Browsing by Author "Gonfa, Gutta"

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    Mesoporous Materials Supported Vernonia Oil Esters and Their Immobilization With Silver Nanoparticles for Catalytic Applications
    (Addis Ababa University, 2018-10-04) Gonfa, Gutta; Chebude, Yonas (PhD); Diaz, Isabel (Professor)
    In our world of rapidly increasing population and fast industrialization, design of value added and ecofriendly high performance organic–inorganic nanocomposites with higher stability for environmental remediation is becoming an active area of research in the field of inorganic material chemistry. The major objectives of this study are to design some typical surface hydrophobic ordered mesoporous nanocomposites by surface modification of their hydrophilic surfaces by supporting with native vernonia oil derivatives and immobilization by silver nanoparticles as potential heterogeneous catalyst for degradation of model organic dyes. In the first part of this work, vernonia oil with unique natural epoxy moiety was extracted from vernonia galamensis seed, which was purified and then derivatized to more active forms such as vernolic acid and vernolic acid mono alkyl esters like methyl, ethyl and propyl esters as well as their mercapto imidazole functionalized derivatives, i.e. methyl ester-IFVAME, ethyl ester-IFVAEE and propyl ester-IFVAPE. The presences of the functional groups were confirmed by FT-IR, 1H and 13C NMR spectroscopy and CHNS elemental analysis. In the second part of this work, vernolic acid methyl ester- VAME, and its mercapto imidazole functionalized (IFVAME) derivatives were supported on three types of ordered mesoporous nanomaterials with different surface properties and pore sizes: OMMs: Al-MCM-41 (Si/Al=3 & 15), SBA-15 & periodic mesoporous organo silica-PMO. The supported materials were studied by powder X ray diffraction, thermogravimetric analysis, FT-IR spectroscopy and nitrogen sorption isotherms. In the third part of this work, silver nanoparticles were synthesized on VAME and IFVAME supported Al-MCM-41, SBA-15, and PMO. The formations of the silver iv nanoparticles were confirmed from wide angle powder XRD and the final distribution of the metal nanoparticles were studied using Transmission Electron Microscopy. Finally, the potential catalytic applications of Ag-impregnated mOMMs were tested for degradation of model organic dyes (methyl orange and methylene blue) which was found to be promising.
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    Synthesis and Characterization of some New Series of Zn(II), Co(II) and Cu(II) Complexes of Tetradentate Tetraaza Macrocycles and Pentaaza Bis(Macrocycles
    (2002) Gonfa, Gutta; Retta, Negussie (Professor)
    In this study the template synthesis and characterization of two new series of Zn(II), Co(II), and Cu(II) metal complexes of polyaza macrocyclic ligands are presented. In the first part of this work template condensation reaction of o-phenylenediamine with succinic acid in a 1:1 molar ratio in the presence of divalent transition metal ions [Zn(II), Co(II) and Cu(II)], led to the formation of new series of polycrystalline macrocyclic complexes. The synthesis is a remarkably facile one requiring only stirring under room temperature for short period of time. Elemental analysis shows that the complexes have a 1:1 ligand to metal stoichiometry. The absence of bands characteristic of primary amines and carboxylic acids functional groups and the presence of bands characteristic of coordinated secondary amine in the N-H and M-N region gave a strong evidence for the formation of the proposed metal complexes. The 1H and the 13C NMR spectra for Zn(II) complex from the first series also confirm the formation of the macrocyclic frame work. The coordination geometry is found to be octahedral for the Zn(II) and Co(II) complexes and square planar for the Co(II) complex. In the second part of the work, template condensation reaction of p-phenylenediamine, ethyelenediamine, formaldehyde and succinic acid in the presence of metal ions [Zn(II), Co(II) and Cu(II)] produced metal complexes of octahedral geometry of bis(macrocycles) framework. The formation of such series of complexes was confirmed by physico-chemical studies such as elemental analysis for the metal and chlorine, infrared spectroscopy, electronic spectral studies and conductivity data. Lastly, preliminary investigation on the potential hydrolytic nature of the Zn(II) metal complexes revealed that the complexes possess no significant catalytic nature in the hydrolysis of p-nitrophenyl phosphate and carboxylate ester. This is probably due to the presence of elctrophilic carbonyl carbon site on the macocycles of the complex that compete for Zn-OH- nucleophile and thereby deactivating its catalytic activity and the formation of polymeric hydroxide precipitate of the complexes at higher pH.