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Search Results: 1 - 10 of 11494 matches for " Seong-Ho Choi "
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One-Step Synthesis of Pd-M/ZnO (M=Ag, Cu, and Ni) Catalysts by -Irradiation and Their Use in Hydrogenation and Suzuki Reaction
Mi-Ran Kim,Seong-Ho Choi
Journal of Nanomaterials , 2009, DOI: 10.1155/2009/302919
Abstract: ZnO-supported Pd, Pd-Ag, Pd-Cu, and Pd-Ni catalysts (Pd-M/ZnO) were prepared in MeOH/H2O mixture (4/1, v/v-%) by -irradiation at room temperature. Small mono- and bimetallic nanoparticles were loaded on the surface of ZnO nanopowder as confirmed with TEM, TEM-EDXS, XRD, and ICP-AES data. The catalytic efficiency against Pd-M/ZnO was determined in hydrogenation and Suzuki reaction and compared with the commercial Pd/C catalyst. The Pd-Ag/ZnO showed the highest catalytic efficiency in the Suzuki reaction.
Cognitive Profiles and Subtypes of Patients with Mild Cognitive Impairment: Data from a Clinical Follow-Up Study  [PDF]
Kyung Won Park, Eun-Joo Kim, Hwan Joo, Sung-Man Jeon, Seong-Ho Choi, Jay C. Kwon, Byoung Gwon Kim, Jae Woo Kim
International Journal of Clinical Medicine (IJCM) , 2012, DOI: 10.4236/ijcm.2012.35068
Abstract: Background: Mild cognitive impairment (MCI) is a heterogeneous condition with a variety of clinical outcomes, the presence of which correlates with risk of Alzheimer’s disease as well as pre-clinical stages of other dementia subtypes. The aims of this study were to assess the specific patterns of cognitive profiles and to identify changes from baseline to 24 weeks in patients with MCI using detailed neuropsychological testing. Methods: We consecutively recruited 120 MCI patients at baseline according to the Petersen’s clinical diagnostic criteria, who were admitted to the Dementia and Memory Clinics. We analyzed patients who fulfilled both inclusion and exclusion criteria for MCI and classified them into four subtypes according to deficits in major cognitive domains; amnestic MCI single domain (aMCI-s), amnestic multiple domain MCI (aMCI-m), non-amnestic single domain MCI (naMCI-s) and non-amnestic multiple domain MCI (naMCI-m). Four groups of MCI were evaluated by a detailed neuropsychological battery test. Results: 83 patients with MCI at the 24-week follow-up were classified into four subtypes. The most frequent subtype was amnestic multi-domain MCI, with the frequency of MCI subtypes as follows: aMCI-s (n = 21, 25.3%), aMCI-m (n = 53, 63.9%), naMCI-s (n = 5, 6.0%) and naMCI-m (n = 4, 4.8%). In the major cognitive items of the SNSB-D, there were significant changes between the initial and follow-up tests in the domains of language, memory and the fron-tal/executive function (p < 0.05), except for attention, in all MCI patient subtypes. At 24-weeks follow-up, the conversion rate to Alzheimer’s disease was 2.4% (n = 2) from a subtype of amnestic multi-domain MCI. Conclusions: Our study revealed the most frequent subtype of MCI to be multiple domain amnestic MCI, with this subtype having a higher tendency of conversion to Alzheimer’s disease.
Development of Amperometric Hydrogen Peroxide Sensor Based on Horseradish Peroxidase-Immobilized Poly(Thiophene-co-EpoxyThiophene)
Hwa-Jung Kim,Ming-Hua Piao,Seong-Ho Choi,Chang-Ho Shin
Sensors , 2008,
Abstract: A modified electrode for hydrogen peroxide (H2O2) sensing was prepared via thiophene (Th) with epoxy group. Thiophene (EpoxyTh) with epoxy group was synthesized by reaction of 3-bromothiophene and glycidyl methacrylate (GMA) in acetonitrile according to Heck Reaction. The electrocopolymerization of Th and EpoxyTh was performed on the surface of indium tin oxide (ITO) electrode by cycling the potential between -1.0 and +2.5 V in mixture of thiophene (Th) and EpoxyTh. Poly(Th-co- EpoxyTh) grown onto the ITO electrode was successfully confirmed by SEM, AFM, and water contact angle analysis, respectively. Finally, the HRP was immobilized on the surface of poly(Th-co-EpoxyTh) electrode by covalent binding. The amperometric response of the HRP-immobilized poly(Th-co-EpoxyTh) electrode for H2O2 was examined by cyclic voltammetry (CV). The HRP-immobilized poly(Th-co-EpoxyTh) electrode showed linearity from 0.1 to 30 mM H2O2, good reproducibility, and long life time.
