• Elastomers and Composites
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• 제47권3호
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• pp.238-245
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• 2012

천연 흑연으로부터 Graphene oxide(GO)를 합성한 후 diisocyanatodicyclohexylmethane($H_{12}MDI$)를 이용하여 GO의 표면을 기능화하였고, hydrazine monohydrate에 의한 환원을 통해 isocyanate-graphene sheet(i-RGO)를 얻었다. 폴리우레탄과 적합한 나노복합체를 형성하기 위하여 GO, i-RGO, 천연흑연 및 열적환원된 graphene을 서로 비교분석하였으며, i-RGO가 가장 적합한 나노충전제로 선정되었다. 선정된 i-RGO의 함량에 따른 폴리우레탄의 물성 향상을 확인하기 위하여 충전제의 함량을 다르게 하여 PU/i-RGO 나노복합체를 합성하였다. 물성 평가에서, i-RGO의 함량이 증가할수록 열적 안정성, 경도 및 접촉각(발수력)이 향상되었는데, 이는 i-RGO의 물성 특성 및 가교점 작용에 기인한 것으로 판단되었다. 다만, 인장강도와 신장률의 경우 함량이 4 wt%를 넘어갈 경우 오히려 물성이 감소하는 것을 확인할 수 있었는데, 이는 과량의 가교점 형성이 원인인 것으로 해석되었다.

• Bulletin of the Korean Chemical Society
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• 제33권11호
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• pp.3761-3766
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• 2012

$Ag_2Se$-Graphene/$TiO_2$ composite was synthesized by a facile sonochemical method. The as-prepared products were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) analysis, transmission electron microscopy (TEM) and UV-vis diffuse reflectance spectrophotometer. During the reaction, both of the reduction of graphene oxide and loading of $Ag_2Se$ and $TiO_2$ particles were achieved. The as-prepared $Ag_2Se$-Graphene/$TiO_2$ composites possessed great adsorptivity of dyes, extended light absorption range, and efficient charge separation properties simultaneously. Hence, in the photodegradation of rhodamine B (Rh.B), a significant enhancement in the reaction rate was observed with $Ag_2Se$-Graphene/$TiO_2$ composites, compared to the pure $TiO_2$. The high activity can be attributed to the synergetic effects of high charge mobility, and red shift in absorption edge of $Ag_2Se$-Graphene/$TiO_2$ composites.

• Journal of Electrochemical Science and Technology
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• 제2권1호
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• pp.1-7
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• 2011

Nanocomposites of reduced graphene oxide and manganese (II,III) oxide can be synthesized by the freeze-drying process of the mixed colloidal suspension of graphene oxide and manganese oxide, and the subsequent heat-treatment. The calcined reduced graphene oxide-manganese (II,III) oxide nanocomposites are X-ray amorphous, suggesting the formation of homogeneous and disordered mixture without any phase separation. The reduction of graphene oxide to reduced graphene oxide upon the heat-treatment is evidenced by Fourier-transformed infrared spectroscopy. Field emission-scanning electronic microscopy and energy dispersive spectrometry clearly demonstrate the formation of porous structure by the house-of-cards type stacking of reduced graphene oxide nanosheets and the homogeneous distribution of manganese ions in the nanocomposites. According to Mn K-edge X-ray absorption spectroscopy, manganese ions in the calcined nanocomposites are stabilized in octahedral symmetry with mixed Mn oxidation state of Mn(II)/Mn(III). The present reduced graphene oxide-manganese oxide nanocomposites show characteristic pseudocapacitance behavior superior to the pristine manganese oxide, suggesting their applicability as electrode material for supercapacitors.

• Journal of Electrochemical Science and Technology
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• 제8권1호
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• pp.61-68
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• 2017

Electrochemical conversion of $CO_2$ and production of $H_2$ were attempted on a three-dimensionally ordered, porous metal organic framework (MOF-74) in which transition metals (Co, Ni, and Zn) were impregnated. A lab-scale proton exchange membrane-based electrolyzer was fabricated and used for the reduction of $CO_2$. Real-time gas chromatography enabled the instantaneous measurement of the amount of carbon monoxide and hydrogen produced. Comprehensive calculations, based on electrochemical measurements and gaseous product analysis, presented a time-dependent selectivity of the produced gases. M-MOF-74 samples with different central metals were successfully obtained because of the simple synthetic process. It was revealed that Co- and Ni-MOF-74 selectively produce hydrogen gas, while Zn-MOF-74 successfully generates a mixture of carbon monoxide and hydrogen. The results indicated that M-MOF-74 can be used as an electrocatalyst to selectively convert $CO_2$ into useful chemicals.

