Center for Materials Engineering

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Now showing 1 - 19 of 19
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    Investigating The Mechanism of Expansive Black Cotton Soil Stabilization With Sewage Sludge Ash Using Experimental & Image Analysis Methods
    (Addis Ababa University, 2023-11) Bereket Mulugeta; Anteneh Marilign (PhD)
    Huge machineries and lots of earthmovings are needed for soil stabilization procedure, which makes it an expensive and labor-intensive process. Finding novel, affordable materials that can advance construction methods and permit the growth of the road network is currently in high demand. Particularly, there has been a rise in interest in the hunt for novel, less expensive soil stabilizers and construction methods. At a height of about 2000 meters above mean sea level, Addis Ababa, the capital city of Ethiopia, is mostly covered in clay expansive soil. In engineering, it is crucial to enhance expansive soil; mechanical strength and swelling-shrinkage characteristics. In this study, an experimental investigation has been carried out to determine the possibility of stabilizing expansive black cotton soil (EBCS) using municipal sewage sludge ash (SSA). Prior to the experimental study compositional analysis of the EBCS and the SSA have been made using complete silicate analysis. The results revealed that the SSA can be used as Alternative supplementary cementitious materials (ASCM) and has more CaO content, which makes it suitable for Hydration and pozolanic reaction. Effect of adding variable composition of SSA, from 4 to 10%, in the EBCS performance characteristic has been analyzed. Parameters which were analyzed as performance indicators were stability conducted in the laboratory to obtain the California bearing ratio (CBR),Maximum Dry Density(MDD), and Atterberg limit (PI, LL, SL). Studying microstructural analysis of soil samples that passed through a 32μm sieve, the EBCS, SSA and soil-SSA composite were analyzed for surface area using a BET, and the results revealed a sizable reduction. Surface area for expansive soil is168.422 m2/gm and after SSA treatment, it was reduced to 145.646 m2/gm. Moreover, microstructural analysis using a scanning electron microscope (SEM) and complete silicate analysis was conducted to gain insight into the material behavior, and images from the SEM were analyzed through the Fiji Image J analyzer in order to characterize the surface texture characteristics of EBCS, SSA and soil-SSA composite. It is concluded from the present study that the SSA could be used for the stabilization of EBCS for highway subgrade. By reducing surface area and filling soil pores with sewage sludge ash, along with hydration reaction and some pozzolanic reaction between EBCS clay particle and SSA, it is possible to change the physical properties of soils to increase their capacity for bearing loads.
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    Value added Consumer Product from Finished Leather Waste Incorporated with Bamboo Fiber for better Strength Property
    (Addis Ababa University, 2023-10) Aster Mekasha; Anteneh Wodaje (PhD)
    Finished leather waste is one of the most highly generated solid wastes. However, there is no proper utilization of these huge amounts of waste. So preparation of leather boards from finished leather waste is economical and helps in reducing environmental pollution, and also incorporating the plant fibers into leather board enhances its mechanical properties. In this research different treatment methods, such as water retaining, alkali treatment, and the combination of water and alkali treatment was used for the extraction of bamboo fiber. Then 5% alkali treatment was the optimum result for this research. After that fiberized finished leather waste mixed with the plant fibers in various proportions of 0, 1%, 5%, 10%, and 15% were used to prepare the composite leather board. Two different types of binders, mainly urea formaldehyde and fevicol synthetic in the proportion of 10%, 15%, 25%, 35%, and 45%, were used for the study. Here also 15% was optimum for both formaldehyde and favicon resin binder. The prepared leather board were characterized using the following techniques: Fourier transform infrared spectroscopy (FTIR), thermal stability (TGA), scanning electron microscope (SEM), tensile strength, water adsorption and desorption, flexing index, chromium six, and formaldehyde content. The results show that plant fibers improve the strength property of leather boards. Among the composite leather boards, composite board with 10% bamboo fiber with 15% urea formaldehyde, and fevicol synthetic resin show better strength property. However, the strength property of urea formaldehyde is better than that of fevicol binder. Therefore, this composite leather board can be used as a raw material for the preparation of leather goods (as a reinforcing material), false roofing, foot wear (insole board), mouse pads, interior decorations, and wall partitioning. The study also envisions the production of cost-effective composite, by converting the waste into wealth and thereby simultaneously reducing environmental pollution.
