Theses
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A long essay or dissertation or thesis involving personal research, written by postgraduates of University of Ghana for a university degree.
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Item Photocatalytic degradation of Rhodamine dyes using zinc oxide nanoparticles(Materials Today: Proceedings, 2020) Dodoo-Arhin, D.; Asiedu, T.; Agyei-Tuffour, B.; et al.This paper presents the synthesis of nanocrystalline zinc oxide (ZnO) particles via the sol-gel method using zinc acetate as a precursor. The calcination temperature of the ZnO was varied to determine its effect on particle size. The resultant samples were characterized using X-ray diffraction (XRD), Fourier Transform Infrared (FTIR), UltraViolet–visible Spectroscopy (UV–Vis) and Scanning Electron Microscopy (SEM). Nanocrystalline wurtzite ZnO particles with crystallite sizes ranging from 16 nm to 30 nm were produced. The Energy Band gap of the synthesized zinc oxide nanoparticles decreased with increasing calcination temperature and crystallite size. SEM Micrographs showed rice-like microstructure morphology of ZnO nanoparticles. The usage of the ZnO nanoparticles as a photocatalyst was also explored in the degradation of Rhodamine B dye using UV light, with particular attention paid to the effect of particle size and catalyst load on the degradation efficiency of the dyes. The nanoparticles calcined at 400 C with a crystallite size of 16 nm resulted in the highest degradation efficiency of 95.41% when 0.2 g catalyst loading was applied. 2019 Elsevier Ltd. All rights reserved. Selection and peer review under the responsibility of the scientific committee of the International Symposium on Nanostructured, Nanoengineered, and Advanced MaterialsItem Modified nanostructured titania photocatalysts for aquatic disinfection applications(Materials Today: Proceedings, 2020) Dodoo-Arhin, D.; Bowen-Dodoo, E.; Agyei-Tuffour, B.; et al.According to SDG 6, everyone on earth should have access to safe and affordable drinking water. In sharing water-treatment technologies that lead to accomplishing this goal, it is imperative to devise ways of removing microbial contaminants such as E. coli from drinking water, especially in resource-limited settings that lack centralized water supply systems. One of the approaches is bacterial disinfection of water at the point of use. In this study, the bactericidal effects of the photocatalysis of titanium dioxide-based nanoparticles under UV and visible light are explored. Pristine and silver doped nanostructured mesoporous titanium dioxide (Ag-TiO2, TiO2) particles with high specific surface area and average crystallite domain size of 7.0–7.5 nm were prepared using the simple and cost-effective sol-gel technique followed by thermal treatment. The addition of Ag+ ions during the hydrolysis/condensation of the Ti(IV) molecular precursor led to the homogeneous dispersion of the Ag+ cations on the titania matrix. The As-prepared nanoparticles were characterized using X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area analysis, Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), thermogravimetry, Fourier Transform Infra-Red (FTIR), and Raman Spectroscopy. X-ray diffraction, FTIR, and Raman spectroscopy confirmed that the crystalline structure of the TiO2 matrix corresponds to the anatase polymorph; however, the presence of the dopant led to an increase in the system disorder due to the rise in the concentration of oxygen vacancies. The As-prepared nanoparticles were used for Escherichia coli (E. coli) inactivation under dark and UV–visible light conditions. Under dark conditions, Ag-doped titania and pristine titania resulted in 95% and 64% E. coli population inactivity while under light conditions, 99% and 97% degradation respectively were observed. Taken together, these results demonstrate that, the synthesized TiO2 nanoparticles have promising applications in the light-mediated point-of-use inactivation of bacterial contaminants in water. 2019 Elsevier Ltd. All rights reserved. Selection and peer review under the responsibility of the scientific committee of the International Symposium on Nanostructured, Nanoengineered, and Advanced Materials.Item Synthesis andApplication of Fe-Doped TiO2-Halloysite Nanotubes Composite and Their Potential Application in Water Treatment(Advances in Materials Science and Engineering, 2019) Nyankson, E.; Agyei-Tuffour, B.; Adjasoo, J.; et al.In this work, the potential application of TiO2-Fe-HNT photocatalyst-adsorbent composite in water treatment technologies was confirmed. ,e photocatalyst-adsorbent composite (TiO2-Fe-HNTs) was synthesized by the hydrothermal method and characterized by X-ray diffraction, thermogravimetric analysis, Fourier-transform infrared spectroscopy, scanning electron mi croscopy-energy dispersive X-ray spectroscopy, and diffuse reflectance spectroscopy. ,e adsorption and photocatalysis mechanism by the TiO2-Fe-HNT composite were examined on methylene