Myeongsoon Lee

Yonsei University, Seoul, Seoul, South Korea

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Publications (4)5.97 Total impact

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    ABSTRACT: Well-defined Au/ZnO nanoparticle composites were prepared by modifying ZnO with preformed Au nanoparticles protected with bifunctional glutathione ligand. In this approach, the Au nanoparticles were highly monodisperse and their loading on ZnO surface could be precisely controlled by the anchoring conditions. Steady-state and time-resolved photoluminescence of the composites revealed the ability of the Au nanoparticles to efficiently extract conduction band electrons from the photoexcited ZnO. The composites exhibited strongly enhanced photocatalytic activity without requiring thermal activation process in degrading organic substrates in both oxidative and reductive pathways. A clear correlation between the photocatalytic activity and the Au loading was found for both oxidative and reductive photocatalytic reactions. These results demonstrate that thiolate-protected AuNPs can significantly enhance the charge separation by extracting electrons from the photoexcited ZnO and consequently improve the photocatalytic activity of the composites.
    ACS Applied Materials & Interfaces 11/2011; 3(11):4531-8. · 5.01 Impact Factor
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    ABSTRACT: This Letter describes size-controlled photocatalytic activity of ZnO nanoparticles coated with glutathione-protected gold nanoparticles with diameters of 1.1, 1.6, and 2.8 nm. The photocatalytic activity of the ZnO–Au composites was found to increase with increasing gold size for both oxidative and reductive catalytic reactions. Photoluminescence decay dynamics of the composites showed that the electron-transfer rate from the photoexcited ZnO to gold nanoparticle also increased as the gold size increased. These results demonstrate that the photogenerated electron transfer and the resulting catalytic activity of the composites can be controlled by the size of the mediating gold capacitors.Keywords: nanocomposite; ZnO; Au nanoparticle; size dependence; electron transfer; photocatalysis; photoluminescence
    The Journal of Physical Chemistry Letters. 10/2011; 2(22).
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    ABSTRACT: We report the preparation and photocatalytic activity of TiO2 nanocomposites modified with monolayer-protected gold clusters (MPCs). Highly monodisperse tiopronin-coated MPCs with core diameters of 2.2 ± 0.2 nm were pre-prepared and then anchored onto a TiO2 surface using the bifunctional tiopronin linker. In this method, the gold core size was preserved after calcination at 260 °C as well as the anchoring process, and the gold loading on TiO2 could be precisely controlled by the experimental condition. The photocatalytic degradation of Rhodamine 590 (Rh-590) was carried out with thus prepared MPC–TiO2 composites. Mechanistic study of the photocatalytic reactions revealed that the degradation of Rh-590 occurs via the oxidative pathway by photogenerated holes. The photocatalytic activity of the MPC–TiO2 composites was found to increase significantly upon calcination at 260 °C, whereas the size of gold particles remained at their initial size. The photocatalytic activity of the composites, however, drastically decreased when the composites were calcined at 400 °C. X-ray photoelectron spectroscopy analysis of the calcined composites was conducted to understand the vastly different calcination results. A significant amount of oxidized sulfur remained in the composites after calcination at 400 °C, which appears to be responsible for the drastic decrease in the photocatalytic activity.
    Canadian Journal of Chemistry 08/2011; 89(8):1001-1009. · 0.96 Impact Factor
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    ABSTRACT: TiO2 nanoparticle photocatalysts modified with uniform gold nanoparticles are prepared by anchoring bifunctional glutathione-coated monolayer-protected gold clusters (MPCs) onto TiO2. In this method, the MPC loading on TiO2 can be precisely controlled in the range of 1−5 wt % without incurring size change upon anchoring. The photocatalytic degradation of Uniblue A (UBA) is carried out with thus prepared MPC−TiO2 composites, which shows, however, no enhancement upon MPC anchoring. The MPC−TiO2 composites are thermally treated to activate the catalytic activity. When the MPC−TiO2 composites are calcined at 250 °C, the glutathione ligand on gold surface is partially removed and the photocatalytic activity of the composites significantly increases, highlighting the role of gold in the photocatalytic reactions. However, when the calcination temperature is raised to 400 °C, the photocatalytic activity of the composites drastically decreased. X-ray photoelectron spectroscopy analysis of the calcined composites reveals that significant amount of oxidized sulfur remains after calcination that appears to act as a recombination center for the photogenerated electrons and holes, resulting in a drastic decrease in the photocatalytic activity. These results emphasize the important role of ligands in the use of MPCs in photocatalysis.
    The Journal of Physical Chemistry C. 10/2010; 114(43):18366–18371.

Publication Stats

12 Citations
5.97 Total Impact Points

Institutions

  • 2011
    • Yonsei University
      • Department of Chemistry
      Seoul, Seoul, South Korea
    • Western Michigan University
      • Department of Chemistry
      Kalamazoo, MI, United States