22 results on '"Lee, Yu Ri"'
Search Results
2. Dual-functionalized ZIF-8 as an efficient acid-base bifunctional catalyst for the one-pot tandem reaction
- Author
-
Kyung Youl Baek, Lee Yu Ri, Xuan Huy Do, and Seung Sang Hwang
- Subjects
chemistry.chemical_classification ,02 engineering and technology ,General Chemistry ,Sulfonic acid ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensation reaction ,Heterogeneous catalysis ,01 natural sciences ,Catalysis ,0104 chemical sciences ,Bifunctional catalyst ,chemistry.chemical_compound ,chemistry ,Polymer chemistry ,Knoevenagel condensation ,0210 nano-technology ,Bifunctional ,Zeolitic imidazolate framework - Abstract
An acid-base bifunctional zeolitic imidazolate framework catalyst (ZIF8-A61-SO3H) with amine and sulfonic acid groups was successfully prepared through simple two step post-synthetic modification: preparation of amine-functionalized ZIF-8 with amine contents of 61% (ZIF8-A61) by the ligand exchange of 2-mIM with 3-amino-1,2,4-triazole (Atz), followed by the sulfonic acid functionalization by the ring-opening reaction of 1,3-propanesultone with –NH2 groups in ZIF8-A61. Amine-functionalized ZIF8-A materials with difference amine contents (15%, 34%, and 61%, respectively) were also prepared by controlling the synthesis time. All obtained ZIF catalysts evaluated as a heterogeneous catalyst for one-pot deacetalization-Knoevenagel condensation tandem reaction. Compared with ZIF-8 and amine-functionalized ZIF-8 catalysts, ZIF8-A61-SO3H catalyst showed good catalytic performance with 100% conversion of the reactant and 98% selectivity of the final Knoevenagel product. An enhanced catalytic activity can be attributed to the co-existence of site-isolated acid-base groups on the ZIF8-A61-SO3H catalyst in close proximity. The heterogeneous nature of the catalytic system was confirmed by a hot-filtering test and the catalyst also exhibited reusable in the five repeated cycles. A plausible catalytic mechanism of deacetalization-Knoevenagel condensation reaction over ZIF8-A61-SO3H was also proposed.
- Published
- 2021
3. Selecting optimal cultural medium, the part of explants for root induction and acclimatization period for spray chrysanthemum in vitro mass propagation
- Author
-
Park Sang Kun and Lee Yu-Ri
- Subjects
Tissue culture ,Horticulture ,Period (gene) ,Mass propagation ,Biology ,Acclimatization ,In vitro ,Explant culture - Published
- 2020
4. Electrocatalytic oxygen reduction over Co@Co3O4/N-doped porous carbon derived from pyrolysis of ZIF-8/67 on cellulose nanofibers
- Author
-
Lee Yu Ri, Jinsub Choi, Wha-Seung Ahn, and Hyeonseok Yoo
- Subjects
Materials science ,Polymers and Plastics ,Nanoparticle ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Electrocatalyst ,01 natural sciences ,0104 chemical sciences ,Catalysis ,chemistry.chemical_compound ,Electron transfer ,chemistry ,Chemical engineering ,Nanofiber ,Cellulose ,0210 nano-technology ,Bimetallic strip ,Pyrolysis - Abstract
Co@Co3O4 nanoparticles highly dispersed on N-doped porous carbon (Co,N–C/TOCNF) were prepared by pyrolysis of the Zn/Co bimetallic ZIF-8/67 in situ grown on the carboxylated cellulose nanofibers (TOCNF) at 900 °C. The physicochemical properties of the material were examined using various instruments, and it was applied as an electrocatalyst for oxygen reduction reaction. The interconnected three-dimensional network in TOCNF prevented aggregation of the catalytically active Co nanoparticles and enhanced electron transfer and mass diffusion, and Co,N–C/TOCNF showed excellent catalytic performance in alkaline medium with improved stability compared to the one by the commercial Pt/C catalyst.
