• The Journal of Engineering Geology
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• v.33 no.4
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• pp.701-716
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• 2023

Microplastics (<5 mm diameter) in aquatic environments adsorb heavy metals, potentially exposing humans to their toxic effects via food chains. We investigated factors influencing the adsorption of heavy metals on microplastics in aquatic environments, examining their adsorption processes and mechanisms. Adsorption characteristics vary with polymer type, crystallinity, particle size, and environmental conditions (pH, temperature, weathering), and the adsorption capacity for heavy metals increases with weathering and reduction in polymer particle size. However, correlations between environment temperature, polymer crystallinity, and adsorption capacity for heavy metals could not be confirmed. The adsorption behavior of heavy metals can be explained in terms of physicochemical adsorption processes and evaluated through adsorption kinetics and isothermal studies, with multiple mechanisms usually being involved. An understanding of the adsorption of heavy metals by microplastics should aid evaluation of the potential risks of microplastics in aquatic environments.

• Journal of the Korean GEO-environmental Society
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• v.11 no.1
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• pp.45-51
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• 2010

Cadmium (Cd) adsorption by the activated carbon containing hydroxyapatite (HAP) was investigated. Cd adsorption with different HAP mass ranged from 10% to 30%. With more HAP, more Cd was adsorbed. These results suggest that the higher HAP dose causes an increase of the ion exchange potential in HAP sorbent. Kinetics and equilibrium studies were investigated in series of batch adsorption experiments. Langmuir and Freundlich isotherm models were fit to the equilibrium data and Cd adsorption on HAP sorbent were found to follow the Freundlich isotherm model well in the initial adsorbate concentration range. The simple kinetic model, the pseudo first order kinetic model and the pseudo second order kinetic model, were used to investigate the adsorption. The adsorption reaction of Cd followed the pseudo second order kinetic model, and the adsorption pseudo second order kinetic constants ($k_2$) increased with increasing initial HAP amounts onto activated carbon. Also, intraparticle diffusion model was used to investigate the adsorption mechanism between adsorbate and adsorbent in the aqueous phase. Surface adsorption reaction and intraparticle diffusion occur simultaneously Cd adsorption mechanism from aqueous phase in this study.

• Journal of the Korea Concrete Institute
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• v.29 no.1
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• pp.65-75
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• 2017

C-S-H phase is the most abundant reaction product, occupying about 50~60% of cement paste volume. The phase is also responsible for most of engineering properties of cement paste. This is not because it is intrinsically strong or stable, but because it forms a continuous layer that binds together the original cement particles into a cohesive whole. The binding ability of C-S-H phase arises from its nanometer-level structure. In terms of chloride penetration in concrete, C-S-H phase is known to adsorb chloride ions, however, its mechanism is very complicated and still not clear. The purpose of this study is to examine the interaction between chloride ions and C-S-H phase with various Ca/Si ratios and identify the adsorption mechanism. C-S-H phase can absorb chloride ions with 3 steps. In the C-S-H phase with low Ca/Si ratios, momentary physical adsorption could not be expected. Physical adsorption is strongly dependent on electro-kinetic interaction between surface area of C-S-H phase and chloride ions. For C-S-H phase with high Ca/Si ratio, electrical kinetic interaction was strongly activated and the amount of surface complexation increased. However, chemical adsorption could not be activated for C-S-H phase with high Ca/Si ratio. The reason can be explained in such a speculation that chloride ions cannot be penetrated and adsorbed chemically. Thus, the maximum chloride adsorption capacity was obtained from the C-S-H phase with a 1.50 Ca/Si ratio.

• Journal of the Korea Concrete Institute
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• v.27 no.1
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• pp.85-92
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• 2015

The chloride ions, responsible for the initiation of the corrosion mechanism, intrude from the external medium into the concrete. A part of the intruding chloride ions will be retained by the hydration products of the binder in concrete, either through chemical adsorption or by physical adsorption. Since the hydration products of cement are responsible for the chloride binding in concrete, this study focused on the chloride binding in individual hydrate. The purpose of this study is to explore the time dependant behaviors of chloride ions adsorption with cement hydrates, focused on its mechanism. AFt phase and CH phase were not able to absorb chloride ion, however, C-S-H phase and AFm phase had a significant chloride adsorption capacity. In particular, AFm phase showed a chemical adsorption with slow rate in 40 days, while C-S-H phase showed binding behaviors with 3 stages including momentary physical adsorption, physico-chemical adsorption, and chemical adsorption. Based on the results, this study suggested theoretical approach to depict chloride adsorption behavior with elapsed time of C-S-H phase and AFm phase effectively. It is believed that the approach suggested in this study can provide us with a good solution to understand the mechanism on chloride adsorption with hydrates and to calculate a rate of chloride penetration with original source of chloride ions, for example, marine sand at initial time or sea water penetration later on.

