Department of Materials Science and Engineering

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    A Comparative Study of Phosgene Sensing Using Carbon and Boron Nitride Nano Materials – A DFT Approach
    (University of Ghana, 2021-04) Kweitsu, E.O.
    Phosgene (COCl2), a valuable industrial compound, maybe a public safety and health risk due to potential abuse and possible accidental spillage. Conventional techniques suffer from issues related to procedural complexity and sensitivity. Therefore, there is a need for the development of simple and highly sensitive techniques that overcome these challenges. Recent advances in nanomaterials science offer the opportunity for the development of such techniques by exploiting the unique properties of the nanostructures. In this study, we investigated the potential of six types of nanomaterials: three carbon-based ([5,0] CNT, C60, C70) and three boron nitride-based (BNNT, BN60, BN70) for the detection of COCl2. The local density approximation (LDA) approach of the density functional theory (DFT) was used to estimate the adsorption characteristics and conductivities of these materials. The results show that the COCl2 molecule adsorbed spontaneously on the Fullerene or nanocages and endothermically on the pristine zigzag nanotubes. Using the magnitude of the bandgap modulation, the order of suitability of the different nanomaterials was established as follows: PBN60 (0.19%) < PC70 (1.39%) < PC60 (1.77%) < PBNNT (27.64%) < PCNT (65.29%) < PBN70 (134.12%). Since the desired criterion for the design of an electronic device is increased conductivity after adsorption due to the resulting low power consumption, PC60 was found most suitable because of its power consumption as it had the largest decrease of 1.77% of the bandgap.
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    The Effects of Inoculum Acclimatisation on the Methanogenesis of Ecklonia Maxima
    (University Of Ghana, 2020-06) Darko, C.N.S.
    In the present scenario of the over dependence and shortcomings of fossil fuels, integrated biorefinery techniques have been developed to process biodegradable and sustainable feedstock for use as green energy. Brown seaweed biomass, recently has been under the spotlight for the production of biogas via anaerobic digestion. In this study, the effects of acclimatising inoculum to Ecklonia maxima, a brown seaweed type for the production of biogas have been investigated. Biomass of Ecklonia maxima were subjected to an acclimatisation period to enable anaerobic microbes cultured on the inoculum adapt to the feedstock. Mixtures of Ecklonia maxima with either acclimatised or unacclimatised inoculum were prepared and anaerobically digested for a period of 20 days. The proximate and ultimate results carried on the feedstock confirmed them suitable for the purpose. The carbon, hydrogen, nitrogen and sulphur (CHNS) content analysis result was used to calculate the theoretical yield potential which was 1844.0 ml/gVS for Ecklonia maxima. SEM - EDX were conducted on the samples to observe their morphology and chemical compositions. Fourier transform infrared (FTIR) spectroscopy was further conducted to identify the bonds and functional groups where both spectra recorded the presence of carboxylic, hydroxyl, ketones and ethers groups. Samples of biogas produced were analysed using gas chromatography to characterise the percentage of carbon dioxide (CO2) and methane (CH4). An optimum amount of ~55% methane was recorded by the mixture of Ecklonia maxima and acclimatised inoculum. The cumulative biogas yield for acclimatised sample was recorded as 1571.8 ml/gVS, very similar to 1564.0 ml/gVS predicted as the biogas potential (A) at a production rate (μ) of 296.2 ml/day using the modified Gompertz equation. The volume of biogas generated from the feedstock implies a positive influence of acclimatising inoculum on E. maxima
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    Design and Fabrication of a Sustainable Construction Brick
    (University Of Ghana, 2019-07) Asante, E.
    The urgent need for affordable housing is driving the research for cheap and sustainable building materials. The nuisance caused by cocoa pod husks, which is an agro waste, could be curbed by the incorporation of potash derived from its ash into brick batch mix. These potash incorporated bricks tend to allow sintering at lower temperatures thus reducing production cost and hence making them cheaper. In this project, the SiO2 – Al2O3 – K2O ternary phase diagram was used to design three compositions for brick batches. Briquette samples for both compositionally designed batches and control batches were fabricated and fired. Hydration and water absorption tests were undertaken for the various samples to ascertain durability and response to moisture. Brick samples were also fabricated and fired at 500 °C and 600 °C respectively, with their water absorptivity and compressive strengths measured. The compressive and water absorption test results were higher for 500 °C than at 600 °C due to the black core effect.
