• Advances in nano research
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• 제6권4호
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• pp.357-375
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• 2018

Two dimensional (2D) atomic layered nanomaterials exhibit some of the most striking phenomena in modern materials research and hold promise for a wide range of applications including energy and biomedical technologies. Graphene has received much attention for having extremely high surface area to mass ratio and excellent electric conductivity. Graphene has also been shown to maximize the activity of surface-assembled metal nanoparticle catalysts due to its unique characteristics of enhancing mass transport of reactants to catalysts. This paper specifically investigates the strategy of pre-formed nanoparticle self-assembly used for the formation of various metal nanoparticles supported on graphene families such as graphene, graphene oxide, and reduced graphene oxide and aims at understanding the interactions between ligand-capped metal nanoparticles and 2D nanomaterials. By varying the functional groups on the ligands between alkyl, aromatic, amine, and alcohol groups, different interactions such as van der Waals, ${\pi}-{\pi}$ stacking, dipole-dipole, and hydrogen bonding are formed as the 2D hybrids produced.

• 폴리머
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• 제37권2호
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• pp.218-224
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• 2013

Hummers and Offeman 방법을 이용하여 흑연으로부터 산화 그래핀(graphene oxide; GO)을 합성하였고, 이를 이용하여 두 가지 다른 작용기화 그래핀(FGS)을 합성하였다. 그래핀 판상(graphene sheet; GS)에 수직방향으로 hexadecylamine(HDA)이 치환된 Ver-HDA-GS을 HDA와 에폭시기를 반응하여 얻었고, 한편으로, 환원된 GO(Reduced-GO; RGO)를 통하여 hexadecanol(HDO)와 알코올을 반응시켜 HDO가 수평 방향으로 치환된 Hor-HDO-GS를 합성하였다. 합성된 GO, RGO, Ver-HDA-GS 그리고 Hor-HDO-GS의 합성여부를 확인하기 위하여 FTIR을 이용하였으며, 합성된 물질들의 열 안정성 및 모폴로지를 각각 확인하였다. 원자간력 현미경(AFM)을 통해서 Ver-HDA-GS는 한 층 또는 두 층 두께의 그래핀으로 이루어졌고, 평균 두께는 1.76 nm임을 확인하였다. 합성된 FGS들의 열 안정성은 GO나 RGO보다 더 나았으며, 분산도의 경우에 Ver-HDA-GS는 DMSO, 톨루엔, 클로로포름, 데카린 등의 일상적인 용매에서 잘 분산되었다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.488.1-488.1
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• 2014

As the society demands the high performance energy storage devices, development of efficient and renewable energy storage materials has been a topic of interest. Here, we report pseudocapacitive behaviors of biopolymer (lignin) that was confined onto reduced graphene oxides (RGOs) for a renewable energy storage system. The strong surface confinement of quinone groups onto the electroconductive RGOs created the renewable hybrid electrodes for supercapacitors (SCs) with fast and reversible redox charge transfer. As a result, the pseudocapacitors fabricated with the hybrid electrodes of lignin and RGO presented the outstanding electrochemical performances of remarkable rate and cyclic performances:~4% capacitance drop after 3000 cycles and a maximum capacitance of 432 F g-1.

• Carbon letters
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• 제15권1호
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• pp.38-44
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• 2014

This paper reports the effect of adding reduced graphene oxide (RGO) as a conductive material to the composition of an electrode for capacitive deionization (CDI), a process to remove salt from water using ionic adsorption and desorption driven by external applied voltage. RGO can be synthesized in an inexpensive way by the reduction and exfoliation of GO, and removing the oxygen-containing groups and recovering a conjugated structure. GO powder can be obtained from the modification of Hummers method and reduced into RGO using a thermal method. The physical and electrochemical characteristics of RGO material were evaluated and its desalination performance was tested with a CDI unit cell with a potentiostat and conductivity meter, by varying the applied voltage and feed rate of the salt solution. The performance of RGO was compared to graphite as a conductive material in a CDI electrode. The result showed RGO can increase the capacitance, reduce the equivalent series resistance, and improve the electrosorption capacity of CDI electrode.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2015년도 제49회 하계 정기학술대회 초록집
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• pp.222.1-222.1
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• 2015

Recently, graphene quantum dots (GQDs) have attracted great attention due to various properties including cost-effectiveness of synthesis, low toxicity, and high photostability. Nevertheless, the origins of photoluminescence (PL) from GQDs are unclear because of extrinsic states of the impurities, disorder structures, and oxygen-functional groups. Therefore, to utilize GQDs in various applications, their optical properties generated from the extrinsic states should be understood. In this work, we have focused on the effect of oxygen-functional groups in PL of the GQDs. The GQDs with nanoscale and single layer are synthesized by employing graphite nanoparticles (GNPs) with 4 nm. The series of GQDs with different amount of oxygen-functional groups were prepared by the chain of chemical oxidation and reduction process. The fabrication of a series of graphene oxide QDs (GOQDs) with different amounts of oxygen-contents is first reported by a direct oxidation route of GNPs. In addition, for preparing a series of reduced GOQDs (rGOQDs), we employed the conventional chemical reduction to GOQDs solution and controlled the amount of reduction agents. The GOQDs and rGOQDs showed irreversible PL properties even though both routes have similar amount of oxyen-functional groups. In the case of a series of GOQDs, the PL spectrum was clearly redshifted into blue and green-yellowish color. On the other hand, the PL spectrum of rGOQDs did not change significantly. By various optical measurement such as the PL excitation, UV-vis absorbance, and time-resolved PL, we could verify that their PL mechanisms of GOQDs and rGOQDs are closely associated with different atomic structures formed by chemical oxidation and reduction. Our study provides an important insights for understanding the optical properties of GQDs affected by oxygen-functional groups. [1]