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    A Study on Optical Quality Enhancement of Alpha-Alumina/Titania Pearlescent Pigment Via Insitu Ph Control
    (Addis Ababa University, 2023-10) Buziye Guye; Anteneh Marilegn (PhD)
    Pigment is a material that changes the color of reflected or transmitted light as the result of wavelength- picky immersion. During high-temperature calcination, there is a problem with the thermal expansion coefficient mismatch between mica and titania and the resulting thermal stress and crack formation. Thermal stress and crack formation is an issue during high-temperature calcination. Formation of cracks in the coating layer results in the scattering of light and the consequent decline of pearl luster. Various researchers have conducted a study on the low temperature rutile phase formation; however, the attempts have resulted in higher rutile phase fraction on the final coating but in most cases with compromised optical quality. In this study, α-Al2O3 platelets of average particle size ⁓ 10μm have been synthesized to be used as a substrate for the pearlescent pigment. Coating of TiO2 on the surface of the synthesized α-Al2O3 was performed via co-precipitation method. Urea was utilized as a hydrolyzing and pH-regulating agent along with TiOSO4 as a precursor to TiO2The sample with lower oxysulfate:urea ratio (i.e. strongly acidic synthesis media) resulted in higher rutile phase fraction (41.5%) while the other two samples, where the oxysulfate:urea ratios are 1:25 (i.e. close to neutral pH) and 1:50 (i.e. strongly basic synthesis media), resulted in extremely lower rutile phase fraction, 2.9% and 1.4% ,respectively. The coated samples' morphology showed that the entire coating was smooth. When compared to samples with lower rutile phase fractions, those with greater rutile phase fractions exhibit higher reflactance in the visible area, according to the optical performance of the samples. The color value measurments have also revealed that, samples with higher rutile fractions exhibit higher lightness values (L*) in comparison to those with lower rutile phase fractions. The study showed that, in general, controlling the rutile phase fraction by adjusting the pH of the synthesis media using in-situ urea decomposition was effective in producing TiO2 coatings with higher rutile phase fractions and better surface smoothness, which in turn results in higher optical quality.
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    First-Principles Study Of Van Der Waals Heterostructures of MoSeTe/ZnO for Investigating Photocatalytic Water-Splitting and Photovoltaic Applications
    (Addis Ababa University, 2023-06) Derese, Abraham; Georgies, Alene (PhD)
    Two-dimensional (2D) heterostructures have allowed for the development of novel properties with interesting applications in photocatalytic water splitting and optoelectronic devices. Electronic properties of ZnO and Janus MoSeTe monolayers were investigated using density functional theory (DFT)-based first-principles calculations, and depending on the lattice mismatch, layered 2D MoSeTe/ZnO heterostructures were produced. In this study, the first-principles van der Waals corrected density functional theory calculations were also performed on ABI_Se, ABI_Te, and ABII_Te heterostructure.Out of eight basic stacking patterns of the ZnO/MoSeTe hetero-bilayer designed, the ABII-Te stacking mode was a more stable stacking type due to the small lattice mismatch and the binding energy. The result showed that the band alignment for ABI_Se, ABI_Te, and ABII_Te was done on the electrical band structure and band edge positions, and confirmed type two band alignment. In addition, the ABI_Se, ABI_Te, and ABII_Te configurations of ZnO/MoSeTe vdW heterostructures are indirect band gap semiconductors. The investigated 2D ZnO/MoSeTe heterostructures have an acceptable band gap for solar applications, according to a first-principles study. The power conversion efficiency of ZnO/MoSeTe heterostructure is computed, and the results exhibit ABI_Se, ABI_Te, and ABII_Te stacking orientations have high efficiency with values of 22.26%, 22.31%and22.17%, respectively. Therefore, our findings show the heterostructures have reasonable band gaps and high PCE, and exhibit type-II band alignment, which are suitable candidates for solar cell application. Furthermore, for full water splitting heterostructures cannot satisfy the band edge requirements; however, the heterostructures are a good photocatalyst for the hydrogen evolution reaction. The heterostructure's ability to split water more effectively can be improved by moving the band edges position using strain and doping.
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    Designing A Solar PV Powered Reverse Osmosis Desalination System Using Rosa to Clean Lake Basaka Water
    (Addis Ababa University, 2023-07) Bethlehem, Terzu; Georgies, Alene (PhD)
    The freshwater shortage is an issue concerning safe water supply. The availability and usage of fresh water are critical for human health as well as economic and ecological stability. The continual increase in salinity and alkalinity hindered the utilization of Lake Basaka for drinking, irrigation, and residential purposes. In this study, ROSA software is used to design an appropriate membrane to filter Lake Basaka water at higher rejection and specified recovery, flux, permeate, and feed flow. The ROSA software-designed TW 30-2540 membrane for the RO System provided the required permeate flow rate of 0.21 gpm with an applied pressure of 100.94 psig, recovery of 14.89%, rejection of 99.56 %, flux of 10.80 gfd, salt passage of 0.44% at an adjusted feed pH of 8, and system temperature of 25 °C. As a consequence, ROSA Software designed the TW 30-2540 membrane for solar-powered RO to filter Lake Basaka water without displaying a design warning. In this regard, a solar-driven reverse osmosis system with five filter stages, including three pretreatment filter stages, one membrane stage, and one post-treatment filter stage, was used to filter Lake Basaka water by removing organic and inorganic components such as suspended particles, dissolved solids, and water pollutants from feed water driven by solar energy as an energy source. The samples collected for water quality examination were 4 liters of water in a clean plastic bottle as part of the sampling procedures from Lake Basaka and RO-filtered Lake Basaka water is evaluated by using AAS and MP-AES, respectively. As comparing Lake Basaka water analyzed before and after RO filtration Na, Mg, Ca, K, Co3 2-, HCo3 -, Cl-, Barium, Nitrate, Fluoride, Sulfate, Silicon, and Boron all showed a reduction in mg/l after RO filtration.
