https://repository.ju.edu.et//handle/123456789/138 2026-04-08T14:25:58Z 2026-04-08T14:25:58Z Tariku Temesgen Tamene Tadesse Getu Sisay https://repository.ju.edu.et//handle/123456789/10203 2026-03-06T14:19:11Z 2024-12-07T00:00:00Z

An Analysis Of The Effects Of S/N Co-Doping Nio Nanoparticle Cles On Its Energy Band Gap, Photo catalytic Activity, And Antibacterial Properties. Tariku Temesgen; Tamene Tadesse; Getu Sisay Nickel oxide has garnered significant interest as a photo catalyst due to its high efficiency, photochemical stability, low cost, and eco-friendliness. However, its large band gap and rapid electron-hole recombination limit its performance in the visible light region. In this study, pure NiO nanoparticles (NiO-NPs) and S/N co-doped NiO nanocomposites (S/N-NiO-NCs) were synthesized via the co-precipitation method to enhance their photocatalytic and antibac terial properties. Doping with 4% sulfur and 6% nitrogen reduced the band gap from 3.75 eV to 2.74 eV and decreased the crystalline size from 20.49 nm to 17.89 nm. Under optimal con ditions (pH 10), 40 mg of S/N-NiO-NCs achieved 98.9% degradation of 10 ppm methylene blue dye within 60 minutes of sunlight exposure, outperforming pure NiO-NPs. Antibacterial activity, assessed through inhibition zone measurements, showed significant improvement: NiO-NPs exhibited zones of 5–10 mm, while S/N-NiO-NCs achieved 13–17 mm against Ba cillus cereus, Escherichia coli, Salmonella typhi, and Staphylococcus aureus. UV-Vis, FT-IR, XRD, and SEM analyses confirmed successful doping and structural modifications, contrib uting to improved charge separation and extended light absorption. These results highlight the potential of S/N co-doping in enhancing the multi functionality of NiO.

2024-12-07T00:00:00Z Michael Asfaw Tamene Tadesse Jabessa Negasa https://repository.ju.edu.et//handle/123456789/10201 2026-03-05T08:24:35Z 2025-04-22T00:00:00Z

Synthesis and Characterization of ZnO/CuO Nanocomposites Decorated with Carbon Dots for Photocatalytic Degradation of MB and Antibacterial Applications Michael Asfaw; Tamene Tadesse; Jabessa Negasa Zinc oxide nanoparticles (ZnO-NPs) are gaining significant attention due to their catalytic and antibacterial properties. However, their effectiveness in pure form is limited by several factors, including a large energy bandgap, high exciton binding energy, electron-hole recombination, poor absorption of visible light, and insufficient photocatalytic activity. To address these challenges, we propose the incorporation of transition metal oxides, such as copper (II) oxide (CuO), along with trace amounts of carbon nanomaterials. This study focuses on enhancing the photocatalytic degradation of methylene blue (MB) dye by adding only 9% CuO nanoparticles and 2% carbon dots (C-dots) to the ZnO-NPs. The inclusion of these materials reduced the energy bandgap of ZnO-NPs from 3.08 eV to 2.51 eV, leading to a significant improvement in their photocatalytic activity. Our results indicated that nearly complete degradation of MB (98.7%) was achieved within 60 min of visible light irradiation when 70 mg of the C-dot decorated ZnO/CuO composite was used. This performance is considerably better than that of the pure ZnO-NPs, which only degraded 76.16% of the MB dye after the same duration of light exposure. Additionally, the incorporation of CuO and C-dots significantly enhanced the antibacterial activity of ZnO-NPs against selected gram-positive and gram-negative bacteria. The zones of inhibition for B.Seraus, E.coli, S.typhi and S.ureus were 8±0.25, 12±0.20, 13±0.10, and 10±0.30 mm, respectively, evaluated against ZnO-NPs. Also the zones of inhibition for B.Seraus, E.coli, S.typhi and S.ureus were 14±0.20, 17±0.20, 18±0.15, 16±0.35mm, respectively, evaluated against ZnO/CuO@C-dot-NCs. The substantial improvement in both photocatalytic and antibacterial effectiveness can be attributed to enhanced surface charge and stability. To our knowledge, this represents the most significant improvement in photocatalytic and antibacterial efficacy achieved by adding small amounts of C-dot material to ZnO/CuO nanocomposites.