Synthesis of Hollow Conductive Polypyrrole Balls by the Functionalized Polystyrene as Template
Choo Hwan Chang,Pyung Soo Son,Jeong-Ah Yoon,Seong-Ho Choi
Journal of Nanomaterials , 2010, DOI: 10.1155/2010/168025
Abstract: We report the preparation of hollow spherical polypyrrole balls (HSPBs) by two different approaches. In the first approach, core-shell conductive balls, CSCBs, were prepared with poly(styrene) as core and polypyrrole (PPy) as shell by in situ polymerization of pyrrole in the presence of polystyrene (PS) latex particles. In the other approach, CSCBs were obtained by in situ copolymerization of pyrrole in the presence of PS(F) with hydrophilic groups like anhydride, boronic acid, carboxylic acid, or sulfonic acid, and then HSPBs were obtained by the removal of PS or PS(F) core from CSCBs. TEM images reveal the spherical morphology for HSPBs prepared from PS(F). The conductivity of CSCBs and HSPBs was in the range of 0.20–0.90 S/cm2.
Electrocatalytic Activity for CO, MeOH, and EtOH Oxidation on the Surface of Pt-Ru Nanoparticles Supported by Metal Oxide
Kwang-Sik Sim,Sin-Mook Lim,Hai-Doo Kwen,Seong-Ho Choi
Journal of Nanomaterials , 2011, DOI: 10.1155/2011/614983
Abstract: This paper describes the electrocatalytic activity for CO, MeOH, and EtOH oxidation on the surface of Pt-Ru nanoparticles supported by metal oxide (Nb- -H) prepared for use in a fuel cell. To prepare Nb- -supported Pt-Ru nanoparticles, first, the Nb- supports were prepared by sol-gel reaction of titanium tetraisopropoxide with a small amount of the niobium ethoxide in polystyrene (PS) colloids. Second, Pt-Ru nanoparticles were then deposited by chemical reduction of the Pt4+ and Ru3+ ions onto Nb- supports (Pt-Ru@Nb- -CS). Nb element was used to reduce electrical resistance to facilitate electron transport during the electrochemical reactions on a fuel cell electrode. Finally, the Pt-Ru@Nb- -H catalysts were formed by the removal of core-polystyrene ball from Pt-Ru@ -CS at . The successfully prepared Pt-Ru electrocatalysts were confirmed via TEM, XPS, and ICP analysis. The electrocatalytic efficiency of Pt-Ru nanoparticles was evaluated via CO, MeOH, and EtOH oxidation for use in a direct methanol fuel cell (DMFC). As a result, the Pt-Ru@Nb- -H electrodes showed high electrocatalytic activity for the electrooxidation of CO, MeOH, and EtOH. 1. Introduction Many researcher efforts have been devoted to improving the catalytic performance of carbon supported Pt-Ru catalysts [1–3]. In a colloidal method, dispersion and adsorption of catalytic nanoparticles on the surface of carbon supports is done in the presence of protecting agents to avoid aggregation of particles. It should be noted that the protecting agent is likely to reduce the catalytic activities of catalyst particles. In another method known as the impregnation method, a metal precursor is reduced by the carbon supports dispersed in the solution [4–6]. Carbon supports should be dispersed well without interference of a protecting agent in the suspension. In previous papers [7, 8], the Pt-Ru nanoparticles were deposited on various carbon supports using γ-irradiation to use as anode catalysts in a direct methanol fuel cell (DMFC). However, the life time of the electrode was reduced, since the carbon supports were slowly oxidized in the fuel cell, as shown in In general, the support materials should possess the following properties: (1) a high surface area for a high level of dispersion of the nanosized catalysts, (2) low electrical resistance to facilitate electron transport during the electrochemical reactions, (3) a pore structure suitable for fuel or oxidant contact and by product release, and (4) strong interaction between the catalyst nanoparticles and the supports. Oxide materials are widely
