• 한국재료학회지
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• 제31권12호
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• pp.710-718
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• 2021

Recently, due to high theoretical capacitance and excellent ion diffusion rate caused by the 2D layered crystal structure, transition metal hydroxides (TMHs) have generated considerable attention as active materials in supercapacitors (or electrochemical capacitors). However, TMHs should be designed using morphological or structural modification if they are to be used as active materials in supercapacitors, because they have insulation properties that induce low charge transfer rate. This study aims to modify the morphological structure for high cycling stability and fast charge storage kinetics of TMHs through the use of nickel cobalt hydroxide [NiCo(OH)₂] decorated on nickel foam. Among the samples used, needle-like NiCo(OH)₂ decorated on nickel foam offers a high specific capacitance (1110.9 F/g at current density of 0.5 A/g) with good rate capability (1110.9 - 746.7 F/g at current densities of 0.5 - 10.0 A/g). Moreover, at a high current density (10.0 A/g), a remarkable capacitance (713.8 F/g) and capacitance retention of 95.6% after 5000 cycles are noted. These results are attributed to high charge storage sites of needle-like NiCo(OH)₂ and uniformly grown NiCo(OH)₂ on nickel foam surface.

• 대한화학회지
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• 제36권1호
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• pp.3-15
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• 1992

크롬이움, 몰리브덴늄, 텅그스텐의 carbene 착물인 $(CO)_5Cr=CCHCH_2(XCH_3)\;,\;(CO)_5Mo=CCHCH_2(XCH_3)\;,\;(CO)_5W=CCHCH_2(XCH_3)$에 대해서 확장된 Huckel 방법으로 계산하여 이들의 전자구조와 반응성 등을 고찰하였다. fragment들의 궤도함수 상관도로부터 M=Ccarb 이중결합의 특성을 알 수 있다. M=Ccarb 이중결합의 ${\sigma}$결합은 carbene의 HOMO로부터 $(CO)_5M$의 LUMO로 전자가 이동하므로 형성되고 ${\pi}$결합은 전이금속의 축퇴된 d${\pi}$ 궤도함수로부터 carbene의 LUMO로 전자가 역이동하므로서 형성된다. M=Ccarb 결합에서 전하분극은 Mo, W-착물에 대해서 M쪽이 더욱 양으로 계산되었다. 화학적 또는 물리적 성질은 carbene 탄소원자의 양전하에 의하여 결정되며 carbene 탄소원자의 친전자적 반응성은 전하에 의해서가 아니라 frontier orbital의 LUMO에 의해서 지배받는다.

• Bulletin of the Korean Chemical Society
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• 제31권5호
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• pp.1199-1203
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• 2010

Second-order rate constants ($k_N$) have been measured spectrophotometrically for Michael-type reactions of 1-(X-substituted phenyl)-2-propyn-1-ones (2a-f) with a series of alicyclic secondary amines in MeCN at $25.0{\pm}0.1^{\circ}C$. The $k_N$ value increases as the incoming amine becomes more basic and the substituent X changes form an electron-donating group (EDG) to an electron-withdrawing group (EWG). The Br${\o}$nsted-type plots are linear with ${\beta}_{nuc}$ = 0.48 - 0.51. The Hammett plots for the reactions of 2a-f exhibit poor correlations but the corresponding Yukawa-Tsuno plots result in much better linear correlations with ${\rho}$ = 1.57 and r = 0.46 for the reactions with piperidine while ${\rho}$ = 1.72 and r = 0.39 for those with morpholine. The amines employed in this study are less reactive in MeCN than in water for reactions with substrates possessing an EDG, although they are ca. 8 pKa units more basic in the aprotic solvent. This indicates that the transition state (TS) is significantly more destabilized than the ground state (GS) in the aprotic solvent. It has been concluded that the reactions proceed through a stepwise mechanism with a partially charged TS, since such TS would be destabilized in the aprotic solvent due to the electronic repulsion between the negative-dipole end of MeCN and the negative charge of the TS. The fact that primary deuterium kinetic effect is absent supports a stepwise mechanism in which proton transfer occurs after the rate-determining step.

