• Journal of the Korean Society of Food Science and Nutrition
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• v.37 no.11
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• pp.1485-1490
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• 2008

The effects of $\gamma$-irradiation on antioxidant and physicochemical properties of powder and 70% fermented ethanol extracts of Ishige okamurai (I. okamurai) were investigated. In case of powder, although yields were increased, there were no significant changes in total phenolic compounds (TPC) and 2,2-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging effect by $\gamma$-irradiation at 3, 7, and 20 kGy. In case of 70% fermented ethanol extracts, the results of TPC and DPPH radical scavenging effects showed no significant changes. However, antioxidant index increased in the 20 kGy irradiated I. okamurai extracts and decreased in 3 kGy irradiated ones. The optical density value of UV spectrum at 427 nm significantly decreased depending on increasing irradiation dosage. In conclusion, irradiated extracts of I. okamurai can be applied to the food industry due to irradiation stability on antioxidant properties. Also, irradiated extracts can be more useful for food processing as a result of a decrease of extracts color by irradiation.

• Journal of the Korean Wood Science and Technology
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• v.38 no.4
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• pp.333-340
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• 2010

The Korean Dendropanax lacquer, made from a natural resinous sap from Dendropanax orbifera Lev., was used as a golden and transparent varnish for the traditional artifacts (armor uits, helmets, arrowheads, etc.) to make them be brilliant golden color. The cured film of the acquer has excellent protective properties such as weatherability, water resistance, and nticorrosive. But, one of disadvantages is that takes a long time and much energy to fulfill curing the lacquer. The chemical constituents of the lacquer contained conjugated diene compounds s the photopolymerizable monomers. These monomers easily polymerized in sunlight to form olden-colored, hard-coating films in a short time. Photooxidation may be one of the most mportant reactions in the chemistry of the lacquer. Although the Korean Dendropanax Lacquer hould be dried to a thoroughly dry stage to achieve optimal film properties, curing with elevated emperatures may be required for the protracted curing time at atmospheric temperature. So we ntended to accelerate the curing rate of the lacquer by dual curing of thermal and radiation uring. The effect of thermal initiator on the thermal curing reaction was evaluated by monitoring he changes in double bond peak with FT-IR. Then the curing rate of the lacquer blended with hermal initiator and photoinitiator together was measured during dual curing using a RPT with V spot curing machine. Thermal initiator not only accelerated the curing rate but also improved he physical property. And the curing rate of the Korean Dendropanax lacquer was improved by ual curing method of thermal and UV curing. According to these results, the application area of he Korean Dendropanax lacquer could be expanded to surface coatings for electronic devices uch as mobile phones or electronics.

• Journal of Korean Society of Environmental Engineers
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• v.27 no.1
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• pp.1-10
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• 2005

The purpose of this study was to evaluate the potential of a gamma irradiation to decompose 2,4,6-trinitrotoluene(TNT) in an aqueous solution. The decomposition reaction of TNT by gamma irradiation was a pseudo first-order kinetic over the applied initial concentrations($25{\sim}100mg/L$). The dose constant was strongly dependent on the initial TNT concentration. The removal of TNT was more efficient at pH below 3 and at pH above 11 than at neutral pH(pH 5-9). The required irradiation dose to remove over 99% of TNT was 40, 80 and 10 kGy, individually at pH 2, 7 and 13. The dose constant was increased by 1.6 fold and over 15.6 fold at pH 2 and 13, respectively, when compared with that at pH 7 When irradiation dose of 200 kGy was applied, the removal efficiencies of TOC were 91, 46 and 53% at pH 2, 7 and 13, respectively. Ammonia and nitrate were detected as the main nitrogen byproducts of TNT and glyoxalic acid and oxalic acid were detected as organic byproducts. The results showed that a gamma irradiation was an attractive method for the decomposition of TNT in an aqueous solution. However, regarding the application of high energy radiation for the TNT decomposition and mineralization, an application of an acidic pH below 3 to the solution before irradiation should be considered.