• 한국결정성장학회지
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• 제16권6호
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• pp.250-255
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• 2006

본 연구에서는 수용액에서 화학적 환원 방법을 사용하여 나노미터 수준의 은을 합성하는데 있어서 입자크기 및 응집에 영향을 줄 수 있는 $NaBH_4$의 농도, 반응 온도, 반응물 첨가속도 및 laponite의 농도에 대하여 연구하였다. laponite가 없는 조건하에서는 $NaBH_4/AgNO_3$의 몰 비가 3일 때 안정한 나노 은 졸이 형성되었으며 또한 환원반응의 온도가 증가 할수록 은 입자의 평균 크기는 증가하였다. 또한 $AgNO_3$의 첨가속도가 빠르면 초기반응단계에서 형성된 높은 농도의 은 입자들이 응집되어 입자크기가 큰 나노 은이 생성됨을 보여 주고 있다. 보호층 콜로이드로 laponite를 사용하였을 때 고온 $(>\;100^{\circ}C)$에서 안정한 나노 은 졸을 합성할 수 있었다.

• Bulletin of the Korean Chemical Society
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• 제26권1호
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• pp.103-106
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• 2005

In order to investigate the catalytic mechanism for the growth of carbon nanotubes (CNTs), a comprehensive study was conducted using carbon materials synthesized at 680 ${^{\circ}C}$ with a gas mixture of CO-H$_2$ after reduction at 800 ${^{\circ}C}$ by H$_2$ gas from iron oxide, and metal Pt. The resulting material was observed by scanning electron microscopy (SEM) and X-ray diffraction patterns (XRD) after a variety of reaction times. The carbon materials synthesized by metal Pt were little affected by reaction time and the sintered particles did not form CNTs. Xray analysis revealed that metal Fe was completely converted to iron carbide (Fe$_3$C) without Fe peaks in the early stage. After 5 min, iron carbide (Fe$_3$C) and carbon (C) phases were observed at the beginning of CNTs growth. It was found that the intensity of the carbon(C) peak gradually increased with the continuous growth of CNTs as reaction time increases. It was also found that the catalyst of growth of CNTs was metal carbide.

• Bulletin of the Korean Chemical Society
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• 제31권4호
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• pp.874-880
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• 2010

A series of 13- and 14-membered cyclic enkephalin analogs based on the moderately $\mu$ selective prototype compound Tyr-C[D-$A_2bu$-Gly-Phe-Leu] 8a were synthesized to investigate the structure-activity relationship. The modifications of sequence were mainly focused on two positions 3 and 5, critical for the selective recognition for $\mu$ and $\delta$ opioid receptors. The substitution of hydrophobic $Leu^5$ with hydrophilic $Asp^5$ derivatives led to Tyr-C[D-$A_2bu$-Gly-Phe-Asp(N-Me)] 7 and Tyr-C[D-Glu-Phe-gPhe-rAsp(O-Me)] 5, the peptides with a large affinity losses at both $\mu$ and $\delta$ receptors. The substitution of $Phe^3$ with $Gly^3$ led to Tyr-C[D-Glu-Gly-gPhe-rLeu] 3 and Tyr-C[D-Glu-Gly-gPhe-D-rLeu] 4, the peptides with large affinity losses at $\mu$ receptors, indicating the critical role of phenyl ring of $Phe^3$ for $\mu$ receptor affinities. One atom reduction of the ring size from 14-membered analogs Tyr-C[D-Glu-Phe-gPhe-(L and D)-rLeu] 6a, 6b to 13-membered analogs Tyr-C[D-Asp-Phe-gPhe-(L and D)-rLeu] 1, 2 reduced the affinity at both $\mu$ and $\delta$ receptors, but increased the potency in the nociceptive assay, indicating the ring constrain is attributed to high nociceptive potency of the analogs. For the influence of D- or L-chirality of $Leu^5$ on the receptor selectivity, regardless of chirality and ring size, all cyclic diastereomers displayed marked $\mu$ selectivity with low potencies at the $\delta$ receptor. The retro-inverso analogs display similar or more active at $\mu$ receptor, but less active at $\delta$ receptor than the parent analogs.

