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991.
Electrochemical carbon dioxide and bicarbonate reduction on copper in weakly alkaline media 总被引:1,自引:0,他引:1
R. Kortlever K. H. Tan Y. Kwon M. T. M. Koper 《Journal of Solid State Electrochemistry》2013,17(7):1843-1849
The electrochemical reduction of CO2 on copper is an intensively studied reaction. However, there has not been much attention for CO2 reduction on copper in alkaline electrolytes, because this creates a carbonate buffer in which CO2 is converted in HCO3 ? and the pH of the electrolyte decreases. Here, we show that electrolytes with phosphate buffers, which start off in the alkaline region and, after saturation with CO2, end up in the neutral region, behave differently compared to CO2 reduction in phosphate buffers which starts off in the neutral region. In initially alkaline buffers, a reduction peak is observed, which is not seen in neutral buffer solutions. In contrast with earlier literature reports, we show that this peak is not due to the formation of a CO adlayer on the electrode surface but due to the production of formate via direct bicarbonate reduction. The intensity of the reduction peak is influenced by electrode morphology and the identity of the cations and anions in solution. It is found that a copper nanoparticle-covered electrode gives a rise in intensity in comparison with mechanically polished and electropolished electrodes. The peak is observed in the SO4 2?-, ClO4 ?-, and Cl?- containing electrolytes, but the formate-forming peak is not seen with Br? and I?. 相似文献
992.
Joon Yub Kwon Seo Bong Chang Yong Oh Jang Mohamed Dawod Doo Soo Chung 《Journal of separation science》2013,36(12):1973-1979
Electrokinetic supercharging is one of the most powerful sample‐stacking methods that combines field amplified sample injection and transient ITP. In counter‐flow electrokinetic supercharging, a constant counter pressure is applied during sample injection in order to counterbalance the movement of the injected sample zone. As a result, there will be a pronounced increase in the amount of sample injected and the portion of the capillary available for electrophoresis. In this report, counter‐flow electrokinetic supercharging optimization factors such as the electric field application in the constant voltage and constant current modes, the magnitude of counter pressure, and the terminating electrolyte concentrations were investigated. The enrichments obtained with a 30 min injection of 10 nM catecholamines in 5 mM terminating electrolyte solution in the constant voltage mode applying a counter pressure of 1.3 psi were 41000‐fold for dopamine, 50 000‐fold for norepinephrine, and 32 000‐fold for epinephrine, yielding detection limits of 1.3, 1.4, and 1.2 nM, respectively, with absorbance detection at 200 nm. 相似文献
993.
Joong-Ho Kwon Jae-Jun Ahn Kashif Akram Ik-Jae Son Sang-O Lee 《Analytical and bioanalytical chemistry》2013,405(12):4225-4234
Two kinds (20 each) of gamma-irradiated (0, 5, and 10 kGy) tea samples, blended powders and packed in sachets (tea bags), were investigated using photostimulated luminescence (PSL), thermoluminescence (TL), and electron spin resonance spectroscopy (ESR) to identify their irradiation status. PSL-based rapid screening was possible for all the control samples except for one packed and two powdered samples. The irradiated samples presented a good dose-dependent PSL count except two powdered samples with very low PSL sensitivity. TL analysis provided the most reliable results, in which all the irradiated samples were identified using a well-defined high-intensity TL glow curve in a temperature range of 150–250 °C. The TL results were also confirmed by determining the TL ratio (TL1/TL2), which was <0.1 in all the non-irradiated samples and >0.1 in the irradiated ones. ESR spectroscopy was effective for only 3 packed and 6 powdered samples showing the radiation-induced cellulosic and sugar radical signals, respectively. Figure
TL-based detection of irradiated teas 相似文献
994.