• Journal of the Society of Cosmetic Scientists of Korea
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• v.39 no.3
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• pp.195-203
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• 2013

In this study, antioxidative effects of the extracts of different species and flowering periods of Inula britannica were investigated. According to the free radical (1,1-diphenyl-2-picrylhydrazyl, DPPH) scavenging activity of the extracts, The I. britannica var. chinensis flower extract (500 ${\mu}g/mL$) was measured in a 79.89% free radical scavenging activity, but the flower extracts of similar species (I. britannica var. linariaefolia Regel, I. britannica var. ramosa, I. salicina var. asiatica) did not show any effect on the free radical scavenging activity. The effects of the free radical scavenging activity of I. britannica var. chinensis flower extracts were exhibited in the order of full bloom (93.68%), bud (43.28%), and fallen blossom (14.11%). Next, we established optimum condition of extract solvent, temperature, extraction time. The extract from ethanol at $60^{\circ}C$ showed the most free radical scavenging activity among other conditions and extraction time not relevant in free radical scavenging activity. The protective effects of the extract of I. britannica var. chinensis flower on the photohemolysis of human erythrocytes by using rose bengal were increased in a concentration-dependent manner (5 ~ 50 ${\mu}g/mL$). In particular, the extract in 50 ${\mu}g/mL$ concentration exhibited better protective activity (${\tau}_{50}$ = 116.1 min) than (+)-${\alpha}$-tocopherol (${\tau}_{50}$ = 73.44 min), which is a known lipophilic antioxidant. Principle component of I. britannica var. chinensis flower was identified as quercetin of flavonoids by high-performance liquid chromatography (HPLC). These results indicate that the extract of I. britannica var. chinensis flower can function as antioxidants in biological systems, particularly skin exposed to UV radiation by scavenging free radical and $^1O_2$, and protect cellular membranes against ROS. It is concluded that the antioxidative effects of the extract of I. britannica var. chinensis flower could be applicable to functional cosmetics.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.97.1-97.1
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• 2010

유연금속기판위에 DC 마그네트론 스퍼터링을 이용하여 Ag/ZnO 이중구조의 후면반사막을 증착하고 Ag 표면조도 변화에 따른 후면반사막의 반사특성 변화와 플렉서블 비정질 실리콘 박막 태양전지의 셀 특성에 미치는 영향을 조사하였다. Substrate구조를 갖는 플렉서블 실리콘 박막 태양전지에서는 실리콘 박막 광흡수층의 상대적으로 낮은 광 흡수율로 인하여 입사광에 대한 태양전지 내에서의 광 산란 및 포획이 태양전지 효율을 증대시키는데 매우 중요한 역할을 하는 것으로 알려져 있다. 플렉서블 실리콘 박막 태양전지에서의 후면반사막은 광 흡수층에서 흡수되지 않는 입사광을 다시 반사시켜 광 흡수를 증대시키며 이때 후면반사막 표면에서 반사 빛을 효율적으로 산란시켜 이동경로를 증대시킴으로써 광 흡수율을 더욱 향상시킬 수 있다. 본 연구에서는 유연금속 기판위에 Ag와 ZnO:Al($Al_2O_3$ 2.5wt%) 타겟을 사용한 DC 마그네트론 스퍼터링법으로 Ag/AZO 이중구조의 후면반사막을 제조하고, Ag 박막의 표면형상 변화와 이에 따른 후면반사막의 반사도 변화를 비교, 분석하였다. 증착 조건 변화에 따른 표면 형상 및 반사 특성은 Atomic Force Mircroscope(AFM), Scanning electron miroscopy(SEM), UV-visible-nIR spectrometry를 통하여 분석하였다. 서로 다른 표면 거칠기를 갖는 후면반사막 위에 n-i-p구조의 a-Si:H 실리콘 박막 태양전지를 제조한 후 태양전지 동작 특성에 미치는 영향을 조사하였다. n,p층은 13.56MHz PECVD, i층은 60MHz VHF CVD를 사용하여 각각 제조 하였으며, Photo I-V, External Quantum Efficiency(EQE) 분석을 통하여 태양전지 특성을 조사 하였다. SEM 분석결과 공정 온도가 증가 할수록 Ag 박막의 표면 결정립 크기도 증가하였으며, AFM분석을 통한 Root-mean-square(Rms)값은 상온에서 $500^{\circ}C$로 증착온도가 증가함에 따라 6.62nm에서 46.64nm까지 증가하였다. Ag 박막의 표면 거칠기 증가에 따라 후면반 사막의 확산 반사도도 함께 증가하였다. 공정온도 $500^{\circ}C$에서 증착된 후면반사막을 사용하여 a-Si:H 태양전지를 제조하였을 때 상온에서 제조한 후면반사막에 비하여 단락전류밀도 (Jsc)값은 9.94mA/$cm^2$에서 13.36mA/$cm^2$로 증가하였으며, 7.6%의 가장 높은 태양전지 효율을 나타내었다.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.143.1-143.1
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• 2010