• 대한화학회지
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• 제31권6호
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• pp.520-526
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• 1987

피리디니움 옥소이소치오시안네이토 몰리브데이트(V)와 아민 카르복실기를 가진 이미노디아세틱액시드 유도체를 반응시켜 아민 카르복실기를 가진 디옥소-디-뉴우-옥소-디몰리브데이트(V) 착물을 합성하였다. 이들에 대한 원소분석, 스펙트라의 해석 그리고 전기전도도의 측정으로 부터 착물의 성질과 그 구조를 추정하였다. 적외선 스펙트라에서 $Mo=O_t$ 신축진동에 기인한 두 개의 흡수띠가 900~$980cm^{-1}$ 영역에서 관찰되었으며, $MoO_2Mo$의 비대칭신축진동 및 대칭신축진동은 720~$750cm^{-1}$, 440~$485cm^{-1}$ 에서 각각 나타났었고, 카르복실기와 금속결합간의 비대칭 신축진동이 1585~$1,640cm^{-1}$에서 흡수띠가 관찰되었다. 전자흡수스펙트럼 결과 $^2B_2{\to}^2B_1$의 결정장 전이는 24,800∼$28,000cm^{-1}$, 전하이동 전이는 32,500~$33,800cm^{-1}$, 42,000~$47,500cm^{-1}$에서 각각 나타났다. 이들 착물은 노란색 혹은 오렌지색이며 반자성체 물질이였다.

• 한국표면공학회지
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• 제56권3호
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• pp.201-207
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• 2023

Eu³⁺-doped SnO² (SnO²:Eu³⁺) phosphor thin films were grown on quartz substrates by radio-frequency magnetron sputtering. The deposition temperature was varied from 100 to 400 ℃. The X-ray diffraction patterns showed that all the thin films had two mixed phases of SnO₂ and Eu₂Sn₂O₇. The 880 nmthick SnO²:Eu³⁺ thin film grown at 100 ℃ exhibited numerous pebble-shaped particles. The excitation spectra of SnO²:Eu³⁺ thin films consisted of a strong and broad peak at 312 nm in the vicinity from 250 to 350 nm owing to the O^2--Eu3+ charge transfer band, irrespective of deposition temperature. Upon 312 nm excitation, the SnO²:Eu³⁺ thin films showed a main emission peak at 592 nm arising from the ⁵D₀→⁷F₁ transition and a weak 615 nm red band originating from the ⁵D₀→⁷F₂ transition of Eu³⁺. As the deposition temperature increased, the emission intensities of two bands increased rapidly, approached a maximum at 100 ℃, and then decreased slowly at 400 ℃. The thin film deposited at 200 ℃ exhibited a band gap energy of 3.81 eV and an average transmittance of 73.7% in the wavelength range of 500-1100 nm. These results indicate that the luminescent intensity of SnO²:Eu³⁺ thin films can be controlled by changing the deposition temperature.

• 설비공학논문집
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• 제10권6호
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• pp.763-772
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• 1998

The effects of an inserted coil on flow patterns and heat transport performance for a horizontal rotating heat pipe have been studied experimentally. Especially, the present study is to see an internally inserted helical coil inside a RHP would lead to the same kind of results as internal fins. Visualization test conducted for an acryl tube, charged water with at a volumetric rate of 20%. When the flow kept pool regime at a low RPM(less than 1,000 RPM), the movement of coil forced the water to flow in axial direction. But this pumping effect of coil disappeared, when the pool regime changed to annular one which could be created by increasing RPM. The pumping effects for RHP with an inserted coil resulted enhancement both in condensation heat transfer coefficient and heat transport limitation, as obtained in case of using internal fins. But all these effects became negligible in the range of higher RPM(above 1,000∼1,200) with the transition of flow regime to annular flow.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2010년도 제39회 하계학술대회 초록집
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• pp.114-114
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• 2010

