Hai-Doo Kwen

Radiolytic synthesis of Pt-Ru catalysts based on functional polymer-grafted MWNT and their catalytic efficiency for CO and MeOH

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 FPMWNTsupports by the reduction of metal ions using γ-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.

Fabrication of a Microbial Biosensor Based on QD-MWNT Supports by a One-Step Radiation Reaction and Detection of Phenolic Compounds in Red Wines

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.

Fabrication of Nonenzymatic Glucose Sensors Based on Multiwalled Carbon Nanotubes with Bimetallic Pt-M (M = Ru and Sn) Catalysts by Radiolytic Deposition

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.

REMOVAL OF AGGREGATES FROM MICRON-SIZED POLYMETHYL METHACRYLATE (PMMA) LATEX BEADS USING FULL FEED DEPLETION MODE OF GRAVITATIONAL SPLITT FRACTIONATION (FFD-GSF)

Split-flow thin cell (SPLITT) fractionation (SF) provides separation of colloidal particles or macromolecules into two fractions. A gravitational SF (GSF) system was constructed and its applicability was tested for removal of aggregates from mass-produced polymethyl methacrylate (PMMA) latex beads. The full-feed depletion (FFD) mode of GSF (FFD-GSF) was found to be a simpler alternative to the conventional mode for removal of the aggregates. Unlike in the conventional mode, where two inlets are used for feeding of the sample suspension and the carrier liquid respectively, only one inlet (for the sample feeding) is used in the FFD mode, allowing easier control of the flow rate. Also the sample suspension is not diluted during FFD mode operation. Aggregated particles were found only in one of the two fractions, allowing removal of the aggregates. The sample was continuously fed into the GSF system, showing potential application to a large quantity operation for removal of the PMMA aggregates.

Electrocatalytic activity of the bimetallic Pt-Ru catalysts doped TiO 2 -hollow sphere nanocomposites

This paper describes the electrocatalytic activity for the oxidation of small biomolecules on the surface of Pt-Ru nanoparticles supported by -hollow sphere prepared for use in sensor applications or fuel cells. The -hollow sphere supports were first prepared by sol-gel reaction of titanium tetraisopropoxide with poly(styrene-co-vinylphenylboronic acid), PSB used as a template. Pt-Ru nanoparticles were then deposited by chemical reduction of the and ions onto -hollow sphere (). The prepared nanocomposites were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), and elemental analysis. The electrocatalytic efficiency of Pt-Ru nanoparticles was evaluated via ethanol, methanol, dopamine, ascorbic acid, formalin, and glucose oxidation. The cyclic voltammograms (CV) obtained during the oxidation studies revealed that the nanocomposites showed high electrocatalytic activity for the oxidation of biomolecules. As a result, the prepared Pt-Ru catalysts doped onto -H sphere nanocomposites supports can be used for non-enzymatic biosensor or fuel cell anode electrode.

Characterization of CdS-quantum dot particles using sedimentation field-flow fractionation (SdFFF)

Abstract: CdS-QD particles are a nano-sized semiconducting crystal that emits light. Their optical propertiesshow great potential in many areas of applications such as disease-diagnostic reagents, optical technologies,media industries and solar cells. The wavelength of emitting light depends on the particle size and thus thequality control of CdS-QD particle requires accurate determination of the size distribution. In this study, CdS-QD particles were synthesized by a simple γ-ray irradiation method. As a particle stabilizer polyvinyl pyrrolidone(PVP) were added. In order to determine the size and size distribution of the CdS-QD particles, sedimentationfield-flow fractionation (SdFFF) was employed. Effects of carious parameters including the the flow rate, externalfield strength, and field programming conditions were investigated to optimize SdFFF for analysis of CdS-QD particles. The Transmission electron microscopy (TEM) analysis show the primary single particle size was~4 nm, TEM images indicate that the primarty particles were aggregated to form secondary particles havingthe mean size of about 159 nm. As the concentration of the stabilizer increases, the particle size tends to decrease.Mean size determined by SdFFF, TEM, and dynamic light scattering (DLS) were 126, 159, and 152 nm,respectively. Results showed SdFFF may become a useful tool for determination of the size and its distributionof various types of inorganic particles. 요약: CdS 양자점 입자는 특정 파장의 빛을 방출하는 반도체 나노 결정으로 이러한 광학적 특성 때문에 질병 진단 시약, 광학기술, 미디어 산업 및 태양전지와 같은 다양한 분야에서 응용되는 물질이다. 방출하는 빛의 색은 입자의 크기에 의존하기 때문에 CdS 양자점 입자의 크기 및 크기분포를 정확하게 분석하는 것이 필요하다. 본 연구에서는 CdS 양자점 입자를 감마-선 조사법(γ-ray irradiation method)을 이용하여 합성하고, 크기 및 크기 분포도를 결정하기 위하여 침강 장-흐름 분획법 (SdFFF)를 이용하였다.

Chapter 8:Polymer Nanocomposites by Radiolytic Polymerization

The γ-ray irradiation polymerization is beneficial technology that is environmentally friendly and energy efficient in the preparation of polymer nanocomposites. Two active species such as a free radical and a hydrated electron generated during γ-ray irradiation are used in preparing polymer-clay nanocomposites, polymer-metal nanocomposites, and polymer-carbon nanotube at room temperature and under ambient pressure. Various polymer-clay nanocomposites using γ-ray polymerization of the desired monomers can be prepared in a one step process. The prepared polymer-clay nanocomposites have the improved mechanical properties, enhanced thermal stability, and reducing gas permeability. Precious metals have been studied most extensively among polymer-metal nanocomposites and used as catalysts, in sensors, photochromic and electrochromic devices, and recording materials. Various functional groups can be introduced on the CNT surface by γ-ray irradiation polymerization as a one-step process. The polymer-CNT nanocomposites can be used as supports to immobilize biomolecules in the biosensor. This radiolytic preparation of polymer nanocomposites is expected to have actual applications in industrial fields because this method is very simple, has low cost, and can be produced at room temperature, with or without solvents.