• Carbon letters
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• 제14권4호
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• pp.247-250
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• 2013

In this study, we present a facile method of fabricating graphene oxide (GO) films on the surface of polyimide (PI) via layer-by-layer (LBL) assembly of charged GO. The positively charged amino-phenyl functionalized GO (APGO) is alternatively complexed with the negatively charged GO through an electrostatic LBL assembly process. Furthermore, we investigated the water vapor transmission rate and oxygen transmission rate of the prepared (reduced GO $[rGO]/rAPGO)_{10}$ deposited PI film (rGO/rAPGO/PI) and pure PI film. The water vapor transmission rate of the GO and APGO-coated PI composite film was increased due to the intrinsically hydrophilic property of the charged composite films. However, the oxygen transmission rate was decreased from 220 to 78 $cm^3/m^2{\cdot}day{\cdot}atm$, due to the barrier effect of the graphene films on the PI surface. Since the proposed method allows for large-scale production of graphene films, it is considered to have potential for utilization in various applications.

• Carbon letters
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• 제13권1호
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• pp.48-50
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• 2012

Mass production of graphene-based materials, which have high specific surface area, is of importance for industrial applications. Herein, we report on a facile approach to produce thermally modified graphene oxide (TMG) in large quantities. We performed this experiment with a hot plate under environments that have relatively low temperature and no using inert gas. TMG materials showed a high specific surface area (430 $m^2g^{-1}$). Successful reduction was confirmed by elemental analysis, X-ray photoelectron spectroscopy, thermogravimetic analysis, and X-ray diffraction. The resulting materials might be useful for various applications such as in rechargeable batteries, as hydrogen storage materials, as nano-fillers in composites, in ultracapacitors, and in chemical/bio sensors.

• Bulletin of the Korean Chemical Society
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• 제35권6호
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• pp.1799-1805
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• 2014

In this article, we described about the preparation and electrochemical properties of a flexible energy storage system based on a plastic polyethylene terephthalate (PET) substrate. The PET treated with UV/ozone was fabricated with multilayer films composed of 30 polyaniline (PANi)/graphene oxide (GO) bilayers using layer-by-layer assembly of positively charged PANi and negatively charged GO. The conversion of GO to the reduced graphene oxide (RGO) in the multilayer film was achieved using hydroiodic acid vapor at $100^{\circ}C$, whereby PANi structure remained nearly unchanged except a little reduction of doping state. Cyclic voltammetry and charge/discharge curves of 30 PANi/RGO bilayers on PET substrate (shorten to PANi-$RGO_{30}$/PET) exhibited an excellent volumetric capacitance, good cycling stability, and rapid charge/discharge rates despite no use of any metal current collectors. The specific capacitance from charge/discharge curve of the PANi-$RGO_{30}$/PET electrode was found to be $529F/cm^3$ at a current density of $3A/cm^3$, which is one of the best values yet achieved among carbon-based materials including conducting polymers. Furthermore, the intrinsic electrical resistance of the PANi-$RGO_{30}$/PET electrodes varied within 20% range during 200 bending cycles at a fixed bend radius of 2.2 mm, indicating the increase in their flexibility by a factor of 225 compared with the ITO/PET electrode.

• 한국수소및신에너지학회논문집
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• 제27권4호
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• pp.329-334
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• 2016

Hydrogen is eco-friendly alternative energy source and the photoelectrochemical water splitting is believed to be one of the promising methods for hydrogen production. Many researchers have studied several potential photocatalysts to increase the photoelectochemical performance efficiency for hydrogen conversion. In this study, the GO (graphene oxide) was prepared by Tour's method and was dispersed in precursor solutions of $WO_3$ and $BiVO_4$. Those precursor solutions were spin-coated on FTO glass and several photocatalyst thin films of $WO_3$, $BiVO_4$ and $WO_3/BiVO_4$ were prepared by calcination. The morphologies of prepared photocatalyst thin films were measured by scanning electron microscope. The photoelectrochemical performances of photocatalyst thin films with rGO (reduced graphene oxide) and without rGO were analyzed systematically.

• 한국레이저가공학회지
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• 제15권4호
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• pp.1-5
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• 2012

We demonstrate that reduced graphene oxide (rGO) coated thin aluminum film is an effective optoacoustic transmitter for generating high pressure and high frequency ultrasound previously unattainable by other techniques. The rGO layer of different thickness is deposited between a 100 nm-thick aluminum film and a glass substrate. Under a pulsed laser excitation, the transmitter generates enhanced optoacoustic pressure of 64 times the aluminum-alone transmitter. A promising optoacoustic wave generation is possible by optimizing thermoelasticity of metal film and thermal conductivity of rGO in the proposed transmitter for laser-induced ultrasound (LIUS) applications.