- Published
- 2020
5. The Study on the Mediating Effect of Caring Empowerment in the Relationship between Caring Burden and Life Design of Caregivers of Disabled Children
- Author
-
Lee Yu-Ri
- Subjects
Psychotherapist ,Nursing ,business.industry ,media_common.quotation_subject ,Medicine ,business ,Empowerment ,media_common - Published
- 2017
6. Sonochemical synthesis of Zr-based porphyrinic MOF-525 and MOF-545: Enhancement in catalytic and adsorption properties
- Author
-
Wha-Seung Ahn, Jin Young Seo, Lee Yu Ri, Kwangsun Yu, Kyung Youl Baek, and Young-Min Chung
- Subjects
Thermogravimetric analysis ,Materials science ,fungi ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Porphyrin ,0104 chemical sciences ,Catalysis ,chemistry.chemical_compound ,Adsorption ,chemistry ,Mechanics of Materials ,Zirconyl chloride ,Trifluoroacetic acid ,General Materials Science ,Inductively coupled plasma ,0210 nano-technology ,Nuclear chemistry ,Benzoic acid - Abstract
The synthesis of metal-organic frameworks (MOFs) with in-built porphyrin units remains challenging. It takes long synthesis time under carefully controlled reaction conditions, and a mixed-phase with different crystal morphologies is still frequently observed. In this work, Zr-based porphyrinic MOF-525 and MOF-545 in high purity and uniform size were produced through a sonochemical route in 2.5 and 0.5 h, respectively, using zirconyl chloride octahydrate and tetrakis (4-carboxyphenyl) porphyrin. Benzoic acid was used as a modulator for MOF-525, and trifluoroacetic acid for MOF-545. The physicochemical properties of the MOF products were examined by X-ray diffraction, scanning electron microscopy, and N2 adsorption-desorption isotherms. Additionally, the defect sites in the MOF samples were analyzed by UV–vis spectrometry, thermogravimetric analysis, and inductively coupled plasma mass spectrometer. The sonochemically synthesized MOF samples had more defect sites than the conventionally prepared ones and exhibited improved textural properties. In particular, the MOF-545 had a significantly smaller (ca. 1.0 μm) particle size than the conventionally prepared sample (ca. 4.8 μm). The MOF-525 and MOF-545 prepared by the sonochemical route exhibited enhanced hydrolysis of the chemical warfare simulant dimethyl-4-nitrophenyl phosphate (DMNP) and a faster and higher bisphenol-A adsorption than the conventionally prepared MOF samples.
- Published
- 2021
7. Structural Basis for Design of New Purine-Based Inhibitors Targeting the Hydrophobic Binding Pocket of Hsp90
- Author
-
Sang Chul Shin, Ashraf K. El-Damasy, Lee Yu Ri, Eunice EunKyeong Kim, Ju Hyeon Lee, Young Ho Seo, Ji Hyun Kim, Ji Hoon Yu, Eun Kyoung Bang, Gyochang Keum, and Seon Hee Seo
- Subjects
0301 basic medicine ,Purine ,Pyridines ,Hsp90 inhibitor ,lcsh:Chemistry ,hydrophobic binding pocket ,Mice ,chemistry.chemical_compound ,0302 clinical medicine ,BIIB021 analogs ,polycyclic compounds ,Isoxazole ,Purine metabolism ,lcsh:QH301-705.5 ,Spectroscopy ,biology ,Chemistry ,General Medicine ,Hsp90 ,Computer Science Applications ,030220 oncology & carcinogenesis ,MCF-7 Cells ,Hsp90 inhibitors ,Protein Binding ,Stereochemistry ,Stacking ,Antineoplastic Agents ,Article ,Catalysis ,Inorganic Chemistry ,Structure-Activity Relationship ,03 medical and health sciences ,Heat shock protein ,Animals ,Humans ,HSP90 Heat-Shock Proteins ,Physical and Theoretical Chemistry ,Binding site ,Molecular Biology ,X-ray crystallography ,Binding Sites ,Adenine ,isoxazole ,Organic Chemistry ,Isoxazoles ,HCT116 Cells ,030104 developmental biology ,lcsh:Biology (General) ,lcsh:QD1-999 ,biology.protein - Abstract
Inhibition of the molecular chaperone heat shock protein 90 (Hsp90) represents a promising approach for cancer treatment. BIIB021 is a highly potent Hsp90 inhibitor with remarkable anticancer activity, however, its clinical application is limited by lack of potency and response. In this study, we aimed to investigate the impact of replacing the hydrophobic moiety of BIIB021, 4-methoxy-3,5-dimethylpyridine, with various five-membered ring structures on the binding to Hsp90. A focused array of N7/N9-substituted purines, featuring aromatic and non-aromatic rings, was designed, considering the size of hydrophobic pocket B in Hsp90 to obtain insights into their binding modes within the ATP binding site of Hsp90 in terms of &pi, &ndash, &pi, stacking interactions in pocket B as well as outer &alpha, helix 4 configurations. The target molecules were synthesized and evaluated for their Hsp90&alpha, inhibitory activity in cell-free assays. Among the tested compounds, the isoxazole derivatives 6b and 6c, and the sole six-membered derivative 14 showed favorable Hsp90&alpha, inhibitory activity, with IC50 values of 1.76 µ, M, 0.203 µ, M, and 1.00 µ, M, respectively. Furthermore, compound 14 elicited promising anticancer activity against MCF-7, SK-BR-3, and HCT116 cell lines. The X-ray structures of compounds 4b, 6b, 6c, 8, and 14 bound to the N-terminal domain of Hsp90 were determined in order to understand the obtained results and to acquire additional structural insights, which might enable further optimization of BIIB021.
