• Journal of the Korean Vacuum Society
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• v.4 no.2
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• pp.150-155
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• 1995

Mo 단결정 표면에 황을 흡착시켜 형성된 상층구조를 AES와 LEED로써 연구하였다. 황의 피복률은 sulfur gun으로부터 생성되는 S2 flux로써 조절하였으며, 여러 가지 흡착된 황의 상층구조를 LEED로써 관찰하였다. 황화된 Mo 표면에서 탈산소반응(HDO)의 모델 분자로서, Furan의 흡착과 반응을 승온반응분광법(TPRS)으로 조사하였다. 낮은 온도에서 Furan 분자의 헤테로 원자는 직접 이탈하여 안정한 기체상의 반응 생성물인 일산화탄소를 형성하였으며, 이 반응은 Mo의 (100) 및 (110)면에서 각각 깨끗한 표면 및 황화된 표면에 관계없이 일어났다. 이를 바탕으로 Mo 표면에서 Furan의 분해반응에 대한 메카니즘을 제안하였다.

• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.153-153
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• 2000

Si 산화는 반도체 공정상 필요한 과정으로 산업적으로나 학문적으로 중요하고 많이 연구되었다. 이중에서 Si(1110-7x7표면에서 초기 흡착된 산소는 준안정적 상태로 존재하며 표면온도, 산소의 노출량 그리고 진공도에 따라 그 수명이 제한된다. 이러한 준안정적 상태의 산소의 화학적 성질은 여러 표면분석장비가 동원되어 연구되었으나 아직까지 논쟁이 되고 있다. 이 경우 산소가 어떤 상태로 존재하는가는 표면화학종을 검출함으로서 해결될 수 있다. 저에너지 Cs+ 이온 반응성 산란은 이러한 요구를 충족시킬수 있는 가장 적합한 실험 방법중의 하나이다. 저에너지 Cs+ 이온 산란의 특징 중의 하나는 입사된 Cs+ 이온이 표면에 흡착된 화학종과 충돌후 탈착되면서 반응을 하여 송이 이온을 형성한다는 것이다. 이 송이 이온을 관측함으로서 표면에 존재하는 화학종을 알아 낼 수 있다. 이에 산소가 흡착된 Si(111)-7x7 표면에서의 산소의 준안정적 상태가 저에너지 Cs+ 이온 산란 실험을 통하여 연구되었다. 실험은 0.2-2L(1Langmuir = 10-6 Torr x 1 sec) 산소 노출량과 -15$0^{\circ}C$ - $25^{\circ}C$의 표면온도 그리고 5eV - 20eV의 Cs+ 이온 충돌에너지에서 CsSiO+ 이온이 유일한 생산물로서 검출되었다. CsSiO+ 이온은 입사된 Cs+ 이온과 표면에 존재하는 SiO 분자가 충돌 후 반응하여 탈착된 것으로 생각된다. 이것은 낮은 산소 노출량 즉, 초기 산화 단계에서 SiO가 표면에 존재한다는 것을 의미한다. 즉, 산소 분자는 산화단계의 초기에 해리되어 표면에 흡착되고 선구물질인 SiO를 형성함을 제시한다. 최근의 이론적 계산인 density functional calculation에서도 산소분자가 Si(111)-7$\times$7 표면의 준안정적 산화상태의 선구물질일 가능성을 배제한다. 이는 본 저에너지 Cs+ 이온 반응성 산란실험을 뒷받침하는 계산 결과이다. 높은 Cs+ 이온 충돌에너지에서 CsSi+, Si+, SiO+, Si2+, Si2O+ 등이 추가로 검출되었다. 이는 CsSi 이온을 제외하고 수 keV의 충돌에너지를 사용하는 이차 이온 질량 분석법과 비슷한 결과이다.