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    Citrate Stabilized Magnetic Nanoparticles (Fe3 O4 ) for the Removal of Pb 2+ Ions in Wastewater
    (Addis Ababa University, 2022-06) Solomon, Mamuye; Tesfaye, Refera (PhD)
    Water contaminations by heavy metals are a major environmental problem due to their acute toxicity and their accumulation in food chains. One of such toxic heavy metals is Pb 2+ ions. In this study the synthesis of bare magnetite nanoparticles (B-MNPs), and citric acid coated magnetite nanoparticles (Cit-MNPs) to remove heavy metal Pb Page IV 2+ ions from wastewater is reported. The Fe 3 O 4 MNPs were synthesized using standard coprecipitation methods. The as such prepared MNPs were characterized by AAS, XRD, FTIR, BET, and Zetasizer. Citric acid was used as surface coating and functionalization of MNPs to increase the selectivity of the magnetic MNPs towards Pb 2+ ions. Using a permanent magnet, the Cit-MNPs were easily separated from the mixture after adsorption of Pb 2+ ions. The adsorption of Pb 2+ ions from synthetic wastewater was tested using a batch experiment to assess the feasibility of the prepared MNPs. The main operational parameters namely pH, adsorbent mass, initial Pb 2+ ions concentration, and contact time were investigated to understand the optimal experimental conditions for removal of Pb 2+ ions. The adsorption efficiency was highly pH-dependent. The maximum removal efficiencies of Pb 2+ ions on Cit-MNPs and B-MNPs were over 96.1% and 83.3%, using adsorbent dose: 0.1 g/L , at pH: 5, contact time: 60 minutes, initial metal ions concentration: 50 mg/L, shaker speed: 200 rpm, and temperature: normal, respectively. The sorption of Pb 2+ ions onto nanoadsorbents obeyed the Freundlich adsorption isotherm model. The maximum adsorption capacity achieved by Cit-MNPs is about 200 mg/g, which is higher than B-MNPs, i.e., 111.1 mg/g. A kinetic study confirms more the pseudo-second-order model with R 2 = 0.99. The first-order rate constant of K 1 and second-order rate constant of K 2 were found to be, K 1 = 1.1x10 -2 minute -1 , K 2 = 1.3x10 -2 minute -1 for B-MNPs and K 1 = 1.9x10 -2 minute -1 , K 2 = 1.4x10 -2 minute -1 for Cit-MNPs, respectively. This result confirmed that the synthesized MNPs nanoadsorbents are considered the most promising sorbent with high efficiency and more feasible to remove Pb 2+ , a heavy metal ions from synthetic wastewater.
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    Synthesis and Characterization of Titanium Dioxide Immobilized Water Hyacinth based Activated Carbon Catalyst for Methylene Blue Removal
    (Addis Ababa University, 2021-08) Abebayehu, Kefyalew; Anteneh, Marelign (PhD); Shimeles, Kebede (PhD)
    Several treatment methods are available to remove pollutant dyes from textile wastewater streams. Adsorption of pollutant dyes by activated carbon (AC) is one of the technically feasible and cost-effective methods. Incorporating photocatalytic materials such as TiO2 in AC can improve removal efficiency by imparting photodegradation besides adsorption. In this study, titanium dioxide-immobilized water hyacinth-based activated carbon catalyst (TiO2/WHAcc) was used to remove Methylene blue (MB) from artificially constituted wastewater. The AC extracted from lignocellulosic biomass was utilized to adsorb MB and further impregnation of AC with TiO2 enhanced the MB removal efficiency. The source of lignocellulosic biomass in this work was water hyacinth biomass (WHB). Sol-gel method was employed to synthesize TiO2/WHAcc. The WHAC and TiO2/WHAcc were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Brunauer-Emmett-Teller (BET) surface area analysis, and Barrett-Joyner-Halenda (BJH) pore size and volume analysis, field emission scanning electron microscopy equipped with Energy Dispersive x-ray spectroscopy (FE-SEM with EDX), and proximate analyses. In addition, the effect of photocatalytic parameters was investigated using Box-Behnken Design (BBD) response surface methodology. Effects of initial MB dye concentration, catalyst dose, and contact time on percentage removal of MB were studied. The maximum MB removal efficiency of 91.05 % was recorded at 0.092 g adsorbent dosage in 100 ml MB dye solution, 24.58 min contact time, and a MB dye concentration of 20.00 mg L-1. The comparison of TiO2/WHAcc and WHAC on the removal of MB revealed that the incorporation of TiO2 in the WHAC enhances the MB removal efficiency and can be a good adsorbent for the removal of MB from wastewater streams.
