• 전기화학회지
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• 제2권1호
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• pp.23-26
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• 1999

백금$(Pt)/0.1M\;H_2SO_4$, 전해질 계면에서 교류임피던스 측정과 위상이동 방법을 사용하여 Langmuir 흡착등온식을 정성적으로 해석하였다. 위상이동$(\phi)$은 음전위(E<0)와 주파수(f)에 따르며, Pt 일전극(음극)에 흡착된 수소원자$(H_{ads})$의 표면피복율$(\theta)$에 반비례한다. 중간주파수대$(1\~100 Hz)$에서 위상이동 변화$(\phi\;vs.\;E)$는 Langmuir 흡착등온식$(\theta\;vs.\;E)$의 계산과 해석에 사용할 수 있는 실험적인 방법이다. $Pt/0.1M\;H_2SO_4$ 전해질 계면에서 흡착평형상수(K)와 표준자유에너지$({\Delta}G_{ads})$는 각각 $3\times10^{_4}$와 20.1kJ/mol이다.

• Journal of Electrochemical Science and Technology
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• 제4권2호
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• pp.81-87
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• 2013

Inhibition of corrosion of mild steel in sulphuric acid by acidic extract of Jatropha Curcas leaves has been studied using weight loss and thermometric measurements. It was found that the leaves extract act as a good corrosion inhibitor for mild steel in all concentrations of the extract. The inhibition action depends on the concentration of the Jatropha Curcas leaves extract in the acid solution. Results for weight loss and thermometric measurements indicate that inhibition efficiency increase with increasing inhibitor concentration. The adsorption of Jatropha curcas leaves extract on the surface of the mild steel specimens obeys Langmuir adsorption isotherm. Based on the results, Jatropha curcas leaves extract is recommended for use in industries as a replacement for toxic chemical inhibitors.

• 전기화학회지
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• 제7권4호
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• pp.194-200
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• 2004

The constant correlation factors between the Temkin and the Langmuir or the Frumkin adsorption isotherms of over-potentially deposited hydrogen (OPD H) for the cathodic H2 evolution reaction (HER) at poly-Pt and Re/0.5M $H_2SO_4$ and poly-Ni/0.05 M KOH aqueous electrolyte interfaces have been experimentally and consistently found using the phase-shift method. At intermediate values of the fractional surface coverage $(\theta),\;i.e.,\;02<{\theta}<0.8$, the Langmuir and Temkin adsorption isotherms of OPD H for the cathodic HER are correlated to each other even though the adsorption conditions or processes are different from each other. At the same range of $\theta$, correspondingly, the Frumkin and Temkin adsorption isotherms of OPD H for the cathodic HER are correlated to each other. The equilibrium constants $(K_o)$ for the Temkin adsorption isotherms $({\theta}\;vs.\; E)$ are consistently ca. 10 times greater than those (K, Ko) for the corresponding Langmuir or Frumkin adsorption isotherms ($({\theta}\;vs.\; E)$. The interaction parameters (g) for the Temkin adsorption isotherms $({\theta}\;vs.\; E)$ are consistently ra. 4.6 greater than those (g) for the corresponding Langmuir or Frumkin adsorption isotherms $({\theta}\;vs.\; E)$. These numbers (10 times and 4.6) can be taken as constant correlation factors between the corresponding adsolftion isotherms (Temkin, Langmuir, Frumkin) at the interfaces. The Temkin adsorption isotherm corresponding to the Langmuir or the Frumkin adsorption isotherm, and vice versa, can be effectively verified or confirmed using the constant correlation factors. Both the phase-shift methodand constant correlation factors are useful and effective for determining or confirming the suitable adsorption isotherms (Temkin, Langmuir, Frumkin) of intermediates for sequential reactions in electrochemical systems.

• 전기화학회지
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• 제6권2호
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• pp.119-129
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• 2003

