Myeongsoon Lee

Pukyong National University, Busan, Busan, South Korea

Are you Myeongsoon Lee?

Claim your profile

Publications (11)35.03 Total impact

  • Myeongsoon Lee · Don Kim
    [Show abstract] [Hide abstract]
    ABSTRACT: We have demonstrated a simple and inexpensive method of carbohydrate detection using a field effect transistor (FET) with Au nanoparticles (AuNPs) attached to multiwall carbon nanotubes (MWCNT), which does not require any enzymes or catalysts. The high sensitivity (3.4 mM-1 for sucrose and 6.9 mM-1 for glucose) of the sensor is adequate to diagnosis diabetes from a patient serum. The sensor is more sensitive to glucose than sucrose. The hypothesized detection mechanism of the FET sensor is a change of the potential barrier of the conductive MWCNT by the adsorption of the carbohydrates to the attached AuNPs.
    No preview · Article · Feb 2016
  • Myeongsoon Lee · Don Kim

    No preview · Article · Jun 2015 · Bulletin of the Korean Chemical Society
  • Source
    Myeongsoon Lee · Don Kim · Yong Tae Yoon · Yeong Il Kim
    [Show abstract] [Hide abstract]
    ABSTRACT: A pellet of polycrystalline CuGaO2 with a delafossite structure was prepared from Ga2O3 and CuO by high-temperature solid-state synthesis. The CuGaO2 pellet was a p-type semiconductor for which the electrical conductivity, carrier density, carrier mobility and Seebeck coefficient were 5.34 x 10(-2) Omega(-1) cm(-1), 3.5 x 10(20) cm(-3), 9.5 x 10(-4) cm(2)V(-1)s(-1) at room temperature, and +360 mu V/K, respectively. It also exhibited two optical transitions at about 2.7 and 3.6 eV. The photoelectrochemical properties of the CuGaO2, pellet electrode were investigated in aqueous electrolyte solutions. The flat-band potential of this electrode, determined using a Mott-Schottky plot, was +0.18 V vs SCE at pH 4.8 and followed the Nernst equation with respect to pH. Under UV light illumination, a cathodic photocurrent developed, and molecular hydrogen simultaneously evolved on the surface of the electrode due to the direct reduction of water without deposition of any metal catalyst.
    Full-text · Article · Nov 2014 · Bulletin- Korean Chemical Society
  • Myeongsoon Lee · Don Kim
    [Show abstract] [Hide abstract]
    ABSTRACT: The clear insulator (Monoclinic-VO2) to metal (Rutile-VO2) transition (IMT) was observed in electrical conductivity and differential scanning calorimeter (DSC) measurements at around 340 K, which is IMT temperature (TH), in the hydrothermally prepared VO2 crystals. The occurrence of metal to insulator transition (MIT) temperature (TC) was observed below 333 K during the first resistance measurement cycle in the most of cases. The sudden jump of the electrical resistance at IMT and MIT points was amplified several times than that of the first cycle during the repeated successive thermal cycles (heating and cooling across the IMT and MIT temperatures). TC and TH shifted to higher temperature by the repeated successive thermal cycles. This shift and the amplified jump might be related to the mechanical stress between the VO2 crystals, i.e. extrinsic properties. However, the starting point of MIT, TCS = ~ 336 K, and the starting point of IMT, THS = ~ 338 K, keep almost constant during the repeated thermal cycles.(< 10 times) These two temperatures may be related to the intrinsic properties of the VO2: the phase transitions initiated at these temperatures regardless the number of the repeated thermal cycles. The neat surface of the VO2 crystals was severely damaged and the average size of particles reduced from 110 nm to 70 ~ 90 nm after extensively repeated thermal cycles (> 70 times). The damaged surface and the smaller particles, which would be originated from the mechanical stress caused by crystal volume change during the first order transition of the VO2, would be weaken the electrical conduction path (loosen grain boundaries) between the VO2 single crystals and would result the amplified jump at the followed MIT. This report may boost the study for the improved stability and lifetime of the VO2 based electronic devices.
    No preview · Article · Mar 2014 · Materials Characterization
