• Environmental Engineering Research
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• v.19 no.3
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• pp.247-253
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• 2014

The aim of this study was to characterize quintinite in fluoride removal from aqueous solutions, using batch experiments. Experimental results showed that the maximum adsorption capacity of fluoride to quintinite was 7.71 mg/g. The adsorption of fluoride to quintinite was not changed at pH 5-9, but decreased considerably in highly acidic (pH < 3) and alkaline (pH > 11) solution conditions. Kinetic model analysis showed that among the three models (pseudo-first-order, pseudo-second-order, and Elovich), the pseudo-second-order model was the most suitable for describing the kinetic data. From the nonlinear regression analysis, the pseudo-second-order parameter values were determined to be $q_e=0.18mg/g$ and $k_2=28.80g/mg/hr$. Equilibrium isotherm model analysis demonstrated that among the three models (Langmuir, Freundlich, and Redlich-Peterson), both the Freundlich and Redlich-Peterson models were suitable for describing the equilibrium data. The model analysis superimposed the Redlich-Peterson model fit on the Freundlich fit. The Freundlich model parameter values were determined from the nonlinear regression to be $K_F=0.20L/g$ and 1/n=0.51. This study demonstrated that quintinite could be used as an adsorbent for the removal of fluoride from aqueous solutions.

• Environmental Engineering Research
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• v.19 no.2
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• pp.157-163
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• 2014

The adsorption of Cr(VI) from aqueous solutions to activated carbon fiber (ACF) was investigated using both batch and flow-through column experiments. The batch experiments (adsorbent dose, 10 g/L; initial Cr(VI) concentration, 5-500 mg/L) showed that the maximum adsorption capacity of Cr(VI) to ACF was determined to 20.54 mg/g. The adsorption of Cr(VI) to ACF was sensitive to solution pH, decreasing from 9.09 to 0.66 mg/g with increasing pH from 2.6 to 9.9; the adsorption capacity was the highest at the highly acidic solution pHs. Kinetic model analysis showed that the Elovich model was the most suitable for describing the kinetic data among three (pseudo-first-order, pseudo-second-order, and Elovich) models. From the nonlinear regression analysis, the Elovich model parameter values were determined to be ${\alpha}$ = 162.65 mg/g/h and ${\beta}$ = 2.10 g/mg. Equilibrium isotherm model analysis demonstrated that among three (Langmuir, Freundlich, Redlich-Peterson) models, both Freundlich and Redlich-Peterson models were suitable for describing the equilibrium data. In the model analysis, the Redlich-Peterson model fit was superimposed on the Freundlich fit. The Freundlich model parameter values were determined to be $K_F$ = 0.52 L/g and 1/n = 0.56. The flow-through column experiments showed that the adsorption capacities of ACF in the given experimental conditions (column length, 10 cm; inner diameter, 1.5 cm; flow rate, 0.5 and 1.0 mL/min; influent Cr(VI) concentration, 10 mg/L) were in the range of 2.35-4.20 mg/g. This study demonstrated that activated carbon fiber was effective for the removal of Cr(VI) from aqueous solutions.

• Korean Journal of Soil Science and Fertilizer
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• v.25 no.2
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• pp.111-126
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• 1992

Silica sorption isotherm belonged to the C-type with weak L-type characteristics according to the classification system of adsorption isotherm. Silica sorption isothem fitted well to the Freundlich and Tempkin equation but not to the Langmuir equation. The color interference probably due to $Fe^{2+}$ during spectrometric silca determination by Molybdenum-blue method affected the sorption isotherm in reduced soils or low pH. Four parameters such as the intercept of Freundlich equation, the slope of Tempkin equation, the "Silica reactivity", and the "C-type slope", where the last two parameters were termed in the current study, were examined to assess treatment effects on silica sorption. Among them the "C-type slope" was found out to be the best parameter. The C-type isotherms showed the same high correlation coefficient as Freundlich and Tempkin equation when regressed to the sorption isothem. Plotting the C-type slope on a logarithmic scale vs. the pH showed high linearity. Using the "C-type slope" as a perameter, the pH and soil type affected the silica sorption while the effect of redox condtion was not significant. All Fe and Al extracted by the various reagents, and OM were highly correlated to silica sorption. Among them $Fe_d$ was identified as the highest influencing soil property. Since there is no equivalent reliable method to discriminate the forms of the soil Al-oxides their likely importance remains unclear.

