• Journal of the Korean Chemical Society
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• v.26 no.6
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• pp.369-377
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• 1982

The technique of combined-measurement of reflectance and ellipsometric parameters was used for studying the anodic film formed on nickel surface in basic solutions. An ellipsometer was automated for transient measurements by way of modulating the plane-polarized light with the Faraday effect. Surface film was formed electrochemically by applying a potential step from the reduction potential range to the passivation range on a polished, high-purity, polycrystalline nickel specimen. From that instant, the changes in the reflectance(r) and the ellipsometric parameters(${\Delta},{\Psi}$) of the surface film were recorded by the automatic ellipsometer. Three exact simultaneous equations including these optical signals, ${\Delta},{\Psi}$ and r were solved numerically with a computer in order to determine the optical properties, n, k, and the thickness, ${\tau}$, of the surface film. From the computed results which showed dependence on pH and time, it was found that passivation of nickel can be effectively attained by surface film thinner than $15{\AA}$ and this passivation film has a small optical absorption coefficient. It seemed that a high pH environment enhances the rate of passivation and is favorable for a denser structure of the surface film. The experimental evidence is in accordance with the hypothesis that the composition of the passive film can be approximated by $Ni(OH)_2$ in the early stage of passivation and that as time passes the composition changes partially toward that of NiO through dehydration.

• Journal of the Microelectronics and Packaging Society
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• v.18 no.4
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• pp.39-42
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• 2011

The composite electroplating is accomplished by adding inert materials during the electroplating. Permalloy is the term for Ni-Fe alloy and it is used for industrial applications due to its high magnetic permeability, surface wear resistance, corrosion protection. Microhardness for microdevices is enhanced after composite coating and it increases the life cycle. However, the hydroxyl group on the silica makes their surface susceptible to moisture and it causes the silica nanoparticles to be agglomerated in the aqueous solution. The agglomeration problem causes poor dispersion which eventually interrupts uniform deposition of silica nanoparticles. In this study, the dispersion of silica nanoparticles in the permalloy electroplated layer is reported with variation of additives and current densities. The optimum current density was 20 $mA/cm^2$ and the silica content was 9 at% at $50^{\circ}C$. The amount of silica nanopowder codeposition and surface morphologies were influenced with variation of additives. In the bath, smooth surface morphology and relatively high contents of silica nanopowder codeposition were obtained with addition of sodium lauryl sulfate.

• Ecology and Resilient Infrastructure
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• v.7 no.1
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• pp.63-71
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• 2020

Various types of amendments have been studied for heavy metal stabilization in soil. However, researches on the effect of amendments on alkali soil and their effects on the plants at various edible parts are insufficient. The aim of this study was to evaluate the stabilization efficiency of heavy metals and their transfer into edible parts of food crops. Abandoned mine area was selected and 3 types of amendments (lime stone, LS; steel slag, SS; acid mine drainage sludge, AMDS) was applied with 3% (w/w). in field. After 6 month aging, Chinese cabbage (leafy), bok choy (leafy), garlic (root) and red pepper (fruit) were transplanted and cultivated. For chemical assessment, total concentration and bioavailability using Mehlich-3 solution were determined. For biological assessment, fresh weight and heavy metal uptakes were analyzed. It was revealed that AMDS reduced bioavailability most effectively, resulting in the decrease in heavy metal concentration in edible parts of all crops. When explaining the heavy metal uptake of plants, the bioavailability was more appropriate than the total contents of soil heavy metals. Therefore, bioavailability-based further research and management practices should be carried out continuously for the sustainable environment management, safe crop production, and human health risk reduction.

• Journal of the Korean Magnetics Society
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• v.16 no.1
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• pp.102-106
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• 2006

Magnetic nanoparticles can be used for a variety of biomedical applications. They can be used in the targeted delivery of therapeutic agents in vivo, in the hyperthermic treatment of cancers. in magnetic resonance (MR) imaging as contrast agents and in the biomagnetic separations of biomolecules. We have synthesized magnetite $(Fe_3O_4)$ nanoparticles using chemical coprecipitation technique with sodium oleate as surfactant. Nanoparticle size can be varied from 2 to 8nm by controlling the sodium oleate concentration. Magnetite phase nanoparticles could be observed from X-ray diffraction. Magnetic colloid suspensions containing particles with sodium oleate and chitosan have been prepared. Nanoparticles, both oleate-coated and chitosan-coated, have been characterized by several techniques. Atomic farce microscope (AFM) was used to image the coated nanoparticles. Magnetic hysteresis measurement were performed using a superconducting quantum interference device (SQUID) magnetometer at room temperature to investigate the magnetic properties of the magnetite nanoparticles. The SQUID measurements revealed superparamagnetism of nanoparticles.

