• Journal of the Mineralogical Society of Korea
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• v.12 no.2
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• pp.91-95
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• 1999

• Journal of the Korean Ceramic Society
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• v.32 no.11
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• pp.1276-1282
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• 1995

• Korean Journal of Soil Science and Fertilizer
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• v.26 no.3
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• pp.160-171
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• 1993

Surface charge characteristics of Ultisol(Luisiana soil from Philippines), Alfisol(Maahas soil from Philippines), and Inceptisol(Yongii soil from Korea) were studied by way of potentiometric titration, backtitration technique, and ion adsorption method(or CEC - AEC method). The PZNC(point of zero net charge) values determined by ion adsorption method were much lower than the natural pHs in all soils, indicating that all soil samples bore net negative surface charge. The PZSE (point of zero salt effect) values determined by potentiometric titration and backtitration technique were identical in Luisiana and Yongii soils but not in Maaghas soil. All soils showed higher PZSE values than PZNC values probably due to the influence of permanent negative charge. The permanent charge calculated by the theory of Uehara and Gillman (1980) occupied quite low portion of the CEC measured at pH 7 in all soils. Backtitration technique corrected errors of potentiometric titration at extreme pH. However, it still overestimate the surface charge compared with ion adsorption method. Therefore, the ion adsorption method was recommanded for the surface charge measurement of the usual soils which have high negative charge components.

• Journal of the Korean institute of surface engineering
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• v.41 no.3
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• pp.114-120
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• 2008

The pyrolysized carbon xerogel and aerogels were prepared from the sol-gel polymerization of resorcinol-formaldehyde(RF) followed by the dry process under ambient pressure and supercritical carbon dioxide condition respectively. The thermal behaviour of RF polymer xerogel was investigated with TGA analyzer to correspond with the pyrolysis process. The surface properties such as particle size, morphology and the point of zero charge of the pyrolysized porous carbon aerogels were studied for the precious metal catalyst supported media. It was found that the volume of the polymer aerogel decreased because of the significant linear shrinkage and weight loss of polymer gel during the carbonization. The point of zero charge of the carbon aerogel pyrolysized at $1050^{\circ}C$ under inert gas flow was about 10.

• Environmental Engineering Research
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• v.8 no.4
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• pp.222-227
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• 2003

• Journal of Electrochemical Science and Technology
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• v.8 no.3
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• pp.244-249
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• 2017

This paper presents the results of an investigation into the isoamperic point of cyclic voltammograms, which is defined as the singular point where the voltammograms of various scan rates converge. The origin of the unique point is first considered from a theoretical perspective by formulating the voltammetric curves as a system of linear equations, the solution of which indicates that a trivial solution is only available at the potential at which the net current is zero during the reverse potential scan. In addition, by way of a mathematical formulation, it was also shown that the isoamperic point is dependent on the switching potential of the potential scanning. To validate these findings, theoretical and practical cyclic voltammmograms were studied using finite-element based digital simulations and 3-electrode cell experiments. The new understanding of the nature of the isoamperic point provides an opportunity to measure the charge transfer effects without the influence of the mass transfer effects when determining the thermodynamic and kinetic characteristics of a faradaic system.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2002.04a
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• pp.38-43
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• 2002

A series of tests were performed to investigate the effects of pH and contamination level on cation exchange capacity and zeta potential in kaolinite loaded with lead. Test results show that cation exchange capacity of kaolinite is found to be in the range from 4 to 20meq/100g and it increased with increasing pH up to the converged number about 20meq/100g over pH 8. And then CEC has a tendency to reduce and converge to zero with increasing the concentration of Pb in the kaolinite surface. Moreover, zeta potential of kaolinite contaminated with lead is found to be in the range from -10 to 5mV, and zero point of charge is measured at about pH 3.5. Zeta potential of kaolinite contaminated with lead decreases with increasing pH values and decreasing Pb concentration of kaolinite.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2003.09a
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• pp.132-135
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• 2003

Solution chemistry, sorbate chemistry, and sorbent chemistry were widely investigated to find important factors that affect PAH sorption on mineral surfaces and to elucidate its microscopic mechanism. The solution chemistry, pH and ionic strength caused measurable change of HOC sorption reaction to minerals. The detectable change of Ka occurred at a pH region crossing the PZC (Point of Zero Charge) of each mineral. The PAH hydrophobicity, one of sorbate chemistry, was observed to have a strong correlation with PAM sorption to mineral. Mineral surface area was not found to be a predominant factor controlling PAH sorption. The mineral type might be more likely to play a crucial role in controlling the PAH sorption behavior. The CEC (Cation Exchange Capacity) of mineral, representing surface charge density, has meaningful correlation with regression slope of sorption coefficients (log $K_{d}$) versus aqueous activity coefficients (log Υ$_{w}$).).).

• Applied Biological Chemistry
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• v.37 no.5
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• pp.414-420
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• 1994

Birnessite, pyrolusite and hausmannite were synthesized and tested for the ability to oxidize Cr(III) to Cr(VI). These oxides differed in zero point of charge, surface area, and crystallinity. The kinetic study showed that Cr(III) oxidation on the Mn-oxide surface is a first-order reaction. The reaction rate was various for different oxide at different conditions. Generally the reaction by hausmannite, containing Mn(III), was faster than the others, and oxidation by pyrolusite was much slower. Solution pH and initial Cr(III) concentration had a significant effect on the reaction. Inhibited oxidation at higher pH and initial Cr(III) concentration could be due to the chance of Cr(III) precipitation or complexing on the oxide surface. Oxidations by birnessite and hausmannite were faster at lower pH, but pyrolusite exhibited increased oxidation capacity at higher pH in the range between 3.0 and 5.0. Reactions were also temperature sensitive. Although calculated activation energies for the oxidation reactions at pH 3.0 were higher than the general activation energy for diffusion, there is no experimental evidence to suggest which reaction is the rate limiting step.

• Economic and Environmental Geology
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• v.42 no.2
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• pp.95-105
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• 2009

Systematic studies are performed for arsenic adsorption on synthesized lepidocrocite. The synthesized lepidocrocite with high surface area of $94.8\;g/m^2$ has shown that the point of zero charge(PZC) is 6.57 determined by potentiometric titration, suggestive of high capacity of arsenic removal. Results show that arsenite[As(III)] uptake by synthesized lepidocrocite is greater than that of arsenate[As(V)] at pH $2{\sim}12$, indicating that the lepidocrocite has high affinity toward arsenite rather than arsenate. Adsorption of arsenate decreases with increasing pH from 2 to 12, whereas arsenite sorption increases until pH 8.0, and then decreases dramatically with increasing pH, suggesting that changes in surface charge of the lepidocrocite as a function of pH playa important role in aresinc uptake by the lepidocrocite. Upon kinetic experiments, our results demonstrate that both arsenite and arsenate sorption on the lepidocrocite increases rapidly for the first 4 h followed by little changes during the duration of the experiment, showing that adsorption plays a key role in aresenic uptake by the lepidocrocite. Our results also show that power function and elovich models are the best fit for the adsorption kinetics of arsenite and aesenate on the lepidocrocite.