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Design and Fabrication of Gold Nanocatalyst for Aerobic Oxidation

Shidpour, Reza | 2014

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 47945 (48)
  4. University: Sharif University of Technology
  5. Department: Institute for Nanoscience and Nanotechnology
  6. Advisor(s): Vossoughi, Manoochehr; Simchi, Abdolreza
  7. Abstract:
  8. Aerobic oxidation plays important role in industrial processes and pollutant remediation. The catalysts accelerating oxidation reaction rate are included thermal (typical) catalysts such as Pt or Au on oxide supports and photocatalysts such as TiO2 or ZnO. Although well-studied Au/TiO2 system have been under deep
    investigations but Au/ZnO system have less investigated because Au/ZnO has low activity relative to Au/ZnO. Gold nanoparticles supported on ZnO nanostructures were prepared through a simple chemical-thermal method and characterized by SEM, TEM, XRD, BET and photo luminescence (PL) spectroscopy. Effect of
    annealing temperature on catalytic activity of these Au/ZnO nanocatalysts were investigated by aerobic oxidation of benzyl alcohol. The results indicated that the catalyst with ZnO nanowire support annealed at 300 oC exhibited more activity than Au/ZnO catalyst supported on ZnO nanoparticles annealed at 600 oC. The
    Au/ZnO-nanowire achieved to increase the benzaldehyde selectivity and yield to 93.7 % and 85.6 %, respectively, at 60 oC whereas in Au/ZnO-nanoparticle the benzaldehyde selectivity and yield to 85.1 % and 69.9 %, respectively at 80 oC. This superior activity of Au on ZnO supports can be related to defect structure of zinc oxide. To find mechanism of bond breaking on catalytic active sites, this idea was proposed that gold atoms attaching to ZnO compose a pair atomic center exhibiting nti-ferromagnetism. It was shown that these atomic centers able to break covalent bond of an adsorbed molecule. In continue, effect of morphology of ZnO nanostructures on photocatalytic activity was investigated. The fabrication of strong photocatalysts applied to the degradation of organic pollutants is necessary in environmental applications. In a single-stage method, acetate precursor and poly vinyl pyrolydine (PVP) are used to produce ZnO nanostructures with various morphologies in annealing temperatures ranging from 300 to 900 oC. The physical properties of the prepared nanostructures were characterized by SEM, TEM, XRD, BET, DRS, CHN analysis and PL spectroscopy. The SEM images exhibit a variety of the as prepared hexagonal zinc oxides including wires, rods, particles and porous network of welded particles of ZnO nanoparticles. The results of the photocatalytic degradation of methylene blue as an organic dye in aqueous suspension showed that the morphology of ZnO nanostructures influences on the photocatalytic efficiency of ZnO nanostructures, greatly. For the best result, the highest MB degradation occurs by ZnO nanowires within 16 min and in others samples, degradation of higher than 98% occurs within 16 min. The XRD and PL spectroscopy revealed neither VZn nor Oi are in all of samples but only VO−, VO2− and Zni exist in ZnO nanostructures. To compare our work with other published investigations one dimensionless factor as an extended quantum yield including effective parameters
  9. Keywords:
  10. Benzyl Alcohol ; Oxidation ; Methylene Blue ; Photocatalyst ; Nano Catalyst ; Gold ; Zinc Oxide ; Magnetic Interaction

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