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    Synthesis, Characterization and Investigation of Tio2 Based Nano-Catalysts for Water Treatment Application
    (University of Ghana, 2019-07) Bowen-Dodoo, E.
    Nano titanium dioxide (TiO2) has been found to possess enhanced antibacterial properties and has thus been employed in various photocatalytic applications. Studies have confirmed higher photocatalytic activity when the TiO2 photocatalyst is doped with silver (Ag). The reported enhancement is due to valence band electrons being excited at longer wavelengths, hence extending absorbance further into the visible light region. For nano catalysts that interact in such a region, they are termed visible light active (VLA) photocatalysts. It is favourable to produce such catalysts since visible light accounts for about 50% of the solar spectrum whereas ultraviolet (UV) light accounts for just around 5%. Pristine TiO2 and Ag doped TiO2 nanoparticles were synthesized by the sol-gel method. The nanoparticles were characterized by X-Ray diffraction (XRD), Brunauer Emmett Teller (BET), Thermogravimetric analysis (TGA), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). COMSOL Multiphysics software was used to model the optical properties of undoped and Ag doped TiO2. Bacteria inactivation in light conditions was mainly due to the generation of reactive oxygen species (ROS). Photocatalytic activity in the visible light region was successfully demonstrated by the Ag doped TiO2 nanoparticles for the degradation of Escherichia coli (E. coli) bacteria. The results for Ag doped TiO2 indicate 100% inactivation of E. coli after 2 hours under UV-A irradiation and 99% bacteria inactivation 4 hours when exposed to visible light. Photocatalytic experiments with bare TiO2 nanoparticles rendered E. coli colonies inactive at time of 4 hours in UV-A light condition. The inactivation rate was 100%. Under visible light, the undoped titania showed significant inactivation but it was clear that the photocatalytic effect could not improve due to insufficient ROS production. In dark condition, both Ag doped titania and bare titania had an effect on the E. coli population. This was attributed to direct contact with Ag ions resulting in the formation of toxic Ag species and effect of adsorption stresses respectfully. COMSOL simulations confirmed the surface plasmonic resonance effect of the Ag nanoparticles. This gave an insightful explanation to the experimental photocatalytic bacteria studies conducted.
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    Fabrication and Characterisation of Biodegradable Polymer Composites for Packaging Applications.
    (University of Ghana, 2019-06) Tuah, J.A.
    Environmental pollution by non-biodegradable plastics, gradual reduction and increase in cost of petroleum products used have affected lives over the years. With people using different kinds of packaging, it has a part of human daily living. Therefore, it is very important to find lasting and sustainable ways of producing and managing the wastes generated by these plastics. In this work, starch based biocomposites are fabricated and characterised to access its opportunities to replace petroleum based plastics. The modifiers that were considered for reinforcement purposes were nanokaolin and cellulose nanofibers extracted from rice husk. Stress strain diagrams were obtained from the tensile test method. From the stress-strain curve, the yield strength, ultimate tensile strength and the fracture strength of the various biocomposites were determined. The material that was shown to give good response to the tensile load in terms of the yield, and fracture was seen to be TPS-0.2kaolin biocomposite. This can be associated to goof interphase reaction between the nanoclay and the starch polymer at nanoclay volume fraction of 0.2. Water vapour transmission test also pointed to biocomposites of cellulose volume fraction 0.5 as the appropriate material with best water vapour barrier properties. This is associated to the reason that at cellulose volume fraction of 0.5, the cellulose whiskers are very compact and dispersed all over the biocomposites and hence restricts the escape of water in the form of gas from the film. This confirms the reason why the strength of the TPS-cellulose biocomposite is higher at volume fraction of 0.5. FTIR analysis was conducted for thermoplastic starch (TPS) only, TPS-nanokaolin biocomposites and TPS-cellulose biocomposites. The spectra for TPS only pointed to the presence of OH-stretching due to the water used during fabrication, CH- bending and some C-C bonds. The spectra for TPS-nanokaolin was similar to that of thermoplastic starch, however, there was a new band showing the presence of Si-O-C bonds due to the chemical reaction of the nanokaolin (alumino-silicate) to the water and starch. The spectra for TPS-cellulose showed the presence of OH- stretching bond, CH-bends, C-C bonds. The FTIR results showed the presence of water and other chemiclas that affect the strength of the biocomposites prepared. This gives an idea of what to expect for the results of the mechanical properties. Scanning Electron Microscope micrographs shows that nanokaolin particles were successfully introduced into the TPS matrix and it was uniformly dispersed in TPS-nanokaolin nanocomposite films at optimum nanokaolin volume fractions. The micrographs for TPS-cellulose biocomposites showed that cellulose fiber was successfully introduced into the TPS matrix but the fibers were not uniformly distributed. Energy Dispersive X-ray spectroscopy (EDX) also gave the representation of elements present in the TPS-nanokaolin and TPS-cellulose biocomposites. This analysis technique confirmed the presence of Al, Si, O (known to be present in nanokaolin), and C (known to be present in starch and glycerol) in TPS-nanokaolin biocomposites. Also, the presence of O, C, Ca, Si, Na was confirmed in TPS-cellulose biocomposites. With C, O representing the elements in cellulose, Ca and Si known to be elements which are present in rice husk. The Na was recorded as a traces left after the extraction process. Biocomposites prepared from starch, glycerol, and nanokaolin composites are seen to show broad peaks which is known for semi-crystalline materials. However, the degree of crystallinity increases as the volume fraction of nanokaolin increases.