• Carbon letters
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• 제15권1호
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• pp.67-70
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• 2014

In this work, nanocomposites of epoxy resin and chemically reduced graphene oxide (RGO) were prepared by thermal curing process. X-ray diffractions confirmed the microstructural properties of RGO. Differential scanning calorimetry was used to evaluate the curing behaviors of RGO/epoxy nanocomposites with different RGO loading amounts. We investigated the effect of RGO loading amounts on the mechanical properties of the epoxy nanocomposites. It was found that the presence of RGO improved both flexural strength and modulus of the epoxy nanocomposites till the RGO loading reached 0.4 wt%, and then decreased. The optimum loading achieved about 24.5 and 25.7% improvements, respectively, compared to the neat-epoxy composites. The observed mechanical reinforcement might be an enhancement of mechanical interlocking between the epoxy matrix and RGO due to the unique planar structures.

• Journal of Industrial and Engineering Chemistry
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• 제67권
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• pp.478-485
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• 2018

The effect of reduced graphene oxide (RGO) addition on the dielectric and piezoelectric behavior of the polyvinylidene fluoride (PVDF) films was studied. Dielectric constant increased by four times and piezoelectric coefficient also increased twice by the addition of RGO in the PVDF films. Based on capacitance-voltage and ellipsometry measurements and the Kramers-Kronig transformation, it is concluded that the enhanced dielectric and piezoelectric properties of the PVDF/RGO films resulted from the increased orientational polarization due to a phase transition from nonpolar crystalline ${\alpha}$ phase to polar crystalline ${\beta}$ phase in the PVDF structure.

• Current Optics and Photonics
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• 제6권4호
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• pp.367-374
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• 2022

A photodetector based on a reduced graphene oxide (RGO)/n-Si heterojunction with high responsivity, detectivity and fast response speed is presented. Here, we put forward a simple vacuum filtration method to prepare RGO film and transfer it onto an n-Si substrate to form an RGO/n-Si heterojunction. The experimental results show that the heterojunction has good rectification characteristics, and the response and recovery time are less than 0.31 s and 0.25 s, respectively. Under 470 nm light conditions at -2 V applied voltage, the responsivity and detectivity of the device are 65 mA/W and 4.02 × 10¹⁰ cmHz^1/2W^-1, respectively. The simple preparation process and good performance of the RGO/n-Si heterojunction make it a promising material for photoelectric detection, especially in the near-ultraviolet band.

• Composites Research
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• 제34권2호
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• pp.108-114
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• 2021

일반적으로 그래핀 플레이크는 산화그래핀을 화학적 또는 열적 환원 공정을 통해 환원그래핀으로 변환하여 대량 생산하고 있다. 그래핀 플레이크는 다양한 형태로 응용되는데, 그 중 진공여과를 이용한 적층 공정을 통해 종이형 필름으로 제작이 가능하다. 그래핀 종이는 신축성이 부족한 단점이 있어 신축성 소자 응용에 제약이 있다. 본 연구에서는 신축성이 있는 그래핀 종이를 제작하기 위하여, 그래핀 종이에 주름을 만들었다. 신축성이 뛰어난 접착 필름을 미리 늘린 후, 그 위에 그래핀 종이를 붙이고, 접착 필름을 원래 상태로 놓아 주어 그래핀 종이에 주름을 만들었다. 이 때, 접착 필름에 가하는 당김 정도 및 젖은 상태에 따라 주름의 형상이 변하는 것을 실험적으로 관찰하였다. 특히, 그래핀 종이와 접착 필름의 전단 탄성 계수 차에 의하여 주름의 주기가 바뀌는 현상을 관찰하였다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제42회 동계 정기 학술대회 초록집
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• pp.195-195
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• 2012

Recently, graphene based solution-gated field-effect transistors (SGFETs) have been received a great attention in biochemical sensing applications. Graphene and reduced graphene oxide (RGO) possess various advantages such as high sensitivity, low detection limit, label-free electrical detection, and ease of fabrication due to their 2D nature and large sensing area compared to 1D nanomaterials- based nanobiosensors. Therefore, graphene or RGO -based SGFET is a good potential candidate for sensitive detection of protons (H+ ions) which can be applied as the transducer in various enzymatic or cell-based biosensing applications. However, reports on detection of H+ ions using graphene or RGO based SGFETs have been still limited. According to recent reports, clean graphene grown by CVD or exfoliation is electrochemically insensitive to changes of H+ concentration in solution because its surface does not have terminal functional groups that can sense the chemical potential change induced by varying surface charges of H+ on CVD graphene surface. In this work, we used RGO -SGFETs having oxygen-containing functional groups such as hydroxyl (OH) groups that effectively interact with H+ ions for expectation of increasing pH sensitivity. Additionally, we also investigate RGO based SGFETs for bio-sensing applications. Hydroloytic enzymes were introduced for sensing of biomolecular interaction on the surface of RGO -SGFET in which enzyme and substrate are acetylcholinesterase (AchE) and acetylcholine (Ach), respectively. The increase in H+ generated through enzymatic reaction of hydrolysis of Ach by AchE immobilized on RGO channel in SGFET could be monitored by the change in the drain-source current (Ids).