• Journal of Korean Society for Atmospheric Environment
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• 제17권E2호
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• pp.35-42
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• 2001

Recent development of photocatalytic degradation method that is mediated by TiO$_2$ is of interest in the treatment of volatile organic compounds(VOCs). In this study, trichloroethylene(TCE) and acetone were closely examined in a batch scale of photo-reactor as a function of water vapor, oxygen, and temperature. Water vapor inhibited the photocatalytic degradation of acetone, while there was an optimum concentration in TCE. A lower efficiency was found in nitrogen atmosphere than air, and the effect of oxygen on photocatalytic degradation of acetone was greater than on that of TCE. The optimum reaction temperature on photocatalytic degradation was about 45$^{\circ}C$ for both compounds. NO organic byproducts were detected for both compounds under the present experimental conditions. It was ascertained that the photocatalytic reaction in a batch scale of photo-reactor was very effective in removing VOCs such as TCE and acetone in the gaseous phase.

• Bulletin of the Korean Chemical Society
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• 제33권8호
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• pp.2669-2674
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• 2012

Crown ether is one of well-known host molecules and able to selectively sequester metal cation. We employed M06-2X density functional theory with IEFPCM and SMD continuum solvation models to study selectivity of dibenzo-18-crown-6-ether (DB18C6) for alkaline earth dications, $Ba^{2+}$, $Sr^{2+}$, $Ca^{2+}$, and $Mg^{2+}$ in the gas phase and in aqueous solution. $Mg^{2+}$ showed predominantly strong binding affinity in the gas phase because of strong polarization of CO bonds by cation. In aqueous solution, binding free energy differences became smaller among these dications. However, $Mg^{2+}$ had the best binding, being incompatible with experimental observations in aqueous solution. The enthalpies of the dication exchange reaction between DB18C6 and water cluster molecules were computed as another estimation of selectivity in aqueous solution. These results also demonstrated that $Mg^{2+}$ bound to DB18C6 better than $Ba^{2+}$. We speculated that the species determining selectivity in water could be 2:1 complexes of two DB18C6s and one dication.

• Bulletin of the Korean Chemical Society
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• 제31권11호
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• pp.3283-3290
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• 2010

The gas-phase dehydration of glycerol to acrolein was carried out over 10 wt % HSiW catalysts supported on different supports, viz. $\gamma-Al_2O_3$, $SiO_2-Al_2O_3$, $TiO_2$, $ZrO_2$, $SiO_2$, AC, $CeO_2$ and MgO. The same reaction was also conducted over each support without HSiW for comparison. Several characterization techniques, $N_2$-physisorption, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), the temperature-programmed desorption of ammonia ($NH_3$-TPD), temperature-programmed oxidation (TPO) with mass spectroscopy and CHNS analysis were employed to characterize the catalysts. The glycerol conversion generally increased with increasing amount of acid sites. Ceria showed the highest 1-hydroxyacetone selectivity at $315^{\circ}C$ among the various metal oxides. The supported HSiW catalyst showed superior catalytic activity to that of the corresponding support. Among the supported HSiW catalysts, HSiW/$ZrO_2$ and HSiW/$SiO_2-Al_2O_3$ showed the highest acrolein selectivity. In the case of HSiW/$ZrO_2$, the initial catalytic activity was recovered after the removal of the accumulated carbon species at $550^{\circ}C$ in the presence of oxygen.

• Bulletin of the Korean Chemical Society
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• 제28권6호
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• pp.1031-1034
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• 2007

The R- and Z-substituent effects for the gas-phase thermal decompositions of carbamates, R2NC(=O)- OCH2CH2Z, have been investigated theoretically at B3LYP level with 6-31G(d) and 6-31++G(d,p) basis sets. Both the Z- and R-substituent effects on reactivity (ΔH≠) were well consistent with experimental results, although the R-substituent effect was underestimated theoretically. No correlations were found between activation enthalpies and reaction enthalpies. The substituent effects on reactivity seemed to be complicated at a glance, but were understandable by concurrent electronic and steric factors. Variations of bond lengths at TS structures were well correlated with the Taft's σ* values and the TS structures became tighter as the Zsubstituent became a stronger electron-acceptor (δσ* > 0). However the effects of R-substituents on the TS structures were much smaller when compared to those of Z-substituents.

• 한국자기학회지
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• 제18권6호
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• pp.217-220
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• 2008

Rare-earth iron oxide $ErFe_2O_4$의 다결정체 시료의 자기적 특성을 연구하였다. 단일상의 다결정체 $ErFe_2O_4$ 시료를 CO/$CO_2$ gas 분위기에서 고체상태반응법으로 합성하였다. X-ray diffraction 측정을 통해 $ErFe_2O_4$ 시료는 space group R3m Rhombohedral 구조를 가지며, 온도에 의존하는 magnetization 측정을 통해 250 K에서는 자기적 전이가, 220 K에서는 구조적 전이가 일어나는 2단계 상전이 현상을 확인하였다.

• Bulletin of the Korean Chemical Society
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• 제22권1호
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• pp.25-29
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• 2001

Nucleophilic substitution reactions of O-imidomethyl derivatives of phenols with OH- were studied theoretically using the semiempirical AM1 and Solvation Model 2.1 (SM2.1) methods in the gas phase and aqueous solution, respectively. In the gas phase, the two reaction paths, in which the imide (1a) or phenol (1b) is functioning as a leaving group, can occur competitively. In contrast, in aqueous solution, path (1b) becomes more favorable than (1a) because the transition states (TS) of path (1b) are more stabilized by solvent. Differences in solvation energies are caused by the structural differences of TS, i.e., the TS via path (1b) is more dissociative than that via path (1a). Therefore we conclude that the solvent effects play an important role in the hydrolysis of O-imidomethyl derivatives of phenols. However, reactivity is dependent on the acidities of both the imide and the phenol fragments since the ρz values vary progressively from 4.2 (Z' = I) to 2.5 (Z' = IV) as the acidities of imide increase. These are in good agreement with the experimental results.

