• Bulletin of the Korean Chemical Society
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• v.31 no.6
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• pp.1596-1600
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• 2010

Surface functionalization of multi-walled carbon nanotubes (MWNTs) was carried out by means of acid treatment. The presence of oxygen functional groups on the surface of acid-treated MWNTs was confirmed with the aid of Fourier transform infrared spectroscopy and X-ray spectroscopy. In addition, carboxylic groups generally formed on the surface of acid-treated MWNTs, and the dispersion was increased by the duration of the acid treatment. The zeta-potential indicated the surface charge transfer and the dispersion of MWMTs. Morphological characteristics of acid-treated MWNTs were also observed using a transmission electron microscopy, X-ray diffraction, and Raman analysis, which was revealed the significantly unchanged morphologies of MWNTs by acid treatment. The hydrogen adsorption capacity of the MWNTs was evaluated by means of adsorption isotherms at 77 K/1 atm. The hydrogen storage capacity was dependent upon the acid treatment conditions and the formation of oxygen functional groups on the MWNT surfaces. The latter have an important effect on the hydrogen storage capacity.

• Journal of Microbiology and Biotechnology
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• v.14 no.5
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• pp.991-995
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• 2004

Immobilized sensor spots were applied for online measurement of dissolved $O_2$, in test tubes. Oxygen transport was quantified at varied shaking frequency and filling volumes. The k$_{L}$ a increased with increasing shaking frequency and decreasing filling volume. In non-baffled tubes the maximum $k_{L}a$ value was $70h^{-1}$, equivalent to a maximum $O_2$ transfer capacity of 15mMh^{-1}$. Monitoring of the hydrodynamic profile revealed that the liquid bulk rotated inside the tube with an inclined liquid surface, whereby the angle between the surface and tube wall increased with increasing shaking frequency. The $k_{L}a$ clearly correlated to the surface area. Placement of four baffles into the tubes improved the oxygen transfer up to 3-fold. The highest increase in $k_{L}a$ was observed at high filling volume and high shaking frequency. The maximum $k_{L}a$ in baffled tubes was $100 h^{-1}$.

• Journal of Hydrogen and New Energy
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• v.14 no.1
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• pp.24-34
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• 2003

For gaseous fuel combustion with inherent $CO_2$ capture and low NOx emission, chemical-looping combustion may yield great advantages for the savings of energy to $CO_2$ separation and suppressing the effect on environment, In chemical-looping combustor, fuel is oxidized by metal oxide medium in a reduction reactor. Reduced particles are transported to oxidation reactor and oxidized by air and recycled to reduction reactor. The fuel and the air are never mixed, and the gases from reduction reactor, $CO_2$ and $H_2O$, leave the system as separate stream. The $H_2O$ can be easily separated by condensation and pure $CO_2$ is obtained without any loss of energy for separation. In this study, five oxygen carrier particles such as NiO/bentonite, NiO/YSZ, $(NiO+Fe_2O_3)VYSZ$, $NiO/NiAl_2O_4$, and $Co_{\chi}O_y/CoAl_2O_4$ were examined &om the viewpoints of reaction kinetics, oxygen transfer capacity, and carbon deposition characteristics. Among five oxygen particles, NiO/YSZ particle is superior in reaction rate, oxygen carrier capacity, and carbon deposition to other particles. However, at high temperature ($>900^{\circ}C$), NiO/bentonite particle also shows enough reactivity and oxygen carrier capacity to be applied in a practical system.

• Korean Journal of Soil Science and Fertilizer
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• v.50 no.4
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• pp.203-214
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• 2017

Environmental toxicity due to cadmium (Cd) pollution in croplands causes critical problems worldwide. Rice (Oryza sativa L.) is an important crop in Asia, including South Korea, and numerous studies have evaluated the relationship between Cd and antioxidants to alleviate Cd uptake from the soil into plants. However, information about the relationship between phosphorus (P) and antioxidants in rice seedlings is still limited with regard to Cd phytotoxicity. We therefore investigated the physiological responses of rice (Oryza sativa L. cv 'Dongjin') seedlings to Cd toxicity and the effect of P application on reactive oxygen species (ROS) and antioxidant changes. The exposure of rice seedlings to $30{\mu}M$ Cd inhibited plant growth; increased the contents of superoxide, hydrogen peroxide, and malondialdehyde; and induced Cd uptake by the roots and leaves. Application of P to Cd-exposed seedlings decreased Cd-induced oxidative stress by enhancing the capacity of ascorbate (AsA) production and ROS-scavenging, and decreased Cd transfer from the roots to the leaves. These results suggest that P application alleviated Cd-induced growth inhibition and oxidative damage by restricting Cd translocation from the roots to the leaves and maintaining sufficient levels of AsA.

