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311 results on '"Kwon, Soonchul"'

105. Mg‐Ion Inversion in MgO@MgO−Al2O3 Oxides: The Origin of Basic Sites.

Author

Hiremath, Vishwanath, Kwon, Hyuk Jae, Jung, In‐Sun, Kwon, Soonchul, Kwon, Sung Hyun, Lee, Seung Geol, Lee, Hyun Chul, and Seo, Jeong Gil

Subjects
MAGNESIUM ions, MAGNESIUM hydride, OXIDES, NUCLEAR magnetic resonance spectroscopy
Abstract

Although MgO−Al2O3 is well known as having a spinel structure, the inversion of which occurs by exchange of the trivalent (Al3+) and divalent (Mg2+) cations, little analytical study of the degree of inversion has been carried out. This study concerns a simple methodology to identify the inversion by solid‐state NMR spectroscopy, whereby its correlation with the CO2 capture capacity of MgO‐rich MgO@MgO−Al2O3 spinel structures is verified. Through 27Al and 25Mg NMR spectroscopy, temperature‐programmed CO2 desorption, and thermogravimetric analysis, higher inversion is found to occur at low Mg/Al ratios and the inversion is found to decrease as the Mg/Al ratio increases. Moreover, the degree of inversion correlates with CO2 sorption, which is associated with the medium‐strength basic sites induced by formation of the unsaturated O2− species. These results will open new pathways to exploit defects in complex oxides beyond spinels and their derivatives for desired applications. This demonstration of MgO−Al2O3 for CO2 sorption can contribute to the design of future CO2 sorbents. [ABSTRACT FROM AUTHOR]

Published
2019
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112. Effect of bimodal surface modification of graphyne on enhanced H2 storage: Density functional theory study.

Author

Kwon, Yongju, Kim, Jeongho, Kim, Taeyoon, Shin, Hyun Suk, and Kwon, Soonchul

Subjects
GRAPHENE, HYDROGEN storage, DENSITY functional theory
Abstract

Studies on hydrogen storage materials are proceeding worldwide to enhance adsorptive capacity with a proper adsorption energy between physisorption and chemisorption. Graphyne is the carbon allotropes having sp- and sp2-hybridized carbon atoms. It has not been synthesized yet, but have taken the center stage for decades owing to its promising electronic properties and applicability. Therefore, we performed geometry optimization using density functional theory calculation to determine the adsorptive behaviors of graphyne with decoration and doping approaches for improving hydrogen storage. Graphyne decorated with alkali metal cations showed highly adsorptive properties owing to the enhanced basicity by cations, whereas doped graphyne showed a lower adsorption energy within the desirable hydrogen storage range (−0.20 eV to −0.70 eV). Therefore, we applied bimodal surface modification using doped/co-doped graphyne in the presence of alkali decoration. We found that both decoration and doping approaches compensated each other, yielding an energy suitable for hydrogen storage (min: −0.24 eV, max: −0.32 eV), which elucidates the promising properties of a hydrogen storage material. [ABSTRACT FROM AUTHOR]

Published
2018
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113. Enhanced Electrochemical Stability of a Zwitterionic-Polymer-Functionalized Electrode for Capacitive Deionization

Author

Jung, Youngsuk, Yang, Yooseong, Kim, Taeyoon, Shin, Hyun Suk, Hong, Sunghoon, Cha, Sungmin, and Kwon, Soonchul

Abstract

In capacitive deionization, the salt-adsorption capacity of the electrode is critical for the efficient softening of brackish water. To improve the water-deionization capacity, the carbon electrode surface is modified with ion-exchange resins. Herein, we introduce the encapsulation of zwitterionic polymers over activated carbon to provide a resistant barrier that stabilizes the structure of electrode during electrochemical performance and enhances the capacitive deionization efficiency. Compared to conventional activated carbon, the surface-modified activated carbon exhibits significantly enhanced capacitive deionization, with a salt adsorption capacity of ∼2.0 × 10–4mg/mL and a minimum conductivity of ∼43 μS/cm in the alkali-metal ions solution. Encapsulating the activated-carbon surface increased the number of ions adsorption sites and the surface area of the electrode, which improved the charge separation and deionization efficiency. In addition, the coating layer suppresses side reactions between the electrode and electrolyte, thus providing a stable cyclability. Our experimental findings suggest that the well-distributed coating layer leads to a synergistic effect on the enhanced electrochemical performance. In addition, density functional theory calculation reveals that a favorable binding affinity exists between the alkali-metal ion and zwitterionic polymer, which supports the preferable salt ions adsorption on the coating layer. The results provide useful information for designing more efficient capacitive-deionization electrodes that require high electrochemical stability.

Published
2024
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124. Silicon carbide-free graphene growth on silicon for lithium-ion battery with high volumetric energy density

Author

Son, In Hyuk, primary, Hwan Park, Jong, additional, Kwon, Soonchul, additional, Park, Seongyong, additional, Rümmeli, Mark H., additional, Bachmatiuk, Alicja, additional, Song, Hyun Jae, additional, Ku, Junhwan, additional, Choi, Jang Wook, additional, Choi, Jae-man, additional, Doo, Seok-Gwang, additional, and Chang, Hyuk, additional

Published
2015
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128. Predictive Guide for Collective CO2 Adsorption Properties of Mg−Al Mixed Oxides.

