• Applied Chemistry for Engineering
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• v.27 no.2
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• pp.115-122
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• 2016

Melanin is a common name used for a certain type of natural dark pigments existing in living organisms, particularly in human hair, eyes, and skin. The unique free radical scavenging effect of melanine could help protecting cells and tissues from harmful UV light. While their exact molecular structures in nature are not still well defined, their multifunctional properties including electrical and ionic conductivities, antioxidation, wet adhesion, and metal ion chelation, are highlighted for the potential applications in bioorganic electronics including biomedical sensors and devices. In this mini-review, we will discuss sources, synthesis methods, structures and multifunctional properties of melanin materials in addition to current research directions on a wide range of applications.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.34 no.5
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• pp.348-356
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• 2021

Field-effect transistors (FETs) are the key elements of conventional electronics; hence, have drawn a lot of research and commercial interests. In recent years, metal halide perovskite materials have achieved a remarkable efficiency of 29.15% in the field of photovoltaics, and have drawn the scientific community's attention to promote their use in the field of optoelectronics, such as FETs and phototransistors. The MAPbI₃ (methylammonium lead iodide) perovskite TFT has achieved a record hole mobility of 21.41 cm²/V-s in the year 2020. In this review, we will briefly discuss the physical structure of MAPbI₃ perovskite and the essential factors that stimulate these devices, together with the role of defects, the ion migration concept, and the implication of both dielectric and electrode materials on the device's performance.

• Journal of the Mineralogical Society of Korea
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• v.28 no.4
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• pp.299-308
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• 2015

The six natural zeolites collected in Pohang area, Kyungsangbuk-do, Korea, were characterized by XRD, XRF, DTA, TGA, and CEC analysis. The primary species of these zeolite are modenite, albite, and quarts in Kuryongpo-A (Ku-A), Kuryongpo-B (Ku-B), Kuryongpo-C (Ku-C), Donghae-A (Dh-A), Donghae-B (Dh-B), and Donghae-C (Dh-C) samples. The XRF analysis showed that the six zeolites contain Si, Al, Na, K, Mg, Ca, and Fe. Cation exchange capacity of Kuryongpo-C (Ku-C) zeolite was the highest compared to other zeolites. The capabilities of removing heavy metal ions such as $Pb^{2+}$, $Cd^{2+}$ and $Cu^{2+}$ were compared. The effect of reaction time in removing heavy metal ions was studied. The experimental results showed that the efficiency of removal was low for $Pb^{2+}$, $Cd^{2+}$ and $Cu^{2+}$ ions. These may be caused by the low content of zeolite in the six natural zeolites. This indicates that the adsorption capacity roughly tends to depend on the zeoite contents, ie., the grade of zeolite ore.

• Applied Chemistry for Engineering
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• v.32 no.6
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• pp.664-670
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• 2021

Stainless steel was applied as bipolar plate (BP) of polymer electrolyte membrane fuel cell (PEMFC) due to high mechanical strength, electrical conductivity, and good machinability. However, stainless steel was corroded and increased contact resistance resulting PEMFC performance decrease. Although the corrosion resistance could be improved by surface treatment such as noble metal coating, there is a disadvantage of cost increase. The stainless steel corrosion behavior and passive layer influence on PEMFC performance should be studied to improve durability and economics of metal bipolar plate. In this study, SUS316L bipolar plate of 25 cm² active area was manufactured, and experiments were conducted for corrosion behavior at an anode and cathode. The influence of SUS316L BP corrosion on fuel cell performance was measured using the polarization curve, impedance, and contact resistance. The metal ion concentration in drained water was analyzed during fuel cell operation with SUS316L BP. It was confirmed that the corrosion occurs more severely at the anode than at the cathode for SUS316L BP. The contact resistance was increased due to the passivation of SUS316L during fuel cell operation, and metal ions continuously dissolved even after the passive layer formation.

• KSBB Journal
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• v.17 no.1
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• pp.63-67
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• 2002

Silver-alginate and copper-alginate were prepared with Na-alginate extracted from marine brown algae(Sargassum fluitans). The antibacterial effect of Ag-alginate or Cu-alginate against Staphylococcus aureus and Escherichia coli was carried out by measuring optical density of liquid culture at 600 nm. The cell growth of Staphylococcus aureus and Escherichia coli was very active at pH 7, and was inhibited by adding Ag-alginate with more than 0.006 wt.% of silver content. The antibacterial effect of Ag-alginate against S. aureus and E. coli was better than that of Cu-alginate at the same metal concentration. The cell growth of S. aureus was less inhibitory than E. coli at the same concentration of Ag-alginate. The cell growth of S. aureus and E. coli was also influenced by the characteristics of counter ion of silver.

