• 한국결정성장학회지
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• 제23권6호
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• pp.325-328
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• 2013

Phosphate has been removed in waste water by chemically synthesized graphene oxide. Removing efficiency of phosphate was investigated using phosphate dispersion aqueous solution, and 70 % of phosphate was removed in phosphate dispersion solution by chemically synthesized graphene oxide solution. Removing efficiency of phosphate was increased from 70 % to 80 % with assistant of iron nano-particle in chemically synthesized graphene oxide solution. Phosphate removing capacity was up to 89.37 mg/g at initial phosphate concentration of 100 mg/l and temperature of 303 K. The Freundlich was applied to describe the equilibrium isotherms and the isotherm constants were determined.

• Carbon letters
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• 제14권3호
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• pp.186-189
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• 2013

We report a highly sensitive $NO_2$ gas sensor based on multi-layer graphene (MLG) films synthesized by a chemical vapor deposition method on a microheater-embedded flexible substrate. The MLG could detect low-concentration $NO_2$ even at sub-ppm (<200 ppb) levels. It also exhibited a high resistance change of ~6% when it was exposed to 1 ppm $NO_2$ gas at room temperature for 1 min. The exceptionally high sensitivity could be attributed to the large number of $NO_2$ molecule adsorption sites on the MLG due to its a large surface area and various defect-sites, and to the high mobility of carriers transferred between the MLG films and the adsorbed gas molecules. Although desorption of the $NO_2$ molecules was slow, it could be enhanced by an additional annealing process using an embedded Au microheater. The outstanding mechanical flexibility of the graphene film ensures the stable sensing response of the device under extreme bending stress. Our large-scale and easily reproducible MLG films can provide a proof-of-concept for future flexible $NO_2$ gas sensor devices.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.210.1-210.1
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• 2014

The hexagonal boron nitride (h-BN) sheet, a 2D material like graphene sheet, is comprised of boron and nitrogen atoms. Similar to graphene, h-BN sheet has attractive mechanical properties while it has a wide band gap unlike graphene. Recently, many experimental groups studied the growth of single BN layer by chemical vapor deposition (CVD) method on the copper substrate. To study the initial stage of h-BN growth on the copper surface, we have performed density functional theory calculations. We investigate several adsorption sites of a boron or nitride atom on the Cu surfaces. Then, by increasing the number of adsorbed B and N atoms, we study formation behaviors of the BN flakes on the surface. Several types of BN flakes atoms such as triangular, linear, and hexagonal shapes are considered on the copper surface. We find that the formation of the BN flake in triangular shape is most favorable on the surface. On the basis of the theoretical results, we discuss the growth mechanism of h-BN layer on the copper surfaces in terms of its shapes in the initial stage of growth.

• 한국전기전자재료학회논문지
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• 제36권4호
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• pp.376-384
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• 2023

Nitrogen-doped graphene was synthesized by a hydrothermal method using graphene oxide (GO) as the raw material, urea as the reducing agent and nitrogen as the dopant. The morphology, structure, composition and electrochemical properties of the samples are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption-desorption analysis, electrical conductivity and electrochemical tests. The results show that urea can effectively reduce GO and achieve nitrogen doping under the hydrothermal conditions. By adjusting the mass ratio of raw materials to dopants, the graphene with different nitrogen doping contents can be obtained; the nitrogen content range is from 5.28~6.08% (atomic fraction percentage).When the ratio of dopant to urea is 1:30, the nitrogen doping content reaches a maximum of 6.08%.The supercapacitor performance test shows that the nitrogen content prepared by the ratio of 6.08% is the best at 0.1 A·g^-1. The specific capacitance is 95.2 F·g^-1.

