• Bulletin of the Korean Chemical Society
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• 제33권2호
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• pp.519-523
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• 2012

A kinetic study is reported on nucleophilic displacement reactions of benzyl 2-pyridyl carbonate 6 with alkalimetal ethoxides, EtOM (M = Li, Na, and K), in anhydrous ethanol at $25.0{\pm}0.1^{\circ}C$. The plots of pseudo-firstorder rate constant $k_{obsd}$ vs. [EtOM] curve upward, a typical phenomenon reported previously for alkaline ethanolysis of esters in which alkali-metal ions behave as a Lewis-acid catalyst. The kobsd value for the reaction of 6 with a fixed EtOK concentration decreases rapidly upon addition of 18-crown-6-ether (18C6), a complexing agent for $K^+$ ion up to [18C6]/[EtOK] = 1.0 and then remains constant thereafter, indicating that the catalytic effect exerted by K+ ion disappears in the presence of excess 18C6. The reactivity of EtOM towards 6 increases in the order $EtO^-$ < EtOLi < EtONa < EtOK, which is contrasting to the reactivity order reported for the corresponding reactions of 2-pyridyl benzoate 4, i.e., $EtO^-$ < EtOK < EtONa < EtOLi. Besides, 6 is 1.7 and 3.5 times more reactive than 4 towards dissociated $EtO^-$ and ion-paired EtOK, respectively. The reactivity difference and the contrasting metal-ion selectivity are discussed in terms of electronic effects and transition-state structures.

• Korean Chemical Engineering Research
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• 제46권6호
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• pp.1063-1068
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• 2008

화학기상증착법으로 제조된 $TiO_2$ 광촉매 볼을 이용하여 마이크로웨이브와 자외선을 동시에 조사시켜 메틸렌블루 수용액의 광촉매 분해실험을 하였다. 광촉매반응에 마이크로웨이브와 자외선을 같이 사용하기 위하여 마이크로웨이브에 의해 방전되는 무전극자외선램프를 개발하였다. 실험결과 마이크로웨이브의 강도, 반응수용액의 순환유속 그리고 산화보조제의 첨가량이 증가할수록 광촉매분해속도가 증가하였다. 특히 과산화수소를 첨가한 광촉매반응에 마이크로웨이브를 부가한 실험의 반응속도상수는 $0.0197min^{-1}$이고 광촉매반응에 과산화수소만을 첨가한 경우의 속도상수는 $0.0061min^{-1}$로 약 3배정도 높은 값을 나타내었다. 본 연구의 결과로부터 광촉매반응에 마이크로웨이브가 미치는 영향을 정량적으로 평가하기는 어렵지만, 과산화수소가 첨가되는 광촉매반응에 마이크로웨이브의 조사가 매우 중요한 인자인 것을 알 수 있었다.

• Bulletin of the Korean Chemical Society
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• 제23권1호
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• pp.123-131
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• 2002

Solvolyses rate constant of 1- and 2- naphthoyl chlorides (1 and 2) are reported for aqueous binary mixtures with methanol, ethanol, fluorinated alcohol, acetonitrile and dioxane. Kinetic solvent isotope effects (KISE) in methanol and product selectivities (S) of 2-naphthoyl chloride (2) in alcohol-water are also reported. Dispersions in Grunwald-Winstein correlations $(r{\leq}0.901)$ are discussed by multiple regression analysis incorporating ionizing power $(Y_{Cl})$ scale and rate-rate profiles. Major causes for these phenomena are investigated as an aromatic ring solvation effects, in conjunction with weakly nucleophilic solvation effects ($S_N2$ character), for solvolyses of 1 and for solvolyses of 2, as dual reaction channels, described as $S_N1$-$S_N2$ and $S_AN$-$S_N2$ processes. Distinct border lines between the two pathways are derived from solvolyses rates of 2 in 18 solvent using the results of $log(k/k_o)=mY_{Cl}+lN_T+hI$ plot with values of 1.13 for m, 0.37 for l and 0.15 for h value in 5 aqueous fluorinated alcohol mixtures. Using rate-product correlation, the validity of a third order model based on a general base catalyzed by solvent and contribution from these rate constants, $k_{aa},\;k_{aw}$ and $k_{aw}$, are investigated for $S_AN$-$S_N2$ solvolyses of 2 favored in more rich alcohol media and gradual addition of water to alcohol solvent shows a great shift away from stoichiometric solvation to predominantly medium effects. Rate-rate correlation between solvolyses of 2 and trimethyl acetylchloride (5) with alkyl group in the 29 aqueous solvent mixtures shows appreciable linearity (slope = 0.84, r = 0.987), caused by the same pathway ($S_N1$-$S_N2$ process), even if this correlation coincides with appreciable dispersion (different solvation effect).