Dr. Amit Kumar Dr. Nitee Kumari Dr. Sateesh Dubbu Dr. Sumit Kumar Taewan Kwon Dr. Jung Hun Koo Jongwon Lim Inki Kim Prof. Yoon-Kyoung Cho Prof. Junsuk Rho Prof. In Su Lee 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(24):9547-9556
Interest and challenges remain in designing and synthesizing catalysts with nature-like complexity at few-nm scale to harness unprecedented functionalities by using sustainable solar light. We introduce “nanocatalosomes”—a bio-inspired bilayer-vesicular design of nanoreactor with metallic bilayer shell-in-shell structure, having numerous controllable confined cavities within few-nm interlayer space, customizable with different noble metals. The intershell-confined plasmonically coupled hot-nanospaces within the few-nm cavities play a pivotal role in harnessing catalytic effects for various organic transformations, as demonstrated by “acceptorless dehydrogenation”, “Suzuki–Miyaura cross-coupling” and “alkynyl annulation” affording clean conversions and turnover frequencies (TOFs) at least one order of magnitude higher than state-of-the-art Au-nanorod-based plasmonic catalysts. This work paves the way towards next-generation nanoreactors for chemical transformations with solar energy. 相似文献
995.
Nguyen Thi Minh Hien Joo Hee Chung Xiang‐Bai Chen Woo Jun Kwon Chul Sung Kim In‐Sang Yang 《Journal of Raman spectroscopy : JRS》2015,46(11):1161-1165
LiFe1 − xMnxPO4 olivines are promising material for improved performance of Li‐ion batteries. Spin–phonon coupling of LiFe1 − xMnxPO4 (x = 0, 0.3, 0.5) olivines is studied through temperature‐dependent Raman spectroscopy. Among the observed phonon modes, the external mode at ~263 cm−1 is directly correlated with the motions of magnetic Fe2+/Mn2+ ions. This mode displays anomalous temperature‐dependent behavior near the Néel temperature, indicating a coupling of this mode with spin ordering. As Mn doping increases, the anomalous behavior becomes clearly weaker, indicating the spin–phonon coupling quickly decreases. Our analyses show that the quick decrease of spin–phonon coupling is due to decrease of the strength of spin–phonon coupling, but not change of spin‐ordering feature with Mn doping. Importantly, we suggest that the low electrochemical activity of LiMnPO4 is correlated with the weak spin–phonon coupling strength, but not with the weak ferromagnetic ground state. Our work would play an important role as a guide in improving the performances of future Li‐ion batteries. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
996.
Four kinds of poly(4-methacryloyloxychalcone) (PCEMA) photo-alignment materials were synthesized. The effect of the cinnamoyl group on liquid crystal (LC) aligning capabilities and electro-optical characteristics of photo-aligned twisted nematic (TN) liquid crystal displays (LCDs) was investigated by photo-dimerization. Uniform NLC alignment by linearly polarized UV exposure at normal incidence on the PCEMA surfaces having a high density of cinnamoyl groups was observed. Also, excellent voltage-transmittance (V-T) curves for the photo-aligned TN-LCDs on the PCEMA surfaces was achieved. We find that the V-T and response time characteristics can be improved by increasing the density of cinnamoyl groups. 相似文献
997.
Yun‐Hi Kim Jong‐Won Park Dong‐Cheol Shin Hong You Soon‐Ki Kwon 《Journal of polymer science. Part A, Polymer chemistry》2007,45(5):900-907
A new poly(1,4‐spirobifluorenylenevinylene) having advantage PPV and spirobifluorene as new emissive family was synthesized. Compared with PPV derivatives that usually have a tolane bisbenzyl defect, the polymer has the defect free structure because of the steric hindrance of the asymmetric bulky spirobifluorenyl group. Compared with spirobifluorene derivatives that usually have a low solubility, the polymer has the good solubility in common organic solvents. The polymer was amorphous and showed high PL quantum efficiency and high thermal stability with high Tg. The PL emission peaks were shown at 480–490 nm in solution and film, respectively, which may represent the bluest emission peak reported for fully conjugated PPV derivatives. The study of thermal annealing of PL spectrum showed excimer formation inhibited. The thermal and optoelectronic properties of the polymer imply that it is a promising material for the PLED application. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 900–907, 2007. 相似文献
998.