• Asian Journal of Atmospheric Environment
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• 제5권2호
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• pp.97-104
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• 2011

Recent studies have indicated that the observed nitric acid ($HNO_3$) uptake rates ($R_{HNO_3}$) onto dust particles are much slower than $R_{HNO_3}$ used in the previous modeling studies. Three factors that possibly affect $R_{HNO_3}$ onto dust particles are discussed in this study: (1) the magnitude of reaction probability of $HNO_3$ (${\gamma}_{HNO_3}$), (2) aerosol surface areas, and (3) gas-phase $HNO_3$ mixing ratio. Through the discussion presented here, it is shown that the use of accurate ${\gamma}_{HNO_3}$ is of primary importance. We suggest that the use of ${\gamma}_{HNO_3}$ values between $\sim10^{-3}$ and $\sim10^{-5}$ produces more realistic results than the use of ${\gamma}_{HNO_3}$ values between $\sim10^{-1}$ and $\sim10^{-2}$ does, more accurately modeling the nitrate formation characteristics on/in dust particles. We also discuss two different types of aerosol surface area, active and geometric, since the use of different aerosol surface areas often leads to an erroneous result in $R_{HNO_3}$. In addition, the levels of the gas-phase $HNO_3$ are investigated with the example cases of TRACE-P DC-8 flights in East Asia. The $HNO_3$ levels were found to be relatively high, indicating that they can not limit nitrate formation in dust particles.

• 대한방사성의약품학회지
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• 제8권2호
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• pp.95-101
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• 2022

Microfluidic radioimmunoassay (RIA) platform called µ-RIA spends less reagent and shorter reaction time for the analysis compared to the conventional tube-based radioimmunoassay. This study reported the design of µ-RIA chips optimized for the gamma counter which could measure the small samples of radioactive materials automatically. Compared with the previous study, the µ-RIA chips developed in this study were designed to be compatible with conventional RIA test tubes. And, the automatic gamma counter could detect radioactivity from the ¹²⁵I labeled anti-PSA attached to the chips. Effects of the multi-layer microchannels and two-phase flow in the µ-RIA chips were investigated in this study. The measured radioactivity from the ¹²⁵I labeled anti-PSA was linearly proportional to the number of stacked chips, representing that the radioactivity in µ-RIA platform could be amplified by designing the chips with multi-layers. In addition, we designed µ-RIA chip to generate liquid-gas plug flow inside the microfluidic channel. The plug flow can promote binding of the biomolecules onto the microfluidic channel surface with recirculation in the liquid phase. The ratio of liquid slug and air slug length was 1 : 1 when the ¹²⁵I labeled anti-PSA and the air were injected at 1 and 35 µL/min, respectively, exhibiting 1.6 times higher biomolecule attachment compared to the microfluidic chip without the air injection. This experimental result indicated that the biomolecular reaction was improved by generating liquid-gas slugs inside the microfluidic channel. In this study, we presented a novel µ-RIA chips that is compatible with the conventional gamma counter with automated sampler. Therefore, high-throughput radioimmunoassay can be carried out by the automatic measurement of radioactivity with reduced radiowaste generation. We expect the µ-RIA platform can successfully replace conventional tube-based radioimmunoassay in the future.

• 한국세라믹학회지
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• 제40권2호
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• pp.146-152
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• 2003

지구온난화의 주요 원인인 $CO_2$를 분해시키기 위하여 Ni-Zn 페라이트와 Mn-Zn 페라이트 코어 제조시 대량으로 배출되는 페라이트 폐기물을 이용하였다. 폐기물 페라이트와 페라이트 코어 완제품인 Ni-Zn 페라이트와 Mn-Zn 페라이트는 5% $H_2$/Ar과의 환원반응에서 14~16wt%가 환원되었다. 환원된 페라이트를 이용한 $CO_2$분해 반응에서는 세 종류의 페라이트 모두 약 11wt%에 해당하는 $CO_2$를 분해하였다. 이 반응에서 $CO_2$는 환원된 페라이트 중 Fe와 FeO치 산화에 의해 분해되었으며. 폐기물 페라이트의 경우 $CO_2$분해 반응 후 스피넬 결정상을 형성하였다. 대량으로 버려지는 폐기물 페라이트를 이용하여 저비용으로 $CO_2$분해가 가능한 폐기물 활용기술을 개발하였다.

• 한국수소및신에너지학회논문집
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• 제18권2호
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• pp.132-139
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• 2007

Popular techniques for producing synthesis gas by converting methane include steam reforming and catalyst reforming. However, these are high temperature and high pressure processes limited by equipment, cost and difficulty of operation. Low temperature plasma is projected to be a technique that can be used to produce high concentration hydrogen from methane. It is suitable for miniaturization and for application in other technologies. In this research, the effect of changing each of the following variables was studied using an AC Glidarc system that was conceived by the research team: the gas components ratio, the gas flow rate, the catalyst reactor temperature and voltage. Glidarc plasma reformer was consisted of 3 electrodes and an AC power source. And air was added for the partial oxidation reaction of methane. The result showed that as the gas flow rate, the catalyst reactor temperature and the electric power increased, the methane conversion rate and the hydrogen concentration also increased. With $O_2/C$ ratio of 0.45, input flow rate of 4.9 l/min and power supply of 1 kW as the reference condition, the methane conversion rate, the high hydrogen selectivity and the reformer energy density were 69.2%, 36.2% and 35.2% respectively.