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    Synthesis and Characterization of Zinc Oxide Nano-Particles for Photovoltaic Application
    (University Of Ghana, 2018-07) Takyi, G.K.S.
    The low total conversion efficiency of dye sensitized solar cells have caused researchers to improve the individual components of the cell. This work aims to produce zinc oxide nanoparticles to help improve absorption and also reduce recombination in the photo anode of the dye-sensitized solar cell (DSSC). In this work, zinc oxide nanoparticles were produced using the hydrothermal synthesis technique and the annealing effect was conducted on the prepared samples. The samples prepared were characterized using X-ray diffraction analysis (XRD), Scanning electron spectroscopy (SEM), energy dispersive spectroscopy (EDX), Fourier-transform infrared spectroscopy (FTIR), diffuse reflectance spectroscopy (DRS), thermal analysis (TGA/DSC). The XRD results indicated that hexagonal wurtzite phase were produced with a dominate diffraction peak of (002) at the highest hydrothermal temperature and at the annealing temperature of 500 ℃ for 30 minutes. The SEM results show nearly spherical particles with enhanced agglomeration whiles the EDX results confirmed the presence of zinc and oxygen elements without any impurity. The DRS results show a significant increase in absorption when the samples were annealed. Furthermore, the TGA/DSC results showed the stability of zinc oxide above 400 ℃. This study suggests that the synthesized zinc oxide nanoparticles might perform excellently in DSSC photo anode.
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    Synthesis and Application of Pure and Modified Tio2 for Photocatalytic Remediation of Fractionated Crude Oil.
    (University Of Ghana, 2018-07) Gbogbo, S.
    Oil spills have been a major source of concern due its harmful effect on the environment. To reduce the effect of oil spills, new remediation strategies need to be developed whiles enhancing the efficiency of existing remediation ones. In this study, the potential of TiO2 and its modified form (Fe-TiO2) as a stand-alone or as an add-on remediation strategy was explored. This was carried out by accessing the how TiO2 and Fe-TiO2 photodegrades crude oil fractions (aromatics, paraffins, asphalthenes) under sunlight, visible (400W) and UV light with four (4) hours irradiation time. The TiO2 and the Fe-TiO2 used were synthesized with the mild hydrothermal method and characterized with XRD, UV-Vis, DRS, SEM, EDX, TGA, DSC and FTIR. These characterization techniques confirmed the production of the anatase phase TiO2 and Fe-TiO2 with estimated bandgap of 3.12 eV and 2.90eV, respectively. The Debye Scherrer’s equation was used to compute the crystallite size from the XRD patterns as 4.10 nm and 3.85 nm for TiO2 and Fe-TiO2, respectively. The photodegradation experiments on the aromatics, paraffins and asphalthenes showed that Fe-TiO2 is better at degrading the fractions than TiO2 under visible light and sunlight irradiation. These conclusions were arrived at from the analysis of the photoproducts using UV-Vis, FTIR and GC/MS. The GC/MS spectra showed the formation of new compounds, diminishing in the concentration of existing compounds and the disappearance of existing compounds. It was revealed that, photocatalysis is effective in remediating aromatics than asphaltenes and paraffins. The results from the study showed the potential of photo-remediation as a stand-alone or add-on oil spill response strategy.
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    Effects of Metakaolin as Supplementary Cementitious Material in Mortars for Construction Applications
    (University of Ghana, 2018-07) Marfo, K.K.