- Published
- 2020
8. CO2 Adsorption Over Metal-Organic Frameworks: A Mini Review
- Author
-
Lee Yu Ri, Wha-Seung Ahn, and Chao Chen
- Subjects
Materials science ,Ligand ,Biomedical Engineering ,Bioengineering ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Co2 adsorption ,01 natural sciences ,0104 chemical sciences ,Metal ,Catenation ,Adsorption ,Chemical engineering ,visual_art ,visual_art.visual_art_medium ,Surface modification ,General Materials Science ,Metal-organic framework ,0210 nano-technology ,Porous medium - Abstract
Metal-organic frameworks (MOFs) are a class of porous materials that are comprised of metal ion-containing nodes linked by multi-dentate organic ligand bridges principally through coordination bonding. Over the last few decades, MOFs have been studied widely as CO2 adsorbents. CO2 adsorption in MOFs can be enhanced by tuning their physicochemical properties. This short review discusses CO2 adsorption over MOFs with particular focus on the contributory effects of (1) inherent textural properties, (2) coordinatively unsaturated open metal sites, (3) surface functionalization, (4) structural interpenetration (catenation), and (5) ion-exchange.
- Published
- 2016
9. Multiple Water Source Blending on the Variation of Climate Change in Water Treatment Plant
- Author
-
Park HanBai, Lim Sungil, Lee Jong-Man, Lee Yu ri, and Woo Dal-Sik
- Published
- 2015
10. Fabrication of thin-film gadolinia-doped ceria (GDC) interdiffusion barrier layers for intermediate-temperature solid oxide fuel cells (IT-SOFCs) by chemical solution deposition (CSD)
- Author
-
Jong-Ho Lee, Sun-Young Park, Hae-Weon Lee, Eun-Ok Oh, Ji-Won Son, Kyung Joong Yoon, Lee Yu Ri, Dasari Hari Prasad, Chin-Myung Whang, and Byung-Kook Kim
- Subjects
Materials science ,Process Chemistry and Technology ,Oxide ,Nanotechnology ,Substrate (electronics) ,Electrolyte ,Cathode ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,law.invention ,Anode ,Barrier layer ,chemistry.chemical_compound ,Chemical engineering ,chemistry ,law ,Materials Chemistry ,Ceramics and Composites ,Chemical stability ,Thin film - Abstract
A dense gadolinia-doped ceria (GDC) interdiffusion barrier layer as thin as 300 nm was successfully fabricated on a rigid anode/electrolyte bilayer substrate using the chemical solution deposition (CSD) process for intermediate temperature solid oxide fuel cells (SOFCs). Drying-related macro-defects were removed by employing drying control chemical additives (DCCA), which effectively relieved drying stresses. The major process flaws caused by the constraining effects of the rigid substrate were completely eliminated by the addition of GDC nanoparticles into the chemical solution, which suppressed the generation of microstructural anisotropy by mitigating the predominant bi-axial substrate constraints. As a consequence, a thin film GDC interlayer was successfully deposited with a high volumetric density, effectively preventing the chemical interaction between the electrolyte and cathode during the fabrication process and subsequent operation. The cell test and microstructural analysis confirmed excellent electrochemical performance and structural and chemical stability. The CSD process presented in this paper is considered to be a promising technology for the practical preparation of GDC thin film barrier layers for intermediate temperature SOFCs based on the film quality, processing costs and potential for large-scale production.
