performance of znwo4 nanoparticles multiple doped with selected metals
    (Elsevier B.V., 2025) Muya, Francis Ntumba; Ameh, Alechine Emmanuel; Abubakar, Hassana Ladio
    Box-Behnken Design Optimization of the photocatalytic activity of the synthesized Na@Mg@Ti@ZnWO4 nanocomposite at different mixing ratios for the degradation of malachite green in wastewater was investigated. The synthesized ZnWO4-based nanomaterials were characterized using different analytical techniques. Optical analysis demonstrated a reduction in the band gap energy from 4.68 eV for ZnWO4 to 2.08 eV for the doped ZnWO4. HRTEM/HRSEM images revealed the formation of well-defined nanocrystals with distinct lattice fringes, while EDX confirmed the homogeneous distribution of dopants (Na, Mg, and Ti) on ZnWO4. The XRD analysis showed that the incorporation of the dopant did not change the phase of ZnWO4. In ZnWO4, XPS revealed electron sharing between 3 s (Na and Mg) and 3d (Ti) dopants. The host and doped ZnWO4 surface areas increased from 24.74 m2/g to 156.93 m2/g. Compared to the SPCE/ZnWO4/Na/Mg/Ti electrode, cyclic voltammetry analysis confirmed strong conductive properties. Maximum removal of 99.93 % malachite green (MG) from wastewater was achieved using catalyst load (0.7 g) (ZnWO4@NaMgTi), contact time (35 min), and pH 12. Even after five repeated cycles, ZnWO4 nanocomposite doped with 1 % Na, 1 % Mg, and 1 % Ti exhibited superior photocatalytic behavior than other ZnWO4 nanoparticles. A toxicity test demonstrated that dyeing wastewater treated with ZnWO4@NaMgTi nanocomposites supported aquatic life (juvenile fish) better than untreated dyeing wastewater, standard water of fish farming, and water treated with ZnWO4 nanoparticles alone. The immobilization of ZnWO4 with the dopants contributed to the enhanced photocatalytic and electrochemical performance.
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    Hydrogel encapsulated biosensors for the detection of biologically significant vanadium and selenium
    (University of the Western Cape, 2017) Muya, Francis Ntumba; Baker, Priscilla; Iwuoha, Emmanuel
    Vanadium and selenium salts are toxic in large amounts, but trace amounts are necessary for cellular function in many organisms. Exposure to high level of selenium has been linked to delays in early childhood development as well as the development with onset of diabetes type II. Vanadium is a relatively controversial dietary supplement, used primarily for increasing insulin sensitivity. These metals have been identified as potential human carcinogens that disrupt cellular metabolic processes at high level, causing lung cancer, brain damage and DNA damage. Developing a sensor system that can monitor the level of vanadium and selenium in aqueous and selected real samples is a strong priority.
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    Hydrophilic Polysulfone-Hydrogel Membrane Material for Improved Nanofiltration in Wastewater Treatment
    (University of the Western Cape, 2013) Muya, Francis Ntumba; Baker, Priscilla
    Over the last decade polysulfone membranes have been demonstrated to be one of the best membrane types in wastewater treatment, especially in ultrafiltration, owing to its mechanical robustness, structural and chemical stability. Regrettably these membranes are mostly hydrophobic by nature and therefore highly vulnerable to fouling due to chemosorptive mechanisms. Fouling may be caused by cake formation on the surface of the membrane or by surface assimilation of the foulants. Many studies have been directed at improving hydrophilic properties of polysulfone membranes by introducing different types of nanoparticle composite such as TiO2, ZnO2, Au and Ag nanoparticles to the polymer matrix, in order to reduce fouling potential and increase membrane performance. In the present investigation a hydrogel material was developed by crosslinking polyvinyl alcohol (PVA) with polysulfone (PSF), using glutaraldehyde as crosslinker. PVA has excellent film formation, emulsifying and adhesive properties, it is highly flexible and has high tensile strength. Introducing PVA into the PSF polymer matrix was expected to impart its advantageous properties onto the resulting membrane and enhance hydrophilic characteristics of the membrane. The cross linking of PVA and PSF was controlled at three different ratios to evaluate the effect of the PSF contribution i.e. 25:75, 50:50 and 75:25. The crosslinked polymer composites produced three unique hydrogel materials, which were evaluated for the separation of selected small organic molecules, under hydrodynamic conditions, using rotating disk electrochemistry. The hydrogel thin film behaved as a chemical sensor for the oxidation of tannic acid in aqueous solution, with negligible shift in peak potential as a function of concentration. The nanomaterials prepared were characterised using spectroscopic, morphological and electrochemical techniques. Hydrogel performance in the presence of analyte molecule was evaluated by hydrodynamic voltammetry and electrochemical impedance spectroscopy. From calibration curves based on cyclic voltammetry, hydrodynamic, macroscopic and spectroscopic techniques, the 75% polysulfone and 25 % polyvinyl alcohol hydrogel (75:25 PSF-PVA) presented the best performance for quantitative detection and best sensitivity toward alginic acid and tannic acid than the corresponding composites (50:50 and 25:75 PSF-PVA). Optical results (contact angle) show an agreement with spectroscopic (EC) and microscopic (AFM) result. A decrease in contact angle gives an increase in roughness and diffusion coefficient. High surface roughness was linked to improved hydrophilicity of the polysulfone.