• Korean Journal of Materials Research
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• v.21 no.2
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• pp.89-94
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• 2011

In this work, fabrication and electrochemical analysis of an individual multi-walled carbon nanotube (MWNT) electrode are carried out to confirm the applicability of electrochemical sensing. The reactive ion etching (RIE) process is performed to obtain sensitive MWNT electrodes. In order to characterize the electrochemical properties, an individual MWNT is cut by RIE under oxygen atmosphere into two segments with a small gap: one segment is applied to the working electrode and the other is used as a counter electrode. Electrical contacts are provided by nanolithography to the two MWNT electrodes. Dopamine is specially selected as an analytical molecule for electrochemical detection using the MWNT electrode. Using a quasi-Ag/AgCl reference electrode, which was fabricated by us, the nanoelectrodes are subjected to cyclic voltammetry inside a $2{\mu}L$ droplet of dopamine solution. In the experiment, RIE power is found to be a more effective parameter to cut an individual MWNT and to generate "broken" open state, which shows good electrochemical performance, at the end of the MWNT segments. It is found that the pico-molar level concentration of analytical molecules can be determined by an MWNT electrode. We believe that the MWNT electrode fabricated and treated by RIE has the potential for use in high-sensitivity electrochemical measurement and that the proposed scheme can contribute to device miniaturization.

• Advances in materials Research
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• v.1 no.4
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• pp.299-310
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• 2012

This article describes the synthesis of a novel N-substituted pyrrole monomer containing an azobenzene group. The 2-[N-ethyl-N-[4-[(4-nitrophenyl) azo]-phenyl] amino] ethyl-3-chloropropionate (RedII) compound was synthesized via reaction of 4-nitro-4'-[N-ethyl-N-(2-hydroxyethyl)-amino] azobenzene (RedI) and 3-chloropropionic acid. RedII was reacted with the potassium salt of pyrrole then 2-[N-ethyl-N-[4-[(nitro phenyl) azo] phenyl] amino] ethyl-N-pyrrolyl propionate (Py-RedII) was prepared. Chemical polymerization of Py-RedII and copolymerization of Py-RedII with pyrrole carried out using $FeCl_3$. Poly (2-[N-ethyl-N-[4-[(nitro phenyl) azo] phenyl] amino] ethyl-N-pyrrolyl propionate) (PPy-RedII) was characterized by UV, IR, $^1HNMR$, $^{13}CNMR$ spectroscopies. Electropolymerization of Py-RedII and electroco-polymerization of Py-RedII and pyrrole were studied using conventional three electrodes system, Ag/AgCl reference electrode, platinum counter electrode and GC disk working electrode. Scanning electron microscopy (SEM), thermogravimetry analysis (TGA) and differential scanning calorimetry (DSC) were used for thermal and rheological studies. The TGA curve of PPy-RedII demonstrated a high thermal stability up to 200°C and its DSC thermogram showed two endothermic peaks at 88 and $122^{\circ}C$. The glass transition temperature of the polymer was found to be above the room temperature. Electrical conductivities of PPy-RedII and it's copolymer with pyrrole (PPy-RedII-co-Py) were studied by the four-probe method and produced conductivities of $7.5{\times}10^{-4}$ and $6.5{\times}10^{-3}Scm^{-1}$, respectively.

• Korean Chemical Engineering Research
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• v.50 no.5
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• pp.933-937
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• 2012

In the present study, we evaluate the sensitivity and optimal stripping voltammetry (SV) conditions of copper (Cu), which is one of the main trace heavy metals inducing the environmental contamination, using carbon nanotube (CNT) electrode. In addition, the reaction mechanism of stripping reaction of Cu is investigated. The electrochemical analyses such as squarewave stripping voltammetry (SWSV) and linear scan voltammetry (LSV) are used for the evaluations. As a result of that, the best SWSV conditions like squarewave amplitude of 15 mV, frequency of 60 Hz, deposition potential of -1.0V vs. Ag/AgCl and deposition time of 200s are determined with the measured Cu sensitivity of $1.824{\mu}A/{\mu}M$. As a driving force affecting the stripping reaction of Cu, surface reaction is more dominant one than diffusion. These results are compared with other reference results and it is confirmed that our suggested CNT electrode gives rise to better Cu sensitivity result than other references.

