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Polyacrylonitrile template-assisted formation of LiMn2O4 nanoparticles for lithium-ion batteries
Bon-Ryul Koo 한양대학교 세라믹연구소 2017 Journal of Ceramic Processing Research Vol.18 No.3
In this study, LiMn2O4 (LMO) nanoparticles were fabricated using polyacrylonitrile (PAN) templates and the annealingprocess. In order to optimize their electrochemical performance for LIBs, we adjusted the annealing temperatures to 600, 700,800, and 900 oC. For comparison, the LMO particles were prepared using the solid-state reaction method. Interestingly, dueto the limited grain growth and aggregation of the LMO by the PAN templates, the samples prepared by the PAN templatesannealed at 700 oC revealed the nanoparticles below ~ 150 nm in size. As compared to other samples, the LMO nanoparticlesprepared at 700 oC showed a superb specific discharge capacity of ~103.6 mAh/g at 100 cycles (capacity retention of ~ 82.7%)and a good high-rate performance (~ 81.8 mAh/g at 5 C). These outstanding electrochemical performances are due to theshorted diffusion distance of Li+by the LMO nanoparticles thanks to the PAN templates and the improved electroactive sitesby the correct stoichiometric LMO phases without impurities at the optimum annealing temperature. Thus, these resultsindicate that the LMO nanoparticles formed via the PAN templates annealed at 700 oC could be used as promising cathodematerials for high-performance LIBs.
Koo, Bon-Ryul,Lee, Dae-Hyeok,Ahn, Hyo-Jin,Sung, Yung-Eun American Scientific Publishers 2016 Journal of Nanoscience and Nanotechnology Vol.16 No.10
<P>Carbon-coated SnO2-Co3O4 composite nanowires (NWs) are synthesized to improve the cycling properties of lithium-ion batteries, using electrospinning followed by carbonization using a dopamine precursor. These carbon-coated composite NWs show excellent capacity retention (similar to 542 mAh/g; 50 cycles) compared to bare SnO2 NWs (similar to 101 mAh/g; 50 cycles) and SnO2-Co3O4 composite NWs (similar to 323 mAh/g; 50 cycles). The performance improvement is due to the combined effects of the composite structure of SnO2 and Co3O4 producing the enhanced capacity retention in the NW core region and the carbon coating in the shell region hindering large volume expansion-contraction of the electrode.</P>
Synthesis and characterisation of polygonal indium tin oxide nanocrystals.
Koo, Bon-Ryul,Park, Byung Kyu,Kim, Chang Yeoul,Oh, Sung-Tag,Ahn, Hyo-Jin American Scientific Publishers 2013 Journal of Nanoscience and Nanotechnology Vol.13 No.11
<P>Polygon ITO (Sn-doped In2O3) nanocrystals were synthesised via electrospinning, and their morphology, structural properties, and chemical composition were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). To determine the optimum conditions for the fabrication of polygon ITO nanocrystals, calcination temperature after the electrospinning process was controlled at 500 degrees C, 600 degrees C, 700 degrees C, and 800 degrees C, and the amount of PVP polymer was controlled at 4 wt%, 7 wt%, and 10 wt%. For comparison purposes, single In2O3 nanocrystals were also synthesised via electrospinning and calcination. The results show that ITO nanocrystals fabricated at a calcination temperature of 800 degrees C and with 10 wt% of PVP polymer exhibit clear polygon structure with single-crystallinity, which may be explained in terms of the effect of Sn doping in the In2O3 matrix and the oriented aggregation and Oswald ripening growth during the fusion process of ITO nanocrystals.</P>
Koo, Bon-Ryul,Oh, Dong-Hyeun,Ahn, Hyo-Jin Elsevier BV * North-Holland 2018 Applied Surface Science Vol.433 No.-
<P><B>Abstract</B></P> <P>Nb-doped TiO<SUB>2</SUB> (Nb-TiO<SUB>2</SUB>) blocking layers (BLs) were developed using horizontal ultrasonic spray pyrolysis deposition (HUSPD). In order to improve the photovoltaic properties of the dye-sensitized solar cells (DSSCs), we optimized the Nb doping level of the Nb-TiO<SUB>2</SUB> BLs by controlling the Nb/Ti molar ratio (0, 5, 6, and 7) of the precursor solution for HUSPD. Compared to bare TiO<SUB>2</SUB> BLs, the Nb-TiO<SUB>2</SUB> BLs formed a cascading band structure using the positive shift of the conduction band minimum of the Nb-TiO<SUB>2</SUB> positioned between fluorine-doped tin oxide (FTO) and TiO<SUB>2</SUB>. This results in the increase of the potential current and the suppression of the electron recombination. Hence, it led to the improvement of the electrical conductivity, due to the increased electron concentration by the Nb doping into TiO<SUB>2</SUB>. Therefore, the DSSC fabricated with the Nb-TiO<SUB>2</SUB> BLs at a Nb/Ti molar ratio of 6 showed superior photoconversion efficiency (∼7.50±0.20%) as a result of the improved short-circuit current density. This is higher than those with the other Nb-TiO<SUB>2</SUB> BLs and without BL. This improvement of the photovoltaic properties for the DSSCs can be attributed to the synergistic effects of uniform and compact BL relative to the prevention of the backward electron transport at the FTO/electrolyte interface, efficient electron transport at interfaces relative to a cascading band structure of FTO/Nb-TiO<SUB>2</SUB>/TiO<SUB>2</SUB> multilayers and the facilitated electron transport at the BLs relative to the increased electrical conductivity of the optimized Nb-TiO<SUB>2</SUB> BLs.