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Synthesis, Characterization and Photocatalytic Application of Sol-gel Derived ZnO@CdS Coreshell Nanorods

Zirak, Mohammad | 2010

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 40852 (04)
  4. University: Sharif University of Technology
  5. Department: Physics
  6. Advisor(s): Moshfegh, Alireza
  7. Abstract:
  8. Synthesis, characterization and photocatalytic applications of core-shell like ZnO@CdS nanorods have been studied in this research. The synthesis of core-shell like ZnO@CdS nanorods was carried out in three different steps. At first, ZnO seed layer was formed on glass substrate via sol-gel process under optimum conditions using absolute ethanol solution containing zinc acetate and a stabilizer ( either Monoethanolamine (MEA) or diethanolamine (DEA)). When MEA used as stabilizer, the optimum concentration of sol was found 0.2 M, while increasing the sol concentration caused the seed layer to be grown in a string-like structure. The RMS surface roughness of seed layer prepared by 0.2 M sol was 2.9 nm and the average size of seeds was about 55 nm. According to the AFM image analysis, the optimum conditions for seed layer formation are including: DEA as an appropriate stabilizer, 0.5 M sol concentration and the DEA:sol ratio of 6:5. Under these conditions, the surface roughness of the seed layer was 5.9 nm and the average size of seeds was about 100 nm. ZnO nanorods were grown on pre-deposited ZnO seed layer by hydrothermal process in an aqueous solution containing 0.001 M Zn(NO3)2 and x M NaOH. According to the AFM image analysis, when the concentration of NaOH was 0.1 M (x = 0.1), the maximum surface roughness measured at 23.1 nm. XRD analysis showed that the Wurtzite crystal growth of ZnO nanorods along (002) formed perpendicular to the substrate plane. For the synthesis of core-shell like ZnO@CdS nanorods, first, CdS shells were grown on ZnO nanorods via SILAR method under different solutions concenteration incuding 15, 50, and 100 mM and different cycles including 10,20 and 30. According to the spectrophotometric analysis, by increasing both the concentration of SILAR solutions and number of cycles, the transmittances (T%) of the layers were decreased. By plotting dT/dλ as a function of wavelength(λ), two maxima were obtained corresponding to ZnO and CdS absorbance edges. Intensity of ZnO maxima at 370 nm were decreased by increasing both the concentration of SILAR solutions and number of cycles, while the CdS maxima were increased and shifted toward greater wavelengths. Photocatalytic performance of various core-shell like ZnO@CdS nanorods was examined by the investigation of photodegradation rate of methylene blue (MB) under both UV and visible irradiation. Under the UV light, the maximum rate constant (k) of about 0.012 min-1 was obtained for the layer prepared under SILAR solution with the concentration of about 50 mM and 20 cycles. while Under the visible light, the maximum rate constant (k) of about 0.007 min-1 was obtained for the layer prepared by SILAR solution with the concentration of about 100 mM and 20 cycles.

  9. Keywords:
  10. Sol-Gel Method ; Hydrothermal Method ; Photocatalytic Property ; Core-Shell Structure ; Nanorod ; Zinc Oxide

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