- Published
- 2014
11. Effect of Pt introduced on Ru-based electrocatalyst for oxygen evolution activity and stability
- Author
-
Hyung Suk Oh, Yun Jeong Hwang, Lee Yu Ri, Woong Lee, Chang Hyuck Choi, Jaekyung Yi, Kyung Su Park, and Byoung Koun Min
- Subjects
Reaction mechanism ,Chemistry ,Inorganic chemistry ,Oxygen evolution ,02 engineering and technology ,Thermal treatment ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Electrocatalyst ,01 natural sciences ,0104 chemical sciences ,Catalysis ,lcsh:Chemistry ,lcsh:Industrial electrochemistry ,lcsh:QD1-999 ,Oxidation state ,Electrochemistry ,Water splitting ,0210 nano-technology ,Dissolution ,lcsh:TP250-261 - Abstract
Ru-based electrocatalysts are generally known to be suitable for the oxygen evolution reaction (OER), but they have intrinsic problems in balancing catalytic activity and stability. In this study, we took the strategy, introducing Pt atoms into the structure of crystalline RuO2 to enhance the catalytic property toward OER while maintaining durability. The OER activity of Ru0.9Pt0.1O2/C with high stability was significantly higher than that of RuO2/C. In situ/operando ICP-MS analysis showed that Ru dissolution of Ru0.9Pt0.1O2/C during OER was suppressed by introducing Pt and thermal treatment when compared to Ru/C. The XPS results after OER measurement indicated that the Ru oxidation state of Ru0.9Pt0.1O2/C was higher than that of RuO2, which led to high OER catalytic activity. Based on these results, we hypothesize that the enhanced OER activity of Ru0.9Pt0.1O2/C was due to the change in the reaction mechanism from “adsorbate evolution” to “lattice participation”. Our findings increase the possibility of significantly overcoming the activity and stability limits of Ru-based electrocatalysts for the OER using Pt. Keywords: Water splitting, Oxygen evolution reaction, Ruthenium‑platinum oxide, in situ/operando ICP-MS, Lattice participation mechanism
- Published
- 2019
12. Thin Film Yttria-Stabilized Zirconia (YSZ) Electrolyte Fabricated by a Novel Chemical Solution Deposition (CSD) Process for Solid Oxide Fuel Cells (SOFCs)
- Author
-
Hae June Je, Hae Weon Lee, Lee Yu Ri, Jong Heun Lee, Hae Jin Hwang, Byung-Kook Kim, Ji-Won Son, Eun Ok Oh, Jong Ho Lee, and Chin Myung Whang
- Subjects
Chemical solution deposition ,Materials science ,Porous substrate ,Inorganic chemistry ,Oxide ,Electrolyte ,Electronic, Optical and Magnetic Materials ,chemistry.chemical_compound ,chemistry ,Chemical engineering ,Scientific method ,Fuel cells ,Electrical and Electronic Engineering ,Thin film ,Yttria-stabilized zirconia - Published
- 2012
13. A Study on the Influence of Functioning Level on the Parenting Competency of Mothers with Mental Disorders: Focusing on the Mediating Effect of Spouse Cooperation and Social Support
- Author
-
Lee Yu-Ri
- Subjects
Social support ,Spouse ,Psychology ,Social psychology ,Demography ,Functioning level ,Developmental psychology - Published
- 2012
14. Thin film yttria-stabilized zirconia electrolyte for intermediate-temperature solid oxide fuel cells (IT-SOFCs) by chemical solution deposition
- Author
-
Jong Heun Lee, Lee Yu Ri, Jong-Ho Lee, Chin Myung Whang, Kyung Joong Yoon, Ji-Won Son, Eun Ok Oh, Byung-Kook Kim, and Hae Weon Lee
- Subjects
Spin coating ,Materials science ,Oxide ,Electrolyte ,Anode ,Pulsed laser deposition ,chemistry.chemical_compound ,chemistry ,Materials Chemistry ,Ceramics and Composites ,Solid oxide fuel cell ,Thin film ,Composite material ,Yttria-stabilized zirconia - Abstract
A 500 nm thick thin film YSZ (yttria-stabilized zirconia) electrolyte was successfully fabricated on a conventionally processed anode substrate by spin coating of chemical solution containing slow-sintering YSZ nanoparticles with the particle size of 20 nm and subsequent sintering at 1100 °C. Incorporation of YSZ nanoparticles was effective for suppressing the differential densification of ultrafine precursor powder by mitigating the prevailing bi-axial constraining stress of the rigid substrate with numerous local multi-axial stress fields around them. In particular, adding 5 vol% YSZ nanoparticles resulted in a dense and uniform thin film electrolyte with narrow grain size distribution, and fine residual pores in isolated state. The thin film YSZ electrolyte placed on a rigid anode substrate with the GDC (gadolinia-doped ceria) and LSC (La0.6Sr0.4CoO3−δ) layers deposited by PLD (pulsed laser deposition) processes revealed that it had fairly good gas tightness relevant to a SOFC (solid oxide fuel cell) electrolyte and maintained its structural integrity during fabrication and operation processes. In fact, the open circuit voltage was 1.07 V and maximum power density was 425 mW/cm2 at 600 °C, which demonstrates that the chemical solution route can be a viable means for reducing electrolyte thickness for low- to intermediate-temperature SOFCs.