The Langmuir adsorption isotherms of the over-potentially deposited hydrogen (OPD H) fur the cathodic $H_2$ evolution reaction (HER) at the poly-Au and $Rh|0.5M\;H_2SO_4$ aqueous electrolyte interfaces have been studied using cyclic voltammetric and ac impedance techniques. The behavior of the phase shift $(0^{\circ}{\leq}{-\phi}{\leq}90^{\circ})$ for the optimum intermediate frequency corresponds well to that of the fractional surface coverage $(1{\geq}{\theta}{\geq}0)$ at the interfaces. The phase-shift profile $({-\phi}\;vs.\;E)$ for the optimum intermediate frequency, i.e., the phase-shift method, can be used as a new electrochemical method to determine the Langmuir adsorption isotherm $({\theta}\;vs.\;E)$ of the OPD H for the cathodic HER at the interfaces. At the poly-Au|0.5M $H_2SO_4$ aqueous electrolyte interface, the equilibrium constant (K) and the standard free energy $({\Delta}G_{ads})$ of the OPD H are $2.3\times10^{-6}$ and 32.2kJ/mol, respectively. At the poly-Rh|0.5M $H_2SO_4$ aqueous electrolyte interface, K and ${\Delta}G_{ads}$ of the OPD H are $4.1\times10^4\;or\;1.2\times10^{-2}$ and 19.3 or 11.0kJ/mol depending on E, respectively. In contrast to the poly-Au electrode interface, the two different Langmuir adsorption isotherms of the OPD H are observed at the poly-Rh electrode interface. The two different Langmuir adsorption isotherms of the OPD H correspond to the two different adsorption sites of the OPD H on the poly-Rh electrode surface.

• 전기화학회지
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• 제10권3호
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• pp.219-228
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• 2007

The phase-shift method and correlation constants, i.e., the electrochemical impedance spectroscopy (EIS) techniques for studying linear relationships between the behaviors (${\varphi}\;vs.\;E$) of the phase shift ($0^{\circ}{\leq}-{\varphi}{\leq}90^{\circ}$) for the optimum intermediate frequency and those (${\theta}\;vs.\;E$) of the fractional surface coverage ($1{\geq}{\theta}{\geq}0$), have been proposed and verified to determine the Langmuir, Frumkin, and Temkin adsorption isotherms (${\theta}\;vs.\;E$) of H for the cathodic $H_2$ evolution reaction (HER) at noble and transition-metal/aqueous solution interfaces. At the Pt/0.1 MKOH aqueous solution interface, the Langmuir, Frumkin, and Temkin adsorption isotherms (${\theta}\;vs.\;E$), equilibrium constants ($K=5.6{\times}10^{-10}\;mol^{-1}\;at\;0{\leq}{\theta}<0.81$, $K=5.6{\times}10^{-9}{\exp}(-4.6{\theta})\;mol^{-1}\;at\;0.2<{\theta}<0.8$, and $K=5.6{\times}10^{-10}{\exp}(-12{\theta})\;mol^{-1}\;at\;0.919<{\theta}{\leq}1$, interaction parameters (g = 4.6 for the Temkin and g = 12 for the Frumkin adsorption isotherm), rates of change of the standard free energy ($r=11.4\;kJ\;mol^{-1}$ for g=4.6 and $r=29.8\;kJ\;mol^{-1}$ for g=12), and standard free energies (${\Delta}G_{ads}^0=52.8\;kJ\;mol^{-1}\;at\;0{\leq}{\theta}<0.81,\;49.4<{\Delta}G_{\theta}^0<56.2\;kJ\;mol^{-1}\;at\;0.2<{\theta}<0.8$ and $80.1<{\Delta}_{\theta}^0{\leq}82.5\;kJ\;mol^{-1}\;at\;0.919<{\theta}{\leq}1$) of OH for the anodic $O_2$ evolution reaction (OER) are also determined using the phase-shift method and correlation constants. The adsorption of OH transits from the Langmuir to the Frumkin adsorption isotherm (${\theta}\;vs.E$), and vice versa, depending on the electrode potential (E) or the fractional surface coverage (${\theta}$). At the intermediate values of ${\theta}$, i.e., $0.2<{\theta}<0.8$, the Temkin adsorption isotherm (${\theta}\;vs.\;E$) correlating with the Langmuir or the Frumkin adsorption isotherm (${\theta}\;vs.\;E$), and vice versa, is readily determined using the correlation constants. The phase-shift method and correlation constants are accurate and reliable techniques to determine the adsorption isotherms and related electrode kinetic and thermodynamic parameters. They are useful and effective ways to study the adsorptions of intermediates (H, OH) for the sequential reactions (HER, OER) at the interfaces.

• 전기화학회지
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• 제12권4호
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• pp.311-316
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• 2009

인공해수에서 일어나는 Al의 부식에 대하여 alanine과 methionine의 부식억제 효과를 조사하였다. 이들 아미노산의 낮은 덮힘율로 보아 Al 표면에 alanine과 methionine는 Langmuir adsorption isotherm에 따른 흡착이 일어나며, 아미노산 안의 카르복시 이온만이 Al에 흡착하는 것으로 보인다.

