https://repository.ju.edu.et//handle/123456789/5563 2026-04-20T10:42:36Z 2026-04-20T10:42:36Z TOFIK ACHALU, PROFESSOR FEKADU GASHAW DR. MULUALEM MEKONNEN https://repository.ju.edu.et//handle/123456789/10078 2025-12-23T06:47:29Z 2025-05-01T00:00:00Z

PHOTOCATALYTIC PERFORMANCE OF GRAPHENE BASED ZINC SULFIDE NANOCOMPOSITES UNDER VISIBLE LIGHT: EXPERIMENTAL AND COMPUTATIONAL APPROACH TOFIK ACHALU, PROFESSOR FEKADU GASHAW; DR. MULUALEM MEKONNEN This study aims to investigate photocatalytic potential of graphene based ZnS nanocomposite under experimentally and computationally approach. The synthesis of graphite, GO and rGO used acid treatment, tour method, and chemical treatment, respectively. It used waste dry cell graphite rods for graphene source. Solution growth synthesis approaches were used to produce ZnS nanoparticles and ZnS/rGO nanocomposites. XRD, FTIR, DRS, PL, TGA, RAMAN SPECTROSCOPY and SEM-EDX characterization techniques were utilized for analysis. The experimental findings shown the successful synthesis of exfoliated black-brown rGO, light yellow ZnS nanoparticles, and a ZnS/rGO nanocomposite. Graphite shows a strong peak at a diffraction angle of 26.50, shifted to a lower angle of 25.20 in the case of rGO. Prominent peaks shown at 488 nm when excited at 280 nm for rGO. The transition from rough graphite sheets to smooth, flake-like surface morphology property of rGO was observed. The optical band gaps measured at 3.68 eV for ZnS decrease in to 3.051 eV for the ZnS/rGO nanocomposite because increase rGO concentration. The lower bandgap can be attributed to the formation of a nanocomposite. Similarly, TGA showed three stages of mass loss, and FTIR confirmed the presence of rGO in ZnS/rGO nanocomposite. The photocatalysis experiments were used 0.04 grams of ZnS/rGO, 80 ml MB (15ppm) solution with a pH of 12 under 300 w hydrogen lamp for 90 minutes. Regarding photocatalytic efficiency, ZnS/rGO-12wt % nanocomposites exhibited degradation percentages of 96.99 %. However, ZnS nanoparticles demonstrated a photodegradation efficiency of 70.74%. The enhanced photocatalytic activity shown at ZnS/rGO-12wt % nanocomposite. The photocatalyst shown good stability, with a degradation efficiency of 92.6 % and 86.8 % in first cycle and second, respectively. ALL the experimental results of ZnS/rGO nanocomposites show significant potential for photocatalysis application. Theoretical calculations used the CASTEP module in MATERIAL STUDIO to study the electronic and photocatalytic properties of ZnS/G heterostructures. The theoretical results suggest that the ZnS/G heterostructure exhibits enhanced adsorption capabilities as compared to ZnS. 3×3×1 graphene supercell with a 2×2×1 ZnS with 2.63% mismatch, the calculated band structures reveal a bandgap of 0.3 eV for ZnS/G and 2.7 eV for ZnS. Additionally, the major peaks of absorption coefficients of 8.6 × 10⁴, 17.8 × 10⁴ cm⁻¹ and 28.7 × 10⁴ cm⁻¹ which is indicating a reduced optical bandgap. The findings confirm that ZnS/rGO nanocomposite and ZnS/G heterostructures offer improved photocatalytic efficiency compared to ZnS catalysts.

2025-05-01T00:00:00Z Parveen, J. Shahitha Thirumurugan, M. Dhakshnamoorthy, M. et al. https://repository.ju.edu.et//handle/123456789/9417 2025-03-21T06:56:00Z 2023-01-01T00:00:00Z

Enhanced performance of electrospun poly(ethylene oxide)/reduced graphene oxide polymer electrolyte for lithium-ion batteries Parveen, J. Shahitha; Thirumurugan, M.; Dhakshnamoorthy, M.; et al. A novel polymer membrane based on electrospun poly(ethylene oxide) (PEO) incorporated with different con centrations of reduced graphene oxide (rGO) was prepared using the electrospinning technique. The electrospun PEO/rGO was incorporated with lithium ions to manufacture a gel polymer electrolyte (GPE) and sandwiched inside a coin cell. The electrochemical properties of PEO/rGO electrolytes confirmed good stability of the lithium cell, a satisfactory lithium transference number and improved ionic conductivity in the order of 10 3 S/cm. The GPE developed in this work is well suited for application in reliable, low-cost and eco-friendly energy storage technologies.