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    A DFT study of 2D Van der Waals Heterostructures of Janus Transition Metal Dichalcogenides with WSe2 Monolayer for Energy Applications
    (Addis Ababa University, 2021-09) Samuel, Tilahun; Georgies, Alene (PhD)
    Atomically thin two-dimensional layered semiconductor materials such as Transition Metal Dichalcogenides (TMDs) have a great potential for solar cells applications due to their favorable photon absorption and electronic transport properties. The combination of 2D materials in the form of van der Waals heterostructures has been proved to be an effective approach for improving the electronic properties of the material. In this work, the electronic properties, such as band structure, bandgap, and band alignment of MoSSe/WSe2, WSSe/WSe2, and WSeTe/WSe2 vdW heterostructures were obtained from Density Functional Theory (DFT). The potential of the exchange and correlation was calculated using the Generalized Gradient-Perdew Berk Ernzed (GGA-PBE) approximation. MoSSe/WSe2, WSeTe/WSe2, and WSSe/WSe2 heterostructures have type-II band alignments, which is advantageous for electron-hole pair separation. Photons can be absorbed directly in MoSSe/WSe2 and WSeTe/WSe2 semiconductors because they have direct bandgaps. WSSe/WSe2 semiconductor has an indirect bandgap, which means that a phonon must also be absorbed or emitted for a photon to be absorbed. The most stable stacking order in heterostructures comprising Janus monolayers of TMDs and WSe2 has been ascertained based on interlayer binding energies. The binding energies in MoSSe/WSe2, WSSe/WSe2, and WSeTe/WSe2 heterostructures were found to be -18216.75 eV, -38995.69 eV, and -0.3296 eV at an equilibrium interlayer space of 5.75 Å, 4.02 Å, and 4.72 Å respectively, which are more stable than the other tested configurations. The solar cell and photocatalytic applications of the heterostructures were investigated. The structures were not promising for photocatalytic applications because the band levels of semiconductors were insufficient to support full water splitting. When MoSSe/WSe2, WSSe/WSe2, and WSeTe/WSe2 were used as PV materials, the Power Conversion Efficiency (PCE) was found to be 20.16%, 20.48%, and 19.05%, respectively. The results show that it can serve as a suitable photovoltaic material with high efficiency and opening possibilities to develop solar cells based on 2D TMDs materials.
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    Photocatalytic Degradation of Methylene Blue Using Iron Doped Tio2 Porous Shell under Light Irradiation
    (Addis Ababa University, 2021-09) Mariamsina, Kassahun; Tesfaye, Refera (PhD.)
    Titanium dioxide is a well-known photocatalyst for the photodegradation of dyes like methylene blue. However, its application is limited due to its wide bandgap and higher recombination rate of photogenerated electrons and holes. This work shows that doping transition metals lead to reducing the bandgap and increasing surface area to improve the degradation efficiency of titanium dioxide (TiO2). Iron doped TiO2 hollow and porous spheres with different Fe-doping contents were prepared based on a sol-gel synthesis. Melamine formaldehyde (MF) has been used as a sacrificial template, and cetyltrimethylammonium bromide (CTAB) was used as a pore-directing agent. By calcining the composite spheres at 450, 500, 550 ◦C for three h in air, and in situ Fe doped TiO2 hollow and porous spheres process occurred upon the decomposition of the MF template and CTAB pore-directing surfactant. The 0.25wt% Fe-doped porous TiO2 hollow nanosphere at 450oC exhibited a significantly narrower optical bandgap and higher photocatalytic activity in the removal of Methylene blue (MB) than that of the pure THPNS. The composition and Fe-doping content, thermal stability, morphology, surface area, and pore size distribution, photocatalytic activities, and optical properties of the porous TiO2 hollow spheres derived from different conditions were investigated and compared based on X-ray diffraction (XRD), Fourier-transformation infrared ray spectroscopy (FT-IR), Scanning electron microscope (SEM), Brunauer-Emmett-Teller (BET) Thermogravimetric analysis (TGA/DTA), Diffuse reflection spectroscopy (DRS analysis), Zeta sizer, and Ultraviolet-Visible (Uv-Vis) Spectroscopy techniques. The effect of dye concentration, dopant concentration, pH of the dye solution, catalyst loading, and calcination temperature on the characteristics, photocatalytic activities, and optical properties of the hollow and porous TiO2 Nanosphere has been studied and discussed.