- Published
- 2012
15. Extremely Thin Bilayer Electrolyte for Solid Oxide Fuel Cells (SOFCs) Fabricated by Chemical Solution Deposition (CSD)
- Author
-
Jong-Ho Lee, Lee Yu Ri, Hae-Weon Lee, Sun-Young Park, Eun-Ok Oh, Chin-Myung Whang, Kyung Joong Yoon, Ji-Won Son, and Dasari Hari Prasad
- Subjects
Materials science ,Open-circuit voltage ,Mechanical Engineering ,Bilayer ,Inorganic chemistry ,Temperature ,Oxide ,Metal Nanoparticles ,Oxides ,Substrate (electronics) ,Electrolyte ,Solutions ,Electrolytes ,chemistry.chemical_compound ,Electric Power Supplies ,chemistry ,Chemical engineering ,Mechanics of Materials ,Yttrium ,General Materials Science ,Solid oxide fuel cell ,Zirconium ,Thin film ,Electrodes ,Yttria-stabilized zirconia - Abstract
An extremely thin bilayer electrolyte consisting of yttria-stabilized zirconia (YSZ) and gadolinia-doped ceria (GDC) is successfully fabricated on a sintered NiO-YSZ substrate. Major processing flaws are effectively eliminated by applying local constraints to YSZ nanoparticles, and excellent open circuit voltage and cell performance are demonstrated in a solid oxide fuel cell (SOFC) at intermediate operating temperatures.
- Published
- 2012
16. High glucose‐induced changes in hyaloid‐retinal vessels during early ocular development of zebrafish: a short‐term animal model of diabetic retinopathy
- Author
-
Jung, Seung‐Hyun, Kim, Young Sook, Lee, Yu‐Ri, and Kim, Jin Sook
- Subjects
Vascular Endothelial Growth Factor A ,Diabetic Retinopathy ,Tight Junction Proteins ,Retinal Vessels ,Zebrafish Proteins ,Nitric Oxide ,Research Papers ,Animals, Genetically Modified ,Disease Models, Animal ,Glucose ,NG-Nitroarginine Methyl Ester ,Receptors, Vascular Endothelial Growth Factor ,Larva ,Ranibizumab ,Animals ,Zebrafish - Abstract
Although a variety of animal models have been used to test drug candidates and examine the pathogenesis of diabetic retinopathy, time-saving and inexpensive models are still needed to evaluate the increasing number of therapeutic approaches.We developed a model for diabetic retinopathy using the early stage of transgenic zebrafish (flk:EGFP) by treating embryos with 130 mM glucose, from 3-6 days post fertilisation (high-glucose model). On day 6, lenses from zebrafish larvae were isolated and treated with 3% trypsin, and changes in hyaloid-retinal vessels were analysed using fluorescent stereomicroscopy. In addition, expression of tight junction proteins (such as zonula occludens-1), effects of hyperosmolar solutions and of hypoxia, and Vegf expression were assessed by RT -PCR. NO production was assessed with a fluorescent substrate. Effects of inhibitors of the VEGF receptor, NO synthesis and a VEGF antibody (ranibizumab) were also measured.In this high-glucose model, dilation of hyaloid-retinal vessels, on day 6, was accompanied by morphological lesions with disruption of tight junction proteins, overproduction of Vegf mRNA and increased NO production. Treatment of this high-glucose model with an inhibitor of VEGF receptor tyrosine kinase or an inhibitor of NO synthase or ranibizumab decreased dilation of hyaloid-retinal vessels.These findings suggest that short-term exposure of zebrafish larvae to high-glucose conditions could be used for screening and drug discovery for diabetic retinopathy and particularly for disorders of retinal vessels related to disruption of tight junction proteins and excessive VEGF and NO production.
