• Macromolecular Research
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• v.14 no.1
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• pp.101-106
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• 2006

The transport of reactant gas, electrons and protons at the three phase interfaces in the catalytic layers of membrane electrode assemblies (MEAs) in proton exchange, membrane fuel cells (PEMFCs) must be optimized to provide efficient transport to and from the electrochemical reactions in the solid polymer electrolyte. The aim of reducing proton transport loss in the catalytic layer by increasing the volume of the conducting medium can be achieved by filling the voids in the layer with small-sized electrolytes, such as dendrimers. Generation 1.5 and 3.5 polyamidoamine (PAMAM) dendrimer electrolytes are well-controlled, nanometer-sized materials with many peripheral ionic exchange, -COOH groups and were used for this purpose in this study. The electrochemically active surface area of the deposited catalyst material was also investigated using cyclic voltammetry, and by analyzing the Pt-H oxidation peak. The performances of the fuel cells with added PAMAM dendrimers were found to be comparable to that of a fuel cell using MEA, although the Pt utilization was reduced by the adsorption of the dendrimers to the catalytic layer.

• Korean Journal of Materials Research
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• v.25 no.6
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• pp.265-268
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• 2015

ZnO micro/nanocrystals at large scale were synthesized through the thermal evaporation of Al-Zn mixtures under air atmosphere. The effect of synthetic temperature and time on the morphology of the micro/nanocrystals was examined. It was found that the temperature and time affected the morphology of the ZnO crystals. At temperatures below $900^{\circ}C$, no crystals were synthesized. At a temperature of $1000^{\circ}C$, ZnO crystals with a rod shape were synthesized. With an increase in temperature from $1000^{\circ}C$ to $1100^{\circ}C$, the morphology of the crystals changed from rod shape to wire and granular shapes. As the time increased from 2 h to 3 h at $1000^{\circ}C$, tetrapod-shaped ZnO crystals started to form. XRD patterns showed that the ZnO crystals had a hexagonal wurtzite structure. EDX analysis revealed that the ZnO crystals had high purity. It is believed that the ZnO nanowires were grown via a vapor-solid mechanism because no catalyst particles were observed at the tips of the micro/nanocrystals in the SEM images.

• Macromolecular Research
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• v.15 no.2
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• pp.185-190
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• 2007

Poly(norbornene dimethyl dicarboxylate)s, (PNDMD)s, were prepared by addition polymerization with palladium(II) catalyst from pure exo-monomers, and their structure and properties were compared with those of poly(norbornene dicarboxylic acid dialkyl ester)s, (PNDADA)s. Both polymer series exhibited good solubility in general organic solvents and excellent thermal stability up to $330^{\circ}C$. Wide-angle X-ray scattering (WAXS) study indicated the presence of nano-scale layer-like order in amorphous PNDADAs, while PNDMDs showed random amorphous structure. The glass transition temperatures and dielectric constants of solid polymers were found to decrease as the alkyl side-chain length increases for both polymer series. However, PNDMDs showed lower glass transition temperatures and higher dielectric constants, as compared with those of PNDADAs containing the same alkyl substituents. This difference, caused by the higher side-group mobility of PNDMDs, may be closely related to the nano-scale order in amorphous PNDADAs and its absence in PNDMDs.

• Journal of Integrative Natural Science
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• v.5 no.2
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• pp.79-83
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• 2012

Trialkyltin n-$Bu_3SnH$, an endocrine disruptor, was slowly converted by the catalytic action of group 4 $Cp_2MCl_2$/Red-Al (M = Ti, Zr, Hf) to produce two phases of products: one is an insoluble cross-linked solid, polystannane in 7-23% yield as minor product via redistribution/dehydrocoupling combination process, and the other is an oil, hexabutyldistannane in 69-90% yield as major product via simple dehydrocoupling process. Redistribution/dehydrocoupling process first produced a low-molecular-weight oligostannane possessing partial backbone Sn-H bonds which then underwent an extensive cross-linking reaction of backbone Sn-H bonds, leading to an insoluble polystannane. This is the first exciting example of redistribution/dehydrocoupling of a tertiary hydrostannane catalyzed by early transition metallocenes.

• Korean Journal of Materials Research
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• v.24 no.7
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• pp.388-392
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• 2014

$Cu_2O$ nanowires were synthesized at large scale on copper plate by thermal oxidation in air. The effect of oxidation time and temperature on the morphology of the nanowires was examined. The oxidation time had no effect on the diameter of the nanowires, while it had a great effect on the density and the length of the nanowires. The density and the length of the nanowires increased, and then decreased, with increasing oxidation time. The oxidation temperature had a tremendous effect on the size-distribution as well as the density of the nanowires. When the oxidation temperature was $700^{\circ}C$, uniform size-distribution and high density of the nanowires was achieved. At lower and higher temperatures, the density of the nanowires was lower, and they displayed a broader size-distribution. It is suggested that the $Cu_2O$ nanowires were grown via a vapor-solid mechanism because no catalyst particles were observed at the tips of the nanowires.