• Proceedings of the KSME Conference
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• 2005.11a
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• pp.229.2-229.2
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• 2005

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.215-215
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• 2012

Sillicon Wafer는 순도 99.9999999%의 단결정 규소를 사용하여 만들어진다. 웨이퍼의 표면은 결함이나 오염이 없어야 하고 회로의 정밀도에 영향을 미치기 때문에 고도의 평탄도와 정밀도를 요구한다. 특히 실리콘의 순도는 효율성에 영향을 주는 주요 원인으로 금속의 오염은 실리콘 웨이퍼의 수명을 단축시켜 효율성을 떨어뜨린다. 표면에 흡착된 구리와 니켈은 Silicon 오염의 주요인 중 하나로 알려져 있다. 이 연구는 Silicon Wafer 표면에 흡착된 구리가 내부로 확산되는 메커니즘을 규명하는 것을 목표로 한다. 표면에 구리가 흡착된 상태는 AES 및 LEED로 관찰하였다. 표면에 흡착된 구리의 표면(수평)및 내부(수직)확산은 SIMS를 이용하여 연구하였다.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.342-342
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• 2011

방사광을 이용한 흡수스펙트럼으로부터 그래핀 표면 위 TCPP(Tetra(4-carboxyphenyl)porphine) 유기 분자의 흡착구조에 대하여 연구하였다. 순수한 그래핀 표면의 비활성도는 소자응용 분야에 있어 그 영역을 제한할 수 있는 하나의 걸림돌이 되고 있다. 이를 극복하기 위해 유기분자막의 초기 흡착을 이용한 다양한 방법이 시도되어왔다. 그 중 TCPP 분자막을 이용한 그래핀 표면의 기능성 및 그 우수성을 이미 보고한 바 있다. 그러나 그 분자의 흡착구조에 대해 밝혀진 바 없다. 그래핀 표면과 분자간의 흡착 메커니즘 및 분자 상호간의 역학관계는 그 흡착구조의 규명으로부터 얻어질 수 있는데, 본 연구에서는 C 1s K-edge에 대한 NEXAFS 스펙트럼을 이용하여 TCPP 분자가 그래핀과 평행한 방향으로 흡착됨을 알 수 있었다. 이는 또한 분자흡착량의 증가에 따른 AFM 이미지와 일관됨을 알 수 있었다.

• Resources Recycling
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• v.25 no.4
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• pp.60-67
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• 2016

This study was conducted to establish the adsorption-desorption mechanism and the optimum condition of chromatographic operation for separations of heavy rare earth elements (Gd, Tb, Dy) using a p507-containing resin. By employing Langmuir and Freundlich isotherm together with pseudo first and second order kinetics, absorption-desorption reaction mechanism was investigated. Langmuir and Freundlich isotherm was applied under assumption that adsorption reaction occurs in form of monolayer, and because the result was identical to the assumption, now we know adsorption of heavy rare earth elements occurs in form of monolayer. Concerning the pseudo first and second order kinetic, the pseudo second order seemed to be more suitable to represent heavy rare earth element adsorption mechanism. By using the extraction chromatography to separate heavy rare earth elements, ${\alpha}^{Tb}_{Gd}=1.24$, and ${\alpha}^{Dy}_{Tb}=1.03$ were confirmed in eluent HCl 0.25 M which indicates almost perfect separations of three elements. Furthermore, as concentrations of eluent became higher, the resolution value decreased and the elution area got shortened.

• Applied Chemistry for Engineering
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• v.33 no.2
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• pp.151-158
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• 2022

In this paper, parameter characteristics such as pH effect, isotherm, kinetic and thermodynamic parameters and competitive adsorption of dyes including malachite green (MG), direct red 81 (DR 81) and thioflavin S (TS), which have different functional groups, being adsorbed onto activated carbon were investigated. Langmuir, Freundlich and Temkin isotherm models were employed to find the adsorption mechanism. Effectiveness of adsorption treatment of three dyes by activated carbon were confirmed by the Langmuir dimensionless separation factor. The mechanism was found to be a physical adsorption which can be verified through the adsorption heat calculated by Temkin equation. The adsorption kinetics followed the pseudo second order and the rate limiting step was intra-particle diffusion. The positive enthalpy and entropy changes showed an endothermic reaction and increased disorder via adsorption at the S-L interface, respectively. For each dye molecule, negative Gibbs free energy increased with the temperature, which means that the process is spontaneous. In the binary component system, it was found that the same functional groups of the dye could interfere with the mutual adsorption, and different functional groups did not significantly affect the adsorption. In the ternary component system, the adsorption for MG lowered a bit, likely to be disturbed by the other dyes meanwhile DR 81 and TS were to be positively affected by the presence of MG, thus resulting in much higher adsorption.

• Korean Chemical Engineering Research
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• v.45 no.2
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• pp.166-171
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• 2007

The adsorption behavior of $Pb^{2+}$ was compared between calcium alginate beads and capsules, which have different structures of alginate-gel core beads and liquid core alginate-membrane capsules, respectively. In terms of adsorption kinetics and isotherms, adsorption characteristics depending on pH and hardening time were compared for both adsorbents and also released calcium ion during the adsorption process was monitored. The adsorption of $Pb^{2+}$ on both adsorbents was caused by surface complexation and ion exchange mechanisms, both of which have similar effects on adsorption process regardless of the amount of adsorbed $Pb^{2+}$. The dependence of $Pb^{2+}$ adsorption upon pH was also similar for both adsorbents indicating the existence of similar functional groups on the surface of adsorbents. However, a different $Pb^{2+}$ adsorption behavior was observed considering the adsorption kinetics. The adsorption kinetic of $Pb^{2+}$ on alginate beads was slower than on alginate capsules and the maximum adsorption loading ($Q_{max}$) onto alginate beads was also less than onto alginate capsules by 49%. This drawback of alginate beads compared to capsules were ascribed to a diffusion limitation due to solid gel-core structure of alginate beads.