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Nb-doped TiO<SUB>2</SUB> (Nb-TiO<SUB>2</SUB>) layers prepared by using horizontal ultrasonic spray pyrolysis deposition. </LI> <LI> Nb-TiO<SUB>2</SUB> layers formed a cascading band structure to efficiently suppress the electron recombination. </LI> <LI> Nb-TiO<SUB>2</SUB> layers resulted in the increase of the electrical conductivity by the Nb doping into TiO<SUB>2</SUB>. </LI> <LI> A novel blocking layer for improving the photovoltaic performances of dye-sensitized solar cells. </LI> </UL> </P>
Koo, Bon Chul,Kwon, Mo Sun,Choi, Bok Ryul,Kim, Jin-Hoi,Cho, Seong-Keun,Sohn, Sea Hwan,Cho, Eun Jung,Lee, Hoon Taek,Chang, Wonkyung,Jeon, Iksoo,Park, Jin-Ki,Park, Jae Bok,Kim, Teoan 충남대학교 형질전환복제돼지연구센터 2007 논문집 Vol. No.10
The Moloney murine leukemia virus (MoMLV) -based retrovirus vector system has been used most often in gene transfer work, but has been known to cause silencing of the imported gene in transgenic animals. In the present study, using a MoMLV-based retrovirUs vector, we successfully generated a new transgenic chicken line expressing high levels of enhanced green fluorescent protein (eGFP). The level of eGFP expression was conserved after germline transmission and as much as 100μg of eGFP could be detected per 1 mg of tissue protein. DNA sequencing showed that the transgene had been integrated at chromosome 26 of the G₁and G₂generation transgenic chickens. Owing to the stable integration of the transgene, it is. now feasible to produce G₃generation of homozygous eGFP transgenic chickens that will provide 100% transgenic eggs. These results will help establish a useful transgenic chicken model system for studies of embryonic development and for efficient production of transgenic chickens as bioreactors.
Chul Koo, Bon,Sun Kwon, Mo,Ryul Choi, Bok,Kim, Jin‐,Hoi,Cho, Seong‐,Keun,Hwan Sohn, Sea,Jung Cho, Eun,Taek Lee, Hoon,Chang, Wonkyung,Jeon, Iksoo,Park, Jin‐,Ki,Bok Park, Jae,Kim, Teoa Federation of American Society for Experimental Bi 2006 The FASEB Journal Vol.20 No.13
<P>The Moloney murine leukemia virus (MoMLV) -based retrovirus vector system has been used most often in gene transfer work, but has been known to cause silencing of the imported gene in transgenic animals. In the present study, using a MoMLV-based retrovirus vector, we successfully generated a new transgenic chicken line expressing high levels of enhanced green fluorescent protein (eGFP). The level of eGFP expression was conserved after germline transmission and as much as 100 microg of eGFP could be detected per 1 mg of tissue protein. DNA sequencing showed that the transgene had been integrated at chromosome 26 of the G1 and G2 generation transgenic chickens. Owing to the stable integration of the transgene, it is now feasible to produce G3 generation of homozygous eGFP transgenic chickens that will provide 100% transgenic eggs. These results will help establish a useful transgenic chicken model system for studies of embryonic development and for efficient production of transgenic chickens as bioreactors.</P>
Choi, Bok Ryul,Koo, Bon Chul,Ahn, Kwang Sung,Kwon, Mo Sun,Kim, Jin-Hoi,Cho, Seong-Keun,Kim, Kyoung Mi,Kang, Jee Hyun,Shim, Hosup,Lee, Hyuna,Uhm, Sang Jun,Lee, Hoon Taek,Kim, Teoan JOHN WILEY & SONS LTD 2006 MOLECULAR REPRODUCTION AND DEVELOPMENT Vol.73 No.10
<P>A critical problem of transgenic livestock production is uncontrollable constitutive expression of the foreign gene, which usually results in serious physiological disturbances in transgenic animals. One of the best solutions for this problem may be use of controllable gene expression system. In this study, using retrovirus vectors designed to express the enhanced green fluorescent protein (EGFP) gene under the control of the tetracycline-inducible promoter, we examined whether the expression of the transgene could be controllable in fibroblast cells and nuclear transfer (NT) embryos of porcine. Transformed fibroblast cells were cultured in medium supplemented with or without doxycycline (a tetracycline analog) for 48 hr, and the induction efficiency was measured by comparing EGFP gene expression using epifluorescence microscopy and Western and Northern blot analyses. After the addition of doxycycline, EGFP expression increased up to 17-fold. The nuclei of transformed fibroblast cells were transferred into enucleated oocytes. Fluorescence emission data revealed strong EGFP gene expression in embryos cultured with doxycycline, but little or no expression in the absence of the antibiotic. Our results demonstrate the successful regulation of transgene expression in porcine nuclear transfer embryos, and support the application of an inducible expression system in transgenic pig production to solve the inherent problems of side-effects due to constitutive expression of the transgene. Mol. Reprod. Dev. © 2006 Wiley-Liss, Inc.</P>