• Carbon letters
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• 제14권4호
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• pp.206-209
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• 2013

Nanocomposites comprised of graphene oxide (GO) nanosheets and magnesium oxide (MgO) nanoparticles were synthesized by a sol-gel process. The synthesized samples were studied by X-ray powder diffraction, atomic force microscopy, transmission electron microscopy, and energy-dispersive X-ray analysis. The results show that the MgO nanoparticles, with an average diameter of 70 nm, are decorated uniformly on the surface of the GOs. By controlling the concentration of the MgO precursors and reaction cycles, it was possible to control the loading density and the size of the resulting MgO particles. Because the MgO particles are robustly anchored on the GO structure, the MgO/GOs nanocomposites will have future applications in the fields of adsorption and chemical sensing.

• Carbon letters
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• 제27권
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• pp.18-25
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• 2018

In this study, graphene oxide(GO) was used as drug carriers to amorphize poorly watersoluble drugs via a co-spray drying process. Two poorly water-soluble drugs, fenofibrate and ibuprofen, were investigated. It was found that the drug molecules could be in the graphene nanosheets in amorphous or nano crystalline forms and thus have a significantly enhanced dissolution rate compared with the counterpart crystalline form. In addition, the dissolution of the amorphous drug enwrapped with the graphene oxide was higher than that of the amorphous drug in activated carbon (AC) even though the AC possessed a larger specific surface area than that of the graphene oxide. The amorphous formulations also remained stable under accelerated storage conditions ($40^{\circ}C$ and 75% relative humidity) for a study period of 14 months. Therefore, graphene oxide could be a potential drug carrier and amorphization agent for poorly water-soluble drugs to enhance their bioavailability.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2011년도 춘계학술발표대회
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• pp.39.2-39.2
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• 2011

With the steady increase in the demand for flexible devices, mainly in display panels, researchers have focused on finding a novel material that have excellent electrical properties even when it is bended or stretched, along with superior mechanical and thermal properties. Graphene, a single-layered two-dimensional carbon lattice, has recently attracted tremendous research interest in this respect. However, the limitations in the growing method of graphene, mainly chemical vapor deposition on transition metal catalysts, has posed severe problems in terms of device integration, due to the laborious transfer process that may damage and contaminate the graphene layer. In addition, to lower the overall cost, a fabrication technique that supports low temperature and low vacuum is required, which is the main reason why solution-based process for graphene layer deposition has become the hot issue. Nonetheless, a direct deposition method of large area, few-layered, and uniform graphene layers has not been reported yet, along with a convenient method of patterning them. Here, we report an evaporation-induced technique for directly depositing few layers of graphene nanosheets with excellent uniformity and thickness controllability on any substrate. The printed graphene nanosheets can be patterned into desired shapes and structures, which can be directly applicable as flexible and transparent electrode. To illustrate such potential, the transport properties and resistivity of the deposited graphene layers have been investigated according to their thickness. The induced internal flow of the graphene solution during tis evaporation allows uniform deposition with which its thickness, and thus resistivity can be tuned by controlling the composition ratio of the solute and solvent.

• Nano
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• 제13권12호
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• pp.1850148.1-1850148.9
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• 2018

The interconnected three-dimensional Ni-Co-S nanosheets were successfully deposited on ZnO nanorods by a one-step potentiostatic electrodeposition. The Ni-Co-S nanosheets provide a large electrode/electrolyte interfacial area which has adequate electroactive sites for redox reactions. Electrochemical characterization of the ZnO@Ni-Co-S core-shell nanorods presents high specifc capacitance (1302.5 F/g and 1085 F/g at a current density of 1 A/g and 20 A/g), excellent rate capabilities (83.3% retention at 20 A/g) and great cycling stability (65% retention after 5000 cycles at a current density of 30 A/g). The outstanding electrochemical performance of the as-prepared electrode material also can be ascribed to these reasons that the special structure improved electrical conductivity and allowed the fast diffusion of electrolyte ions.