• Korean Chemical Engineering Research
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• v.61 no.4
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• pp.598-603
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• 2023

Electrochemical ammonia production using catalysts offers a promising alternative to the conventional Haber-Bosch process, allowing for ambient temperature and pressure conditions, environmentally friendly operations, and high-purity ammonia production. In this study, we focus on the nitrogen reduction reactions occurring on the surfaces of ruthenium catalysts, employing first-principles calculations. By modeling reaction pathways for nitrogen reduction on the (0001) and (1000) surfaces of ruthenium, we optimized the reaction structures and predicted favorable pathways for each step. We found that the adsorption configuration of N₂ on each surface significantly influenced subsequent reaction activities. On the (0001) surface of ruthenium, the end-on configuration, where nitrogen molecules adsorb perpendicularly to the surface, exhibited the most favorable N₂ adsorption energy. Similarly, on the (1000) surface, the end-on configuration showed the most stable adsorption energy values. Subsequently, through optimized hydrogen adsorption in both distal and alternating configurations, we theoretically elucidated the complete reaction pathways required for the final desorption of NH₃.

• Korean Chemical Engineering Research
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• v.61 no.4
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• pp.604-610
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• 2023

The nitrogen reduction reaction (NRR), which produces NH₃ by reducing N₂ under ambient conditions, is attracting attention as a promising technology that can reduce energy consumption in industrial processes. We investigated the adsorption behaviors at various active sites on the Ni (100) surface, which is widely used among catalytic metal surfaces capable of adsorbing and activating N₂, based on density-functional theory calculations. We also investigated two N₂ adsorption structures, so-called end-on and side-on structures. We find that for the end-on case, N₂ is adsorbed on a top site, and the reaction proceeded in a distal pathway, while for the side-on case, N₂ is adsorbed on a bridge site, and the reaction proceeded with enzymatic pathway. Finally, this study provides insight into the adsorption of metal catalyst surfaces for the NRR reactions based on the calculated Gibbs free energy profiles of the thermodynamically most favorable pathways.

• Journal of Korean Society of Environmental Engineers
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• v.38 no.5
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• pp.242-248
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• 2016

The overall reaction rate of fuel cell is governed by oxygen reduction reaction (ORR) in the cathode due to its slowest reaction compared to the oxidation of hydrogen in the anode. The ORR efficiency can be readily evaluated by examining the adsorption strength of atomic oxygen on the surface of catalysts (i.e., known as a descriptor) and the adsorption energy can be controlled by transforming the surface geometry of catalysts. In the current study, the effect of the surface geometry of catalysts (i.e., strain effect) on the adsorption strength of atomic oxygen on platinum catalysts was analyzed by using density functional theory (DFT). The optimized lattice constant of Pt ($3.977{\AA}$) was increased and decreased by 1% to apply tensile and compressive strain to the Pt surface. Then the oxygen adsorption strengths on the modified Pt surfaces were compared and the electron charge density of the O-adsorbed Pt surfaces was analyzed. As the interatomic distance increased, the oxygen adsorption strength became stronger and the d-band center of the Pt surface atoms was shifted toward the Fermi level, implying that anti-bonding orbitals were shifted to the conduction band from the valence band (i.e., the anti-bonding between O and Pt was less likely formed). Consequently, enhanced ORR efficiency may be expected if the surface Pt-Pt distance can be reduced by approximately 2~4% compared to the pure Pt owing to the moderately controlled oxygen binding strength for improved ORR.

• Resources Recycling
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• v.15 no.3 s.71
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• pp.81-86
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• 2006

Altered Langmuir adsorption isotherm has been suggested for adsorption reactions occurring in aqueous environment based upon the concept of the steric displacement between adsorbates and water molecules at the surface of adsorbent. For the adsorption of $Cd^{2+}$ on activated carbon, the suggested adsorption isotherm was shown to be more well applied to the experimental results compared with the classical Langmuir adsorption isotherm. Based on this, regarding the adsorption system which following the Langmuir model more precise design and controllable operation of the process were considered to be attainable when the adsorption process is analyzed employing the altered adsorption isotherm.