• Textile Coloration and Finishing
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• v.11 no.3
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• pp.15-22
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• 1999

This study investigated the mordanting effect of natural mordants such as camellia ash, bean chaff ash and pyrolignite of iron(Iron(II) Acetate) on silk fabrics dyed with green tea extracts. Experimental variables include the conditions of extraction and dyeing, and types of natural mordants. Inorganic ion contents In natural mordants were analysed by Induced Coupled Plasma Atomic Emission Spectrometer. In the ash Al, Fe, Si and Mn were in % unit, Cr and Ni were detected in ppm unit, and in the aqueous extracts of the ash all the metal ions were in ppm unit. On the other hand, fairly high content of Al(2.13% ) in camellia ash extract and Fe(7.91% ) in the aqueous extracts of pyrolignite iron were detected. The absorbance intensity of green tea extracts in UV-Visible spectrum increased with the temperature and time of extraction. The maximum absorption wavelength of the extracts appeared at 272.5nm and 210.5nm. The US values of silk fabrics dyed with green tea extracts were increased with temperature and time of dyeing. Surface color of silk fabric dyed with green tea extracts was 9.1YR, but it was changed from 7.9YR to 7.5YR by camellia ash extract and 7.4YR to 6.4YR by bean chaff ash extract with increase in mordant concentration. Pre-mordanted and post-mordanted fabrics with pyrolignite of iron were changed from 1.4YR to 1.1R and 7.2P to 4.2P, respectively.

• JSTS:Journal of Semiconductor Technology and Science
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• v.7 no.3
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• pp.196-208
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• 2007

An analytical model is proposed for an optically controlled Metal Semiconductor Field Effect Transistor (MESFET), known as Optical Field Effect Transistor (OPFET) considering the diffusion fabrication process. The electrical parameters such as threshold voltage, drain-source current, gate capacitances and switching response have been determined for the dark and various illuminated conditions. The Photovoltaic effect due to photogenerated carriers under illumination is shown to modulate the channel cross-section, which in turn significantly changes the threshold voltage, drainsource current, the gate capacitances and the device switching speed. The threshold voltage $V_T$ is reduced under optical illumination condition, which leads the device to change the device property from enhancement mode to depletion mode depending on photon impurity flux density. The resulting I-V characteristics show that the drain-source current IDS for different gate-source voltage $V_{gs}$ is significantly increased with optical illumination for photon flux densities of ${\Phi}=10^{15}\;and\;10^{17}/cm^2s$ compared to the dark condition. Further more, the drain-source current as a function of drain-source voltage $V_{DS}$ is evaluated to find the I-V characteristics for various pinch-off voltages $V_P$ for optimization of impurity flux density $Q_{Diff}$ by diffusion process. The resulting I-V characteristics also show that the diffusion process introduces less process-induced damage compared to ion implantation, which suffers from current reduction due to a large number of defects introduced by the ion implantation process. Further the results show significant increase in gate-source capacitance $C_{gs}$ and gate-drain capacitance $C_{gd}$ for optical illuminations, where the photo-induced voltage has a significant role on gate capacitances. The switching time ${\tau}$ of the OPFET device is computed for dark and illumination conditions. The switching time ${\tau}$ is greatly reduced by optical illumination and is also a function of device active layer thickness and corresponding impurity flux density $Q_{Diff}$. Thus it is shown that the diffusion process shows great potential for improvement of optoelectronic devices in quantum efficiency and other performance areas.