고분자 전해질막 연료전지(Polymer Electrolyte Membrane Fuel Cell; PEMFC)는 수소를 이용하여 전기를 발생시키는 친환경적이고 이상적인 발전장치로 고효율과 높은 전류밀도를 가지며 그 응용분야가 다양하다. 저온에서 작동하는 PEM fuel cell은 전극에서 효과적인 산화환원반응을 위해 그 촉매로 활성이 우수한 Pt(Platinum)을 사용하고 있으나, Pt의 높은 가격은 연료전지의 상용화에 걸림돌이 되고 있다. 본 연구에서는 연료전지의 Pt/C 촉매 층에서 Pt의 분산성을 높여 Pt의 담지량을 줄이고 작동 중 발생하는 Pt의 응집 현상을 방지하여 Pt의 수명을 연장시킬 목적으로, Au(gold) 나노입자를 첨가한 Pt-Au/C 복합나노촉매를 제조하였다. 본 발표에서는 합성된 Pt-Au/C 복합촉매 중 Au 첨가량이 Pt 촉매의 활성에 미치는 영향을 조사하기 위하여, 복합촉매 중에 금속(Pt+Au)의 총 함량이 30 wt.%와 40 wt.% 인 Pt-Au/C 촉매에 대하여 각각 Au 첨가량을 변화시켜, cyclic voltammetry 법에 의해 Au 첨가 효과를 조사한 결과에 대하여 보고하고자 한다. Au 나노입자를 제조하기 위한 출발 물질로는 $HAuCl_4{\cdot}4H_2O$를 이용하였고 trisodium citrate와 $NaBH_4$를 환원제로 하여, 입경이 5~8 nm 인 Au 콜로이드를 제조하였다. Pt-Au/C 복합나노촉매를 제조하기 위하여 먼저 Au/C 복합분체가 제조되었다. 0.03g의 carbon이 첨가된 carbon 현탁액에 합성된 Au 콜로이드 수용액을 첨가한 후 24시간 동안 교반하여 Au/C 복합분체를 제조하였다. 이 Au/C 복합분체에 $H_2PtCl_6{\cdot}6H_2O$ 수용액을 현탁하고 methanol 을 환원제로 사용해 Pt를 환원 석출시켜 Pt-Au/C 복합촉매를 제조하였다. Pt-Au/C 복합 나노촉매에서 Pt와 Au를 다양한 비율(3:1, 2.5:1.5, 2:2)로 합성하였으며 Pt-Au/C 복합촉매 중 금속(Pt+Au) 촉매의 총 함량은 30 wt.%와 40 wt.%로 각각 제조되었다. Au 나노입자 콜로이드의 분산성은 UV-visible spectrum의 흡광도에 의해 관찰되었고, Pt-Au/C 복합 나노촉매의 형상 및 분산성 분석은 transmission electron microscopy(TEM)에 의해 이루어졌다. 또한, 촉매의 전기화학적 특성평가는 cyclic voltammetry(CV)에 의해 조사되었다.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.78.2-78.2
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• 2010