Author

Kwon, Hyuk Jae, Kwon, Soonchul, Seo, Jeong Gil, Jung, In Sun, Son, You‐Hwan, Lee, Chan Hyun, Lee, Ki Bong, and Lee, Hyun Chul

Subjects
CARBON monoxide, MIXED oxide catalysts, ADSORPTION (Chemistry), MAGNESIUM compounds, SORBENTS, CRYSTALLINITY
Abstract

Although solid adsorption processes offer attractive benefits, such as reduced energy demands and penalties compared with liquid absorption processes, there are still pressing needs for solid adsorbents with high adsorption capacities, thermal efficiencies, and energy-intensive regeneration in gas-treatment processes. The CO2 adsorption capacities of layered double oxides (LDOs), which are attractive solid adsorbents, have an asymmetric volcano-type correlation with their relative crystallinities. Furthermore, new collective adsorption properties (adsorption capacity, adsorptive energy and charge-transfer amount based on the adsorbent weight) are proposed based on density functional theory (DFT) calculations and measured surface areas. The correlation of these collective properties with their crystallinities is in good agreement with the experimentally measured CO2 adsorptive capacity trend, providing a predictive guide for the development of solid adsorbents for gas-adsorption processes. [ABSTRACT FROM AUTHOR]

Published
2017
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138. Effect of fluorination on haze reduction in transparent polyimide films for flexible substrates.

Author

Yang, Yooseong, Park, Jong Hwan, Jung, Youngsuk, Lee, Seung Geol, Park, Sang Kil, and Kwon, Soonchul

Subjects
POLYIMIDE films, FLUORINATION, CHEMICAL reduction, SUBSTRATES (Materials science), HAZE, DENSITY functional theory
Abstract

ABSTRACT High transmittance is an important parameter for polyimide (PI) films used as flexible display substrates. However, thermal treatment during film fabrication can cause an undesired phenomenon affecting color change in the films, which is called haze. Until now, haze formation in PI films has remained mostly unexplored, suggesting that originates in the composition. In this work, the effect of fluorination on haze reduction was investigated. Both experiments and density functional theory calculations suggest that a high degree of fluorination of PI repeating units results in weaker intra/intermolecular conjugations between polymer chains and higher haze resistance in the following order: one fluorinated group (−1.43 eV) > two fluorinated groups (−0.76 eV) > three fluorinated groups (−0.52 eV) > four fluorinated groups (−0.43 eV). The differences in the haze resistance can influence on haziness in the PI films by thermal gradient inside a lab scale cavity in a furnace. The obtained results indicate that slow heat transfer facilitates the manufacturing process to obtain high transparency in PI films. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44375. [ABSTRACT FROM AUTHOR]

Published
2017
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142. 360-degree color hologram generation for real 3D objects

Author

Chang, Eun-Young, Choi, Jongho, Lee, Sangha, Kwon, Soonchul, Yoo, Jisang, Park, Minsik, and Kim, Jinwoong

Abstract

Recently, holographic display and computer-generated holograms calculated from real existing objects have been more actively investigated to support holographic video applications. In this paper, we proposed a method of generating 360-degree color holograms of real 3D objects in an efficient manner. 360-degree 3D images are generated using the actual 3D image acquisition system consisting of a depth camera and a turntable and intermediate view generation. Then, 360-degree color holograms are calculated using a viewing-window-based computer-generated hologram. We confirmed that floating 3D objects are faithfully reconstructed around a 360-degree direction using our 360-degree tabletop color holographic display.

Published
2018

143. Enhanced Selectivity for CO2Adsorption on Mesoporous Silica with Alkali Metal Halide Due to Electrostatic Field: A Molecular Simulation Approach

Author

Kwon, Soonchul, Kwon, Hyuk Jae, Choi, Ji Il, Kim, Ki Chul, Seo, Jeong Gil, Park, Jung Eun, You, Su Jin, Park, Eun Duck, Jang, Seung Soon, and Lee, Hyun Chul

Abstract

Since adsorption performances are dominantly determined by adsorbate–adsorbent interactions, accurate theoretical prediction of the thermodynamic characteristics of gas adsorption is critical for designing new sorbent materials as well as understanding the adsorption mechanisms. Here, through our molecular modeling approach using a newly developed quantum-mechanics-based force field, it is demonstrated that the CO2adsorption selectivity of SBA-15 can be enhanced by incorporating crystalline potassium chloride particles. It is noted that the induced intensive electrostatic fields around potassium chloride clusters create gas-trapping sites with high selectivity for CO2adsorption. The newly developed force field can provide a reliable theoretical tool for accurately evaluating the gas adsorption on given adsorbents, which can be utilized to identify good gas adsorbents.

Published
2017
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