• Title/Summary/Keyword: graphite oxide

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Direct Comparison of Optical Properties from Graphene Oxide Quantum Dots and Graphene Oxide

  • Jang, Min-Ho;Ha, Hyun Dong;Seo, Tae Seok;Cho, Yong-Hoon
    • Applied Science and Convergence Technology
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    • v.24 no.4
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    • pp.111-116
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    • 2015
  • The graphene oxide (GO) and graphene oxide quantum dots (GOQDs), which have gained research interest as new types of light-emitting materials, were synthesized by the modified Hummers method for oxidation of graphite flake and graphite nanoparticle. The optical properties of GO and GOQDs have been compared by mean of photoluminescence (PL), PL excitation (PLE), UV-vis absorbance, and time-resolved PL. The GO have an absorption peak at 229 nm and shoulder part at 310 nm, whereas the GOQDs show broad absorption with a gradual change up without any absorption peaks. The PL emission of GOQDs and GO showed the green color at 520 nm and the red color at 690 nm, respectively. The red emission of GO showed faster PL decay time than the green emission of GOQDs. In particular, the temporal PL profile of the GO showed redshift from 560 nm to 660 nm after the pump event.

Effect of Electrolyte Additive on the Electrochemical Characteristics of Lithium Vanadium Oxide Anode (전해질 첨가제가 리튬 바나듐 옥사이드 전극의 성능에 미치는 영향)

  • Lee, Je-Nam
    • Journal of the Korean Electrochemical Society
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    • v.21 no.3
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    • pp.55-60
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    • 2018
  • The demand for LIBs with higher energy densities has increased continuously because the emergence of wider and more challenging applications including HEV and EV has became imperative. However, in the case of anode material, graphite is insufficient to meet this need. To meet such demand, several type of negative electrode materials like silicon, tin, SiO, and transition metal oxide have been investigated for the advanced lithium secondary batteries. Recently, lithium vanadium oxide, which has a layered structure, is assumed as one of the promising anode material as alternative of graphite. This material shows a high volumetric capacity, which is 1.5 times higher than that of graphite. However, relative low electrical conductivity and particle fracture, which results in the electrolyte decomposition and loss of electric contact between electrode, induce rapid capacity decay. In this report, we investigated the effect of electrolyte additive on the electrochemical characteristics of lithium vanadium oxide.

Interfacial Microstructure of Diffusion-Bonded W-25Re/Ti/Graphite Joint and Its High-Temperature Stability (확산 접합에 의해 제조된 텅스텐-레늄 합금/티타늄/그래파이트 접합체의 미세구조 및 고온 안정성)

  • Kim, Joo-Hyung;Baek, Chang Yeon;Kim, Dong Seok;Lim, Seong Taek;Kim, Do Kyung
    • Korean Journal of Materials Research
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    • v.26 no.12
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    • pp.751-756
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    • 2016
  • Graphite was diffusion-bonded by hot-pressing to W-25Re alloy using a Ti interlayer. For the joining, a uniaxial pressure of 25 MPa was applied at $1600^{\circ}C$ for 2 hrs in an argon atmosphere with a heating rate of $10^{\circ}C\;min^{-1}$. The interfacial microstructure and elemental distribution of the W-25Re/Ti/Graphite joints were analyzed by scanning electron microscopy (SEM). Hot-pressed joints appeared to form a stable interlayer without any micro-cracking, pores, or defects. To investigate the high-temperature stability of the W-25Re/Ti/Graphite joint, an oxy-acetylene torch test was conducted for 30 seconds with oxygen and acetylene at a 1.3:1 ratio. Cross-sectional analysis of the joint was performed to compare the thickness of the oxide layer and its chemical composition. The thickness of W-25Re changed from 250 to $20{\mu}m$. In the elemental analysis, a high fraction of rhenium was detected at the surface oxidation layer of W-25Re, while the W-25Re matrix was found to maintain the initial weight ratio. Tungsten was first reacted with oxygen at a torch temperature over $2500^{\circ}C$ to form a tungsten oxide layer on the surface of W-25Re. Then, the remaining rhenium was subsequently reacted with oxygen to form rhenium oxide. The interfacial microstructure of the Ti-containing interlayer was stable after the torch test at a temperature over $2500^{\circ}C$.

Influence of Graphene Oxide and Graphite Nanoplatelets on Rheological and Electrical Properties of Polystyrene Nanocomposites (산화 그래핀과 나노 흑연이 폴리스티렌 나노복합재료의 유변물성 및 전기적 물성에 미치는 영향)

  • Yeom, Hyo Yeol;Na, Hyo Yeol;Lee, Seong Jae
    • Polymer(Korea)
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    • v.38 no.4
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    • pp.502-509
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    • 2014
  • Carbon-based nanoplatelets such as graphene oxide (GO) sheets and graphite nanoplatelets (GNPs) are frequently used as conductive nanofillers for polymer nanocomposites. In this study, polystyrene (PS)/GO and PS/GNP nanocomposites were prepared through a latex technology and investigated to compare the effect of nanofillers on rheological and electrical properties of the PS nanocomposites. PS particles were prepared by emulsifier-free emulsion polymerization and GO was synthesized by using the modified Hummers' method from graphite. Hydrophilic GO was dispersed in aqueous PS suspension, but hydrophobic GNPs were dispersed with the help of a surfactant. In comparison with PS/GO nanocomposites, the rheological properties of PS/GNP counterparts were not too high because GNP existed in aggregates of graphene layers. Conducting pathways of PS/GO and PS/GNP nanocomposites were achieved at the electrical percolation threshold of 0.50 and 5.82 wt%, respectively. The reason for enhanced electrical conductivity in PS/GO nanocomposites is that GO was thermally reduced during molding.