Cu(In,Ga)Se2 (CIGS)박막태양전지는 간단한구조와 가격경쟁력 및 고효율화 가능성에 대한 기대감에 의해 많은 연구가 수행되어오고 있다. 특히 높은 흡수계수와 적절한 밴드갭, 큰 결정크기와 같은 물질의 특성들이 장점으로 작용하고 있기 때문이다. 또한 CIGS박막태양전지는 다른 태양전지에 비해 광열화가 적다는 장점도 가지고 있다. CIGS 박막은 CuInSe2내의 In 사이트에 Ga을 도핑함으로서 형성이 되는데 그때의 밴드갭은 약 1.4eV이며 이를 형성하기 위해 많은 방법들이 제안되고 있는데, CIGS박막 형성 시 가장 중요시 여겨야 될 인자는 구성원소로부터 최적화된 조성비를 찾는 것이다. 이러한 관점에서 볼때 evaporation법이나 sputtering법같은 진공방식의 공정법이 비진공방식에 비해 최적의 조성비를 찾는 것이 수월할 것으로 생각된다. selenization을 하기전에, 동시증착이나 다층박막형성을 통해 Cu-In-Se의 조합이 일반적으로 이루어진다. 어떤방법이든 Se의 부가적인 공급이 이루어지는데 시작 전구체의 조합에서 그 해법을 제시하는 것에 대한 논의가 많이 부족한 현실로서, CuInSe2의 단일전구체에 의한 박막형성과 특성평가에 대해 구체적인 논의가 필요하다. 본 실험에서는 Cu-In-Se 전구체를 CuInSe2 단일 타겟에서부터 RF 마그네트론 스퍼터링법을 이용하여 박막증착을 하여 Se의 Rapid Thermal Process(RTA)법을 통해 Se이 순차적으로 공급되었다. 이때 형성되는 박막의 태양전지 흡수층 적용을 위한 광학적, 전기적 및 구조적에 대한 논의된다. Soda lime glass(SLG)와 Corning 1737 유리를 기판으로 하여 아세톤-에탄올을 이용, 초음파세척을 실시하였다. 스퍼터 공정을 하기전에 흡착된 물분자를 제거하기 위하여 약 30분간 $120^{\circ}C$로 열을 가해주었으며, 공정을 위한 총 아르곤 가스의 양은 약 50sccm이며 이때의 공정압력은 20mtorr로 고정하였다. 우선 RF power와 기판온도에 따른 단일전구체 형성을 관찰하기 위하여 각각 30~80W, RT~$400^{\circ}C$로 변화를 주어 박막을 형성한 후 모든 sample에 대하여 $500^{\circ}C$분위기에 effusion cell을 이용하여 Se 분위기에서 결정화를 실시하였다. 샘플의 두께는 Surface profiler로 측정하였고 단면은 전자주사현미경으로 관찰되었다. 동시에 SEM이미지를 통하여 morphology와 grain size 및 EDX를 통하여 조성분석을 하였다. 밴드갭, 투과율 및 흡수계수는 UV-VIS-NIR분광분석법을 통하여 수행되었으며, 전기적 특성분석을 위해 4-point-probe와 Hall effect측정을 수행하였다. 공정변수에 따른 단일타겟으로 얻어 결정화된 CuInSe2박막의 자세한 결과와 논의에 대하여 발표한다.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.189-189
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• 2012