• Korean Chemical Engineering Research
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• v.45 no.5
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• pp.506-514
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• 2007

To select the best oxygen carrier particle for syngas fueled chemical-looping combustor, the reduction reactivity and carbon deposition characteristics were determined in a thermogravimetric analyzer. Four kinds of oxygen carrier particles (NiO/bentonite, $NiO/LaAl_{11}O_{18}$, $Co_xO_y/CoAl_2O_4$, $NiO/NiAl_2O_4$) were tested with the simulated syngas (30% $H_2$, 10% $CO_2$, 60% CO) as a reduction gas. With each of these particles, the maximum conversion and oxygen transfer capacity increase with increasing the reduction temperature At the given experimental range, the optimum operating temperature to maximize oxygen transfer rate is found to be $900^{\circ}C$ and carbon deposition on the particles could avoid at the temperature above $800^{\circ}C$. Among four kinds of oxygen carrier particles, the NiO-based particles exhibits better reactivity than the CoO-based particle. Moreover, the NiO/bentonite particle produces the best reactivity based on the oxygen transfer rate and the degree of carbon deposition. The measured oxygen transfer rate increases as the metal oxide content in NiO/bentonite particle is increased thereby higher metal oxide contents could provide stable operation of chemical-looping combustor.

• Journal of Environmental Science International
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• v.24 no.7
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• pp.947-954
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• 2015

Dielectric barrier discharge plasma is a new technique in water pollutant degradation, which that is characterized by the production of chemically active species such as hydroxyl radicals, ozone, hydrogen peroxide, etc. If dissolving of plasma gas generated in the plasma reaction has increased, it is possible to increase the contaminant removal capacity. In this study, the improvement on the dissolving performance of plasma gas was evaluated by the indirect method measuring the overall oxygen transfer coefficient. Experiments were conducted to examine the effects of nozzle type, distance from water surface, air supply rate and liquid circulation rate. The experimental results showed that the $K_{La}$ value of the 3-prong nozzle is 2.67 times higher than the diffuser. The order of $K_{La}$ value with nozzle type ranked in the following order: 3-prong nozzle (inner diameter, less 1 mm) > circular nozzle (inner diameter, 1.5 mm) > ellipse nozzle (short diameter 1 mm, long diameter 2.5 mm) > circular nozzle (inner diameter, 3 mm). Optimal liquid circulation rate was appeared to be 1.7 L/min, the value of $K_{La}$ was 0.510 1/min. The value of $K_{La}$ with increasing air supply rate was revealed in the form of an exponential such as $K_{La}=0.3581e^{0.2919^*air\;flow\;rate}$.

• Journal of Hydrogen and New Energy
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• v.15 no.3
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• pp.208-219
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• 2004

To find a suitable oxygen carrier particle for a 50kW chemical-looping combustor, which was designed and installed to demonstrate continuous oxidation and reduction, three oxygen carrier particles(NiO/bentonite, $NiO/NiAl_2O_4$, $CoO_x/CoAl_2O_4$) were prepared. The reactivity and the attrition resistance of particles were measured and investigated by a thermo-gravimetrical analyzer and an attrition test apparatus respectively. From the viewpoints of oxygen transfer capacity, optimum reaction temperature(operating temperature range), reaction rate, carbon deposition rate, and attrition resistance, NiO/bentonite particle showed better performance than the other particles, therefore we selected NiO/bentonite particle as an optimum oxygen carrier particle.