• Korean Chemical Engineering Research
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• v.55 no.4
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• pp.514-519
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• 2017

Adsorption characteristics of acid green 27 dye using activated carbon were investigated as function of adsorbent dose, pH, initial concentration, contact time and temperature. Freundlich isotherm explained adsorption of acid green 27 dye very well and Freundlich separation factors (1/n=0.293~0.387) were found that this process could be employed as effective treatment method. Kinetic studies showed that the kinetic data were well described by the pseudo second-order kinetic model. Pseudo second rate constant ($k_2$) decreased with the increase in initial acid green 27 concentration. Activation energy (10.457 kJ/mol) and enthalpy (79.946 kJ/mol) indicated that adsorption process was physisorption and endothermic. Since Gibbs free energy decreased with increasing temperature, spontaneity of adsorption reaction increased with increasing temperature in the temperature range of 298 K~318 K.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.463-463
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• 2012

ITRS (international technology roadmap for semiconductors)에 따르면 MOS(metal-oxide-semiconductor)의 CD (critical dimension)가 45 nm node이하로 줄어들면서 poly-Si/$SiO_2$를 대체할 수 있는 poly-Si/metal gate/high-k dielectric이 대두된다고 보고하고 있다. 일반적으로 high-k dielectric를 식각시 anisotropic 한 식각 형상을 형성시키기 위해서 plasma를 이용한 RIE (reactive ion etching)를 사용하고 있지만 PIDs (plasma induced damages)의 하나인 PIED (plasma induced edge damage)의 발생이 문제가 되고 있다. PIED의 원인으로 plasma의 direct interaction을 발생시켜 gate oxide의 edge에 trap을 형성시키므로 그 결과 소자 특성 저하가 보고되고 있다. 그러므로 본 연구에서는 이에 차세대 MOS의 high-k dielectric의 식각공정에 HDP (high density plasma)의 ICP (inductively coupled plasma) source를 이용한 원자층 식각 장비를 사용하여 PIED를 줄일 수 있는 새로운 식각 공정에 대한 연구를 하였다. One-monolayer 식각을 위한 1 cycle의 원자층 식각은 총 4 steps으로 구성 되어 있다. 첫 번째 step은 Langmuir isotherm에 의하여 표면에 highly reactant atoms이나 molecules을 chemically adsorption을 시킨다. 두 번째 step은 purge 시킨다. 세 번째 step은 ion source를 이용하여 발생시킨 Ar low energetic beam으로 표면에 chemically adsorbed compounds를 desorption 시킨다. 네 번째 step은 purge 시킨다. 결과적으로 self limited 한 식각이 이루어짐을 볼 수 있었다. 실제 공정을 MOS의 high-k dielectric에 적용시켜 metal gate/high-k dielectric CMOSFETs의 NCSU (North Carolina State University) CVC model로 구한 EOT (equivalent oxide thickness)는 변화가 없으면서 mos parameter인 Ion/Ioff ratio의 증가를 볼 수 있었다. 그 원인으로 XPS (X-ray photoelectron spectroscopy)로 gate oxide의 atomic percentage의 분석 결과 식각 중 발생하는 gate oxide의 edge에 trap의 감소로 기인함을 확인할 수 있었다.

• Korean Chemical Engineering Research
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• v.56 no.1
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• pp.96-102
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• 2018

In this study, adsorption characteristics of coconut shell-based granular activated carbon (CS-GAC) on Basic Blue 3 (BB3) were evaluated. As the dosage of CS-GAC increased, the removal efficiency of BB3 tended to increase and the initial dye concentration of 50 mg/L was completely removed at 0.2 g dosage. Adsorption equilibrium achieved within 270 and 420 min at the initial concentrations of 25 and 50 mg/L, respectively, and the experimental data were represented by the pseudo-second-order model. The maximum uptakes ($q_{max}$) predicted by the Langmuir model were 34.45, 46.63 and 53.10 mg/g at 298, 308 and 318 K, respectively. The $q_{max}$ value increased as the temperature increased. Also, the Gibbs free energy (${\Delta}G$) was changed to -7.37, -8.19 and -10.40 kJ/mol with increasing temperature. The enthalpy change (${\Delta}H$) and the entropy change (${\Delta}S$) were 34.47 kJ/mol and 0.15 J/mol K, respectively. Therefore adsorption of BB3 by CS-GAC was spontaneous and endothermic.