• Journal of Microbiology and Biotechnology
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• v.22 no.10
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• pp.1446-1451
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• 2012

Levodopa or L-3,4-dihydroxyphenylalanine (L-DOPA) is the precursor of the neurotransmitter dopamine. L-DOPA is a famous treatment for Parkinson's disease symptoms. In this study, electroenzymatic synthesis of L-DOPA was performed in a three-electrode cell, comprising a Ag/AgCl reference electrode, a platinum wire auxiliary electrode, and a glassy carbon working electrode. L-DOPA had an oxidation peak at 376 mV and a reduction peak at -550 mV. The optimum conditions of pH, temperature, and amount of free tyrosinase enzyme were pH 7, $30^{\circ}C$, and 250 IU, respectively. The kinetic constant of the free tyrosinase enzyme was found for both cresolase and catacholase activity to be 0.25 and 0.4 mM, respectively. A cyclic voltammogram was used to investigate the electron transfer rate constant. The mean heterogeneous electron transfer rate ($k_e$) was $5.8{\times}10^{-4}$ cm/s. The results suggest that the electroenzymatic method could be an alternative way to produce L-DOPA without the use of a reducing agent such as ascorbic acid.

• Journal of the Korean Chemical Society
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• v.36 no.4
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• pp.552-557
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• 1992

Chloramphenicol was studied by differential pulse polarography (DDP). A reduction peak which is dependent on pH of the solution appeared in the voltage range between zero and -1.50 volt vs. Ag/AgCl (sat. KCl) reference electrode. A plot of peak potentials (Ep) measured at room temperature (20$^{\circ}C$) vs. pH of the chloramphenicol solutions showed linear relationship changing slope (Ep/pH) at pH 8.9. The slope was -59.7 mV/pH in pH 2.7∼8.9 and -24.3 mV/pH in pH 8.9∼11.2, respectively. A log plot of peak currents (ip) vs. concentrations showed a linearity at the concentrations between 4.8 ${\times}$ 10$^{-7}$ M and 6.2 ${\times}$ 10$^{-5}$ M (0.16 ppm∼20 ppm) chloramphenicol in pH 8.0 ammonium buffer. Between the DPP method and the reference method measuring absorbance at 278 nm, the correlation coefficient was 0.996, which means an excellent linearity. The DPP method was able to detect degradation products of chloramphenicol in mild alkaline solution (pH = 8.0) more distinctly than the spectrophotometric method.

• The Korean Journal of Nuclear Medicine
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• v.34 no.4
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• pp.336-343
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• 2000

Purpose: Thallous-201 chloride produced at Korea Cancer Center Hospital(KCCH) is used in detecting cardiovascular disease and cancer. Thallium impurity can cause emesis, catharsis and nausea, so the presence of thallium and other metal impurities should be determined. According to USP and KP, their amounts must be less than 2 ppm in thallium and 5 ppm in total. In this study, the detection method of trace amounts of metal impurities in $[^{201}Tl]$TICI injection with polarography was optimized without environmental contamination. Materials and Methods: For the detection of metal impurities, Osteryoung Square Wave Stripping Voltammetry method was used in Bio-Analytical System (BAS) 50W polarograph. The voltammetry was composed of Dropping Mercury Electrode (DME) as a working electrode, Ag/AgCl as a reference electrode and Pt wire as a counter electrode. Square wave stripping method, which makes use of formation and deformation of amalgam, was adopted to determine the metal impurities, and pH 7 phosphate buffer was used as supporting electrolyte. Results: Tl, Cu and Pb in thallous-201 chloride solution were detected by scanning from 300 mV to -800 mV Calibration curves were made by using $TINO_3,\;CuSO_4\;and\;Pb(NO_3){_2}$ as standard solutions. Tl was confirmed at -450 mV peak potential and Cu at -50 mV Less than 2 ppm of Tl and Cu was detected and Pb was not detected in KCCH-produced thallous-201 chloride injection. Conclusion: Detection limit of thallium and copper is approximately 50 ppb with this method. As a result of this experiment, thallium and other metal impurities in thallous-201 chloride injection, produced at Korea Cancer Center Hospital, are in the regulation of USP and KP Polarograph could be applied for the determination of metal impurities in the quality control of radiopharmaceuticals conveniently without environmental contamination.

• Journal of Electrochemical Science and Technology
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• v.14 no.1
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• pp.15-20
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• 2023

Ionic liquids are considered as a promising, alternative solvent for the electrochemical synthesis of metals because of their high thermal and chemical stability, relatively high ionic conductivity, and wide electrochemical window. In particular, their wide electrochemical window enables the electrodeposition of metals without any side reaction of electrolytes such as hydrogen evolution. The electrodeposition of silver is conducted in 1-n-butyl-3-methylimidazolium chloride ([C4mim]Cl) ionic liquid system with a silver source of AgCl. This study is the first attempt to electrodeposit silver nanoparticles without using co-solvents other than [C4mim]Cl. Pulse electrolysis is employed for the synthesis of silver nanoparticles by varying applied potentials from -3.0 V to -4.5 V (vs. Pt-quasi reference electrode) and pulse duration from 0.1 s to 0.7 s. Accordingly, the silver nanoparticles whose size ranges from 15 nm to ~100 nm are obtained. The successful preparation of silver nanoparticles is demonstrated regardless of the kinds of substrate including aluminum, stainless steel, and carbon paper in the pulse electrolysis. Finally, the antimicrobial property of electrodeposited silver nanoparticles is confirmed by an antimicrobial test using Staphylococcus aureus.