2023-01-01T00:00:00Z Degefa, Dita Deme Mereke, Nebiyu Bogale https://repository.ju.edu.et//handle/123456789/9326 2025-01-15T08:05:22Z 2024-08-01T00:00:00Z

Investigation of structural, electrical, dynamical, optical, and thermoelectric properties of Sr‐doped Mg2Si systems using frst‐principles calculations Degefa, Dita Deme; Mereke, Nebiyu Bogale This research article explores the comprehensive characterization of Mg8Si4 and Sr2Mg6Si8 systems, delving into their structural, electrical, dynamical, optical, and thermoelectric properties. Employing GGA and HSE06 hybrid functional calculations alongside semiclassical Boltzmann technique calculations, the study reveals intriguing insights. Through examination of cohesive and formation energies, it is established that Sr2Mg6Si8 exhibits the most stable condition. Phonon dispersion confrms the structural stability of both compounds. Mg8Si4 possesses an indirect band gap of 0.222 eV, whereas Sr2Mg6Si8 showcases a direct band gap of 0.752 eV under HSE06 analysis. Notably, Sr2Mg6Si8 displays superior electrical conductivity and Seebeck coefcient despite low lattice thermal conductivity, resulting in a promising thermoelectric fgure of merit (ZT) of 0.64 at 700 K. Moreover, the composition Sr2Mg6Si4 exhibits a notable Power Factor of 4× 1012 WK−2 m−1 s−1 at 700 K, highlighting its potential for thermoelectric applications.

2024-08-01T00:00:00Z Tewodros Temtime Solomon Demiss Jemal Mohammed https://repository.ju.edu.et//handle/123456789/9275 2024-08-02T13:08:10Z 2024-06-01T00:00:00Z

Sustainable Synthesis And Characterization Of Nh2- Mil-53(Al)/Mil-100(Fe) Heterojunctions For Visible Light Driven Photocatalytic Degradation Of Rhodamine B Dye Tewodros Temtime; Solomon Demiss; Jemal Mohammed Water pollution caused by toxic dyes from the textile industry has become a major concern nowadays. Specifically, rhodamine B (RhB) dyes found in textile wastewater have harmful and toxic impacts on the surroundings and human health. To address these problems, photocatalytic wastewater treatment using metal-organic frameworks (MOFs) and MOF-on-MOF heterojunctions has emerged as a promising and dynamic research area. This is due to the unthinkable properties of MOFs. However, pristine MOFs often have low photocatalytic efficiency due to their wide band gaps and high electron-hole recombination rates, which limits their practical application. Coupling two different MOFs into MOF-on-MOF heterojunctions can help overcome these limitations. The heterojunction structure facilitates precise charge transfer interfaces, thereby increasing the photocatalytic activity of the MOFs. Additionally, the heterojunction can preserve the porous framework of the MOF materials, supporting both adsorption and photocatalytic behaviors. This study describes the sustainable synthesis of pristine MIL-100(Fe) and NH2-MIL-53(Al) MOFs, as well as the NH2-MIL-53(Al)/MIL-100(Fe) heterojunctions. Characterization techniques such as X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, Scanning electron microscopy (SEM), DRS-UV-vis spectroscopy (DRS-UV-vis) and so on were used to confirm the successful synthesis of the materials under environmentally friendly, energy-efficient, and economical (3E) conditions. The formation of the NH2-MIL-53(Al)/MIL-100(Fe) heterojunctions significantly enhanced the photo-responsive range and charge separation efficiency, leading to improved photocatalytic activity in the degradation of RhB dye. Under visible light irradiation, the NH2-MIL-53(Al)/MIL-100(Fe)-1wt% catalyst showed the highest performance, achieving 95.28% degradation efficiency within 140 minutes, outperforming the individual components. The active site trapping study revealed that superoxide radicals (•O2 - ) and holes (h+ ) play crucial roles in the photodegradation of RhB. Moreover, the selected photocatalyst revealed remarkable recyclability, retaining a high photocatalytic degradation efficency of 83.0% even after four cycles of activity.

2024-06-01T00:00:00Z