• Bulletin of the Korean Chemical Society
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• 제33권3호
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• pp.1078-1080
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• 2012

• Bulletin of the Korean Chemical Society
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• 제35권1호
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• pp.309-312
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• 2014

• Korean Chemical Engineering Research
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• 제61권4호
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• pp.627-634
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• 2023

Graphitic carbon nitride (g-C₃N₄) has attracted considerable attention since its discovery for its catalysis of water splitting to hydrogen and oxygen under visible light irradiation. However, pristine g-C₃N₄ confers only low photocatalytic efficiency and requires surface cocatalysts to reach moderate activity due to a lack of accessible surface active sites. Inspired by the high specific surface area and superior electron transfer of graphene, we developed a strongly coupled binary structure of graphene and g-C₃N₄ aerogel with 3D porous skeleton. The as-prepared 3D structure photocatalysts achieve a high surface area that favors efficient photogenerated charge separation and transfer, enhances the light-harvesting efficiency, and significantly improves the photocatalytic hydrogen evolution rate as well. The photocatalyst performance is observed to be optimized at the ratio 3:7 (g-C₃N₄:GO), leading to photocatalytic H₂ evolution of 16125.1 mmol. g^-1. h^-1 under visible light irradiation, more than 161 times higher than the rate achieved by bulk g-C₃N₄.

• 천문학회지
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• 제14권2호
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• pp.55-71
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• 1981

On the basis of observational constraints, particularly the relationship between metal abundance and cumulative stellar mass, a simple two-zone disk-halo model for the chemical evolution of our Galaxy was investigated, assuming different chemical processes in the disk and halo and the infall rates of the halo gas defined by the halo evolution. The main results of the present model calculations are: (i) The halo formation requires more than 80% of the initial galactic mass and it takes a period of $2{\sim}3{\times}10^9$ yrs. (ii) The halo evolution is divided into two phases, a fast collapse phase ($t=2{\sim}3{\times}10^8$ yrs) during which period most of the halo stars $({\sim}95%)$ are formed and a later slow collapse phase which is characterized by the chemical enrichment due to the inflow of external matter to the halo. (iii) The disk evolution is also divided into two phases, an active disk formation phase with a time-dependent initial mass function (IMF) up to $t{\approx}6{\times}10^9$ yrs and a later steady slow formation phase with a constant IMF. It is found that at the very early time $t{\approx}5{\times}10^8$ yrs, the metal abundance in the disk is rapidly increased to ${\sim}1/3$ of the present value but the total stellar mass only to ${\sim}10%$ of the present value, finally reaching about 80% of the present values toward the end of the active formation phase.

• 천문학회보
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• 제44권1호
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• pp.68.2-68.2
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• 2019

Chemical abundance ratios of ultra metal-poor (UMP; [Fe/H] < -4.0) stars can provide important constraints on the early chemical enrichment of the Milky Way (MW), associated with the nucleosynthesis processes that occurred during the evolution of their progenitors, which are presumably the first generation of stars. Despite their importance, only about thirty UMP stars have been discovered thus far. In an effort to identify such stars additionally, we selected UMP candidates from low-resolution (R ~ 2000) spectra from the Sloan Digital Sky Survey and Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST), and obtained with Gemini/GRACES high-resolution (R ~ 40,000) spectra of 15 UMP candidates. In this study, we present the results of the chemical abundance analysis of the UMP candidates. Furthermore, we compare the abundance patterns of our UMP stars with those of various metal-poor stars from literature to understand the early chemical evolution of the MW.

• Journal of Microbiology and Biotechnology
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• 제19권11호
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• pp.1301-1305
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• 2009

The evolution of living organisms occurs via a combination of highly complicated processes that involve modification of various features such as appearance, metabolism and sensing systems. To understand the evolution of life, it is necessary to understand how each biological feature has been optimized in response to new environmental conditions and interrelated with other features through evolution. To accomplish this, we constructed contents-based trees for a two-component system (TCS) and metabolic network to determine how the environmental communication mechanism and the intracellular metabolism have evolved, respectively. We then conducted a comparative analysis of the two trees using ARACNE to evaluate the evolutionary and functional relationship between TCS and metabolism. The results showed that such integrated analysis can give new insight into the study of bacterial evolution.

