• 청정기술
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• 제26권4호
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• pp.329-335
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• 2020

재생에너지로부터 수전해를 통하여 생산된 수소와 포집된 CO2를 활용하여 메탄올을 합성하는 power-to-methanol 기술이 재생에너지를 대용량으로 저장하는 방안으로 제시되고 있다. 본 연구에서는 메탄올을 수소 및 전력 생산에 활용함에 있어 더욱 효율적인 방법으로 연료전지 내부에서 메탄올 수증기개질 반응이 일어나는 내부개질형 용융탄산염 연료전지에 대해 성능 분석을 실시하였다. 용융탄산염 연료전지의 연료극으로 사용되는 다공성 Ni-10 wt%Cr을 촉매로 메탄올 수증기개질 반응을 수행한 결과 연료전지 운전 조건에서 연료극은 메탄올 수증기개질 반응에 충분한 활성을 나타내었다. 메탄올 수용액을 직접 용융탄산염 연료전지의 연료극으로 공급한 결과 연료전지의 성능은 외부 개질기를 통하여 생산된 개질가스를 공급하는 경우에 비해 다소 성능이 낮게 나타났으며, 메탄올 공급유량이 비교적 낮은 경우 고 전류밀도에서 불안정한 성능을 나타내었다. 연료극으로부터 생성된 가스를 재순환시킴으로써 연료전지의 성능을 향상시킬 수 있었으며, 메탄올 전환율도 90% 이상 얻을 수 있었다. 물질수지를 통하여 연료극에서 일어나는 반응을 분석한 결과 전류밀도 및 가스 재순환 유량이 증가함에 따라 메탄올 수증기개질 반응속도가 증가함을 확인하였다. 이상의 결과로부터 별도의 촉매층을 설치할 필요 없이 연료극 만으로도 용융탄산염 연료전지 내에서 메탄올 수증기개질 반응이 가능하며, 메탄올 내부개질형 용융탄산염 연료전지를 통하여 전력과 합성가스를 동시에 생산할 수 있음을 확인하였다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.362-362
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• 2010

Today, vast attention has been paid to periodic arrays of nanostructures due to their potential for applications such as memory with huge storage density. Such application requires large-scale fabrication of well ordered nano-sized structures. One of the most widely used methods for the ordered nanostructures is lithography. This top-down process, however, has the limit to reduce size. Here the promising alternative is the self-organization of ordered nano-sized structures such as large scale 2d carbon-induced reconstructions on W(110). In the present study, we report on the first well-resolved atomic resolution STM studies of the well-known R($15{\times}3$) and R($15{\times}12$) carbon induced reconstruction of the W(110). From the atomic image of R($15{\times}3$) for different values of tunneling gap resistance, we can tell there are no missing atoms in unit cells of R($15{\times}3$) and some atomic displacements are substantial from the clean W(110), even though not all the imaged position of atoms correspond to tungsten, but may include those of carbon. We are considering two cases; First case is related to lattice deformation, or top layer of W(110) is deformed in the process of relief of strain caused by random inserting of carbon atoms possibly in the interstitial position. In the second case, R($15{\times}3$) unit cell results from a coincidence lattice between clean W(110) substrate and tungsten carbide overlayer which has rectangular atomic arrangement and giving R($15{\times}3$) coincidence lattice. beta-W2C showing rectangular unit cell should be a candidate. Further, we report on new reconstructions. Unlike the well-known R($15{\times}12$) consisting of two parts, two inner structures between two "Backbone" structures. The new reconstruction, which we found for the first time, contains more parts between the "Backbone"s. Sometimes we can observe the reconstruction consists of only inner parts without "Backbone" parts. Thus, the observed reconstruction can be built by constructing of two types of "Lego"-like block. Moreover, the rectangle shape of "Backbone" transform to parallelogram-like shape over time, the so-called wavy-R($15{\times}12$). Adsorption of hydrogen can be the reason for this transformation.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.102-102
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• 2016

Water, which is most abundant in Earth surface and very closely related to all forms of living organisms, has a simple molecular structure but exhibits very unique physical and chemical properties. Even though tremendous effort has been paid to understand this nature's core substance, there amazingly still lefts much room for scientist to explore its novel behaviors. Especially, as the scale goes down to nano-regime, water shows extraordinary properties that are not observable in bulk state. One of such interesting features is the formation of nanoscale bubbles showing unusual long-term stability. Nanobubbles can be spontaneously formed in water on hydrophobic surface or by decompression of gas-saturated liquid. In addition, the nanobubbles can be generated during electrochemical reaction at normal hydrogen electrode (NHE), which possibly distorts the standard reduction potential at NHE as the surface nanobubble screens the reaction with electrolyte solution. However, the real-time evolution of these nanobubbles has been hardly studied owing to the lack of proper imaging tools in liquid phase at nanoscale. Here we demonstrate, for the first time, that the behaviors of nanobubbles can be visualized by in situ transmission electron microscope (TEM), utilizing graphene as liquid cell membrane. The results indicate that there is a critical radius that determines the long-term stability of nanobubbles. In addition, we find two different pathways of nanobubble growth: i) Ostwald ripening of large and small nanobubbles and ii) coalescence of similar-sized nanobubbles. We also observe that the nucleation and growth of nanoparticles and the self-assembly of biomolecules are catalyzed at the nanobubble interface. Our finding is expected to provide a deeper insight to understand unusual chemical, biological and environmental phenomena where nanoscale gas-state is involved.