• 한국세라믹학회지
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• 제56권1호
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• pp.65-70
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• 2019

Simple fabrication of a powdered Ge-reduced graphene oxide (Ge-rGO) composite via spray pyrolysis and reduction is introduced herein. Successful incorporation of the rGO nanosheets with Ge hindered the aggregation of Ge and conferred enhanced structural stability to the composite by alleviating the mechanical stress associated with drastic volume changes during repeated cycling. The Li-ion storage performance of Ge-rGO was compared with that of powdered Ge metal. The reversible discharge capacity of Ge-rGO at the $200^{th}$ cycle was $748mA\;h\;g^{-1}$ at a current density of $1.0A\;g^{-1}$ and Ge-rGO showed a capacity of $375mA\;h\;g^{-1}$ even at a high current density of $5.0A\;g^{-1}$. The excellent performance of Ge-rGO is attributed to the structural robustness, enhanced electrical conductivity, and formation of open channels between the rGO nanosheets, which facilitated electrolyte penetration for improved Li-ion diffusion.

• Journal of Electrochemical Science and Technology
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• 제12권1호
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• pp.74-81
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• 2021

Silicon (Si) is recognized as a promising anode material for high-energy-density lithium-ion batteries. However, under a condition of electrode comparable to commercial graphite anodes with low binder content and a high electrode density, the practical use of Si is limited due to the huge volume change associated with Si-Li alloying/de-alloying. Here, we report a novel core-shell composite, having a reversible capacity of ~ 500 mAh g-1, by forming a shell composed of a mixture of nano-Si, graphite nanosheets and a pitch carbon on a spherical natural graphite particle. The electrochemical measurements are performed using electrodes with 2 wt % styrene butadiene rubber (SBR) and 2 wt.% carboxymethyl cellulose (CMC) binder in an electrode density of ~ 1.6 g cm-3. The core-shell composites having the reversible capacity of 478 mAh g-1 shows the outstanding capacity retention of 99% after 100 cycles with the initial coulombic efficiency of 90%. The heterostructure of core-shell composites appears to be very effective in buffering the volume change of Si during cycling.

• Carbon letters
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• 제25권
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• pp.1-13
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• 2018

Gold functionalized graphene oxide (GOAu) nanoparticles were reinforced in acrylonitrile-butadiene rubbers (NBR) via solution and melt mixing methods. The synthesized NBR-GOAu nanocomposites have shown significant improvements in their rate of curing, mechanical strength, thermal stability and electrical properties. The homogeneous dispersion of GOAu nanoparticles in NBR has been considered responsible for the enhanced thermal conductivity, thermal stability, and mechanical properties of NBR nanocomposites. In addition, the NBR-GOAu nanocomposites were able to show a decreasing trend in their dielectric constant (${\varepsilon}^{\prime}$) and electrical resistance on straining within a range of 10-70%. The decreasing trend in ${\varepsilon}^{\prime}$ is attributed to the decrease in electrode and interfacial polarization on straining the nanocomposites. The decreasing trend in electrical resistance in the nanocomposites is likely due to the attachment of Au nanoparticles to the surface of GO sheets which act as electrical interconnects. The Au nanoparticles have been proposed to function as ball rollers in-between GO nanosheets to improve their sliding on each other and to improve contacts with neighboring GO nanosheets, especially on straining the nanocomposites. The NBR-GOAu nanocomposites have exhibited piezoelectric gauge factor (${GF_{\varepsilon}}^{\prime}$) of ~0.5, and piezo-resistive gauge factor ($GF_R$) of ~0.9 which clearly indicated that GOAu reinforced NBR nanocomposites are potentially useful in fabrication of structural, high temperature responsive, and stretchable strain-sensitive sensors.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2018년도 춘계학술대회 논문집
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• pp.114-114
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• 2018