Yun‐Hi Kim Dong‐Cheol Shin Hyung‐Sun Kim Hong You Soon‐Ki Kwon 《Journal of polymer science. Part A, Polymer chemistry》2005,43(24):6515-6523
A new poly(arylene vinylene) derivative, poly(1,4‐fluorenylenevinylene), with the advantages of poly(p‐phenylene vinylene) and polyfluorene (PF), was designed, synthesized, and characterized. The polymer showed a defect‐free structure and a number‐average molecular weight of 32,600. The resulting polymer was thermally stable with a high glass‐transition temperature (200 °C) and was readily soluble in common organic solvents. The polymer film showed a maximum emission at 515 nm and had a photoluminescence quantum yield of 58 ± 5%. A cyclic voltammetry study revealed that the highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels of the polymer were 2.9 and 5.51 eV, respectively. The double‐layer light‐emitting‐diode devices fabricated from the polymer emitted bright green light with a maximum around 515 nm. The device showed a maximum luminous efficiency of 0.13 cd/A and a maximum luminance value of 600 cd/m2 at 17 V. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6515–6523, 2005 相似文献
999.
Mohammad Rezaul Karim Kwon Taek Lim Chul Jae Lee Md Tauhidul Islam Bhuiyan Hee Jin Kim Lee‐Soon Park Mu Sang Lee 《Journal of polymer science. Part A, Polymer chemistry》2007,45(24):5741-5747
Core‐shell silver (Ag)–polyaniline (PAni) nanocomposites have been synthesized by the in‐situ gamma radiation‐induced chemical polymerization method. Aqueous solution of aniline, a free‐radical oxidant, and/or silver metal salt were irradiated by γ‐rays. Reduction of the silver salt in aqueous aniline leads to the formation of silver nanoparticles which in turn catalyze oxidation of aniline to polyaniline. The resultant Ag‐PAni nanocomposites were characterized by using different spectroscopy analyses like X‐ray photoelectron, UV–visible, and infrared spectroscopy. The optical absorption bands revealed that the bands at about 400 nm are due to the presence of nanosilver and the blue‐shifted peak at ~ 555 nm is due to the presence of metallic silver within the PAni matrix. X‐ray diffraction pattern clearly indicates the broad amorphous polymer and the sharp metal peaks. Scanning electron microscopy and transmission electron microscopy of the nanocomposite showed a uniform size distribution with spherical and granular morphology. Thermogravimetric analysis revealed that the composites have a higher degradation temperature than polyaniline alone. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5741–5747, 2007 相似文献
1000.
Ke Min Jung Kwon Oh Krzysztof Matyjaszewski 《Journal of polymer science. Part A, Polymer chemistry》2007,45(8):1413-1423
A series of forced gradient copolymers with different controlled distribution of monomer units along the copolymer backbone were successfully prepared by atom transfer radical polymerization in miniemulsion. The newly developed initiation technique, known as activators generated by electron transfer, was beneficial for forced gradient copolymers preparation because all polymer chains were initiated within the miniemulsion droplets and the miniemulsion remained stable throughout the entire polymerization. Various monomer pairs with different reactivity ratios were examined in this study, including n‐butyl acrylate/t‐butyl acrylate, n‐butyl methacrylate/methyl methacrylate, and n‐butyl acrylate/styrene. In each case, the added monomer diffused across the aqueous suspending medium and gradient copolymers with different forced distributions of comonomer units along the polymer backbone were obtained. The shape of the gradient along the backbone of the copolymers was influenced by the molar ratio of the monomers, the reactivity ratio of the comonomers as well as the feeding rate. The shape of the gradient was also affected by the relative hydrophobicities of the comonomers. Copolymerizations exhibited good control for all feeding rates and comonomer feeding ratios, as evidenced by narrow molecular weight distribution (Mw/Mn = 1.20–1.40) and molecular weight increasing smoothly with polymer yield, indicating high initiation efficiency. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1413–1423, 2007 相似文献