• Applied Biological Chemistry
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• v.41 no.5
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• pp.399-404
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• 1998

Genipin was obtained from hydrolysis of geniposide isolated from gardenia fruits with ${\beta}-glucosidase$. Reaction of genipin with glycine, alanine, histidine, lysine, phenylalanine and glutamate in aqueous buffer solution converted colorless starting materials to blue pigments. Effect of pH for the formation of blue pigments was tested using UV/Vis spectrophotometer. The optimum pH for the formation of blue pigments was 7.0. No pigment and trace amounts were formed at acidic (pH 3.0) and alkaline (pH 12.0) conditions, respectively. The amount and tincture of blue color were distinct with different amino acids. In contrast with lysine $({\lambda}_{max}=573\;nm)$, glycine $({\lambda}_{max}=595\;nm)$, phenylalanine $({\lambda}_{max}=602\;nm)$ and alanine $({\lambda}_{max}=595\;nm)$, the reaction of genipin with histidine $({\lambda}_{max}=601\;nm)$ and glutamate $({\lambda}_{max}=601\;nm)$ produced relatively small amounts of blue pigments. Rate constants for the formation of blue pigments from genipin with amino acids at various temperatures $(60,\;70,\;80,\;90^{\circ}C,\;pH\;7.0\;phosphate\;buffer)$ were obtained. Rate constants of genipin with basic amino acids were larger than neutral or acidic amino acids. Arrhenius activation energies of the formation of blue pigments indicated that activation energy of glycine $(E_A=9.8\;kcal/mol)$ was especially lower than those of other amino acids $(E_A=13.3{\sim}15.4\;kcal/mol)$.

• Journal of Life Science
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• v.18 no.1
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• pp.58-62
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• 2008

A novel agar-degrading bacterium SL-12 was isolated from seashore of Kijang at Busan, Korea, and cultured in marine broth 2216 media. Isolated bacterium SL-12 was identified as Glaciecola genus by 16S rDNA sequencing with 98% identity. The optimum pH of the enzyme activity was 7.0 and the optimum temperature for the reaction was $30^{\circ}C$. The enzyme hydrolyzed neoagarohexaose to yield neoagarobiose as the main product, indicating that the enzyme is ${\beta}$-agarase. Thus, isolated bacterium and the enzyme would be useful for the industrial production of neoagarobiose.

• Journal of the Korean Chemical Society
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• v.38 no.10
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• pp.753-762
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• 1994

Dephosphorylation of diphenyl- or isopropylphenyl-4-nitrophenylphosphinate (DPNPIN or IPNPIN) mediated by $OH^-$ or o-iodosobenzoate ion ($IB^-$) are relatively slow in aqueous solution. The reactions in CTAX micellar solutions are, however, very accelerated, because CTAX micelles can accommodate both reactants in their Stern layer in which they can easily react, while hydrophilic $OH^-$(or $IB^-$) and hydrophobic phosphinates are not mixed in water. Even though the concentrations (> $10^{-3}$ M) of $OH^-$(or $IB^-$) in CTAX solutions are much larger amounts than those ($6{\times}10^{-6}$ M) of phosphinates, the rate constants of the dephosphorylations are largely influenced by change of the concentration of the ions, which means that the reactions are not followed by the pseudo first order kinetics. In comparison to effect of the counter ions of CTAX in the reactions, CTACl is more effective on the dephosphorylation of DPNPIN (or IPNPIN) than CTABr due to easier expelling of $Cl^-$ ion by $OH^-$(or $IB^-$) ion from the micelle, because of easier solvation $Cl^-$ ion by water molecules. The reactivity of IPNPIN with $OH^-$(or $IB^-$) is lower than that of DPNPIN. The reason seems that the 'bulky' isopropyl group of IPNPIN hinders the attack of the nucleophiles. The mechanism of reaction of IPNPIN with IB- ion concluded as 'nucleophilic' instead of 'general basic' by a trapping experiment and a measured kinetic isotope effect.

• Economic and Environmental Geology
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• v.56 no.5
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• pp.603-618
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• 2023