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    First Principles Investigation of Van Der Waals Heterostructures of Mos2 and Janus Transition Metal Dichalcogenides for Energy Applications
    (Addis Ababa University, 2021-09) Birhan, Tesfaye; Georgies, Alene (PhD)
    Recent research on the Janus transition metal dichalcogenide (JTMD) with an asymmetric structure has revealed that this material possesses interesting unique properties, notably in solar cells. This work is based on cutting-edge density functional theory (DFT) computations utilizing Generalized Gradient Approximation- Perdew–Burke–Ernzerhof functional (GGA-PBE) as implemented in the Quantum ESPRESSO and VASP codes. To find the most stable optimized heterostructures, eight basic stacking patterns were designed. Then, for MoSSe/MoS2, WSSe/MoS2, and MoSTe/MoS2 heterobilayer, the AAII-S stacking mode was more stable than the other stacking types. According to the findings, the band alignment was type-I for MoSSe/MoS2, MoSTe/MoS2, and type-II for WSSe/MoS2, within, 1.03, 0.30 and 0.84 eV are estimated bandgap, respectively. The electrical band structure, as well as band edge placements, was investigated. When the water redox and oxidation potentials of heterostructures were compared, it was discovered that MoSSe/MoS2, MoSTe/MoS2, and WSSe/MoS2 were not applicable for photocatalytic materials for full water splitting. On the other hand, MoSSe/MoS2 and MoSTe/MoS2 heterostructures were placed lower than the oxidation potential of O2/H2O, making them applicable for oxygen evolution reaction (OER). This work reveals that JTMDs/MoS2 heterostructures are often subsequent material that promotes the development of photovoltaic devices, specially MoSSe/MoS2, and WSSe/MoS2 vdWH. The power conversion efficiency (PCE) of the heterostructures is calculated, and the results show that MoSSe/MoS2 and WSSe/MoS2 show very good efficiency with values of 19.41% and 16.25%, respectively. The result is good when compared to other similar studies: GaTe-InSe (9.1%), MoS2/p-Si (5.23%), organic solar cells (11.7%), and PN-WSe2 (13.8 % ). Since the results are encouraging, we believe it is a good idea to do additional experiments on the heterostructures and adapt them to solar cell applications.
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    Study on the Effect of Marble Waste Powder and Fly Ash in Compressed Stabilized Earth Block Materials
    (Addis Ababa University, 2021-10) Nigat, Melak; Tesfaye, Refera (PhD)
    In this study, suitability of industrial wastes, fly ash (FA), and marble waste powder (MWP) are estimated along with cement as stabilizers for producing CSEBs with soil ingredients and water. The aim of this research is to manufacture and investigate alternative wall-making material that can be produced by locally available raw materials. Compressed Stabilized Earth Block (CSEB) has identified as low-cost, reducing environmental pollution and increasing energy efficiency building construction material. And also this study has analyzed the influence of these industrial wastes when used as certain percentage replacements of cement in provide adequate compressive strength and durability of the CSEB blocks. This experimental study on CSEB prepared using fly ash and marble waste as a replacement of cement in certain proportions has brought out the effectiveness of these binding materials with cement in improving the 28th -day compressive strength and durability. This can be done by identifying the physical properties and chemical composition of the materials and the characteristics of the CSEBs. Different tests were conducted to determine the physical properties of the material like grain size distribution, water absorption, moisture content, specific gravity, silt content, compressive, and tensile strengths. Chemical composition and characterization of the CSEB blocks were investigated by XRD. The microstructural behavior of the CSEBs was analyzed by using SEM images to determine the anatomic changes and morphology that occurred at different marble waste and fly ash contents. Based on the test results, it has observed that fly ash 10% and marble waste powder 5% to achieve the maximum dry-and wet compressive strength values of the block which were 3.84 Mpa and 3.01Mpa respectively. It has also demonstrated water absorption (11.6%) after 28th days curing. The cost of CSEB with only cement is higher than that of FA and MWP in combination with cement. The cost comparison of CSEB with the other conventional wall making construction material, like HCB, was preferred because it is a more economical construction material; the construction cost is low, and has to input less energy and environmental impacts including raw material use, waste generation, energy consumption and its associated air emissions (CO2) and has simple building techniques. The results of this thesis work have shown that CSEB block can be used as an alternative wall making material and significant cost reduce can be achieved in low cost housing rural, semi-urban, and urban. Any concerned body can use this construction material as an alternative building material without compromise its quality.
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    Selective Electrochemical Reduction of Carbon Dioxide on CuS (001) Surface using Density Functional Theory
    (Addis Ababa University, 2020-10) Nigussie, Birhanu; Georgies, Alene (PhD)
    Electrochemical carbon dioxide reduction reaction (ECR) on surface CuS (001) is one of the most capable approaches to convert CO2 gases to formic acid and carbon monoxide products. Geometry optimization and Gibbs free energy calculation were carried out using density functional theory with general gradient approximation of Perdew–Burke–Ernzerhof (PBE) as implemented in quantum ESPRESSO and VASP software package with computational hydrogen electrode (CHE) approaches. In this work the bulk CuS, CuS (001) surface and adsorbate configuration structures of intermediate species (*H, *OCHO, *COOH, and *CO) and reduction mechanisms were optimized geometry structure and calculated Gibbs free energy. Herein, the two elementary reaction paths are proposed * + CO2  *OCHO  HCOOH, and * + CO2  *COOH  *CO + H2O CO for the formation of formic acid and carbon monoxide and their activation barrier energy for intermediate *OCHO, *COOH_Cu, *COOH_S, *CO_Cu, and *CO_S are -0.03eV, +0.74 eV, +1.47 eV, -0.32 eV, and -1.05 eV respectively at 0V vs RHE. Intermediate *OCHO and *COOH_Cu have smallest activation barrier energy than the others. This study revealed that easier reaction would be occurred on *OCHO and *COOH_Cu intermediate. So that CuS (001) surface has highly selective catalyst and favourable to the formation of formic acid and good selective to carbon monoxide through *OCHO and *COOH-Cu intermediate, respectively.
