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Jin J.-K.,KAIST | Choi J.-K.,KAIST | Kim B.-J.,KAIST | Kang H.-B.,KAIST | And 2 more authors.
Macromolecules | Year: 2011

A new series of polysilafluorene-type low-bandgap polymers containing 3,6-dialkyloxy-9,9-dialkylsilafluorene and 4,7-di-2-thienyl-2,1,3- benzothiadiazole units has been synthesized. UV/vis absorption spectroscopy and grazing incident X-ray diffraction results showed that the alkoxy moiety on the silafluorene unit broadens the absorption band of the polymers because of its electron-donating property, enabling more efficient harvesting of photons from the solar spectrum. Furthermore, the silicon atoms of the polymers lead to a highly ordered structure, which is essential for high charge-carrier mobility. In addition, high molecular weight polymers can be prepared by using long octyloxy/hexyl solubilizing groups. The blend of new poly[2,7-(3,6-dioctyloxy-9, 9-dihexylsilafluorene)-alt-5,5-(4′,7′-di-2-thienyl-2′, 1′,3′-benzothiadiazole)] (P4H) and [6,6]-phenyl-C 71-butyric acid methyl ester (PC71BM) exhibited a power-conversion efficiency of 4.05% with an open-circuit voltage of 0.67 V, a short-circuit current density of 11.1 mA cm-2, and a fill factor of 54.3% under simulated 100 mW cm-2 air mass 1.5 global (AM1.5G) illumination. © 2011 American Chemical Society.

Kim Y.H.,KRICT | Gim M.-J.,KAIST | Jung H.-T.,KAIST | Yoon D.K.,KAIST
RSC Advances | Year: 2015

We have fabricated very well ordered periodic arrays of torons using cholesteric liquid crystal phase (CLC) in microchannels. The liquid crystal (LC) director exhibited different orientations with variations in the microchannel width. In particular, LC molecules were homeotropically aligned to the bottom substrate of the microchannel when the microchannel width was less than the helical pitch of the CLC, while wound CLC structures ("fingers") grew from the sidewall of the microchannels that were wider than the helical pitch. The thermal quenching process generated torons that were locally isolated from the microchannel surfaces due to the thermal gradient from top/bottom to the centre position of the microchannel. The individually grown torons were periodically arranged in a row with a uniform size-distribution and long-term stability under ambient conditions. This journal is © The Royal Society of Chemistry.

Kim J.,Pohang University of Science and Technology | Lee C.W.,KRICT | Choi W.,Pohang University of Science and Technology
Environmental Science and Technology | Year: 2010

This study aims to understand the visible light photocatalytic activities of platinized WO3 (Pt/WO3) on the degradation of aquatic pollutants and the role of main photooxidants. The presence of Pt on WO 3 is known to facilitate the multielectron reduction of O 2, which enables O2 to serve as an electron acceptor despite the insufficient reduction potential of the conduction band electrons (in WO3) for the one-electron reduction of O2. The concurrent oxidative reactions occurring on WO3 were markedly enhanced in the presence of Pt and accompanied the production of OH radicals under visible light, which was confirmed by both a fluorescence method (using a chemical trap) and a spin trap method. The generation of OH radicals mainly comes from the reductive decomposition of H2O2 that is produced in situ from the reduction of O2 on Pt/WO3. The rate of in situ production of H2O2 under visible light was significantly faster with Pt/WO3 than WO3. Six substrates that were tested for the visible light (λ > 420 nm) induced degradation on Pt/WO3 included dichloroacetate (DCA), 4-chlorophenol (4-CP), tetramethylammonium (TMA), arsenite (As(III)), methylene blue (MB), and acid orange 7 (AO7). The degradation (or conversion) of all six substrates was successfully achieved with Pt/WO3 and the role of OH radicals in Pt/WO3 photocatalysis seemed to be different depending on the kind of substrate. In the presence of tert-butyl alcohol (TBA: OH radical scavenger), the photocatalytic degradation was markedly reduced for 4-CP or completely inhibited for DCA and TMA whereas that of As(III), MB, and AO7 was little affected. Pt/WO3 photocatalyst that oxidizes various substrates under visible light with a sufficient photostability can be applied for solar water treatment. © 2010 American Chemical Society.