• 대한의생명과학회지
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• 제11권4호
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• pp.487-492
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• 2005

The baculovirus/insect cell expression system is of great value in the study of structure-function relationships in mammalian glucose-transport proteins by site-directed mutagenesis and for the large-scale production of these proteins for mechanistic and biochemical studies. Spodoptera frugiperda Clone 21 (Sf2l) cells grow well on TC-100 medium that contains $0.1\%$ D-glucose as the major carbon source, strongly suggesting the presence of endogenous glucose transporters. However, very little is known about the properties of the endogenous sugar transporter(s) in Sf2l cells, although a saturable transport system for hexose uptake has been previously revealed in the Sf cells. In order to further examine the substrate and inhibitor recognition properties of the Sf2l cell transporter, the ability of hexoses to inhibit 2-deoxy-D-glucose (2dGlc) transport was investigated by measuring inhibition constants $(K_i)$. The $K_i's$ for reversible inhibitors were determined from plots of uptake versus inhibitor concentration. Transport was effectively inhibited by D-mannose and D-glucose. Of the hexoses tested, L-glucose had the least effect on 2dGlc transport in the Sf2l cells, indicating that the transport is stereoselective. Unlike the human HepG2 type glucose transport system, D-mannose had a somewhat greater affinity for the Sf2l cell transporter than D-glucose, implying that the hydroxyl group at the C-2 position is not necessary for strong binding. However, epimerization at the C-4 position of D-glucose (D-galactose) resulted in a dramatic decrease in affinity of the hexose for the Sf2l cell transporter. Such a lowering of affinity might be the result of the involvement of the C-4 hydroxyl in hydrogen bonding. It is therefore suggested that Sf2l cells were found to contain an endogenous sugar transport activity that in several aspects resembles the human HepG2 type glucose transporter, although the insect and human transporters do differ in their affinity for cytochalasin B.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.221-221
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• 2013

Striving to replace the well known silicon nanocrystals embedded in oxides with solution-processable charge-trapping materials has been debated because of large scale and cost effective demands. Herein, a silicon quantum dot-polystyrene nanocomposite (SiQD-PS NC) was synthesized by postfunctionalization of hydrogen-terminated silicon quantum dots (H-SiQDs) with styrene using a thermally induced surface-initiated polymerization approach. The NC contains two miscible components: PS and SiQD@PS, which respectively are polystyrene and polystyrene chains-capped SiQDs. Spin-coated films of the nanocomposite on various substrate were thermally annealed at different temperatures and subsequently used to construct metal-insulator-semiconductor (MIS) devices and thin film field effect transistors (TFTs) having a structure p-$S^{++}$/$SiO_2$/NC/pentacene/Au source-drain. C-V curves obtained from the MIS devices exhibit a well-defined counterclockwise hysteresis with negative fat band shifts, which was stable over a wide range of curing temperature ($50{\sim}250^{\circ}C$. The positive charge trapping capability of the NC originates from the spherical potential well structure of the SiQD@PS component while the strong chemical bonding between SiQDs and polystyrene chains accounts for the thermal stability of the charge trapping property. The transfer curve of the transistor was controllably shifted to the negative direction by chaining applied gate voltage. Thereby, this newly synthesized and solution processable SiQD-PS nanocomposite is applicable as charge trapping materials for TFT based memory devices.

• 공업화학
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• 제17권6호
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• pp.633-637
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• 2006

본 연구에서는 triazole계 항진균제인 이트라코나졸의 대량합성을 위한 효과적인 합성법을 제시하였다. Janssen Pharmaceutica에 의해 발표된 기존의 의약화학적 합성경로는 2,4-dichloroacetophenone을 출발물질로 하는 직렬(linear) 합성의 14 단계로서 전체수율이 1.4%에 불과하였고 대량합성에 부적합한 위험물질로서 methanesulfonyl chloride ($CH_{3}SO_{2}Cl$)와 수소기체 및 sodium hydride (NaH)를 사용하고 있다. 또한 고가의 1-acetyl-4-(4-hydroxyphenyl)piperazine 및 팔라듐을 사용함으로써 생산 단가가 높은 문제점이 있었다. 이를 개선하기 위해서 병렬(convergent) 합성 전략을 수립하였는데, 이트라코나졸의 대략 반에 해당하는 중간체 II와 III을 각각 합성한 다음 두 부분을 결합시키는 12단계의 합성공정을 개발하였고 전체 수율은 12.0%로서 합성효율이 크게 개선되었다. 이 과정에서 공정을 간략화하고 위험물질 및 고가의 반응물의 사용을 배제함으로써 생산 원가를 크게 절감시킬 수 있었다.