• 한국재료학회지
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• 제14권12호
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• pp.840-845
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• 2004

Tin dioxide ($SnO_2$) thin films were prepared on Si(100) substrate by PE-ALD using the $DBDTA((CH_{3}CO_2)_{2}Sn[(CH_2)_{3}CH_3]_2)$ Precursor. The properties were studied as a function of source temperature, substrate temperature, and purging time. Scanning probe microscopic images at the source temperature $50^{\circ}C$ and the substrate temperature $300^{\circ}C$ shows lower roughness than those $40/60^{\circ}C$ source and $200/400^{\circ}C$ substrate temperature samples. The purging time for optimum process was 8sec and the deposition rate was about 1 nm per 10 cycles. The conductance of $SnO_2$ thin film showed a constant region in the range of $200^{\circ}C\;to\;500^{\circ}C$. The thin films deposited for 200 cycle show a better sensitivity to CO gas.

• 한국재료학회지
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• 제31권10호
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• pp.552-561
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• 2021

For the purpose of manufacturing a high efficiency TiO₂ photocatalyst, B-doped TiO₂ photocatalysts are synthesized using a plasma electrolytic oxidation method in 0.5 M H₂SO₄ electrolyte with different concentrations of H₃BO₃ as additive. For the B doped TiO₂ layer fabricated from sulfuric electrolyte having a higher concentration of H₃BO₃ additive, the main XRD peaks of (101) and (200) anatase phase shift gradually toward the lower angle direction, indicating volume expansion of the TiO₂ anatase lattice by incorporation of boron, when compared with TiO₂ layers formed in sulfuric acid with lower concentration of additive. Moreover, XPS results indicate that the center of the binding energy peak of B1s increases from 191.45 eV to 191.98 eV, which suggests that most of boron atoms are doped interstitially in the TiO₂ layer rather than substitutionally. The B doped TiO₂ catalyst fabricated in sulfuric electrolyte with 1.0 M H₃BO₃ exhibits enhanced photocurrent response, and high efficiency and rate constant for dye degradation, which is ascribed to the synergistic effect of the new impurity energy band induced by introducing boron to the interstitial site and the improvement of charge transfer reaction.

• Bulletin of the Korean Chemical Society
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• 제15권7호
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• pp.563-567
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• 1994

The electroreduction of dioxygen at glassy carbon electrodes with irreversible self-assembly of N-hexadecyl-N'-methyl viologen $(C_{16}VC_1)$ proceeds at potentials more positive than those where the reduction occurs at bare electrodes. The electrocatalyzed reduction takes place at potentials well ahead of those where the catalyst is reduced in the absence of dioxygen and the limiting currents observed at rotating disk electrodes did not deviate from the thoretical Levich line up to 6400 rpm, indicating that the electrocatalysis is extremely rapid. The rate constant for the heterogeneous reaction between $C_{16}V^+C_1$ immobilized on the electrode surface and $O_2$ in solution was estimated to be ca. $10^8\;M^{-1}s^{-1}$. The half-wave potential of dioxygen reduction was independent of solution pH.