• Environmental Sciences Bulletin of The Korean Environmental Sciences Society
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• v.4 no.3
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• pp.173-183
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• 2000

This study measured the zeta potential of both latex colloidal particles with carboxylate surface groups and glass beads (collectors) with silanol surface group employing various solution with different chemical characteristics. The results have been compared with the surface chemistry theory. The zeta potential of the particle and collector increased with increasing pH up to 5.0 regardless of the solution chemistry. For a monovalent electrolyte solution(sodium chloride solution) the zeta potential steadily increased until the pH reached 9.5. In contrast, little change in zeta potential was made between 5.0 and 9.5 for a divalent electrolyte solution (sodium chloride solution) the zeta potential steadily increased until the pH reached 9.5. In contrast, little change in zeta potential was made between 5.0 and 9.5 for a divalent electrolyte solution (calcium chloride solution). In other words, the more the pH decreases, the larger the effect of neutral salts, such as NaCl and CaCl$_2$, have on the ζ-potential values. In this study, the PZPC(point of zero proton condition) of the particle and collector occurred below a pH of 3.1, H(sup)+ and OH(sup)- acted as a PDI (potential determining ion), and Na(sup)+ acted as an IDI(indifferent ion). The magnitude of the negative ζ-potential values of the particle and collector monotonically increased as the concentrations of Na(sup)+ or Ca(sup)2+([Na(sup)+] or [Ca(sup)2+]) decreased (the values of pNa or pCa increased). In the case of latex particles, the ζ-potential should aproach zero (isoelectric point; IEP) asymptotically as the pNa approaches zero, while in the case of calcium chloride electrolyte, ζ-potential reversal may be expected to occur around 3.16$\times$10(sup)-2MCaCl$_2$(pCa=1.5). pH, valance and ionic strength can be used in various ways to improve the water treatment efficiency by modifying the charge characteristics of the particle and collector. Predictive capability is far less certain when EDL(electrical double layer) repulsive forces exist between the particle and collector.

• Journal of the Korean Chemical Society
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• v.37 no.10
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• pp.881-887
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• 1993

A cobalt(II) ion-selective carbon-paste electrode (CPE) was constructed with ${\iota}$-sparteine. Cobalt(II) ion in aqueous solution was chemically deposited through the complexation with ${\iota}$-sparteine onto the CPE. The surface of CPEs were characterized by cyclic voltammetry and differential pulse voltammetry in an acetate buffer solution, separately. Exposure of the CPEs to an acid solution could regenerate surface to reuse it for the deposition. In more than 5 deposition / measurement / regeneration cycles, the response was reproducible and linear up to $5.0{\times}10^{-6}$M with linear sweep voltammetry. The peaks at 0.17V / 0.27V were correspond to the redox of Co(II)-SP complex deposited on CPE. The anodic peak of which appeared after scan over the cathodic peak of 0.17 V to more negative scan. In case of using the differencial pulse voltammetry (DPV), we have obtained the linear response $2.0{\times}10^{-7}$M with relative standard deviation ${\pm}5.6%$. The detection limit was $1.0{times}10^{-7}$M for 20 minutes of the deposition. We have also investigated the interference effect of various metal ions, which are expected to form the complex with the ligand on the electrode.

• Food Science and Preservation
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• v.21 no.2
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• pp.276-285
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• 2014

The purpose of this study was to develop a new fermented product (named as Cheonggeumjang) using Sigumjang, Cheonggukjang and Oak mushroom. This study was conducted to evaluate the effects of Sigumjang, Cheonggukjang, and Cheonggeumjang, which were mixed in a different ratio as A (Sigumjang: Cheonggukjang = 1:2), B (Sigumjang: Cheonggukjang = 1:1) and C (Sigumjang: Cheonggukjang = 2 : 1). Then, the functions and physicochemical properties of products were investigated. We found that the crude protein content in Cheonggeumjang was higher than in Sigumjang whereas fat and calories content was less than that of Cheonggukjang. Free sugar content in Cheonggeumjang C 5.8681 g/100g was the highest. Moroever, Cheonggeumjang C and Sigumjang has an antioxidant activities. The electron donating capacity, SOD like activity and the inhibitory effect on xanthine oxidase of these two were significantly high than other group. Fat rancidity is promoted in the presence of metal ion, Cheonggeumjang group has higher inhibitory effect on $Fe^{2+}$ion than on $Cu^{2+}$ ion. The rancidity of fat is also increased by reactive oxygens species, Cheonggeumjang group inhibited $H_2O_2$ in higher extent than $KO_2$. Also, ${\alpha}$-glucosidase inhibition activity of Cheonggeumjang C in all of the concentrations (300 ppm, 500 ppm and 700 ppm) is higher than other groups. In sensory evaluation, Cheonggeumjang C groups is ranked significantly higher than the other groups while considering color, flavor, taste and the overall acceptability. Taken together, the results of this study suggest that Cheonggeumjang is best ingredient for increasing the consumer acceptability and functionality.