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Kang I.-S.,Korea Advanced Institute of Science and Technology | So H.-M.,Korea Advanced Institute of Science and Technology | Bang G.-S.,Korea Advanced Institute of Science and Technology | Kwak J.-H.,Korea Advanced Institute of Science and Technology | And 2 more authors.
Applied Physics Letters | Year: 2012

We report a development of reduced graphene oxide (rGO)-based gas sensors with a practical recovery by facile functionalization with tin dioxide nanoclusters. Upon the introduction of UV illumination to this nanostructure, the reaction on surfaces of tin dioxide nanoclusters was activated and thereby the nanoscale heterojunction barriers between the rGO sheet and the nanoclusters were developed. This lowered the conductance to quickly recover, which was intensified as the cluster density has reached to the percolation threshold. However, after the formation of the cluster percolating network, the sensor response has totally changed into a deterioration of the sensitivity as well as the recovery. © 2012 American Institute of Physics.

Lee M.H.,Dong - A University | Hong K.S.,Korea Research Institute of Chemistry Technology | Malhotra S.,Dong - A University | Park J.-H.,Dong - A University | And 5 more authors.
Applied Microbiology and Biotechnology | Year: 2010

Soil metagenome constitutes a reservoir for discovering novel enzymes from the unculturable microbial diversity. From three plant rhizosphere metagenomic libraries comprising a total of 142,900 members of recombinant plasmids, we obtained 14 recombinant fosmids that exhibited lipolytic activity. A selected recombinant plasmid, pFLP-2, which showed maximum lipolytic activity, was further analyzed. DNA sequence analysis of the subclone in pUC119, pELP-2, revealed an open reading frame of 1,191 bp encoding a 397-amino-acid protein. Purified EstD2 exhibited maximum enzymatic activity towards p-nitrophenyl butyrate, indicating that it is an esterase. Purified EstD2 showed optimal activity at 35 °C and at pH 8.0. The K m and K cat values were determined to be 79.4 μM and 120.5/s, respectively. The esterase exhibited an increase in enzymatic activity in the presence of 15% butanol and 15% methanol. Phylogenetic analysis revealed that the lipolytic protein EstD2 may be a member of a novel family of lipolytic enzymes. Several hypothetical protein homologs of EstD2 were found in the database. A hypothetical protein from Phenylobacterium zucineum HLK1, a close homolog of EstD2, displayed lipolytic activity when the corresponding gene was expressed in Escherichia coli. Our results suggest that the other hypothetical protein homologs of EstD2 might also be members of this novel family. © 2010 Springer-Verlag.

Mi D.,Pusan National University | Kim J.-H.,Pusan National University | Yoon S.C.,Korea Research Institute of Chemistry Technology | Lee C.,Korea Research Institute of Chemistry Technology | And 2 more authors.
Synthetic Metals | Year: 2011

A novel carbazole-group-containing fullerene derivative (CBZ-C 60) with good solubility in common organic solvents was synthesized. This derivative was analyzed by using many techniques such as NMR, FAB-MS, FTIR and UV-vis absorption spectroscopy. Further, bulk heterojunction photovoltaic devices were fabricated. Since the LUMO energy level of CBZ-C60 was higher than that of fullerene, the open-circuit voltage (Voc) of devices based on CBZ-C60 was higher than that of devices based on fullerene. The power-conversion efficiency was highest for devices with composite thin films that have P3HT/CBZ-C60 composition ratios of 1:1 and were annealed at 150 °C for 10 min. The maximum Voc, short-circuit current density, and PCE of the best device were 0.64 V, 2.32 mA/cm2, and 0.48%, respectively. © 2011 Elsevier B.V. All rights reserved.

Lee S.-Y.,Pusan National University | Jung C.-H.,Kumoh National Institute of Technology | Kang J.,Kumoh National Institute of Technology | Kim H.-J.,Kumoh National Institute of Technology | And 5 more authors.
Journal of Nanoscience and Nanotechnology | Year: 2011

An alternating conjugated copolymer composed of pyrene and bithiophene units, poly(DHBT-alt-PYR) has been synthesized. The synthesized polymer was found to exhibit good solution processibility and thermal stability, losing less than 5% of their weight on heating to approximately 370 °C. The synthesized polymer showed its maximum absorption and peak PL emission at 401 and 548 nm, respectively. The optical band gap energy of the polymer was determined by absorption onset to be 2.64 eV. Highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of the polymer was determined to be-5.48 and-2.84 eV by cyclic voltametry (CV) and the optical band gap. The polymer photovoltaic devices were fabricated with a typical sandwich structure of ITO/PEDOT:PSS/active layer/LiF/Al using poly(DHBT-alt-PYR) as an electron donor and C 60-PCBM or C 70-PCBM as electron acceptors. The open circuit voltage, short circuit current and fill factor of the device using C 70-PCBM as an acceptor were 0.75 V, 3.80 mA/cm 2 and 0.28, respectively, and the maximum power conversion efficiency of the device was 0.80%. Copyright © 2011 American Scientific Publishers All rights reserved.

Oh J.H.,Kumoh National Institute of Technology | Kim J.-H.,Pusan National University | Kim Y.T.,Pusan National University | Shin W.S.,Korea Research Institute of Chemistry Technology | And 5 more authors.
Journal of Nanoscience and Nanotechnology | Year: 2012

Semiconducting polymers composed of 2,2'-(9,9-dioctyl-9H-fluorene-2,7-diyl) dithiophenes (F8T2s) and (2E,2'E)-3,3'-(2,5-bis(octyloxy)-1,4-phenylene) bis(2-(5-bromothiophene-2-yl)acrylonitrile)s (OPTANs) have been synthesized through Pd(0)-catalyzed Suzuki coupling polymerization by controlling the monomer ratio. The synthesized polymers were confirmed to exhibit good solubility in common solvents, simple processability, and thermal stability up to 350 C. The highest occupied molecular orbitals (HOMOs), lowest unoccupied molecular orbitals (LUMOs), and optical bandgap energies were determined using cyclic voltammetry (CV) and UV-visible spectrometry. The synthesized polymers showed their maximum absorption and edge at around 520 and 650 nm, respectively. The optical band-gap energies of the polymers were determined to be 1.89 eV. Bulk heterojunction organic solar cells were fabricated using the conjugated polymer as the electron donor, and 6,6-phenyl C61-butyric acid methylester (PC61BM) or 6,6-phenyl C 71-butyric acid methylester (PC 71BM) as the electron acceptor. The power conversion efficiencies (PCEs) of the solar cells based on polymer:PC 71BM (1:1) and polymer:PC 71BM (1:2) were 0.68% and 1.22%, respectively, under air mass 1.5 global (AM 1.5 G) illumination at 100 mW/cm 2. Copyright © 2012 American Scientific Publishers. All rights reserved.

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