blue dye, rhodamine blue dye, naproxen sodium (pharmaceutical drug waste), and imidacloprid (pesticide). ,e TiO2-Fe-HNT composite was active in UV and visible regions of the electromagnetic spectrum. ,e adsorption and photocatalytic efficiency increased with increasing amounts of HNTs. ,e photocatalyst-adsorbent composite exhibited excellent removal efficiency for pharmaceutical waste (naproxen sodium) and pesticides (imidacloprid). An adsorption equilibrium data fitted well with the pseudo-second-order kinetics for both methylene blue and rhodamine blue dyes with the intraparticle model describing its rate-controlling steps. ,e Langmuir and Freundlich isotherm models further described the adsorption of methylene blue and rhodamine blue molecules, respectively.Item Effects of substrates on the performance of optoelectronic devices: A review(Cogent Engineering, 2020) Asare, J.; Agyei-Tuffour, B.; Dodoo-Arhin, D.; et al.This review discusses the effects of substrates on devices fabricated for optoelectronic applications. It includes the types and characteristics of substrates, synthesis, and fabrication of substrates, and the influence of substrates on the optical properties, surface morphology, and current-voltage behavior of optoelectronic devices. The study showed that two main types of substrates: planar and textured are commonly used in the industry. Flexibility, semi-rigidity, and rigidity are characteristics of the substrates and they vary in modulus, transparency, and texture. Whereas glass and metal substrates can be produced via melt casting, polydimethylsiloxane (PDMS), polyethylene terephthalate (PET), etc are produced by crosslinking polymer base materials with curing agents. The mechanical and current-voltage characteristics are also shown for planar and textured substrate-based devices. The textured substrates showed ridges, wrinkles, and buckled surface morphology whereas the planar showed uniform and largely flat morphology. Textured substrates also recorded higher optical absorbance and improved device efficiencies than planar substrates. The molecular configuration of the polymer chains is edged-on for planar substrates and edge-on and face-on for textured substrates. The findings and their implications have been discussed to highlight the importance of substrates in the fabrication and performance of optoelectronic devices.Item Cyclic-induced deformation and the degradation of Al-doped LLZO electrolytes in all-solid-state Li-metal batteries(Journal of Power Sources, 2023) Adjah, J.; Orisekeh, K.I.; Agyei-Tuffour, B.; et al.This paper presents the results of a study of the mechanical degradation of Li-oxide garnet solid electrolyte, Li7La3Zr2O12 (LLZO) in all-solid-state lithium metal batteries. A coupled thermo-electro-chemo-mechanical the model was used to analyze the stress-strain distribution and cracking phenomena within the electrolyte. A combination of in-situ/ex-situ microscopic observations, strain mapping, and finite element modeling was deployed to study the progressive deformation and cracking phenomena that occur as a result of electrochemical charging and discharging, thermal runaway, and joule heating phenomena. The results show that strains induced during discharge cycles are more significant than those induced during the charging phase. The accumulation of strains during charging and discharging is also shown to result ultimately in cracking that impedes Li-ion transport, while accelerating electrochemical degradation. The implications of these processes are discussed for the development of robust and durable all-solid-state batteries.Item Awaso bauxite red mud-cement based composites: Characterisation for pavement applications(Case Studies in Construction Materials, 2017) Dodoo-Arhin, D.; Nuamah, R.A.; Agyei-Tuffour, B.; et al.This paper presents the development of Bauxite residue (red mud) based cement composite mortar blocks for applications in pavement construction. The experimental techniques considered include the structural, thermal, morphological, and microscopy analysis of the raw bauxite and red mud samples calcined at 800 °C. Composite mortar blocks of different batch formulations were produced and their physicochemical properties were investigated. The results show that the compressive strength of the as-prepared composite mortar blocks increased by ∼40% compared to the type M mortar strength of ∼2500 N/mm2 . The load-bearing applications of the composites are discussed to influence the adoption of the calcined red mud as a supplement in the production of low-cost Portland cement-based composite mortar blocks for the construction industry.Item Comparative analyses of rice husk cellulose fiber and kaolin particulate reinforced thermoplastic cassava starch biocomposites using the solution casting technique(Polymer Composites, 2021) Agyei-Tuffour, B.; Asante, J.T.; Nyankson, E.; et al.The potential of biodegradable packaging materials from thermoplastic cassava starch (TPS) reinforced with rice husk cellulose