Radiolytic Synthesis of Pt-Ru Catalysts Based on Functional Polymer-Grafted MWNT and Their Catalytic Efficiency for CO and MeOH
Dae-Soo Yang,Kwang-Sik Sim,Hai-Doo Kwen,Seong-Ho Choi
Journal of Nanomaterials , 2011, DOI: 10.1155/2011/134721
Abstract: Pt-Ru catalysts based on functional polymer-grafted MWNT (Pt-Ru@FP-MWNT) were prepared by radiolytic deposition of Pt-Ru nanoparticles on functional polymer-grafted multiwalled carbon nanotube (FP-MWNT). Three different types of functional polymers, poly(acrylic acid) (PAAc), poly(methacrylic acid) (PMAc), and poly(vinylphenyl boronic acid) (PVPBAc), were grafted on the MWNT surface by radiation-induced graft polymerization (RIGP). Then, Pt-Ru nanoparticles were deposited onto the FP-MWNT supports by the reduction of metal ions using -irradiation to obtain Pt-Ru@FP-MWNT catalysts. The Pt-Ru@FP-MWNT catalysts were then characterized by XRD, XPS, TEM ,and elemental analysis. The catalytic efficiency of Pt-Ru@FP-MWNT catalyst was examined for CO stripping and MeOH oxidation for use in a direct methanol fuel cell (DMFC). The Pt-Ru@PVPBAc-MWNT catalyst shows enhanced activity for electro-oxidation of CO and MeOH oxidation over that of the commercial E-TEK catalyst.
Introduction of Bifunctional Group onto MWNT by Radiation-Induced Graft Polymerization and Its Use as Biosensor-Supporting Materials
Yu-Jin Lee,Da-Jung Chung,Sang-Hyub Oh,Seong-Ho Choi
Journal of Nanomaterials , 2012, DOI: 10.1155/2012/127613
Abstract: A biosensor comprising tyrosinase immobilized on bifunctionalized multiwalled carbon nanotube (MWNT) supports was prepared for the detection of phenolic compounds in drinks such as red wine and juices. The MWNT supports were prepared by radiation-induced graft polymerization (RIGP) of epoxy-containing glycidyl methacrylate (GMA), to covalently immobilize the tyrosinase, and vinyl ferrocene (VF), which can act as an electron transfer mediator via redox reactions. The bifunctionalized MWNTs were characterized by X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). Electrodes prepared with the MWNTs showed increased current with increasing VF content. A biosensor comprising tyrosinase immobilized on the bifunctionalized MWNTs could detect phenol at 0.1–20 mM. Phenolics in red wine and juices were determined using the biosensor after its calibration.
Tyrosinase-Immobilized Biosensor Based on the Functionalized Hydroxyl Group-MWNT and Detection of Phenolic Compounds in Red Wines
Ji-Hoon Yang,Jae-Chan Lee,Seong-Ho Choi
Journal of Sensors , 2009, DOI: 10.1155/2009/916515
Abstract: The tyrosinase-immobilized biosensor was developed with the hydroxyl group-functionalized multiwall carbon nanotube (MWNT) for phenol detection. The hydroxyl group-modified MWNT was modified to include poly(GVPB)-g-MWNT, or poly(HEMA), by a radiation-induced graft polymerization of glucosyl 4-vinylphenylboronate (GVPB) or 2-hydroxyethyl methacrylate (HEMA) on the surface of MWNT. The response of biosensor was in the range of 0.6–7.0 mM for concentration and in the range of 0.05–0.35 mM for phenol in a phosphate buffer solution, respectively. Various parameters influencing biosensor performance have been optimized: for pH, temperature, and the response to various phenolic compounds. The biosensor was then tested on phenolic compounds contained in three different commercial red wines.