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    Synthesis and Characterization of Cellulose-based Aerogel from Mixed Organic Solid Wastes
    (Addis Ababa University, 2020-10) Kidist, Worku; Dawit, Ayana (PhD)
    Cellulose-based aerogels are materials that are produced from cellulose, which is the most abundantly available natural polymer. Like other aerogels, cellulose-based aerogels have low density and highly porous structure made from interconnected network of cellulose fibers. Those properties of cellulose-based aerogels prepared from easily available raw materials, that make it potential alternative material applicable for the removal of oil and organic solvents. The direct discharge of oil and organic solvent containing waste water damages the marine ecological environment and intoxicate life thereby, imposing immediate and longtime damages. In this work, cellulose-based aerogels were synthesized by mixing cellulose-rich organic solid waste materials. Cellulose-based aerogels were produced combining textile cotton fabric (100 % cotton), waste paper, and waste banana peel without pretreatment. Sol-gel process followed by freeze drying was executed to successfully fabricate the cellulose-based aerogel. Precooled NaOH/urea solution was used at standard NaOH/Urea/water (7:12:81) ratio for cellulose dissolution by varying precursor/solvent ratio and dissolution time. Further, hydrophobic modification using carbon nanoparticles/acetone solution was performed to the cellulose-based aerogel with the best characteristic properties. This gave the aerogel an oil/organic solvent selectivity property during waste water treatment. A cellulose-based aerogel with the lowest density of 0.127 g/cm3 that showed a macroporous structure with 91.5 % porosity and specific surface area of 192.24 m2/g. Sorption capacity and removal efficiency tests were done for cooking oil, engine/motor oil, ethanol, and benzene. Accordingly, sorption capacities of 15.74, 13.81, 13.98, and 13.98 g/g were recorded respectively. After the removal tests the efficiency of cellulose-based aerogels were found to be 80.89 % for cooking oil, 77.2 % for engine/motor oil, 76.48 % for ethanol, and 74.1 % for benzene. The aerogel was recycled to be reused a number of times in which it was able to remove more than 50 % of contaminants up to the third cycle. Hence, the characteristics and pollutant removal performance of cellulose-based aerogel make it a potential candidate for oily and organic solvent containing waste water treatment.
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    Computational Modeling of ZnO/WSSe van Der Waals Heterostructures for Solar Cell Applications
    (Addis Ababa University, 2020-09) Girma, Mekonnen; Georgies, Alene (PhD)
    Stacking of two-dimensional materials into layered Van der Waals heterostructures are recently considered as a promising candidate for applications on photovoltaic devices because they can combine advantages of individual‟s 2D materials. Janus transition metals dichalcogenides (WSSe) have emerged because of favorable electronic properties as an attractive absorbing material. We therefore systematically examine the geometric features, electronic properties, work function, and density of states, band alignment of monolayer ZnO and WSSe and their heterostructures in this work using density functional theory methods (DFT) with PBE calculations as implemented in the Quantum ESPRESSO and VASP codes. It was found that, the negative binding energies indicate all the four configurations of ZnO-WSSe heterostructures are stable and feasible. Moreover, three configurations B, C and D exhibit indirect band gaps of 1.6248 eV, 1.6319 eV and 1.3126 eV, respectively. But the other configuration A has direct band gap of 1.7106 eV. In addition, it is found that all four configurations show band alignment type-II. In type-II alignment, donor-acceptor interface band heterojunctions can easily promote electron and hole carrier transfer and separation at interface, which can significantly enhance the efficiency of photovoltaic solar cells. With direct band gap, configuration A is the preferred heterostructure for photovoltaic devices applications.
