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    BIOSYNTHESIZED NITROGEN-ZINC-CODOPED COPPER OXIDE NANOPARTICLES FOR PHOTOCATALYTIC DEGRADATION OF METHYLENE BLUE
    (HAWASSA UNIVERSITY, 2024-06) YOHANNES SHUKA JARA
    Herein, nitrogen-zinc-codoped copper nanoparticles (N-Zn-CuO NPs) was successfully synthesized by using Pycnostachys Abyssinica Fresen plant leaf extract as a bioreducing and capping agent for the photocatalytic degradation of methylene blue under natural sunlight irradiation. Additionally, pure CuO NPs, N-CuO NPs, and Zn-CuO NPs were also biosynthesized for comparison. Characterization techniques of UV-Vis, XRD, SEM, FT-IR revealed that N-Zn-codoping narrowed the band gap (1.72 to1.07 eV), reduced the crystallite size (25 to11.23 nm), distortion of monoclinic crystal lattice (rhombus and diamond like shape with an average diameter of 2.25 µm to irregular shape with an average size of 2.75 µm), and towards redshift of the Cu-O characteristic peaks (617 to 529 cm-1 ) of CuO NPs, respectively, confirmed the successful incorporation of dopants into CuO NPs. The effects of key parameters on the photocatalytic degradation efficiency of all biosynthesised NPs were investigated. The optimal conditions with maximum degradation for N-Zn-CuO NPs were determined to be 3% dopant concentration for both N and Zn, 120 mg of photocatalyst dosage, pH of solution at 11, 20 ppm of Initial dye concentration and 30 minutes of reaction time. Photocatalytic activity towards methylene blue (MB) dye degradation under 30 minutes exposure to sunlight was 99.75% for N-ZnCuO NPs, outperforming pure CuO NPs (95.76%), N-CuO NPs (97.93%), and Zn-CuO NPs (98.26%) under optimal conditions. The enhanced photocatalytic performance of NZn-CuO NPs is attributed to their tailored optical properties, leading to improved charge separation and reduced recombination. Kinetic studies revealed a strong fit (R2=0.99799) with the BMG kinetic model for N-Zn-CuO NPs, indicating surface-mediated degradation of MB. Furthermore, the nanocatalysts exhibited excellent reusability and stability over four cycles. This finding highlights the potential of biosynthesized N-Zn-CuO NPs as highly efficient, simple, eco-friendly and sustainable solutions for the degradation organic pollutants.
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    BIOSYNTHESIS OF Fe3O4/Co3O4 NANOCOMPOSITE FOR PHOTOCATALYTIC DEGRADATION OF CONGO RED AND MALACHITE GREEN DYES UNDER SOLAR IRRADIATION
    (HAWASSA UNIVERSITY, 2024-11) AKINAW AGALU TAYE
    The global concern regarding environmental pollution caused by organic pollutants, as population growth and industrial expansion, has increased the demand for the development of efficient nanomaterials for pollution control. In this study, Fe₃O₄, Co₃O₄ NPs, and Fe₃O₄/Co₃O₄ NCs were synthesized using a green method involving the extract of B. spectabilis flowers. Characterization of the synthesized nanomaterials was conducted using UV-Vis, FT-IR, SEM, and XRD. UV-Vis analysis confirmed the successful synthesis and optical properties of Fe₃O₄, Co₃O₄ NPs, and Fe₃O₄/Co₃O₄ NCs at the nanoscale via green methods, with energy band gaps measured at 2.18 eV, 2.2 eV, and 1.98 eV respectively. FTIR analysis indicated the presence of peaks corresponding to Fe-O 484 cm-1 and Co-O 558 cm-1 bonds. SEM images revealed that the Fe₃O₄, Co₃O₄ NPs, and Fe₃O₄/Co₃O₄ NCs exhibited a smooth surface with non-uniform, rough, and closely packed irregular granular structures. A sponge-like morphology characterized by numerous irregular pores was observed, combined with surface functionalization of Fe₃O₄ due to Co₃O₄ nanoparticle agglomeration, which displayed a smooth and uniform morphology. The average particle size distributions were determined to be 1949 nm, 1437 nm, and 1622 nm respectively. XRD analysis confirmed the successful synthesis of Fe₃O₄, Co₃O₄ NPs, and Fe₃O₄/Co₃O₄ NCs, revealing planes indicative of a high degree of crystallinity in the iron oxide phase and a cubic spinel structure for cobalt oxide. Multiple diffraction peaks corresponding to the spinel structures of both Fe₃O₄ and Co₃O₄ were observed, with crystallite sizes determined to be 31.02 nm 19.05 nm, and 24.2 nm respectively. Photocatalytic activity towards CR and MG using Fe₃O₄/Co₃O₄ NCs, maximum degradation efficiencies of 96.13% for CR (catalyst dose of 0.09 g, initial concentration of 20 ppm, exposure time of 75 min, pH of 6) and 94.40% for MG (catalyst dose of 0.06 g, initial concentration of 15 ppm, exposure time of 90 min, and pH of 8). The degradation efficiencies of 93.65% for CR and 91.39% for MG by Fe₃O₄ NPs, as well as Co₃O₄ NPs, which demonstrated efficiencies of 92.57% for CR and 90.57% for MG were achieved under optimal conditions. Kinetic studies revealed that the Fe₃O₄/Co₃O₄ NCs follow a pseudo-first-order kinetic model for the degradation of CR, exhibiting the highest correlation coefficient (R² = 0.988). In contrast, the degradation of MG follows a pseudo-second-order kinetic model, with the highest correlation coefficient (R² = 0.997)