Fabrication of Nonenzymatic Glucose Sensors Based on Multiwalled Carbon Nanotubes with Bimetallic Pt-M (M = Ru and Sn) Catalysts by Radiolytic Deposition
Sun-Young Kwon,Hai-Doo Kwen,Seong-Ho Choi
Journal of Sensors , 2012, DOI: 10.1155/2012/784167
Abstract: Nonenzymatic glucose sensors employing multiwalled carbon nanotubes (MWNTs) with highly dispersed Pt-M (M?=?Ru and Sn) nanoparticles (Pt-M@PVP-MWNTs) were fabricated by radiolytic deposition. The Pt-M nanoparticles on the MWNTs were characterized by transmittance electron microscopy, elemental analysis, and X-ray diffraction. They were found to be well dispersed and to exhibit alloy properties on the MWNT support. Electrochemical testing showed that these nonenzymatic sensors had larger currents (mA) than that of a bare glassy carbon (GC) electrode and one modified with MWNTs. The sensitivity (A?mM?1), linear range (mM), and detection limit (mM) (S/N?=?3) of the glucose sensor with the Pt-Ru catalyst in NaOH electrolyte were determined as 18.0, 1.0–2.5, 0.7, respectively. The corresponding data of the sensor with Pt-Sn catalyst were 889.0, 1.00–3.00, and 0.3, respectively. In addition, these non-enzymatic sensors can effectively avoid interference arising from the oxidation of the common interfering species ascorbic acid and uric acid in NaOH electrolyte. The experimental results show that such sensors can be applied in the detection of glucose in commercial red wine samples. 1. Introduction The measurement of glucose concentrations is important not only to diabetes diagnosis but also to the food and textile industries, wastewater treatment, and environmental monitoring [1–4]. The first enzyme electrode capable of this was reported in 1962 [5]; sensors' sensitivities, selectivities and reliabilities, detection limits, costs, and response times have all seen much improvement since. There have been several improvements in the immobilization of enzymes and designs of redox systems [6, 7]. Glucose oxidase (GOx), an enzyme catalyst, has been widely used in electrochemical biosensors as it has the advantages of high sensitivity and selectivity, simple instrumentation, low production cost, and promising response speed. However, the low stabilities of enzymatic sensors and the interference of some electro-oxidizable species remain problems in its application [8, 9]. To address these issues, nonenzymatic sensors based on the direct electrocatalytic oxidation of glucose are being investigated. The majority of nonenzymatic electrochemical glucose sensors rely on the current response of glucose oxidation directly at the electrode surface. Therefore, the electrocatalytic activity of the electrode strongly affects both the sensitivity and selectivity of glucose detection. Initial research developing nonenzymatic sensors focused on the use of noble metals, such as Pt
Fabrication of a Microbial Biosensor Based on QD-MWNT Supports by a One-Step Radiation Reaction and Detection of Phenolic Compounds in Red Wines
Seul-Ki Kim,Hai-Doo Kwen,Seong-Ho Choi
Sensors , 2011, DOI: 10.3390/s110202001
Abstract: An Acaligense sp.-immobilized biosensor was fabricated based on QD-MWNT composites as an electron transfer mediator and a microbe immobilization support by a one-step radiation reaction and used for sensing phenolic compounds in commercial red wines. First, a quantum dot-modified multi-wall carbon nanotube (QD-MWNT) composite was prepared in the presence of MWNT by a one-step radiation reaction in an aqueous solution at room temperature. The successful preparation of the QD-MWNT composite was confirmed by XPS, TEM, and elemental analysis. Second, the microbial biosensor was fabricated by immobilization of Acaligense sp. on the surface of the composite thin film of a glassy carbon (GC) electrode, which was prepared by a hand casting method with a mixture of the previously obtained composite and Nafion solution. The sensing ranges of the microbial biosensor based on CdS-MWNT and Cu2S-MWNT supports were 0.5–5.0 mM and 0.7–10 mM for phenol in a phosphate buffer solution, respectively. Total concentration of phenolic compounds contained in commercial red wines was also determined using the prepared microbial immobilized biosensor.
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