• 한국재료학회지
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• 제10권6호
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• pp.450-455
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• 2000

실리콘 소자가 더욱 미세화되면서, 발생되는 power consumption, crosstalk와 interconnection delay 등을 감소시키기 위해 $SiO_2$ 대신에 저유전 상수막의 적용이 고려되어진다. 본 논문에서는, 저유전 상수 층간 절연막 재료로 유망한 폴리이미드의 식각 특성에 $O_2/SF_6$ 가스가 미치는 영향을 연구하였다. 폴리이미드의 식각률을 SF(sub)6 가스의 첨가에 따라 산소와 hydrocarbon 폴리머 간의 반응을 억제하는 비휘발성 물질은 fluorine 화합물의 형성에 의해 감소되었다. 반면에, 기판 전극의 전압 증가는 물리적인 충격을 통해 식각 공정을 증가시켰다. 또한 작은 량의 SF(sub)6 가스 첨가는 식각 topography에 바람직하였다. 폴리이미드 식각을 위한 $SiO_2$ hard mask 사용은 산소 플라즈마 식각 하에서 효과적이었다(선택비-30). 반면에 $O_2SF_6$ 가스 조성은 식각 선택비를 4로 저하시키게 되었다. 이러한 결과를 기초로, $1-2\mu\textrm{m}$ 선폭을 가진 PI 2610의 식각을 원활히 수행할 수 있었다.

• 대한화학회지
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• 제31권4호
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• pp.344-351
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• 1987

$[Mo_2O_4(H_2O)_6]^{2+}$와 티오시안산과의 착물생성에 대한 속도론적 연구는 분광광도법으로 수행하였다. 이 반응의 관찰된 속도상수 $k_{obsd}$는 다음과 같이 주어진다. $k_{obsd}=\{\\k_0+k_H[H^+]\}\;[SCN^-]^2+k_r$. 이온세기가 2.84이고 온도가 $25^{\circ}C$일때 $k_f$와 $k_r$의 값은 각각 $5.96{\pm}0.35\;M^{-2}s^{-1}$ 과 $(5.45{\pm}4.77){\times}10^{-4}s^{-1}$이다. $20^{\circ}$∼$35^{\circ}C$일 때 활성화파라미터는 ${\Delta}H^*=38.04{\pm}5.31kJmol^{-1}$ 이고 ${\Delta}S^*=-172.69JK^{-1}mol^{-1}$ 이다. 이들 반응의 메카니즘에 대하여 논의 된다.

• Environmental Engineering Research
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• 제24권4호
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• pp.646-653
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• 2019

Recovery of valuable metals in the industrial wastewater and sludge has attracted an attention owing to limited metallic resources in the earth. In this study, we firstly fabricated Ti/Ir-Ru electrodes by spin coating technique for effective recovery of Cu in electrowinning process. Two different Ti/Ir-Ru electrodes were fabricated using 100 and 500 mM of precursors (i.e., Ir-Ru). SEM-EDX and AFM revealed that Ir and Ru were homogenously distributed on the surface of Ti plate by the spin coating, in particular the electrode prepared by 500 mM showed distinct boundary line between Ir-Ru layer and Ti substrate. XRD, XPS, and cyclic voltammetry also revealed that characteristics of IrO₂, RuO₂, and TiO₂ and its electrocatalytic property increased as the concentration of coating precursor increased. Finally, we carried out Cu recovery experiments using two Ti/Ir-Ru as anodes in electrowinning process, showing that both anodes showed a complete removal of Cu (1 and 10 g/L) within 6 h reaction, but much higher kinetic rate constant was obtained by the anode prepared by 500 mM. The findings in this study can provide a fundamental knowledge for surface characteristics of Ti/Ir-Ru electrode prepared by spin coating method and its potential feasibility for effective electrowinning process.

• 한국수소및신에너지학회논문집
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• 제15권1호
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• pp.46-53
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• 2004

Redox characteristics of cobalt oxide-based oxygen carriers were tested for chemical-looping combustion. Cobalt oxide was chosen as active metal oxide and $CoAl_2O_4$ was compared with YSZ(yttria-stabilized zirconia) as a binder. Cobalt oxide/$CoAl_2O_4$ was prepared by sol-gel method. Hydrogen fuel was reacted with metal oxide and then the reduced metal was successively oxidized by air. The effects of reaction temperature were measured and the regenerabilies during 10 cycles were examined by a TGA. In regenerability of cobalt oxide/YSZ and cobalt oxide/$CoAl_2O_4$, after they showed above 90% conversion in first reduction, they were stabilized in about 70-75% conversion. From reaction rate constant obtained, the activation energies of cobalt oxide/YSZ in oxidation and reduction were 51.47kJ/mol and 7.71kJ/mol respectively.