The Reactions of the Ti Melt with CaO and Graphite and the Effect of Pressure on the Formation of Gas Porosity (티타늄 용탕의 산화칼슘 및 흑연과의 반응 및 기포 결함의 형성에 미치는 압력의 영향)

  • Bae, Chang-Gun;Kwon, Hae-Wook
    • Journal of Korea Foundry Society
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    • v.20 no.4
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    • pp.247-253
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    • 2000
  • Titanium was melted in the CaO-coated alumina crucible and the reaction between the melt and the coating layer was negligible. The volume fraction of the gas porosity was decreased with increasing pressure and the sound bar castings with no porosity was obtained under the Ar atmosphere of the pressure of $300kN/mm^2$. The surface of the casting obtained from CaO-coated graphite mold was slightly rougher than that from graphite without coating. The reaction product of titanium melt with the layer of CaO was mainly titanium oxide and that with graphite crucible was titanium cabide with small amount of titanium nitride.

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Oxidation-treated of Oxidized Carbons and its Electrochemical Performances for Electric Double Layer Capacitor (산화처리 탄소 및 이를 이용한 EDLC 특성)

  • Yang, Sun-Hye;Kim, Ick-Jun;Jeon, Min-Je;Moon, Seong-In;Kim, Hyun-Soo;An, Kye-Hyeok;Lee, Yun-Pyo
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.20 no.6
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    • pp.502-507
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    • 2007
  • The oxidation treatment of several carbon materials with a sodium chlorate and 70 wt.% of nitric acid, combined with heat treatment, were attempted to achieve an electrochemical active material with a larger capacitance. Among pitch, needle coke, calcinated needle coke and natural graphite, the structure of needle coke and calacinated needle coke were changed to the graphite oxide structure with the expansion of the inter-layer. On the other hand, the calcinated needle coke after oxidation and heating at $200^{\circ}C$ has exhibited largest capacitance per weight and volume of 29.5 F/g and 24.5 F/ml at the two-electrode system in the potential range of 0 to 2.5 V. The electrochemical performance of the calcinated needle coke was discussed with the phenomenon of the electric field activation and the formation of new pores between the expanded inter-layer at first charge.

Battery Electrode Characteristics of Si-based Composite by Mechanical Alloying Method (기계적 합금화법에 의한 실리콘계 복합물질의 전지전극특성)

  • Lee, Churl-Kyoung;Lee, Jong-Ho;Lee, Sang-Woo
    • Journal of Powder Materials
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    • v.16 no.6
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    • pp.389-395
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    • 2009
  • A Si-CuO-graphite composite was prepared by a mechanical alloying (MA) method. The Si-CuO composite has a mixture structure, where CuO is homogeneously dispersed in Si. Also, $Cu_2O$ and $Cu_3Si$ phases were formed during MA and heat treatment. Graphite with the Si-CuO composite was mixed in the same mill for 30 minutes with weight ratio of Si-CuO composite and graphite as 1:1. The Si-CuO composite was homogeneously covered with graphite. SiC phase was not formed. Electrochemical tests of the composite have been investigated, and the first charge and discharge capacities of the material were about 870mAh/g and 660mAh/g, respectively. Those values are about 76% of the first cycle efficiency. The cycle life of the composite showed that the initial discharge capacity of 660 mAh/g could be maintained up to 92% after 20 cycles.

Facile synthesis of ZnBi2O4-graphite composites as highly active visible-light photocatalyst for the mineralization of rhodamine B

  • Nguyen, Thi Mai Tho;Bui, The Huy;Dang, Nguyen Nha Khanh;Ho, Nguyen Nhat Ha;Vu, Quang Huy;Ngo, Thi Tuong Vy;Do, Manh Huy;Duong, Phuoc Dat;Nguyen, Thi Kim Phuong
    • Korean Journal of Chemical Engineering
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    • v.35 no.12
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    • pp.2442-2451
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    • 2018
  • Novel highly active visible-light photocatalysts in the form of zinc bismuth oxide ($ZnBi_2O_4$) and graphite hybrid composites were prepared by coupling via a co-precipitation method followed by calcination at $450^{\circ}C$. The asprepared $ZnBi_2O_4$-graphite hybrid composites were tested for the degradation of rhodamine B (RhB) solutions under visible-light irradiation. The existence of strong electronic coupling between the two components within the $ZnBi_2O_4$-graphite heterostructure suppressed the photogenerated recombination of electrons and holes to a remarkable extent. The prepared composite exhibited excellent photocatalytic activity, leading to more than 93% of RhB degradation at an initial concentration of $50mg{\cdot}L^{-1}$ with 1.0 g catalyst per liter in 150 min. The excellent visible-light photocatalytic mineralization of $ZnBi_2O_4-1.0graphite$ in comparison with pristine $ZnBi_2O_4$ could be attributed to synergetic effects, charge transfer between $ZnBi_2O_4$ and graphite, and the separation efficiency of the photogenerated electrons and holes. The photo-induced $h^+$ and the superoxide anion were the major active species responsible for the photodegradation process. The results demonstrate the feasibility of $ZnBi_2O_4-1.0graphite$ as a potential heterogeneous photocatalyst for environmental remediation.