• 천문학회보
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• 제35권2호
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• pp.73.2-73.2
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• 2010

In order to understand internal dynamics of starless cores, molecular line emissions are usually observed. From profiles of the molecular lines, internal motions of starless cores have been deduced using a simple radiative transfer model such as the two-layer model (Myers et al.1996). This brings complexities arising from the chemical evolution. The motivation of this study is to follow the chemical evolution of a starless core that goes through gravitational contraction. For this purpose, we have performed hydrodynamical simulations with a marginally unstable Bonnor-Ebert sphere as an initial condition. We follow the chemical evolution of this core with changing conditions such as the chemical reaction rate at the dust surface and the strength of radiation field that penetrate into the core. At the core center, the molecules suffer from a higher degree of molecular depletion on the dust covered by ice rather than on the bare silicate dust. The stronger radiation field dissociates more molecules at the core envelope. From analysis on the line profile using the two-layer model, we found that the speed of inward motion deduced from the HCN F = 2-1 line adequately traces the true infall speed, when the dust is covered by ice and the core is exposed to the diffuse interstellar radiation field. Under different conditions, the two-layer model significantly underestimate the infall speed.

• 상하수도학회지
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• 제31권5호
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• pp.373-381
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• 2017

$RuO_2$ is a common active component of Dimensionally Stable Anodes (DSAs) for chlorine evolution that can be used in wastewater treatment systems. The recent improvement of chlorine evolution using nanostructures of $RuO_2$ electrodes to increase the treatment efficiency and reduce the energy consumption of this process has received much attention. In this study, $RuO_2$ nanorod and nanosheet electrodes were simply fabricated using the sol-gel method with organic surfactants as the templates. The obtained $RuO_2$ nanorod and nanosheet electrodes exhibit enhanced electrocatalytic activities for chlorine evolution possibly due to the active surface areas, especially the outer active surface areas, which are attributed to the increase in mass transfers compared with a conventional nanograin electrode. The electrocatalytic activities for chlorine evolution were increased up to 20 % in the case of the nanorod electrode and 35% in the case of the nanosheet electrode compared with the nanograin electrode. The $RuO_2$ nanorod 80 nm in length and 20-30 nm in width and the $RuO_2$ nanosheet 40-60 nm in length and 40 nm in width are formed on the surface of Ti substrates. These results support that the templated $RuO_2$ nanorod and nanosheet electrodes are promising anode materials for chlorine evolution in future applications.

• Bulletin of the Korean Chemical Society
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• 제16권9호
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• pp.845-850
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• 1995

A systematic method is presented to analyze the bandgaps of conjugated polymers in terms of geometrical relaxations and electronic effect of moieties using the equation of Eg=ΔEδr + ΔE1-4 + ΔEel. The relationship between ΔEδr and δr is derived from trans-PA and is transferred to other conjugated polymeric systems. By applying this method to heterocyclic polymers, very useful information is obtained to understand the evolution of bandgaps of PT, PPy and PF in connection with the chemical structures and electronic effect of the heteroatoms. We believe that this method is very helpful to understand the evolution of bandgaps of various conjugated polymers in connection with the chemical structures and electronic effect of moieties. Also, the method is expected to provide valuable information to design a small bandgap polymers.

• Korean Chemical Engineering Research
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• 제57권5호
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• pp.701-705
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• 2019

알칼라인 조건에서의 산소발생 반응(oxygen-evolution reaction: OER)은 다양한 에너지 시스템에 중요한 반응으로 여겨지고 있다. 큰 overpotential을 감소시키기 위해 다양한 촉매들이 개발되고 있으며, 그 중 NiO는 높은 활성도에 대한 가능성으로 인해 연구가 활발하게 진행되고 있다. 촉매의 표면에서 OER에 대한 메커니즘은 정확하게 규명되지는 않았지만, 산화물 촉매에서 Ni 또는 O vacancy와 같은 결함들은 많은 전기화학반응에서 활성점으로 여겨진다. 따라서, 본 연구에서는 nitrogen을 ethylenediamine을 이용하여 NiO의 O위치에 치환하여 Ni vacancy를 형성하고 그로 인해서 OER의 activity와 내구성에 어떠한 영향을 미치는지에 대해 분석해 보았다.