News Article | January 30, 2016
Site: phys.org

From top left are Professor Soojin Park, Dr. Sinho Choi, researcher Jieun Kim (KRICT) and from bottom left are Professor Sang Kyu Kwak and researcher Dae Yeon Hwang. Credit: UNIST. Contents by: Sinho Choi, Design by: Dukgi Lee A team of Korean researchers, affiliated with UNIST has recently pioneered in developing a new simple nanowire manufacturing technique that uses self-catalytic growth process assisted by thermal decomposition of natural gas. According to the research team, this method is simple, reproducible, size-controllable, and cost-effective in that lithium-ion batteries could also benefit from it. In their approach, they discovered that germanium nanowires are grown by the reduction of germanium oxide particles and subsequent self-catalytic growth during the thermal decomposition of natural gas, and simultaneously, carbon sheath layers are uniformly coated on the nanowire surface. This study is a collaboration among scientists, including Prof. SooJin Park (School of Energy and Chemical Engineering) and Prof. Sang Kyu Kwak (School of Energy and Chemical Engineering), Dr. Sinho Choi (UNIST), Combined M.S./Ph.D. Student Dae Yeon Hwang (UNIST), and Researcher Jieun Kim (Korea Research Institute of Chemical Technology). In a study, reported in the January 21, 2016 issue of Nano Letters, the team demonstrated a new redox-responsive assembly method to synthesize hierarchically structured carbon-sheathed germanium nanowires (c-GeNWs) on a large scale by the use of self-catalytic growth process assisted by thermally decomposed natural gas. According to the team, this simple synthetic process not only enables them to synthesize hierachially assembled materials from inexpensive metal oxides at a larger scale, but also can likely be extended to other metal oxides as well. Moreover, the resulting hierarchically assembled nanowires (C-GeNWs) show enhanced chemical and thermal stability, as well as outstanding electrochemical properties. The team states, "This strategy may open up an effective way to make other metallic/semiconducting nanomaterials via one-step synthetic reactions through an environmentally benign and cost-effective approach." Explore further: Simple and inexpensive process to make a material for CO2 adsorption More information: Sinho Choi, Jieun Kim, Dae Yeon Hwang, Hyungmin Park, Jaegeon Ryu, Sang Kyu Kwak* and Soojin Park* "Generalized redox-responsive assembly of carbon-sheathed metallic and semiconducting nanowire heterostructures". Nano Lett. (2016)

Cho H.-Y.,Inha University | Yang D.-A.,Inha University | Kim J.,Inha University | Jeong S.-Y.,KRICT | Ahn W.-S.,Inha University
Catalysis Today | Year: 2012

High-quality Co-MOF-74 crystals were successfully synthesized in 1 h by microwave heating (Co-MOF-74(M)). The XRD pattern and textural properties of Co-MOF-74(M) including the BET surface area (1314 m 2 g -1) were virtually identical to those of a sample synthesized in 24 h by the solvothermal method (Co-MOF-74(S), 1327 m 2 g -1). Average particle size of the former (ca. 50 μm long and 8 μm wide) was, however, significantly smaller than that of the latter (ca. 300 μm long and 70 μm wide). The H 2O adsorption capacities of the crystals at 25°C were 466 and 605 mg g -1 for Co-MOF-74(M) and Co-MOF-74(S), respectively. The adsorption isotherms of Co-MOF-74(M) for CO 2 and N 2 showed a high CO 2 adsorption capacity (288 mg g -1) and excellent selectivity over N 2 (>25:1) at 25°C. Eight consecutive adsorption-desorption cycles established that there was no deterioration in the adsorption capacity, which showed reversible adsorbent regeneration at 100°C under He flow for a total duration of 1100 min. Co-MOF-74(M) also demonstrated excellent catalytic performance in cycloaddition of CO 2 to styrene oxide under relatively mild reaction conditions (2.0 MPa, 100°C) with close to 100% selectivity to carbonate confirmed by GC-MS, 1H NMR, and FT-IR. Styrene oxide conversion increased with CO 2 pressure and reaction temperature. No appreciable effect of catalyst particle size was detected, and Co-MOF-74(M) could be reused 3 times without loss of catalytic activity and with no structural deterioration. © 2011 Elsevier B.V. All rights reserved.

Youn H.-K.,Inha University | Kim J.,Inha University | Chandrasekar G.,Inha University | Jin H.,KRICT | Ahn W.-S.,Inha University
Materials Letters | Year: 2011

Nanoporous carbons were synthesized by chemical vapor deposition using furfuryl alcohol/butylene as a carbon source and zeolite Y as a hard template (ZYC). The ZYC were characterized by PXRD, N2 sorption, and SEM. The carbon materials exhibited predominant microporosity, and the specific surface area increased from 2563 to 3010 m2 g-1 as the pyrolysis temperature was raised from 800 to 1000 °C. ZYC prepared at 1000 °C showed a CO2 adsorption capacity of 986 mg g-1 adsorbent at 40 bar 298 K, which surpasses the capacities of commercial carbons and mesoporous carbon CMK-3, and closely approaches the best performance of the metal organic framework MOF-177. The CO2 adsorption capacities of the adsorbents were found to be closely correlated with the BET surface areas of the materials tested. © 2011 Elsevier B.V. All rights reserved.

