Browsing by Author "Kwakye-Awuah, Bright"

Now showing 1 - 2 of 2
  • No Thumbnail Available
    Item
    Electronic and Magnetic Properties of Transition Metal-Doped MoS2 Monolayer: First-Principles Calculations
    (PSS, 2023) MARTIN, HENRY; Boakye, Dennis; Labik, Linus K.; Britwum, Akyana; Nunoo, Oswald Ashirifi; Elloh, Van W.; Kwakye-Awuah, Bright; Yaya, Abu; Abavare, Eric K. K.; 0000-0003-0173-1238
    Density functional theory in the framework of generalized gradient approximation (GGA) of Perdew–Burke–Ernzerhof to investigate the effects of some selected transition metal (TM) and rare-earth metal (RE) dopants on the electronic and magnetic properties of a 2D molybdenum disulfide (MoS2) monolayer is reported. The results demonstrate that it is energetically stable to incorporate Ni and Cu in MoS2 structure under Mo-rich conditions. The pristine MoS2 monolayer has a calculated direct bandgap of 1.70 eV and experiences significant reduction in the gap due to the defects. There is observed induced magnetic behavior due to the tight binding effect originating from the localized dopants and the nearest-neighbor Mo atoms, with magnetic moments ranging between 0.82 and 3.00 μB. Some of the dopants result in 100% spin polarization which is useful for engineering spin filter devices on magnetic MoS2 nanostructures.
  • Thumbnail Image
    Item
    Production of silver-loaded zeolites and investigation of their antimicrobial activity
    (University of Wolverhampton, 2008-12) Kwakye-Awuah, Bright
    The production of silver-loaded zeolites either by ion exchange method or by isomorphous substitution of silver ions into zeolites frameworks and their antimicrobial activity is presented. Silver-loaded zeolites produced by ion-exchange in this work include silver-exchanged zeolite X, silver-exchanged zeolite A and silver-exchanged high-alumina Phillipsite. Silver-doped Analcime was produced by isomorphous substitution of silver ions into the Analcime framework. The silver-loaded zeolites were characterized by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, particle size analysis and Fourier transformed infrared (FTIR) spectroscopy. Studies showed that the amount of silver ions loaded into the zeolites frameworks differed for each zeolite. XRD analysis showed little or no changes in the phase purity of all zeolites before and after ion exchange or before and after substitution of silver ions. SEM analysis and particle size analysis showed that the morphology of each zeolite particles was closely related before and after ion exchanged or before and after substitution of silver ions. The antimicrobial activity of these silver-loaded zeolites was investigated by exposing Escherichia coli K12W-T, Staphylococcus aureus NCIMB6571 and Pseudomonas aeruginosa NCIMB8295 suspended in tryptone soya broth (TSB) to the silver-loaded zeolites. The first stage of the investigation involved the exposure of the strains to silver-loaded zeolites in TSB for a duration of 24 hours at different concentration of silver-loaded zeolites. The second stage involved the exposure of the strains to silver-loaded zeolites in TSB over a period of two hours. The persistency of antimicrobial activity of silver-loaded zeolites was investigated by retrieving i each silver-loaded zeolite from the first exposure cultures, washed copiously with de-ionised water and adding to fresh bacterial suspensions. To understand the mode of antimicrobial activity of the silver-loaded zeolites, the uptake of silver ions by the strains, composition of fatty acid, as well as the DNA content of Escherichia coli K12W-T was studied. The results obtained showed silver ions appeared to elute from the zeolites frameworks into the TSB in anomalous trend. All three microorganisms were completely inhibited within one hour with the silver-loaded zeolites retaining their antimicrobial activity. The release of silver ions from the zeolites frameworks followed first-order kinetics with varying rate constants and halflives. The fatty acid composition of all strains as well as the DNA content of Escherichia coli K12W-T were affected by the action of silver ions.