• 공업화학
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• 제25권6호
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• pp.581-585
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• 2014

Reduced graphene oxide (RGO)를 수용성 고분자인 poly(styrene sulfonate) (PSS)로 wrapping한 수분산성 그래핀 치환체인 G-PSS와 전도성 고분자인 poly(3,4-ethylenedioxythiophene)/poly(styrene sulfonate) (PEDOT/PSS)의 복합화에 관하여 연구하였다. G-PSS의 존재 하에서 PEDOT/PSS의 제자리 화학 중합 반응을 수행하여 복합체(GP)를 얻었다. 생성물의 XPS, IR 및 Raman 분석을 통하여 모노머인 EDOT의 중합이 원활하게 진행되어 PEDOT/PSS가 생성됨과 동시에 그래핀과 복합화되었다는 것을 확인할 수 있었다. 또한 GP는 $4.46{\times}10^2S/m$의 전도도를 나타냈으며, 0.5%의 농도까지 물에 분산이 되어 G-PSS보다 전기적 특성 및 수분산성 모두 우수하였다.

• Carbon letters
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• 제19권
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• pp.40-46
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• 2016

Nitrogen-atom doped graphene oxide was considered to prevent the dissolution of polysulfide and to guarantee the enhanced redox reaction of sulfur for good cycle performance of lithium sulfur cells. In this study, we used urea as a nitrogen source due to its low cost and easy preparation. To find the optimum urea content, we tested three different ratios of urea to graphene oxide. The morphology of the composites was examined by field emission scanning electron microscope. Functional groups and bonding characterization were measured by X-ray photoelectron spectroscopy. Electrochemical properties were characterized by cyclic voltammetry in an organic electrolyte solution. Compared with thermally reduced graphene/sulfur (S) composite, nitrogen-doped graphene/S composites showed higher electroactivity and more stable capacity retention.

• Carbon letters
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• 제25권
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• pp.14-24
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• 2018

Electrochemical properties and performance of composites performed by incorporating metal oxide or metal hydroxide on carbon materials based on graphene and carbon nanotube (CNT) were analyzed. From the surface analysis by field emission scanning electron microscopy and field emission transmission electron microscopy, it was confirmed that graphene, CNT and metal materials are well dispersed in the ternary composites. In addition, structural and elemental analyses of the composite were conducted. The electrochemical characteristics of the ternary composites were analyzed by cyclic voltammetry, galvanostatic charge-discharge tests, and electrochemical impedance spectroscopy in 6 M KOH, or $1M\;Na_2SO_4$ electrolyte solution. The highest specific capacitance was $1622F\;g^{-1}$ obtained for NiCo-containing graphene with NiCo ratio of 2 to 1 (GNiCo 2:1) and the GNS/single-walled carbon $nanotubes/Ni(OH)_2$ (20 wt%) composite had the maximum specific capacitance of $1149F\;g^{-1}$. The specific capacitance and rate-capability of the $CNT/MnO_2/reduced$ graphene oxide (RGO) composites were improved as compared to the $MnO_2/RGO$ composites without CNTs. The $MnO_2/RGO$ composite containing 20 wt% CNT with reference to RGO exhibited the best specific capacitance of $208.9F\;g^{-1}$ at a current density of $0.5A\;g^{-1}$ and 77.2% capacitance retention at a current density of $10A\;g^{-1}$.

• 폴리머
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• 제38권4호
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• pp.484-490
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• 2014

Reduced graphene oxide (RGO) was fabricated using gelatin as a reductant, and it could be stably dispersed in gelatin solution without aggregation. A series of RGO/gelatin composite films with various RGO contents were prepared by a solution-casting method. The structure and thermal properties of the RGO/gelatin composite films were characterized by UV-vis spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), differential scanning calorimeter (DSC) and thermal gravimetric analysis (TGA). The addition of RGO enhances the degree of crosslinking of gelatin films and decreases the swelling ability of the gelatin films in water, indicating that RGO/gelatin composite films have a better wet stability than gelatin films. The glass transition temperature ($T_g$) of gelatin films is also increased with the incorporation of RGO. The presence of RGO slightly increases the degradation temperature of gelatin films due to the very low content of RGO in the composite films. Since gelatin is a natural and nontoxic biomacromolecule, the RGO/gelatin composite films are expected to have potential applications in the biomedical field.

• Carbon letters
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• 제13권4호
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• pp.230-235
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• 2012

In this study, reduced graphene oxide/polyimide (r-GO/PI) composite films, which showed significant enhancement in their electrical conductivity, were successfully fabricated. GO was prepared from graphite using a modified Hummers method. The GO was used as a nanofiller material for the preparation of r-GO/PI composites by in-situ polymerization. An addition of 20 wt% of GO led to a significant decrease in the volume resistivity of composite films by less than nine orders of magnitude compared to that of pure PI films due to the electrical percolation networks of reduced GO created during imidization within the films. A tensile test indicated that the Young's modulus of the r-GO/PI composite film containing 20 wt% GO increased drastically from 2.3 GPa to 4.4 GPa, which was an improvement of approximately 84% compared to that of pure PI film. In addition, the corresponding tensile strength was found to have decreased only by 12%, from 113 MPa to 99 MPa.