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    Investigating the Effect of Partial Substitution of Feldspar by Alkaline-rich Material on the Processing Temperature of Locally Produced Electrical Porcelain Insulator
    (Addis Ababa University, 2020-09) Eaba, Beyene; Sintayehu, Nibret (PhD)
    The demand for electric power supply has been significantly increasing in the world and particularly in Ethiopia. In the power generation sector, it is crucial to develop a high quality insulation material to transmit and distribute the generated power, such as porcelain insulator. Therefore, in this study, we produced an electrical porcelain insulator from locally available clay (Bombowha clay), feldspar (Arero feldspar) and quartz (Arero quartz) and achieved reduced processing temperature without compromising insulator properties. The physical and dielectric properties such as apparent porosity, water absorption, bulk density, and dielectric strength of the as prepared samples were performed. Furthermore, XRD and FE-SEM analysis were utilized to analyze the phase formation and morphology of the phases after firing. The Arero feldspar was partially substituted with alkaline rich materials (sodium carbonate, sodium chloride and glass powder). These preliminary samples were then fired at 1000 oC and the best substitute and processing technique were compared and the one with good dielectric strength was chosen for further study. Reasonable dielectric strength was achieved from the samples containing sodium carbonate as a substitute which was chosen for further study. Experiments were performed using different concentration of sodium carbonate (5%, 7.5% , and 10% of the feldspar composition in the porcelain), and firing temperature of 1000 oC, 1100 oC, and 1200 oC. The XRD and FE-SEM results showed that sufficient amount of the required phase, i.e., mullite phase, formed at 1100 oC and 1200 oC with the addition of the sodium carbonate as a substitute. Furthermore, relatively good dielectric strength values for porcelain insulator were achieved by the samples prepared at a lower temperature of 1200 oC compared to previous studies. The maximum dielectric strength which was achieved by substituting 10% of the feldspar with Na2CO3 is 7.51 kV/mm; the standard for low voltage overhead line porcelain insulator being in the range of 6.1 - 13 kV/mm. Moreover, substituting values of 5% and 7.5 % at 1200 oC exhibited comparable dielectric strength values with the 10 % substitute.
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    Electronic Properties of 2D Vander Waals Heterostructures of Janus Transition Metal Dichalcogenides with WS2 Monolayer for Photovoltaic Devices: A First Principle Study
    (Addis Ababa University, 2020-06) Tsigie, Getie; Sintayehu, Nibret (PhD)
    Building two-dimensional (2D) heterostructure emerges novel properties, with promising applications in photovoltaic (PV) cells. By performing density functional theory (DFT) based firstprinciples calculations, electronic properties of WS2 and Janus transition-metal dichalcogenides (JTMDs) monolayers were calculated and depending on the lattice mismatch, layered 2D JTMDs/WS2 heterostructures were formed. The formation of the JTMDs/WS2 van der Waals (vdW) heterostructures have shown great potential for the design of novel electronic devices. In this study, Janus MoSSe/WS2, WSSe/WS2, and MoSTe/WS2 heterostructures were developed and their structural and electronic properties were evaluated using first principles calculations based on DFT calculations using Quantum ESPRESSO and VASP codes. It was found that the heterostructures bandgap is smaller than the Janus TMDs and WS2 monolayer. Structural relaxations were performed using generalized-gradient approximation (GGA) approaches for both the monolayers and heterostructures. Structural stability and electronic properties of JTMDs/WS2 vdW heterostructures with AC and AD stacking were investigated which are the most stable configuration compared with other configurations based on the binding energy and the interlayer distance. Results show that the Janus MoSTe/WS2, MoSSe/WS2, and AD-configuration of WSSe/WS2 vdW heterostructures are indirect bandgap semiconductor, but WSSe/WS2 with ACconfiguration is a direct bandgap. The JTMDs/WS2 vdW heterostructures exhibited a bandgap in the range of 1.54 to 0.54eV. In addition, MoSSe/WS2 and MoSTe/WS2 heterostructures displayed a type-II band alignment which is important to improve the photoelectric conversion efficiency. However, the band alignment of WSSe/WS2 heterostructure is difficult to identify and need additional calculations. First principles study shows that the investigated 2D heterostructures have a suitable bandgap for photovoltaic applications. Among the JTMDs/WS2 vdW heterostructures, MoSSe/WS2 and MoSTe/WS2 manifest type-II band alignment, making them promising candidates for photovoltaic (PV) applications.
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    Center of Materials Engineering (CME) Enhancing the Cracks-resistant Behavior of Concrete Materials: Combined Effects of TiO2 Nanoparticles and Waste Plastics Fiber
    (Addis Ababa University, 2020-06) Belete, Balta; Dawit, Gemechu (PhD)
    Experimental investigation of the combined effects of TiO2 Nanoparticles (TNP) and Waste Plastic Fiber (WPF) for the modifications of concrete materials has been conducted. The TNP partially substituted cement by the wt. % of (0, 0.5, 1.0, and 1.5) and WPF partially substituted sand by the wt. % of (0, 0.2 and 0.4) in C-25 grade concrete. The strength for modified and unmodified concrete after 3, 7, and 28 days of curing has been tested. The results showed that the maximum strength and durability were achieved by combined effects in comparison to all other concretes for all the curing days. The SEM analysis of concrete modified with both WPF and TNP showed a densified and well-compacted microstructure than unmodified and also only TNP modified concrete. The XRD analysis of concrete modified with both WPF and TNP showed the existence of more phases, which are responsible for strength modification than only TNP modified and unmodified concrete. Furthermore, the thermal analysis of the samples was conducted with DSC-TGA (Differential Scanning Calorimetry-Thermo-Gravimetric Analysis). The maximum weight loss was recorded for unmodified concrete at lower temperatures than modified concrete. The problems associated with conventional concrete materials with respect to a maximum load resistance, compressive strength and splitting tensile strength, and crack-resistant behavior has been modified. Achieving high strength, gaining high quality, and long term serviceability were critical issues to Ethiopian construction sectors and in other countries as well. In this study, the combined effects of TNP and WPF addressed the challenges of concrete cracking and durability properties.