• Journal of Powder Materials
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• v.25 no.6
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• pp.514-522
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• 2018

Layered-double hydroxide (LDH)-based nanostructures offer the two-fold advantage of being active catalysts with incredibly large specific surface areas. As such, they have been studied extensively over the last decade and applied in roles as diverse as light source, catalyst, energy storage mechanism, absorber, and anion exchanger. They exhibit a unique lamellar structure consisting of a wide variety of combinations of metal cations and various anions, which determine their physical and chemical performances, and make them a popular research topic. Many reviewed papers deal with these unique properties, synthetic methods, and applications. Most of them, however, are focused on the form-factor of nanopowder, as well as on the control of morphologies via one-step synthetic methods. LDH nanostructures need to be easy to control and fabricate on rigid substrates such as metals, semiconductors, oxides, and insulators, to facilitate more viable applications of these nanostructures to various solid-state devices. In this review, we explore ways to grow and control the various LDH nanostructures on rigid substrates.

• Food Science of Animal Resources
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• v.41 no.4
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• pp.731-738
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• 2021

Herein, a novel analytical method using a high-performance liquid chromatography-fluorescence detector (HPLC/FLD) is developed for rapidly measuring an L-carnitine ester derivative in infant powdered milk. In this study, solid-phase extraction cartridges filled with derivatized methanol and distilled water were used to effectively separate L-carnitine. Protein precipitation pretreatment was carried out to remove the protein and recover the analyte extract with a high recovery (97.16%-106.56%), following which carnitine in the formula was derivatized to its ester form. Precolumn derivation with 1-aminoanthracene (1AA) was carried out in a phosphate buffer using 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) as the catalyst. Method validation was performed following the AOAC guidelines. The calibration curves were linear in the L-carnitine concentration range of 0.1-2.5 mg/L. The lower limit of quantitation and limit of detection of L-carnitine were 0.076 and 0.024 mg/L, respectively. The intra- and interday precision and recovery results were within the allowable limits. The results showed that our method helped reduce the sample preparation time. It also afforded higher resolution and better reproducibility than those obtained by traditional methods. Our method is suitable for detecting the quantity of L-carnitine in infant powdered milk containing a large amount of protein or starch.

• Korean Journal of Materials Research
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• v.33 no.7
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• pp.279-284
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• 2023

One-dimensional MgO nanostructures with various morphologies were synthesized by a thermal evaporation method. The synthesis process was carried out in air at atmospheric pressure, which made the process very simple. A mixed powder of magnesium and active carbon was used as the source powder. The morphologies of the MgO nanostructures were changed by varying the growth temperature. When the growth temperature was 700 ℃, untapered nanowires with smooth surfaces were grown. As the temperature increased to 850 ℃, 1,000 ℃ and 1,100 ℃, tapered nanobelts, tapered nanowires and then knotted nanowires were sequentially observed. X-ray diffraction analysis revealed that the MgO nanostructures had a cubic crystallographic structure. Energy dispersive X-ray analysis showed that the nanostructures were composed of Mg and O elements, indicating high purity MgO nanostructures. Fourier transform infrared spectra peaks showed the characteristic absorption of MgO. No catalyst particles were observed at the tips of the one-dimensional nanostructures, which suggested that the one-dimensional nanostructures were grown in a vapor-solid growth mechanism.

• Clean Technology
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• v.18 no.4
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• pp.426-431
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• 2012

Carbon-rich coal can be utilized as a fuel for direct carbon fuel cell (DCFC). However, left-behind ash after the electrochemical oxidation may hinder the electrochemical reactions. In this study, we produced ash-free coal (AFC) by thermal extraction and then tested it as a fuel for DCFC. DCFC was built based on solid oxide electrolyte and the electrochemical performance of AFC mixed with $K_2CO_3$ was compared with AFC only. Significantly enhanced power density was found by catalytic steam gasification of AFC. However, an increase of the power density by catalytic pyrolysis was negligible. This result indicated that a catalyst activated the steam gasification reactions, producing much more $H_2$ and thus increasing the power density, compared to AFC only. Results of a quantitative analysis showed much improved kinetics in AFC with $K_2CO_3$ in agreement with DCFC results. A secondary phase of potassium on yttria-stabilized zirconia (YSZ) surface was observed after the cell operation. This probably caused poor long-term behavior of AFC with $K_2CO_3$. A thin YSZ (30 ${\mu}m$ thick) was found to be higher in the power density than 0.9 mm of YSZ.

• Korean Chemical Engineering Research
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• v.50 no.4
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• pp.723-728
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• 2012

The production of biodiesel by transesterification of soybean oil was performed on $MoO_3$, $SnO_2$ and $CeO_2$ mixed oxides. The catalysts were characterized using XRD and $NH_3$-TPD. $MoO_3$ showed the highest activity among the three metal oxides. When 7 wt% of catalysts was introduced into the reactants, the highest activity was obtained and the water added to reactant decreased the catalytic activity. $MoO_3$ and $SnO_2$ mixed with 50:50 showed the highest activity and $CeO_2$ added with 20% on the $MoO_3-SnO_2$ mixed oxide also showed the highest activity. The catalytic activity showed to have a good relationship with the amount of acid site of catalysts. When the waste soybean oil was used as a reactant, the conversion was decreased about 30%.