• Journal of Sensor Science and Technology
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• v.6 no.3
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• pp.207-213
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• 1997

A field effect transistor(FET) type dissolved carbon dioxide($pCO_{2}$) sensor with a double layer structure of hydrogel membrane and $CO_{2}$ gas permeable membrane was fabricated by utilizing a $H^{+}$ ion selective field effect transistor(pH-ISFET) with Ag/AgCl reference electrode as a base chip. Formation of hydrogel membrane with photo-crosslinkable PVA-SbQ or PVP-PVAc/photosensitizer system was not suitable with the photolithographic process. Furthermore, hydrogel membrane on pH-ISFET base chip could be fabricated by photolithographic method with the aid of N,N,N',N'-tetramethyl othylenediarnine(TED) as $O_{2}$ quencher without using polyester film as a $O_{2}$ blanket during UV irradiation process. Photosensitive urethane acrylate type oligomer was used as gas permeable membrane on top of hydrogel layer. The FET type $pCO_{2}$ sensor fabricated by photolithographic method showed good linearity (linear calibration curve) in the range of $10^{-3}{\sim}10^{0}\;mol/{\ell}$ of dissolved $CO_{2}$ in aqueous solution with high sensitivity.

• Korean Journal of Materials Research
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• v.15 no.8
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• pp.528-535
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• 2005

It is inclined to increase that use of hazardous substances such as lead(Pb), mercury (Hg), cadmium(Cd) etc. are prohibited in the electronics according to environmental friendly policies of an advanced nation for protecting environment of earth. As this reasons, many researches for ensuring the reliability were proceeding in Pb free soldering process. n the flux remains on the PCB(printed circuit board) in the soldering process or the electronics exposed to corrosive environment, it becomes the reasons of breakdown or malfunction of the electronics caused by corrosion. Therefore in this studies we researched the polarization and Tafel properties of Sn40Pb and SnCu system solders based on the electrochemical theory. The experimental polarization curves were measured in distilled ionized water and 1 mole $3.5 wt\%$ NaCl electrolyte of $40^{\circ}C$, pH 7.5. Ag/AgCl and graphite were utilized by reference and counter electrodes, respectively. To observe the electrochemical reaction, polarization test was conducted from -250mV to +250mV. From the polarization curves composed of anodic and cathodic curves, we obtained Tafel slop, reversible electrode potential(Ecorr) and exchange current density((cow). In these results, we compared the corrosion rate of SnPb and SnCu solders.

• 한국신재생에너지학회:학술대회논문집
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• 2011.11a
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• pp.100-100
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• 2011

Nanomaterial architecture with highly ordered, vertically oriented $TiO_2$ nanotube arrays shows a good promise for diverse technological applications. As inspired from the literature reports that Nickel modification can improve the photocatalytic activity of $TiO_2$, it was planned to coat Ni into the $TiO_2$ matrix. In this study, first $TiO_2$ nanotubes(TiNTs) were prepared by anodization (60V,3min) in HF-free aqueous electrolyte on ultrasonically cleaned polished titanium sheet substrates ($1{\times}7cm^2$). The typical thickness of the sintered TiNT ($500^{\circ}C$for10min) was ~1 micronas confirmed from the FESEM study. In the next part, as-anodized and sintered TiNT/Ti photoanodes were used to coat Ni by AC electrodeposition from aqueous 0.1M nickel sulphate solution. During AC electrodeposition, conditions such as 1V DC offset voltage, 9V amplitude (peak-to-peak) and 750 Hz frequency were fixed constant and the deposition time was varied as 0.5 min, 1 min, 2 min and 10 min. The photoelectrochemical performance of pristine and Ni modified TiNT/Ti photoanodes was measured in 1N NaOH electrolyte under 1 SUN illumination in the potential range of -1V and 1.2V versus Ag/AgCl reference electrode. The photocurrent performance of TiNT/Ti photoanode decreased upon Ni modification and the results were confirmed after repeated experiments. This suggests us that Ni modification inhibits the photoelectrochemical performance of $TiO_2$ nanotubes.