In this study, structural properties and photoluminescent characteristics of thin film rhombohedral zinc orthosilicate doped with manganese ($Zn_2SiO_4:Mn$) were investigated. The $Zn_2SiO_4:Mn$ films showed a pronounced absorption edge in the near ultraviolet wavelength region and a high optical transparency in the visible spectral range. The maximum transmittance reached 0.922 at 597 nm, which was very close to the transmittance of the fused quartz substrate alone (0.935). The $Zn_2SiO_4:Mn$ films were composed of rhombohedral polycrystalline grains with random crystallographic orientation. The broad-band photoluminescence emission peaked at around 525 nm was observed from the $Zn_2SiO_4:Mn$ films, which was ascribed to the radiative relaxation from the $^4T_1$ lowest excitation state to $^6A_1$ ground state of 3d5 electrons in divalent manganese ion. The excitation band exhibited a peak maximum at 259 nm in the near ultraviolet region, which was considered to be associated with the charge transfer transition of divalent Mn ion in the $Zn_2SiO_4$ system.

• 한국염색가공학회지
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• 제22권3호
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• pp.181-186
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• 2010

A thermoresponsive poly(NIPAM-co-dye) labeled with benzopyran-based D-$\pi$-A type dye was prepared by typical radical copolymerization. It can be also constructed a acid/base-induced molecular switch by modulation of intramolecular charge transfer with protonation/deprotonation. The lower critical solution temperature behavior was investigated by means of UV-vis spectroscopy which allows the measurement of the phase transition from $25^{\circ}C$ to $45^{\circ}C$ in aqueous DMSO solution. The morphology of the internal microstructure of the poly(NIPAM-co-dye) hydrogel was observed by scanning electron microscopy. The reversible switch could be obtained by thermal and acid/base stimuli.

• Bulletin of the Korean Chemical Society
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• 제14권5호
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• pp.621-625
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• 1993

Kinetic studies are conducted for the reactions of Y-benzoyl, Y-benzenesulfonyl and Y-benzyl halides with X-anilines in acetonitrile, and the transition state (TS) structures and their variations with substituents X and Y are discussed. The magnitude of the cross-interaction constants, $\rho$xy, is the largest and the inverse secondary kinetic isotope effect (SKIE), $k_H/k_D$ < 1.0, with deuterated aniline nucleophiles is the smallest for benzoyl fluoride reflecting the tightest TS for this compound. The SKIEs for sulfonyl halides are relatively large due to a relatively large, diffuse nature of the reaction center, S, causing weaker steric hindrance to the vibrations of the two N-H(D) bonds. For benzoyl and sulfonyl halides, the trends in $k_H/k_D$ and $Ir_XI$ variations with $\sigma$Y contradict each other, which is rationalized by the negative charge accumulation on the reaction center, CO and SO$_2$, causing inefficient transfer for the substrate with an electron donating substituent.

• 한국염색가공학회지
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• 제32권4호
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• pp.185-192
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• 2020

A novel binding site for metal ion made by designing molecule with tetrazolo quinoline with hydrazine carboxamide (TQC) and the designed molecule successfully synthesized. The probe works by selectively detecting Al3+ ion via both fluorimetric and colorimetric approach. The probe's effectiveness towards aluminium ion detection is highly sensitive and selective with no substantial interference with other competing ions. The added Al3+ ion to TQC fetched a rapid change of visual color to yellow from colorless, also the response of fluorescence turn-on. The fluorescence turn-on and color change visibly by the probe TQC with Al3+ ion credited to the ICT phenomenon (intramolecular charge-transfer transition). The likely interaction of the probe with aluminium ion has also been there predicted from ESI-MS spectral analysis results. The usefulness of the probe confirmed by practical utility by making a test kit to monitor Al3+ ion in water which showed a naked eye detection by notable color change.