  • Seong-Cheol Hong · Myeongsoon Lee · Don Kim
    [Show abstract] [Hide abstract]
    ABSTRACT: We prepared gold nanoparticles (AuNPs) attached carbon nanotubes (Au@C) by the carbonization of sucrose in the AuNPs coated nanochannels of anodic aluminum oxide in the range of 973 K–1173 K. According to electron microscope (EM) and X-ray diffraction (XRD) observations, the size of the attached AuNPs was 20∼30 nm in diameter with perfect crystallinity of Au. The degree of graphitization of the carbon phase, which is not detected in EM and XRD, was discussed with the G-mode shift and the intensity ratio of G-mode/D-mode (R) change in Raman shift measurement. And graphitization mechanism was also discussed by the Raman study. The Au@C was electrically connected between 100 μm wide gap of two parallel Au electrodes by means of dielectrophoresis to measure the electrical resistance of the structure. The conductivity of Au@C, ∼2.40 × 103S/cm–1, was comparable to that of commercially available multi-wall carbon nanotubes (MWCNTs), ∼5.01 × 103S/cm–1. The Au@C has much better dispersivity than the MWCNTs in isopropanol, because of the interaction between the surface of the attached AuNPs and isopropanol. These suggest the Au@C is a good candidate for the fabrication of functional nanodevices.
    No preview · Article · Mar 2014 · Science of Advanced Materials
  • Myeongsoon Lee · Seong Cheol Hong · Don Kim
    [Show abstract] [Hide abstract]
    ABSTRACT: An easy method is reported for the preparation of bamboo-like conducting carbon nanotubes decorated with Au nanoparticles (Au-CNT), by carbonization of sucrose inside of anodic aluminum oxide (AAO) nanochannels (∼80 nm and ∼30 μm in diameter and length, respectively). First, the AAO membrane nanochannels were coated with Au nanoparticles (∼10 nm in diameter) and the carbon nanotubes were then formed in the same channels below 973 K. Electron microscopy shows long bamboo-like carbon nanotubes, ∼30 μm in length, decorated with crystalline gold nanoparticles, ∼50 nm in diameter. The coalescence of the precoated small Au nanoparticles inside the channel results in the attached large Au nanoparticles. The apparent resistivity of the Au-CNT prepared at 973 K, was ∼16.8 Ω cm. The electrical conductivity of the structure is discussed with relation to electrochemical and micro Raman experiments.
    No preview · Article · Jun 2012 · Carbon
  • Nayane Udawatte · Myeongsoon Lee · Junhyung Kim · Dongil Lee
    [Show abstract] [Hide abstract]
    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.
    No preview · Article · Nov 2011 · ACS Applied Materials & Interfaces
  • Source
    Jaeil Lee · Hyeong Seop Shim · Myeongsoon Lee · Jae Kyu Song · Dongil Lee
    [Show abstract] [Hide abstract]
    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
    Full-text · Article · Oct 2011 · Journal of Physical Chemistry Letters
  • [Show abstract] [Hide abstract]
    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.
    No preview · Article · Aug 2011 · Canadian Journal of Chemistry
  • [Show abstract] [Hide abstract]
    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.
    No preview · Article · Oct 2010 · The Journal of Physical Chemistry C
  • Source
    Myeongsoon Lee · Seong-Cheol Hong · Don Kim
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper presents a facile and efficient way to prepare carbon nanofibers ornamented with Au nanoparticles (Au/CNFs). Gold nanoparticles were first deposited in the channels of an anodized aluminum oxide (AAO) membrane by thermal decomposition of HAuCl4and then carbon nanofibers were produced in the same channels loaded with the Au nanoparticles by decomposition of sucrose at 230 °C. An electron microscopy study revealed that the carbon nanofibers, ~10 nm thick and 6 μm long, were decorated with Au nanoparticles with a diameter of 10 nm. This synthetic route can produce uniform Au nanoparticles on CNF surfaces without using any additional chemicals to modify the AAO channels or the CNF surfaces.
    Preview · Article · Aug 2009 · Nanoscale Research Letters