Bhattacharjee S.,Inha University | Jeong K.-E.,KRICT | Jeong S.-Y.,KRICT | Ahn W.-S.,Inha University
New Journal of Chemistry | Year: 2010

A novel sulfonato-salen-nickel(ii) complex has been immobilized on a Zn(ii)-Al(iii) layered double hydroxide (LDH) host. XRD, FT-IR, TGA and UV-vis spectroscopy, as well as chemical analysis, confirmed the successful incorporation of the nickel-salen complex within the LDH structure. BET surface area measurements, SEM and TEM were also used to characterize the heterogenized catalyst. The sulfonato-salen-nickel(ii) complex-immobilized material, LDH-[nickel-salen], was found to be effective in the oxidation of tetralin, where a combination of trimethylacetaldehyde and dioxygen at atmospheric pressure was employed as the oxidant. At 72.3% conversion, tetralin was converted to 1-tetralone with 72.2% selectivity at 70 °C after 7 h. Tetralin oxidation using tert-butyl hydroperoxide afforded a lower conversion and selectivity of 1-tetralone than with trimethylacetaldehyde and dioxygen as the oxidant. The effect of various reaction parameters on catalytic performance was also investigated. A hot filtration experiment coupled with a blank test revealed that oxidation proceeded mostly on nickel-salen sites in LDH-[nickel-salen]. A reaction mechanism is proposed based on the experimental results. © 2010 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.

Kim J.,Inha University | Bhattacharjee S.,Inha University | Jeong K.-E.,KRICT | Jeong S.-Y.,KRICT | And 3 more authors.
New Journal of Chemistry | Year: 2010

A novel CrAPO-5 material having a unique microporous-mesoporous hierarchical pore structure (CrAPO-5H) was synthesized using an organosilane surfactant to conventional CrAPO-5 reaction mixture by a one-step hydrothermal process. The materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), N2-adsorption isotherm and UV-visible diffuse reflectance spectroscopy, and employed as a catalyst for the liquid phase oxidation of tetralin. CrAPO-5H produced higher activity than conventional microporous CrAPO-5. Acylperoxy radicals, in situ generated from trimethylacetaldehyde and O2, were more effective as oxidant than tert-butyl hydroperoxide (t-BuOOH); 88% conversion of tetralin with 97% selectivity to 1-tetralone was obtained with the former, whereas 57% conversion with 86% selectivity was achieved using the latter at 80 °C after 8 h. The effect of reaction temperature, Cr content, solvent, and the type of aldehyde employed for the in situ generation of acylperoxy radicals on catalytic performance was investigated. Activities of CrAPO-5H remained constant after 1st catalyst recycle. A hot filtration experiment coupled with a blank test revealed that oxidation proceeded mostly on Cr sites in the CrAPO-5H, but a minor contribution from trace amount of leached Cr could not be ruled out. © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.

Upare D.P.,KRICT | Yoon S.,KRICT | Lee C.W.,KRICT | Lee C.W.,Korean University of Science and Technology
Catalysis Letters | Year: 2012

Selective ring opening (SRO) of methylcyclohexane (MCH) and methylcyclopentane (MCP) over 0.9 wt% Ir supported on USY and HZSM-5 catalysts with same SiO 2/Al 2O 3 ratio were compared in a fixed-bed reactor. Temperature of 250-300 °C, H 2 pressure of 30 bar, WHSV of 1.8 h -1 and H 2/feed molar ratio of 40 were used for SRO. The catalysts were synthesized by impregnation method and characterized by BET, H2-chemisorption, H 2-TPR, XRD, HR-TEM and NH3-TPD. 0.9 % Ir/USY catalyst converted 52 % of MCH into 28.6 % of ring opening products selectively, and it gave exclusively 67.4 % of ring opening products selectivity at higher 97 % conversion of MCP. In essence, the obtained catalytic results indicated superior catalytic activity for 0.9 wt% Ir/USY catalyst compared to 0.9 wt% Ir/HZSM-5 catalyst. These catalysts exhibit their stability, as well as activity even after 10 h of reaction time. © 2012 Springer Science+Business Media, LLC.

Upare D.P.,KRICT | Upare D.P.,Korean University of Science and Technology | Yoon S.,KRICT | Lee C.W.,KRICT
Korean Journal of Chemical Engineering | Year: 2011

Porous carbon materials are of interest in many applications because of their high surface area and physicochemical properties. For particular application, the surface of porous carbon material usually needs to be modified or functionalized according to a specific requirement. In this review, methods of synthesis of porous carbon material core shell structure, methods of functionalizing porous carbon material through direct incorporation of heteroatom in carbon synthesis, halogenation, sulfonation, surface oxidation, grafting are examined. The method of characterizing the functionalized carbon material (bulk, surface, internal and external) and its application in the field of catalysis and energy storage (Li-ion batteries, capacitors/supercapacitors), are also subjects of focus. © 2010 Korean Institute of Chemical Engineers, Seoul, Korea.

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