Lead sulfide (PbS) nanocrystal quantum dots (NQDs) are promising materials for various optoelectronic devices, especially solar cells, because of their tunability of the optical band-gap controlled by adjusting the diameter of NQDs. PbS is a IV-VI semiconductor enabling infrared-absorption and it can be synthesized using solution process methods. A wide choice of the diameter of PbS NQDs is also a benefit to achieve the quantum confinement regime due to its large Bohr exciton radius (20 nm). To exploit these desirable properties, many research groups have intensively studied to apply for the photovoltaic devices. There are several essential requirements to fabricate the efficient NQDs-based solar cell. First of all, highly confined PbS QDs should be synthesized resulting in a narrow peak with a small full width-half maximum value at the first exciton transition observed in UV-Vis absorbance and photoluminescence spectra. In other words, the size-uniformity of NQDs ought to secure under 5%. Second, PbS NQDs should be assembled carefully in order to enhance the electronic coupling between adjacent NQDs by controlling the inter-QDs distance. Finally, appropriate structure for the photovoltaic device is the key issue to extract the photo-generated carriers from light-absorbing layer in solar cell. In this step, workfunction and Fermi energy difference could be precisely considered for Schottky and hetero junction device, respectively. In this presentation, we introduce the strategy to obtain high performance solar cell fabricated using PbS NQDs below the size of the Bohr radius. The PbS NQDs with various diameters were synthesized using methods established by Hines with a few modifications. PbS NQDs solids were assembled using layer-by-layer spin-coating method. Subsequent ligand-exchange was carried out using 1,2-ethanedithiol (EDT) to reduce inter-NQDs distance. Finally, Schottky junction solar cells were fabricated on ITO-coated glass and 150 nm-thick Al was deposited on the top of PbS NQDs solids as a top electrode using thermal evaporation technique. To evaluate the solar cell performance, current-voltage (I-V) measurement were performed under AM 1.5G solar spectrum at 1 sun intensity. As a result, we could achieve the power conversion efficiency of 3.33% at Schottky junction solar cell. This result indicates that high performance solar cell is successfully fabricated by optimizing the all steps as mentioned above in this work.

• Journal of the Korean Chemical Society
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• v.28 no.2
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• pp.79-85
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• 1984

The ionic association constant(K) of 2,4,6, N-tetramethyl pyridinium iodide (TeMPI) in 95 volume percentage ethanol-water mixture were determined by a modified UV and conductance method at $25^{\circ}C$ to $50^{\circ}C$ under 1 to 2,000 bars. The K values increase with increasing pressure and have maximum value at $40^{\circ}C$. The partial molar volume hange (${\Delta}V$) has relatively small negative value and the absolute values of ${\Delta}$ are minimum at $40^{\circ}C$. The ion size parameter(a) of TeMPI have maximum value at $40^{\circ}C$. {\Delta}H^{\circ}$ values are zero, positive and negative at 40^{\circ}C$, $25^{\circ}C$ and $50^{\circ}C$ respectively. Other thermodynamic parameters such as the changes of standard entropy ({\Delta}S^{\circ}$) and free energy {\Delta}G^{\circ}$ were evaluated. From these experimental results, we came to conclusion that TeMPI is stabilized by the elevation of pressure and that of temperature below $40^{\circ}C$ but weakly dimerized at $40^{\circ}C$ because of the intermolecular hydrophobic interaction of eight methyl groups of two molecules. And it thermally decomposed above $50^{\circ}C$.

• Applied Chemistry for Engineering
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• v.27 no.4
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• pp.397-401
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• 2016

A new solid oxidizer, pyridinium dinitramide (Py-DN) is a low toxic energetic material which can be utilized as a HPGP (high performance green propellant). In this work, Py-DN was synthesized using various starting materials including potassium sulfamate, pyridine hydrochloride, strong nitric acid and sulfuric acid. Physical and chemical properties of the Py-DN were characterized using UV-Vis, FT-IR and a thermal analyzer and their properties were compared to those of previously prepared salts including ammonium dinitramide[ADN, $NH_4N(NO_2)_2$] and guanidine dinitramide[GDN, $NH_2C(NH_2)NH_2N(NO_2)_2$] in our lab. Endothermic and exothermic decomposition temperatures of Py-DN were $77.4^{\circ}C$ and $144.7^{\circ}C$, respectively. The combustion caloric value was 1739 J/g, which is thermally more sensitive than that of conventional dinitramides. It may enable to lower the decomposition temperature, which can reduce preheating temperature required for satellite thruster applications.