• 공업화학
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• 제30권2호
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• pp.190-197
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• 2019

활성탄을 사용하여 수용액으로부터 메틸 그린 염료의 흡착에 대해 초기농도와 접촉시간 및 온도를 흡착변수로 사용하여 조사하였다. 흡착평형관계는 Freundlich 등온식에 잘 맞았다. 평가된 Freundlich 분리계수(1/n = 0.212~0.305)로부터 이 흡착공정이 효과적인 처리영역(0 < $R_L$ < 1)에 속하는 것을 알았다. BET식으로부터 얻은 등온포화용량은 온도가 증가할수록 커졌다. Dubinin-Radushkevich식으로 구한 흡착에너지값(E = 316.869~340.049 J/mol)으로부터 흡착공정이 물리흡착공정임을 알았다. 흡착속도실험결과는 유사 2차 반응속도식에 잘 맞는 것으로 나타났다. 자유에너지(-5.421~-7.889 kJ/mol)와 엔탈피(31.915 kJ/mol)는 흡착공정이 자발적이고 흡열반응으로 진행되었다고 알려주었다. 등량흡착열은 평형흡착량이 증가함에 따라 커졌으며, 표면 덮임이 증가됨에 따라 흡착제-흡착질의 총 상호작용도 증가하였다.

• 공업화학
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• 제30권5호
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• pp.562-568
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• 2019

Cylindrical shape extrudates of calcium silicate hydrate (CSH) were prepared using different percentages of polyvinyl alcohol (PVA) / sodium alginate (SA) mixtures as binders and an aqueous solution containing 6% $H_3BO_3$ and 3% $CaCl_2$ was used as a cross linking agent. As the quantity of alginate increases, the phosphate removal efficiency and capacity were decreased. Among four different extrudate samples, the sample prepared by 8% PVA + 2% SA showed the highest phosphate removal efficiency (59.59%) and capacity (29.97 mg/g) at an initial phosphate concentration of 100 ppm and 2.0 g/L adsorbent dosage. Effects of the adsorbent dosage, contact time and initial phosphate concentration on the sample were further studied. The removal efficiency and capacity obtained by a 4.0 g/L adsorbent dose at an initial phosphate concentration of 100 ppm in 3 h were 79.38% and 19.96 mg/g, respectively. The experimental data of kinetic and isotherm measurements followed the pseudo-second-order kinetic equation and Langmuir isotherm model, respectively. These results suggested that the phosphate removal was processed via a chemisorption and a monolayer coverage of phosphate anions was on the CSH surface. The maximum adsorption capacity ($q_{max}$) was calculated as 23.87 mg/g from Langmuir isotherm model.

• 공업화학
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• 제28권2호
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• pp.206-213
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• 2017

활성탄을 사용하여 수용액으로부터 crystal violet 염료의 흡착에 대해 조사하였으며, 흡착제의 양, 초기농도와 접촉시간 및 온도를 흡착변수로 사용하여 수행하였다. 흡착평형관계는 Langmuir 등온식에 잘 맞았다. 평가된 Langmuir 분리 계수($R_L=0.02{\sim}0.106$)를 바탕으로 이 흡착공정이 효과적인 처리(0 < $R_L$ < 1)가 가능하다는 것을 알았다. 흡착동력학 데이터는 유사 2차 반응속도식에 잘 맞는 것으로 나타났다. Gibbs 자유에너지(-1.61~-11.66 kJ/mol)와 엔탈피(147.209 kJ/mol)는 흡착공정이 자발적이고 흡열반응으로 진행된다는 것을 나타냈다. 등량흡착열은 표면덮임이 증가됨에 따라 흡착제-흡착질의 상호작용이 제한되어 표면부하량이 증가할수록 작아졌다.

• 대한화학회지
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• 제56권4호
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• pp.401-405
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• 2012

Corrosion inhibition efficiencies of holy basil on Al in HCl solution were studied by weight loss and thermometric methods in presence and in absence of stem extract of three different varieties of holy basil viz. ocimum basilicum ($E_B$), ocimum canum ($E_C$) and ocimum sanctum ($E_S$). Inhibition efficiency increases with the increasing concentration of stem extract and decreases with increases in acid strength. Results show that all varieties under study are good corrosion inhibitors, among which, $E_B$ is most effective. Maximum inhibition efficiency was found 97.09% in 0.5N HCl solution with 0.6% stem extract. The Langmuir adsorption isotherm indicates that surface coverage also increases with increasing in the concentration of extract of stem in HCl solution.