탄소 재료는 뛰어난 물성에서 다양한 재료로의 응용이 기대되고 있다. 특히, 이종 원소 함유 카본 재료는 전기적 특성과 촉매성의 발현 등 새로운 기능을 카본 재료에 부여할 수 있어서 연료 전지, 에너지 저장, 태양 전지 등에의 응용이 기대되고 있다. 최근, 용액 중의 저온 플라즈마인 솔루션 플라즈마(solution plasma process)를 이용하여 벤젠 용액 등에서 탄소 재료 합성에 성공하였다. 그러나 기존의 연구에서는 솔루션 플라즈마 프로세스를 이용하여 합성한 이종원소 카본은 전도성이 낮아 이종원소의 함유량을 낮추는 고온의 열처리가 필요했다. 따라서 본 연구에서는 우수한 물리적 전기적 특성을 갖는 그래핀(graphene)과 같은 이종 원소 카본 나노시트(heteroatom carbon nanosheets)의 합성 및 메커니즘(mechanism)에 대해 검토하였다. 다양한 이종원소를 포함한 유기용매 안에 바이폴라 펄스 전원에 의한 전압을 두 텅스텐 전극 간에 인가하고, 솔루션 플라즈마를 생성하여 이종원소 카본 재료를 합성했다. 플라즈마 생성은 텅스텐 봉을 전극으로 사용하고 전압을 2.0 kV, 펄스 주파수를 200 kHz, 펄스 폭을 $1.0{\mu}s$, 전극 간 거리를 1.5 mm에서 일정하게 유지하며 200 mL 유기용매 중에서 방전시키는 것으로 재료를 합성했다. 플라즈마 방전 후, 필터을 이용하여 흡인 여과한 뒤 $200^{\circ}C$에서 1 시간 동안 건조 시켰다. 건조 후의 이종원소 카본의 물리적 특성을 원소 분석, X선 회절 법(XRD), 저항률 측정, 투과형 전자 현미경(TEM) 및 라만 분광법, 전자 현미경(SEM), X-선광전자분광기(XPS)등을 이용하여 카본의 형상 및 특성을 분석하였다. 그 결과 다양한 이종원소를 포함한 유기용매 중 2-pyrrolidone을 사용했을 때, 이종 원소 카본 나노시트를 합성하는데 성공하였다. 또한, 이 연구방법을 통해서 솔루션 플라즈마 프로세스를 통한 카본 나노시트 합성의 메커니즘을 규명하였다.

• 한국분말재료학회지
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• 제24권4호
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• pp.279-284
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• 2017

The formation mechanism and photocatalytic properties of a multiwalled carbon nanotube (MWCNT)/$TiO_2$-based nanotube (TNTs) composite are investigated. The CNT/TNT composite is synthesized via a solution chemical route. It is confirmed that this 1-D nanotube composite has a core-shell nanotubular structure, where the TNT surrounds the CNT core. The photocatalytic activity investigated based on the methylene blue degradation test is superior to that of with pure TNT. The CNTs play two important roles in enhancing the photocatalytic activity. One is to act as a template to form the core-shell structure while titanate nanosheets are converted into nanotubes. The other is to act as an electron reservoir that facilitates charge separation and electron transfer from the TNT, thus decreasing the electron-hole recombination efficiency.

• Carbon letters
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• 제21권
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• pp.74-80
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• 2017

A highly facile and eco-friendly green synthesis of Annona squamosa (custard apple) leaf extract reduced graphene oxide (CRG) nanosheets was achieved by the reduction of graphene oxide (GO). The as-prepared CRG was characterized with X-ray diffraction (XRD), transmission electron microscope (TEM), Fourier-transform infrared spectroscopy (FT-IR), ultraviolet-visible (UV-Vis), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopic techniques. Removal of oxygen containing moieties from the GO was confirmed by UV-Vis, FT-IR and XPS spectroscopic data. The XRD and Raman data further confirmed the formation of the CRG. TEM images showed the sheet structure of the synthesized CRG. These results show that the phytochemicals present in custard apple leaf extract act as excellent reducing agents. The CRG showed good dispersion in water.