fibers (RHCF) and kaolin particu lates (KP) using the solution casting method has been presented. This involved the blending of TPS and RHCF/KP in a plasticizer of ~4 ml of glycerol and ~45 ml of distilled water at 125 C and stirred at 60 rpm until a gel was formed. The gel was cast into sheets and bone-shaped tensile specimens and allowed to dry for 5 days and characterized. The results show a semicrystalline structure for TPS with a ~36% increase in crystallinity after reinforcement. The O-H bond stretching and the C-H bending bonds due to starch–glycerol reactions were the common functional groups in TPS–RHCF biocomposites, and Si-O-C bonds were characteristics of the silica phase in the kaolin. The water vapor transmission rate (WVTR) reduced to ~34% with KP reinforcements from ~238 g/m.day to 177 g/m. day and to ~74 g/m.day and ~164% for TPS–RHCF. The strength increased with up to 50 wt% kaolin content; ~0.96 MPa yield strength and ~2.60 MPa ultimate tensile strength (UTS) were recorded. For the RHCF reinforced composites, TPS 50 wt% also showed high strengths of ~0.96 MPa yield strength and ~3.50 MPa UTS. The WVTR reduced as the content of kaolin was increased. Typically, from 0 to 30 wt% volume fraction of kaolin, the WVTR was reduced by ~34% to 177 g/m. day for TPS–kaolin and by ~164% to ~74 g/m.day in TPS–RHCF. The as-prepared biocomposites have the potential as good packaging materials.Item Layered Nanomaterials - A Review(2012) Yaya, A.; Agyei-Tuffour, B.; Dodoo-Arhin, D.; et al.Layered materials can become a myriad source of two-dimensional crystals if the layers can be separated from each other, for example via exfoliation. Potential applications for single-layer materials range from energy storage, electronics, and mechanical reinforcement of plastics, to life-saving applications such as drug delivery, medical imaging, and clean-up of toxic materials in the environment. Layered nanomaterials can be found naturally and can also be synthesized in the laboratory to suit certain specific applications. We describe here key layered materials including some naturally occurring (graphite, graphene, clays, layered hydroxides (LDHs)) and others that have been synthesized through chemical combination of some atomic species such as boron nitride (BN), transition metal oxides (TMOs), LDHs, and transition metal dichalcogenides (TDMs), along with a discussion of their properties and potential applications.Item Application of Discarded Rubber Car Tyres as Synthetic Coarse Aggregates in Light Weight Pavement Concretes(American Journal of Materials Science, 2015) Dodoo-Arhin, D.; Mensah, S.A.; Yaya, A.; Agyei-Tuffour, B.The increasingly high cost of building construction materials is a major factor affecting quality housing delivery in Ghana. The current trend of continuous and increasing demand for these natural resources has necessitated extensive research into alternative low-cost construction materials such as recycled materials with comparable properties. The characteristics of concretes produced using locally available discarded rubber car tires as coarse aggregates have been investigated. Batch formulation of 0%, 25%, 50%, 75%, and 100% substitution of natural coarse aggregates with the rubber aggregates is considered. A comparison of the physico-mechanical properties of batch formulations by weight % and volume % have also been investigated. Generally, the compressive strength of the concretes decreased as the percentage of the rubber increased in the two batch formulations. At 25% replacement, the compressive strength of 9.26 N/mm2 (weight %), 11.56 N/mm2 (vol %) as compared to 14.80 N/mm2 and 24.00 N/mm2 respectively for the controlled program were obtained.Item Characteristics Of Stabilized Shrink-Swell Deposits Using Eggshell Powder(2013) Nyankson, E.; Agyei-Tuffour, B.; Annan, E.; et al.Shrink-swell soils expand and heave or contract and crack during periods of high and low moisture content. The expansion and contraction cause the lifting and or sinking of structures, crack development, and eventual collapse of engineering structures. The need to stabilize such plastic soils to improve their load-carrying capacities cannot be overemphasized. Therefore in this article, the effect of lime contained in eggshells and its application in the stabilization of shrink-swell soils have been explored. 4wt% and 8wt% of eggshell powder were mixed with equal masses of two different soil samples from Dodowa (DD) and Adalekope (AD) in Ghana. The samples were characterized with X-ray fluorescence (XRF), Plasticity Index analysis (PI), Free Swell Index (FSI), pH test, and a grading test. The x-ray fluorescence results showed that eggshell contains about 52wt% of CaO, which is largely responsible for soil stabilization. The sample mixed with 8wt% eggshell powder showed a decreased PI, FSI, and a high silt/clay fraction. The results obtained have been discussed and can influence the application of eggshell powders for large-scale stabilization of expansive soils.