• Archives of Pharmacal Research
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• 제20권3호
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• pp.259-263
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• 1997

In the preparation of acyclic thymidine nucleoside analogues, $K_2CO_3$(or NaH) treated thymine in DMSO was alkylated with .omega.-chloroalkyl nitrite (Cl-(CH_2)n-CN; n=1, 2, 3, 4) to provide an isomeric mixture of 1-(${\omega}$-cyanoalkyl)thymine (2a-d) and 1,3-bis(${\omega}$-cyanoalkyl)thymine in approximately 5:1 ratios. Reduction of the cyano function 2a-d with $NaBH_{4}/CoCl_{2}$ center dot$ 6H_{2}O$gave the corresponding 1-(${\omega}$aminoalkyl)thymine (3a-d). The newly formed primary amino function in 3a-d was directly reacted with 2-chloroethylisocyanate to afford the 1-[.omega.($N^{I}$-2-chloroethylureido) alkyl]thymine (4a-d) in good yields. Nitrosation of 1-[5-($ N^{I}-2$-chloroethylureido)pentyl] thymine (4d) with glacial acetic acid and dry $NaNO_{2}$-powder in anhydrous $CH_{2}Cl_{2}$gave two types of regioisomeric nitrosoureas, 1-[5-($N^{I}$--chloroethyl-$N^{I}$--nitrosoureido)pentylithymine (5d) and 1-[5-($N^{I}-2$-chloroethyl-N-nitrosoureido)pentyllthymine in approximately 5 :1 ratios. The in vitro cytotoxicity of the synthesized compounds (2a-d, 3a-d, 4a-d and 5a-d) against three cell lines (K-562, P-388 and FM-3A) are measured as $IC^{50}$ values. Compounds 3b and 4c showed moderate activities against all three cell lines, and all other compounds were found to be not active.

• Bulletin of the Korean Chemical Society
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• 제25권9호
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• pp.1371-1378
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• 2004

A porous stainless steel (SUS) as a substrate of silica composite membranes for hydrogen purification was used to improve mechanical strength of the membranes for industrial application. The SUS support was successfully modified by using submicron Ni powder, $SiO_2$ sols with particle size of 500 nm and 150 nm in turns. Silica top layer was coated on the modified supports under various preparation conditions such as calcination temperature, dipping time and repeating number of dipping-drying process. The calcination temperature for proper sintering was between H ttig temperature and Tamman temperature of the coating materials. Maximum hydrogen selectivity was investigated by changing dipping time. As repeating number of dipping-drying process increased, permeances of nitrogen and hydrogen were decreased and $H_2/N_2$ selectivity was increased due to the reduction of non-selective pinholes and mesopores. For the silica membrane prepared under optimized conditions, permeance of hydrogen was about $3\;{\times}\;10^{-5}\;cm^3{\cdot}cm^{-2}{\cdot}s^{-1}{\cdot}cmHg^{-1}$ combined with $H_2/N_2$ seletivity of about 20.

• Molecules and Cells
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• 제38권10호
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• pp.843-850
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• 2015

The1hepatic cell death induced by acetaminophen (APAP) is closely related to cellular adenosine triphosphate (ATP) depletion, which is mainly caused by mitochondrial dysfunction. Adenosine monophosphate (AMP)-activated protein kinase (AMPK) is a key sensor of low energy status. AMPK regulates metabolic homeostasis by stimulating catabolic metabolism and suppressing anabolic pathways to increase cellular energy levels. We found that the decrease in active phosphorylation of AMPK in response to APAP correlates with decreased ATP levels, in vivo. Therefore, we hypothesized that the enhanced production of ATP via AMPK stimulation can lead to amelioration of APAP-induced liver failure. A769662, an allosteric activator of AMPK, produced a strong synergistic effect on AMPK Thr172 phosphorylation with APAP in primary hepatocytes and liver tissue. Interestingly, activation of AMPK by A769662 ameliorated the APAP-induced hepatotoxicity in C57BL/6N mice treated with APAP at a dose of 400 mg/kg intraperitoneally. However, mice treated with APAP alone developed massive centrilobular necrosis, and APAP increased their serum alanine aminotransferase and aspartate aminotransferase levels. Furthermore, A769662 administration prevented the loss of intracellular ATP without interfering with the APAP-mediated reduction of mitochondrial dysfunction. In contrast, inhibition of glycolysis by 2-deoxy-glucose eliminated the beneficial effects of A769662 on APAP-mediated liver injury. In conclusion, A769662 can effectively protect mice against APAP-induced liver injury through ATP synthesis by anaerobic glycolysis. Furthermore, stimulation of AMPK may have potential therapeutic application for APAP overdose.