- Published
- 2015
17. A Study on the Factors Impacting Main Caregiver Empowerment
- Author
-
Lee Yu-Ri
- Subjects
media_common.quotation_subject ,Psychology ,Empowerment ,Social psychology ,media_common - Published
- 2008
18. Heterolayered Li+–MnO2–[Mn1/3Co1/3Ni1/3]O2 Nanocomposites with Improved Electrode Functionality: Effects of Heat Treatment and Layer Doping on the Electrode Performance of Reassembled Lithium Manganate
- Author
-
In Young Kim, Kyung-Min Lee, Yu Ri Lee, Seong Ju Hwang, Song Yi Han, Tae Woo Kim, Lee, Kyung Min, Lee, Yu Ri, Kim, In Young, Kim, Tae Woo, Han, Song Yi, and Hwang, Seong-Ju
- Subjects
nanosheets ,Materials science ,Materials Science ,Inorganic chemistry ,Oxide ,chemistry.chemical_element ,Materials Science, Multidisciplinary ,metallic compounds ,Metal ,chemistry.chemical_compound ,Oxidation state ,nanocomposites ,Nanoscience & Nanotechnology ,manganese oxide ,Physical and Theoretical Chemistry ,Nanocomposite ,Chemistry, Physical ,Manganate ,self assembly ,phase transitions ,x ray diffraction ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Chemistry ,General Energy ,Lamella (surface anatomy) ,chemistry ,Chemical engineering ,visual_art ,Electrode ,manganese ,visual_art.visual_art_medium ,Science & Technology - Other Topics ,Lithium - Abstract
Novel heterolayered nanocomposites consisting of interstratified MnO2 and [Mn1/3Co1/3Ni1/3]O-2 nanosheets are synthesized by a layer-by-layer self-assembly between negatively charged metal oxide nanosheets and lithium cations. According to powder X-ray diffraction and micro-Raman analysis, all of the as-prepared Li+-xMnO(2)-(1-x)[Mn1/3Co1/3Ni1/3]O-2 nanocomposites with x = 1, 0.7, and 0.4 have a lamella structure with similar basal spacing of similar to 7.1 angstrom, indicating the formation of lithium intercalation structure with cointercalated water bilayers. The nanoscale mixing of MnO2 and [Mn1/3Co1/3Ni1/3]O-2 nanosheets is confirmed by energy-dispersive spectrometry-elemental mapping analysis. Upon a self-assembly with Li+ ions, there occur no marked changes in the octahedral symmetry and mixed oxidation state of M3+/M4+ ions (M = Mn, Co, and Ni) in the precursor metal oxide nanosheets. All of the as-prepared nanocomposites commonly experience a structural transformation from hydrated layered structure to dehydrated layered structure at 200 degrees C, which is followed by the second-phase transition to cubic spinel structure at 600 degrees C. Despite distinct structural changes of the nanocomposites at elevated temperatures, their porous stacking structure is well-maintained up to 400 degrees C. The heat-treatment at 400 degrees C leads to a significant improvement of the discharge capacity of the present nanocomposites because of the dehydration of as-prepared materials and the enhancement of crystallinity. The doping of [Mn1/3Co1/3Ni1/3]O-2 layers enables us not only to increase the discharge capacity of the Li-MnO2 nanocomposite but also to prevent the phase transition of layered manganese oxide to spinel structure during electrochemical cycling. The present study clearly demonstrates that a postcalcination process as well as a partial doping of [Mn1/3Co1/3Ni1/3]O-2 layer is effective in improving the electrode performance of reassembled Li-MnO2 nanocomposites. Refereed/Peer-reviewed
- Published
- 2012
19. Porously Assembled 2D Nanosheets of Alkali Metal Manganese Oxides with Highly Reversible Pseudocapacitance Behaviors
- Author
-
Jayavant L. Gunjakar, Min Sun Song, Tae Woo Kim, Kyung-Min Lee, Seong Ju Hwang, In Young Kim, Yu Ri Lee, Song, Min-Sun, Lee, Kyung Min, Lee, Yu Ri, Kim, In Young, Kim, Tae Woo, Gunjakar, Jayavant Laxman, and Hwang, Seong-Ju
- Subjects
nanosheets ,Materials science ,Materials Science ,Inorganic chemistry ,chemistry.chemical_element ,Materials Science, Multidisciplinary ,Manganese ,Pseudocapacitance ,chemistry.chemical_compound ,Oxidation state ,Lamellar structure ,Nanoscience & Nanotechnology ,manganese oxide ,Physical and Theoretical Chemistry ,Chemistry, Physical ,Manganate ,octahedral symmetry ,Alkali metal ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Chemistry ,General Energy ,chemistry ,Science & Technology - Other Topics ,Crystallite ,Mesoporous material - Abstract