• Proceedings of the Korean Society of Crop Science Conference
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• 2017.06a
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• pp.187-187
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• 2017

Cadmium (Cd) pollution is rapidly increasing in worldwide due to industrialization and urbanization. In addition to its negative effects on the environment, Cd pollution adversely affects human health. Rice (Oryza sativa L.) is an important agricultural crop worldwide, including South Korea, and studies have examined its ability to alleviate Cd uptake from the soil into plants. However, information about the relationship between sulfur (S) and antioxidants in rice seedlings is still limited with regard to Cd phytotoxicity. We therefore investigated the changes in reactive oxygen species (ROS) and antioxidants in rice (Oryza sativa L. 'Dongjin') seedlings exposed to toxic Cd, S treatment, or both. The exposure of rice seedlings to $30{\mu}M$ Cd inhibited plant growth; increased the contents of superoxide, hydrogen peroxide, and malondialdehyde (MDA); and induced Cd uptake by the roots, stems, and leaves. Application of S to Cd-stressed seedlings decreased Cd-induced oxidative stress by increasing the capacity of the glutathione (GSH)-ascorbate (AsA) cycle, promoted S assimilation by increasing cysteine, GSH, and AsA contents in treated plants, and decreased Cd transfer from the roots to the stems and leaves. In conclusion, S application of plants under Cd stress promoted Cys and GSH biosynthesis and GSH-AsA cycle activity, thereby lowering the rate of Cd transfer to plant shoots and promoting the scavenging of the ROS that resulted from Cd toxicity, thus alleviating the overall Cd toxicity. Therefore, these results provide insights into the role of S in regulating the tolerance, uptake, and translocation of Cd in rice seedlings. The results of this study indicate that S application should have potential as a tool for mitigating Cd-stress in cereal crops, especially rice.

• Journal of Hydrogen and New Energy
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• v.26 no.6
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• pp.600-608
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• 2015

As a candidate for cheap oxygen carrier, $CaSO_4$ based oxygen carriers have been developing. However, research on reaction characteristics and side reaction of $CaSO_4$ based oxygen carrier is very limited. There are many possible reactions for main components of syngas from coal. In this study, we prepared three $CaSO_4$ based oxygen carriers ($CaSO_4$-$Fe_2O_3$/bentonite, $CaSO_4$-$K_2CO_3$/bentonite, $CaSO_4$-CaO/bentonite) and performed reduction tests by hydrogen. Cyclic reduction-oxidation tests up to $5^{th}$ cycle are also conducted using hydrogen as fuel. Reduction reactivity of those $CaSO_4$ based oxygen carriers were compared with that of NiO based oxygen carrier (OCN703-1100). Real weight change fractions of $CaSO_4$ based oxygen carriers were higher than theoretical oxyen transfer capacity and reactivity of these particles decreased with the number of cycle increased. To check possible side reaction of $CaSO_4$ based oxygen carriers, $CaSO_4$ decomposition tests were carried out and $SO_2$ was detected even at $700^{\circ}C$. Consequently, we could conclude that $CaSO_4$ based oxygen carriers decompose and release $SO_2$ and this reaction lead reactivity decay of $CaSO_4$ based oxygen carries.

• Korean Chemical Engineering Research
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• v.59 no.2
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• pp.276-280
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• 2021

The oxygen transfer rate at the liquid surface of the reciprocally shaking vessel was studied. The required power of the reciprocally shaking vessel was not proportional to the shaking frequency, unlike the rotational shaking vessel, and the liquid level suddenly fluctuated greatly at a certain frequency as the flow pattern in the vessel was a left and right wave flow different from that of the rotational shaking that has a rotational flow. The effect of the shaking frequency on the required power in the reciprocally shaking vessel was very complex, such as less power required than the rotational shaking vessel when the shaking frequency is more than 3 s-1, but the required power for the range of the generated rotational flow in the reciprocally shaking vessel could be correlated with the equation that was reported for the rotational shaking vessel. The kLa (mass transfer capacity coefficient) in the reciprocally shaking vessel also increased in a complex pattern because the required power for shaking was not consumed in a simple pattern, unlike kLa in the rotational shaking vessel, which increases linearly with increasing frequency. The kLa of the reciprocally shaking vessel was larger than the kLa of the rotational shaking vessel, and as the kLa value increased, the difference between them increased sharply. As a result, the oxygen transfer rate in the reciprocal motion was greater than that of the rotational motion, and could be correlated with the required power per unit volume.