This study focused on evaluating the suitability of the WRK (waste repository Korea) bentonite as a buffer material in the SNF (spent nuclear fuel) repository. The U (uranium) adsorption/desorption characteristics and the adsorption mechanisms of the WRK bentonite were presented through various analyses, adsorption/desorption experiments, and kinetic adsorption modeling at various pH conditions. Mineralogical and structural analyses supported that the major mineral of the WRK bentonite is the Ca-montmorillonite having the great possibility for the U adsorption. From results of the U adsorption/desorption experiments (intial U concentration: 1 mg/L) for the WRK bentonite, despite the low ratio of the WRK bentonite/U (2 g/L), high U adsorption efficiency (>74%) and low U desorption rate (<14%) were acquired at pH 5, 6, 10, and 11 in solution, supporting that the WRK bentonite can be used as the buffer material preventing the U migration in the SNF repository. Relatively low U adsorption efficiency (<45%) for the WRK bentonite was acquired at pH 3 and 7 because the U exists as various species in solution depending on pH and thus its U adsorption mechanisms are different due to the U speciation. Based on experimental results and previous studies, the main U adsorption mechanisms of the WRK bentonite were understood in viewpoint of the chemical adsorption. At the acid conditions (＜pH 3), the U is apt to adsorb as forms of UO₂²⁺, mainly due to the ionic bond with Si-O or Al-O(OH) present on the WRK bentonite rather than the ion exchange with Ca²⁺ among layers of the WRK bentonite, showing the relatively low U adsorption efficiency. At the alkaline conditions (>pH 7), the U could be adsorbed in the form of anionic U-hydroxy complexes (UO₂(OH)₃^-, UO₂(OH)₄^2-, (UO₂)₃(OH)₇^-, etc.), mainly by bonding with oxygen (O^-) from Si-O or Al-O(OH) on the WRK bentonite or by co-precipitation in the form of hydroxide, showing the high U adsorption. At pH 7, the relatively low U adsorption efficiency (42%) was acquired in this study and it was due to the existence of the U-carbonates in solution, having relatively high solubility than other U species. The U adsorption efficiency of the WRK bentonite can be increased by maintaining a neutral or highly alkaline condition because of the formation of U-hydroxyl complexes rather than the uranyl ion (UO₂²⁺) in solution,and by restraining the formation of U-carbonate complexes in solution.

• Korean Chemical Engineering Research
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• v.51 no.1
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• pp.111-115
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• 2013

The optimum synthetic conditions of poly(p-phenylphenol) by horseradish peroxidase in dioxane:water (80:20 v/v) mixtures were studied. The stability against thermal degradation and structural properties of the synthesized phenolic resins were investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), respectively. The synthetic yield of poly(p-phenylphenol) increased upon the increase of the amount of enzyme up to 0.25 mg HRP/mL, then leveled off for further increase of the enzyme usage. When sodium acetate (100 mM, pH 4~6) and sodium phosphate (100 mM, pH 7~9) were used as the buffering salts for the aqueous component (20% v/v), the synthetic yield of the resin increased at higher pH of the aqueous buffer. But when the pHs of the aqueous buffer were 6 and 9, the synthetic yield strongly depended on the types of the buffering salts; if sodium phosphate was used instead of sodium acetate at pH 6, the yield decreased by about 15% and if sodium bicarbonate was used instead of sodium phosphate, the yield decreased by almost 20%. When the pH range of the aqueous buffer was from 4 to 7, the addition of a radical mediator, 2,2'-azinobis (3-ethylbenzothiazoline-6-sulfonate) (ABTS), up to 2 mM improved the synthetic yield of the resin by about 10%. TGA experiments revealed that the thermal stability of the resin synthesized in dioxane:water (100 mM sodium phosphate, pH 9) (80:20 v/v) was high having the char yield of 47% upon the heating at $800^{\circ}C$. DCS results showed that the structures of the polymers synthesized in acidic aqueous buffers were different from those of the polymers synthesized in the basic aqueous buffers. However, all the synthesized resins were found to have the property of the thermosetting resins.

• Korean Journal of Environmental Agriculture
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• v.37 no.1
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• pp.49-56
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• 2018

BACKGROUND: The mobile vortex wet scrubber was developed to remove the harmful chemicals from accidental releases. However, there was a disadvantage that it was limitedly used for volatile organic compounds (VOCs) such as toluene according to the physicochemical properties. This study compared the removal efficiencies of an improved mobile scrubber on toluene and ammonia by applying diverse adsorption and absorption methods. METHODS AND RESULTS: The removal efficiencies on harmful chemicals were examined using various adsorption and absorption methods of water vortex process (C), phosphoric acid-impregnated activated carbon adsorption (PCA), pH-controlled water (pH 2.5) vortex process absorption with sulfuric acid (SWA) after ammonia exposure, granular activated carbon adsorption (GCA), and activated carbon mat adsorption (CMA) after toluene exposure. As a result, the best removal efficiency was shown in the SWA for ammonia and GCA for toluene. Also, the SWA and GCA methods were compared with different concentration levels. In the case of ammonia exposure (5, 10 and 25%), there was no difference by concentration levels, and the concentration in the outlet gradually increased, with pH change from acid to base. In the case of toluene exposure (50, 75 and 100%), the outlet concentration was higher relative to the exposure concentration in the initial 10 min, but the outlet concentration was remained steady after 10 min. CONCLUSION: The newly improved mobile scrubber was also effective in removing VOCs through adsorption techniques (activated carbon, activated carbon fiber, carbon mat filter etc.), as well as removing acid-base harmful chemicals by neutralization reaction.