Porously assembled 2D nanosheets of alkali metal manganese oxides were synthesized via the flocculation of exfoliated MnO2 nanosheets with alkali metal cations. According to X-ray diffraction and electron microscopic analyses, the MnO2 nanosheets were porously restacked with alkali metal cations, resulting in the mesoporous assembly of lamellar crystallites with surface expansion (similar to 50-70 m(2) g(-1)). Mn K-edge X-ray absorption spectroscopy clearly demonstrated that manganese ions in the reassembled materials were stabilized in octahedral symmetry with the mixed oxidation state of Mn3+/Mn4+. The present reassembled manganates showed large capacitances of similar to 140-160 F g(-1) and excellent cyclability of similar to 93-99% up to the 1000th cycle. The electrochemical cycling did not induce notable frustration in the crystal structure of manganate nanosheets, underscoring the high structural stability of the reassembled manganates. This study provided strong evidence for the effectiveness of the exfoliation-reassembling method in enhancing the capacitance performance of layered metal oxides. Refereed/Peer-reviewed
- Published
- 2010
20. Graphene-assisted room-temperature synthesis of 2D nanostructured hybrid electrode materials: dramatic acceleration of the formation rate of 2D metal oxide nanoplates induced by reduced graphene oxide nanosheets
- Author
-
Seong Ju Hwang, Da Young Sung, Tae Woo Kim, Yu Ri Lee, In Young Kim, Jayavant L. Gunjakar, Sung, Da-Young, Gunjakar, Jayavant L, Kim, Tae Woo, Kim, In Young, Lee, Yu Ri, and Hwang, Seong-Ju
- Subjects
Oxide ,Nanotechnology ,Spectrum Analysis, Raman ,Catalysis ,Nanocomposites ,law.invention ,room temperature synthesis ,chemistry.chemical_compound ,law ,hybrid materials ,nanostructures ,Electrodes ,Nanosheet ,Nanocomposite ,Chemistry ,Graphene ,Manganate ,Organic Chemistry ,graphene ,Temperature ,Oxides ,General Chemistry ,Persulfate ,Nanostructures ,electrodes ,Manganese Compounds ,Electrode ,Graphite ,Crystallization ,Hybrid material ,Porosity - Abstract
A new prompt room temperature synthetic route to 2D nanostructured metal oxide-graphene-hybrid electrode materials can be developed by the application of colloidal reduced graphene oxide (RGO) nanosheets as an efficient reaction accelerator for the synthesis of δ-MnO2 2D nanoplates. Whereas the synthesis of the 2D nanostructured δ-MnO2 at room temperature requires treating divalent manganese compounds with persulfate ions for at least 24h, the addition of RGO nanosheet causes a dramatic shortening of synthesis time to 1h, underscoring its effectiveness for the promotion of the formation of 2D nanostructured metal oxide. To the best of our knowledge, this is the first example of the accelerated synthesis of 2D nanostructured hybrid material induced by the RGO nanosheets. The observed acceleration of nanoplate formation upon the addition of RGO nanosheets is attributable to the enhancement of the oxidizing power of persulfate ions, the increase of the solubility of precursor MnCO3, and the promoted crystal growth of δ-MnO 2 2D nanoplates. The resulting hybridization between RGO nanosheets and δ-MnO2 nanoplates is quite powerful not only in increasing the surface area of manganese oxide nanoplate but also in enhancing its electrochemical activity. Of prime importance is that the present δ-MnO2-RGO nanocomposites show much superior electrode performance over most of 2D nanostructured manganate systems including a similar porous assembly of RGO and layered MnO2 nanosheets. This result underscores that the present RGO-assisted solution-based synthesis can provide a prompt and scalable method to produce nanostructured hybrid electrode materials. Refereed/Peer-reviewed
- Published
- 2013
21. Mixed colloidal suspensions of reduced graphene oxide and layered metal oxide nanosheets: useful precursors for the porous nanocomposites and hybrid films of graphene/metal oxide
- Author
-