2025-04-22T00:00:00Z Muluken Ayele Alemayehu Yifiru Shimeles Addisu https://repository.ju.edu.et//handle/123456789/10200 2026-03-05T08:16:35Z 2024-08-22T00:00:00Z

Poly (Amino-Naphthalene Sulfonic Acid) As A Low Cost Electrode Modifier For Electrochemical Sensing, Reaction Kinetics And Rate Constant Study Of Dopamine. Muluken Ayele; Alemayehu Yifiru; Shimeles Addisu Electrochemical methods are a class of techniques in chemistry which study an analyte by measuring the potential and/or current in an electrochemical cell containing the analyte. It is an attractive alternative for sensing owing to its advantages of sensitivity, simplicity, low cost, and easy miniaturization. Various materials for modification on the electrode surfaces have been widely utilized to enhance sensitivity and chemical specificity of electrochemical sensors. The aim of this work is to develop a sensitive analytical method for determination of Dopamine (DA) at poly amino-naphthalene sulfonic acid modified glassy carbon electrode (poly (ANSA)/GCE). Poly(ANSA)/GCE is prepared by electrochemical polymerization of amino-naphthalene sulfonic acid (ANSA) by successive potential scanning between -0.8 and +1.8 V at 0.1 Vs−1 for 12 scans in 0.1 M HNO3 solution at GCE using cyclic voltammetry (CV). The electrochemical active surface areas of bare and modified electrode in [Fe (CN) 6]-3/-4 were 0.07cm2 and 0.11cm2, respectively. These results indicated that the modification of GCE with poly (ANSA) results high surface area. The oxidation of DA was examined at both bare GCE and poly (ANSA)/GCE. Poly (ANSA)/GCE exhibited higher oxidation current than bare GCE. The higher oxidation current at poly (ANSA)/GCE attributed to the higher electroactive surface area and the presence of amino and sulfonic groups in its structure that can facilitate electron transfer processes. Common electrochemical parameters have been optimized for better electroanalytical performance of poly ANSA/GCE. It was calculated that the rate constant (K) and diffusion coefficient (D) of DA were 4.4×103 M−1s−1 and 8.7 × 10−6 cm2 s−1, respectively, at poly (ANSA)/GCE. A detection limit and a dynamic working linear range of DA at poly-ANSA/GCE were 0.089 μM and 0.5 μM - 100 μM, respectively which was studied using linear sweep voltammetry (LSV). For practical applicability poly (ANSA)/GCE was evaluated by detecting DA in DA injection sample. Hence, a percentage recovery in the range of 94.1 - 102.4% was obtained which it can be a good candidate for the practical useability of the proposed electrochemical sensor for DA detection. The poly (ANSA)/GCE additionally displays good repeatability and reproducibility and satisfactory selectivity.

2024-08-22T00:00:00Z Meseret Gezahagn Geyito Tsegaye Girma Shimeles Addisu https://repository.ju.edu.et//handle/123456789/10181 2026-03-03T08:39:34Z 2025-03-11T00:00:00Z

Removal of Hexavalent Chromium from Aqueous Solution Using Iron Modified Bio chars Derived from Industrial and Municipal Waste Meseret Gezahagn Geyito; Tsegaye Girma; Shimeles Addisu Chromium (VI) contamination in water poses serious health and environmental threats. This study investigates the removal of Cr (VI) from water using brewery spent grain and sewage sludge (BSG/SS), municipal sewage sludge (MSS), and metal processing slag (MPS) collected from industrial sites in Addis Ababa. The compositions of raw, Fe-modified, and heat-treated BSG, BSS, MSS, and MPS were analyzed. Based on initial screening, Fe-modified and heat treated BSG pyrolyzed at 500 °C was further characterized using BET, FTIR, XRD, and SEM. Batch experiments optimized contact time, pH, Cr (VI) concentration, and adsorbent dose to maximize Cr (VI) removal. Under optimal conditions (7 hours, pH 3, 10 mg/L Cr (VI), 2 g/L adsorbent), Fe-BSG biochar achieved 99.88% Cr (VI) removal at 20 mg/L. The pseudo-second order model accurately described the kinetics of Cr (VI) removal (R2 = 0.98012), indicating chemisorption. The Freundlich isotherm fit the data well, with Fe-BSG biochar exhibiting an estimated adsorption capacity of 24.775 mg/g. The potential for recycling suggests that Fe BSG biochar is a valuable material for Cr (VI) removal from aqueous solution. Transforming industrial byproducts into resources benefits environmental pollution mitigation. Future research should evaluate its performance in real wastewater.

2025-03-11T00:00:00Z