    This work presents the effects of metakaolin as a supplementary cementitious material in mortars for construction applications. Kaolin from Teleku Bokazo was calcined at 650oC and partially used to replace Portland limestone cement to produce mortars and paste. The metakaolin was successfully used in a cement paste and its effect observed in the different cement replacements proportions. The replacements ranged from 10% - 35% by mass and characterised after 3, 7, 14 and 28 days of curing. Kaolin was characterized using X-ray diffractometer (XRD) with illite, kaolinite and quartz as the main crystalline phases. The metakaolin was also characterised using XRD with quartz as the main crystalline phase. Calcium silicate hydrate, calcium aluminium silicate hydrate, portlandite, calcite and ettringite were some of the hydrated compounds formed in the hydrated pastes. Fourier transform infrared spectroscopy was used to determine the functional groups of the hydrated cement products formed from the metakaolin cement paste. Other test including initial setting and water consistency were also carried out. Water consistency and setting times generally increased with increase in metakaolin addition. The optimum metakaolin replacement for flexural strength after 28 days curing was 15 and 20% whereas the compressive strength after 28 days curing was 20% metakaolin replacement. Generally, the metakaolin reduced the amount of water absorbed by capillary action for the 28 days cured mortar bars. The results suggest that 20% metakaolin replacements of Portland limestone possess characteristics that can be adopted for use in mortars for construction applications.
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    Effects of Metakaolin as Supplementary Cementitious Material in Mortars for Construction Applications
    (University of Ghana, 2018-07) Marfo, K.K.
    This work presents the effects of metakaolin as a supplementary cementitious material in mortars for construction applications. Kaolin from Teleku Bokazo was calcined at 650oC and partially used to replace Portland limestone cement to produce mortars and paste. The metakaolin was successfully used in a cement paste and its effect observed in the different cement replacements proportions. The replacements ranged from 10% - 35% by mass and characterised after 3, 7, 14 and 28 days of curing. Kaolin was characterized using X-ray diffractometer (XRD) with illite, kaolinite and quartz as the main crystalline phases. The metakaolin was also characterised using XRD with quartz as the main crystalline phase. Calcium silicate hydrate, calcium aluminium silicate hydrate, portlandite, calcite and ettringite were some of the hydrated compounds formed in the hydrated pastes. Fourier transform infrared spectroscopy was used to determine the functional groups of the hydrated cement products formed from the metakaolin cement paste. Other test including initial setting and water consistency were also carried out. Water consistency and setting times generally increased with increase in metakaolin addition. The optimum metakaolin replacement for flexural strength after 28 days curing was 15 and 20% whereas the compressive strength after 28 days curing was 20% metakaolin replacement. Generally, the metakaolin reduced the amount of water absorbed by capillary action for the 28 days cured mortar bars. The results suggest that 20% metakaolin replacements of Portland limestone possess characteristics that can be adopted for use in mortars for construction applications.
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    Effects of Metakaolin as Supplementary Cementitious Material in Mortars for Construction Applications
    (University of Ghana, 2018-07) Marfo, K.K.
    This work presents the effects of metakaolin as a supplementary cementitious material in mortars for construction applications. Kaolin from Teleku Bokazo was calcined at 650oC and partially used to replace Portland limestone cement to produce mortars and paste. The metakaolin was successfully used in a cement paste and its effect observed in the different cement replacements proportions. The replacements ranged from 10% - 35% by mass and characterised after 3, 7, 14 and 28 days of curing. Kaolin was characterized using X-ray diffractometer (XRD) with illite, kaolinite and quartz as the main crystalline phases. The metakaolin was also characterised using XRD with quartz as the main crystalline phase. Calcium silicate hydrate, calcium aluminium silicate hydrate, portlandite, calcite and ettringite were some of the hydrated compounds formed in the hydrated pastes. Fourier transform infrared spectroscopy was used to determine the functional groups of the hydrated cement products formed from the metakaolin cement paste. Other test including initial setting and water consistency were also carried out. Water consistency and setting times generally increased with increase in metakaolin addition. The optimum metakaolin replacement for flexural strength after 28 days curing was 15 and 20% whereas the compressive strength after 28 days curing was 20% metakaolin replacement. Generally, the metakaolin reduced the amount of water absorbed by capillary action for the 28 days cured mortar bars. The results suggest that 20% metakaolin replacements of Portland limestone possess characteristics that can be adopted for use in mortars for construction applications.