• 한국대기환경학회지
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• 제22권3호
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• pp.337-351
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• 2006

In this study, to describe the basic characteristics of strong odorous sources, the emissions of odorous compounds from a large-scale sewage treatment plant in K city were investigated. According to this study, the emission patterns of major odorous compounds were distinguished clearly by several factors such as treatment processing types, chemical compositions of odors released, and temporal changes (e.g., seasonal variations). For the purpose of this study, emission rates of odorous compounds were quantified using a dynamic flux chamber (DFC) method from three major treatment (T) processes including T1 (Grit sedimentation basin), T2 (Aeration tank), and T3 (Final sedimentation). When the relative strengths of each emission source were compared, the strongest one was seen from T1 with the maximum of $NH_{3}\;(34.5\;{\mu}g/m^{2}/min)$ followed by $H_{2}S\;(20.4\;{\mu}g/m^{2}/min)($. While the strongest emissions of most odorous compounds were seen commonly from T1, those seen from T2 and T3 were significantly reduced relative to the ones found in T1. Considering the general patterns of odorous emission, it is concluded that control of odors from T1 unit is most important because of its considerably high emission strengths.

• 천문학회지
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• 제47권2호
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• pp.49-67
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• 2014

A novel method to characterize the topology of the early-universe intergalactic medium during the epoch of cosmic reionization is presented. The 21-cm radiation background from high redshift is analyzed through calculation of the 2-dimensional (2D) genus. The radiative transfer of hydrogen- ionizing photons and ionization-rate equations are calculated in a suite of numerical simulations under various input parameters. The 2D genus is calculated from the mock 21-cm images of high-redshift universe. We construct the 2D genus curve by varying the threshold differential brightness temperature, and compare this to the 2D genus curve of the underlying density field. We find that (1) the 2D genus curve reflects the evolutionary track of cosmic reionization and (2) the 2D genus curve can discriminate between certain reionization scenarios and thus indirectly probe the properties of radiation-sources. Choosing the right beam shape of a radio antenna is found crucial for this analysis. Square Kilometre Array (SKA) is found to be a suitable apparatus for this analysis in terms of sensitivity, even though some deterioration of the data for this purpose is unavoidable under the planned size of the antenna core.

• Korean Chemical Engineering Research
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• 제60권4호
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• pp.506-511
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• 2022

화학물질관리법에서 장외영향평가서 및 위해관리계획서를 화학사고예방관리계획서로 일원화하는 제도가 시행되었다. 화학사고예방관리계획서에서 다루는 유해화학물질 중 사고대비물질은 화학사고의 발생 가능성이 높거나 화학사고가 발생한 경우에 그 피해 규모가 클 것으로 우려되는 화학물질로서 지정하고 있다. 본 연구에서는 사고대비물질별 규정수량 기준에 따른 위험도를 비교하고자 상위/하위 규정수량이 비슷한 화학물질을 특정하여 동일한 사고 시나리오를 선정하고 위험도 평가를 실시하였다. 연구대상물질은 암모니아, 염화수소, 이황화탄소, 벤젠 등 총 4종의 물질을 선정하였으며, DNV 사의 정량적 위험성 평가 프로그램인 Safeti 8.0을 활용하여 위험도를 비교 분석하였다. 그 결과, 비슷한 상위/하위규정수량임에도 불구하고 상대적으로 높은 위험도를 가지고 있는 물질을 확인할 수 있었다.

• Journal of Electrochemical Science and Technology
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• 제14권4호
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• pp.388-396
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• 2023

Photoelectrochemical (PEC) water splitting is a vital source of clean and sustainable hydrogen energy. Moreover, the large-scale H₂ production is currently necessary, while long-term stability and high PEC activity still remain important issues. In this study, a GaN-based photoelectrode was modified by an additional NH₃ treatment (900℃ for 10 min) and its PEC behavior was monitored. The bare GaN exhibited a highly crystalline wurtzite structure with the (002) plane and the optical bandgap was approximately 3.2 eV. In comparison, the NH₃-treated GaN film exhibited slightly reduced crystallinity and a small improvement in light absorption, resulting from the lattice stress or cracks induced by the excessive N supply. The minor surface nanotexturing created more surface area, providing electroactive reacting sites. From the surface XPS analysis, the formation of an N-Ga-O phase on the surface region of the GaN film was confirmed, which suppressed the charge recombination process and the positive shift of E_FB. Therefore, these effects boosted the PEC activity of the NH₃-treated GaN film, with J values of approximately 0.35 and 0.78 mA·cm^-2 at 0.0 and 1.23 V_RHE, respectively, and an onset potential (V_on) of -0.24 V_RHE. In addition, there was an approximate 50% improvement in the J value within the highly applied potential region with a positive shift of V_on. This result could be explained by the increased nanotexturing on the surface structure, the newly formed defect/trap states correlated to the positive V_on shift, and the formation of a GaO_xN_1-x phase, which partially blocked the charge recombination reaction.