• Clean Technology
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• v.23 no.4
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• pp.413-420
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• 2017

The batch experiments and response surface methodology (RSM) have been applied to the investigation of the Cs adsorption with zeolite X synthesized using coal fly ash generated from the thermal power plant. Regression equation formulated for Cs adsorption was represented as a function of response variables. The model was highly relevant because the decision coefficient ($r^2$) was 0.9630. It was confirmed from the statistical results that the removal efficiency of Cs was affected by the order of experimental factors as pH > Cs concentration > temperature. The adsorption kinetics were more accurately represented by a pseudo second-order model. The maximum adsorption capacity calculated from the Langmuir isotherm model was $151.52mg\;g^{-1}$ at 293 K. Also, according to the thermodynamic parameters calculated from Vant Hoff equation, it could be confirmed that the adsorption reaction was an endothermic reaction and a spontaneous process.

• Journal of Energy Engineering
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• v.4 no.1
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• pp.76-84
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• 1995

본 연구에서는 코코넛 껍질로부터 제조한 활성탄을 열 및 산소-암모니아의 혼합가스로 전처리하여 표면의 특성 변화와 이산화황 흡착능에 미치는 영향을 살펴보았다. 전처리한 활성탄으로 이산화황 흡착실험을 수행한 결과, 전처리한 활성탄은 기본 활성탄 시료보다 높은 흡착능력을 보였다. 본 연구의 전처리 실험에서는 산소와 암모니아를 주입하여 활성점을 제공하는 산소와 환원성 분위기를 조성하는 질소관능기를 도입하였다. 전처리 조건은 0∼25%의 암모니아와 473∼1273K의 온도이며 처리조건을 변화시킴으로써 표면 기능의 척도가 되는 세공구조와 원소조성 및 표면 관능기 등에 직접적인 영향을 주었다. 흡착능력은 고정층 반응기에서 전자 비틀림 저울로 이산화황 흡착량을 측정하여 비교하였고, 이 과정 중의 활성탄 표면의 특성변화를 원소분석, 승온탈착법, 산-염기 적정법, 주사현미경법 등의 분석 방법을 통해서 알아보았다. 그 결과, 이산화황의 최대 흡착 능력은 온도조건 973∼1173K에서 나타났다. 또한, 암모니아로 처리하지 않은 활성탄에 비하여 암모니아로 처리한 활성탄은 그 주입농도에 관계없이 이산화황의 흡착제거율을 약 48% 정도 향상시켰다.

• KSBB Journal
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• v.7 no.4
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• pp.318-324
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• 1992

The adsorption characteristics of bovine serum albumin(BSA) on the modified carbon fiber and cellulose surfaces were investigated. In order to define the effects of solid surface characteristics on protein adsorption, surfaces of carbon fiber and cellulose were modified by physical and chemical treatment. The amounts of BSA adsorbed onto various solid surfaces were evaluated by batch method under various pH and ionic strength. The amount of adsorbed BSA was highly dependent on pH as well as surface functional groups.

• Journal of the Mineralogical Society of Korea
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• v.15 no.2
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• pp.104-113
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• 2002

The sorption of Cd$^{2+}$ on calcite was studied in aqueous solutions of several electrolytes. The Cd$^{2+}$ concentration, 10$^{-8}$ M, was kept well below saturation with respect to CdCO$_3$(s). Sorption behavior of Cd$^{2+}$ in different ionic strengths of NaClO$_4$solutions shows that sorption is independent of ionic strength. This result suggests that Cd$^{2+}$ sorption on calcite surface is of a specific nature, and adsorption is controlled by an inner-sphere type of surface complex. Two stages in the sorption behavior could be identified: an initial rapid uptake, followed by slower uptake reaching a maximum steady state by 145 hrs. No evidence was observed for surface precipitation, although it can not be entirely ruled out. Desorption of Cd$^{2+}$ from the calcite surface after resuspension into Cd-free solution is initially very rapid, but depends partly on the previous sorption history. Desorption behavior of Cd$^{2+}$ show that an initial rapid desorption followed either by slow uptake reaching a maximum, as in the adsorption experiments, or slowing desorption to reach a steady state minimum. This irreversible behavior of Cd$^{2+}$ sorption and desorption may act as one of the controls for regulating the mobility of dissolved Cd$^{2+}$ natural aqueous systems. Calculated adsorption partition coefficients suggest that overall sorption and desorption process in the concentration range are controlled by d single mechanism.ingle mechanism.