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    Synthesis of Cetyltrimethylammonium chloride Coated Diatomite Ceramic Membrane Impregnated with TiO2 Nanoparticles for the Removal of Hexavalent Chromium(VI)
    (Addis Ababa University, 2019-06) Daniel, Getachew; Anteneh, Marlgn
    In this study, manufacture of ceramic membranes modified by nanomaterials (Tio2) and CTAC was done. Materials were synthesized by the application of the sol-gel method with respective amounts measured in the molar ratio of Ti: Ethanol: HCL: H2O as 1:15:0.3:5. The coating of Tio2 was done by two methods. The first method involves coating the sample with the prepared sol and subsequently letting the gelation process to occur. The gel-coated ceramic was then calcinated at 550 c resulting in a Tio2 coated ceramic sample. The second method involves preparing Tio2 particles with the formed 0 0 c resulting in Tio2 powders. Taking the newly formed Tio2 powder with Nitric acid (HNO3) in the ratio of 0.5 gm Tio2 powder: 10ml of HNo3; rigorous mixing for three hours has yielded a solution. Whereby a second sample was Immersed and calcined at the previous temperature. The prepared samples were then Immersed again in a solution formed by CTAC and water at a ratio of 5gm:100ml. The coated samples where finally dried and prepared for the testing. Material characterization and filtration tests were conducted to check whether or not the samples were acceptable. SEM/EDS Mapping as well as XRD tests was done to determine the morphology and phase composition of the manufactured material. Performance in the form of efficiency was also conducted by the use of filtration test as another form of characterization. The results obtained confirmed that the prepared membrane has met all the objectives of the study and has successfully removed hexavalent chromium from water solution. The calculated efficiency value of the respected modified and unmodified membranes has been found to be 73.01% for the unmodified gel calcination at 550 membrane while Tio2 modified is found to be 80.05% and CTAC modified 85.44% respectively.
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    Synthesis of High Refractive Index La3+ Doped BaTiO3 Nanoparticles for Retroreflective Application Via Water Assisted Solid State Reaction
    (Addis Ababa University, 2019-06) Hailu, Redae; Sintayehu, Nibret (PhD)
    To guarantee the safe and well-organized movement of traffic on highway during bad weather and nighttime conditions, traffic signs, markings, helmet and safety textile paints have to be illuminated and made of retro-reflective materials. Materials having collective fluorescent and retro-reflective properties importantly improve visibility. For production of these materials Ceramics of glass having high refractive index are used. Most ceramic materials for different applications are synthesized by a conventional solid state reaction (SSR) method. In solid state reaction ionic diffusion in an ionic crystal is very sluggish at about room temperature Therefore it needs a high temperature conditions for boosting the reactivity between raw materials. Liquid phase reaction also can arise at relatively low temperature to SSR but needs additional temperature to dry the solvent and superior equipment for separation. Methods currently used to synthesis glass beads such as Container less flamespray, Conventional SSR, Molten salt etc. requires high temperature (780 ºC-1300ºC) to synthesize high purity glass beads. Furthermore, products obtained using these methods have large bead/ powder sizes. activated BaTiO3 at 100ºc. The starting materials, La2O3, TiO2, and Ba(OH)2.8H2O, weighed according to the stoichiometric ratio and mixed for 15 minutes with 8% of deionized water, Store in an automatic Oven for 6 hours at 100ºc. The La doping level were 0%, 5% and 10%. In this study, a WASSR route is employed to synthesize nano-sized La 3+ X-ray diffraction of the as prepared new material confirmed the product has a structure of Tetragonal BaTiO3 having a size ranging from 19.39 to 21.64nm.EDS mapping of the as prepared sample showed uniform distribution of components. From UV-Vi spectrometry, the La 3+ activated BaTiO3 nanoparticles has shown a refractive index of 3.392 when La doping was 1%. Raman spectroscopy also confirmed the structure of the as prepared sample is Tetragonal. The refractive index of nanoparticles greatly increased the wide wavelength range (426–900 nm), which is very useful for some special surfaces that require illumination from reflection of light rays, such as protective reflective helmet or clothes, road side signs, etc. In addition, it can be used as heat reflective layer, which solves the urban heat island effect.