Seong Ju Hwang, Jang Mee Lee, Tae Woo Kim, In Young Kim, Yu Ri Lee, Lee, Yu Ri, Kim, In Young, Kim, Tae Woo, Lee, Jang Mee, and Hwang, Seong-Ju
- Subjects
Chemistry, Multidisciplinary ,Inorganic chemistry ,Oxide ,Lithium ,composites ,Catalysis ,law.invention ,Nanomaterials ,Nanocomposites ,Colloid ,chemistry.chemical_compound ,Electrophoretic deposition ,Suspensions ,law ,hybrid materials ,Electrochemistry ,nanomaterials ,Nanocomposite ,Graphene ,Manganate ,Organic Chemistry ,Oxides ,General Chemistry ,self-assembly ,electrodes ,Chemistry ,chemistry ,Manganese Compounds ,Metals ,Graphite ,Hybrid material - Abstract
Homogeneously mixed colloidal suspensions of reduced graphene oxide, or RGO, and layered manganate nanosheets have been synthesized by a simple addition of the exfoliated colloid of RGO into that of layered MnO 2. The obtained mixed colloidal suspensions with the RGO/MnO 2 ratio of ≤0.3 show good colloidal stability without any phase separation and a negatively charged state with a zeta (ζ) potential of -30 to -40 mV. The flocculation of these mixed colloidal suspensions with lithium cations yields porous nanocomposites of Li/RGO-layered MnO 2 with high electrochemical activity and a markedly expanded surface area of around 70-100 m 2 g -1. Relative to the Li/RGO and Li/layered MnO 2 nanocomposites (≈116 and ≈167 F g -1), the obtained Li/RGO-layered MnO 2 nanocomposites deliver a larger capacitance of approximately 210 F g -1 with good cyclability of around 95-97 % up to the 1000th cycle, thus indicating the positive effect of hybridization on the electrode performances of RGO and lithium manganate. Also, an electrophoretic deposition of the mixed colloidal suspensions makes it possible to easily fabricate uniform hybrid films composed of graphene and manganese oxide. The obtained films show a distinct electrochemical activity and a homogeneous distribution of RGO and MnO 2. The present experimental findings clearly demonstrate that the utilization of the mixed colloidal suspensions as precursors provides a facile and universal methodology to synthesize various types of graphene/metal oxide hybrid materials. Refereed/Peer-reviewed
- Published
- 2012
22. Synthesis and electrochemical characterization of reduced graphene oxide-manganese oxide nanocomposites
- Author
-
Seong Ju Hwang, Min Sun Song, Kyung-Min Lee, In Young Kim, Yu Ri Lee, Lee, Yu Ri, Song, Min-Sun, Lee, Kyung Min, Kim, In Young, and Hwang, Seong-Ju
- Subjects
porous structure ,Materials science ,nanocomposite ,Graphene ,Inorganic chemistry ,Oxide ,Infrared spectroscopy ,chemistry.chemical_element ,Manganese ,Electrochemistry ,reduced graphene oxide ,Pseudocapacitance ,law.invention ,chemistry.chemical_compound ,chemistry ,law ,Calcination ,manganese oxide ,Graphene oxide paper ,pseudocapacitance - Abstract
Nanocomposites of reduced graphene oxide and manganese (II,III) oxide can be synthesized by the freeze-drying process of the mixed colloidal suspension of graphene oxide and manganese oxide, and the subsequent heat-treatment. The calcined reduced graphene oxide-manganese (II,III) oxide nanocomposites are X-ray amorphous, suggesting the formation of homogeneous and disordered mixture without any phase separation. The reduction of graphene oxide to reduced graphene oxide upon the heat-treatment is evidenced by Fourier-transformed infrared spectroscopy. Field emission-scanning electronic microscopy and energy dispersive spectrometry clearly demonstrate the formation of porous structure by the house-of-cards type stacking of reduced graphene oxide nanosheets and the homogeneous distribution of manganese ions in the nanocomposites. According to Mn K-edge X-ray absorption spectroscopy, manganese ions in the calcined nanocomposites are stabilized in octahedral symmetry with mixed Mn oxidation state of Mn(II)/Mn(III). The present reduced graphene oxide-manganese oxide nanocomposites show characteristic pseudocapacitance behavior superior to the pristine manganese oxide, suggesting their applicability as electrode material for supercapacitors. Refereed/Peer-reviewed
- Published
- 2011
Catalog
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.