• Carbon letters
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• 제22권
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• pp.1-13
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• 2017

Porous materials play a vital role in science and technology. The ability to control their pore structures at the atomic, molecular, and nanometer scales enable interactions with atoms, ions and molecules to occur throughout the bulk of the material, for practical applications. Three-dimensional (3D) porous carbon-based materials (e.g., graphene aerogels/hydrogels, sponges and foams) made of graphene or graphene oxide-based networks have attracted considerable attention because they offer low density, high porosity, large surface area, excellent electrical conductivity and stable mechanical properties. Water pollution and associated environmental issues have become a hot topic in recent years. Rapid industrialization has led to a massive increase in the amount of wastewater that industries discharge into the environment. Water pollution is caused by oil spills, heavy metals, dyes, and organic compounds released by industry, as well as via unpredictable accidents. In addition, water pollution is also caused by radionuclides released by nuclear disasters or leakage. This review presents an overview of the state-of-the-art synthesis methodologies of 3D porous graphene materials and highlights their synthesis for environmental applications. The various synthetic methods used to prepare these 3D materials are discussed, particularly template-free self-assembly methods, and template-directed methods. Some key results are summarized, where 3D graphene materials have been used for the adsorption of dyes, heavy metals, and radioactive materials from polluted environments.

• 접착 및 계면
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• 제22권4호
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• pp.153-157
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• 2021

이차원 탄소 동소체인 그래핀은 기존 재료보다 우수한 기계적, 전기적 특성을 지니고 있다. 특히, 그래핀의 전하이동도는 실리콘 대비 100배가량 높다고 알려져 차세대 전자소자의 핵심재료로 각광을 받고 있다. 하지만, 그래핀은 외부 환경의 변화에 매우 민감하여 수분 혹은 산소에 취약하여 그래핀 기반 전자소자의 안정성이 취약하다는 단점이 존재하기에 이를 해결하기 위해 다양한 시도가 이뤄지고 있다. 본 연구에서는 그래핀 전계효과 트랜지스터의 절연막을 전사시에 사용되는 고분자 층의 표면 에너지를 조절하여 안정성을 크게 향상시키는 연구를 수행하였다. 절연층으로 쓰인 고분자의 표면 에너지가 낮아짐에 따라 물 분자 혹은 산소와 같은 대기중의 불순물 흡착을 효과적으로 제어함으로써, 안정성을 향상시킬 수 있었다.

• 접착 및 계면
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• 제23권3호
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• pp.75-79
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• 2022

그래핀은 벌집 모양의 sp² 혼성 오비탈 결합으로 이루어진 이차원 탄소 동소체이다. 우수한 전기적, 기계적 특성을 보이며, 차세대 전자소자의 핵심 재료로써 각광을 받고 있다. 그러나, 소자를 구성하는 소재 간의 불안정한 계면 형성으로부터 쉬운 외부 불순물의 침투 혹은 흡착으로 인해 낮은 환경 안정성을 보이고 있다. 따라서 본 연구에서는 고체탄화수소를 그래핀의 전구체로 활용한 직성장을 통해 그래핀 기반 전계효과 트랜지스터의 낮은 환경 안정성을 해결하고자 한다. 직성장으로부터 합성된 그래핀은 이를 활용한 전자소자에서 전하 이동도 및 Dirac 전압의 변화 감소를 통해 높은 구동 안정성을 보였다. 이를 통해 차세대 전자소자의 핵심 재료로써 그래핀을 활용하기 위한 새로운 접근 방법을 제시하였다.

• Composites Research
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• 제35권2호
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• pp.98-105
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• 2022

본 연구에서는, 미세유체 시스템 기반 폴리바이닐알코올(PVA)/그래핀 옥사이드(GO)/산화철(Fe₃O₄) 자성 마이크로겔을 제조하고 겔의 염료 흡착성능을 평가하였다. 겔의 흡착성능(q_e)은 염료의 농도, pH, 및 접촉시간을 변수로 하여 평가하였다. 사용된 염료는 메틸렌 블루(MB), 크리스탈 바이올렛(CV), 말라카이트 그린(MG)이며, 마이크로겔은 메틸렌 블루에 대해 가장 높은 흡착성능(191.1 mg/g)을 나타내었다. pH에 따른 겔의 흡착성능은 염료가 가지고 있는 atomic nitrogen 이온(N⁺)의 영향으로 모든 염료에서 pH가 10일 때 가장 높은 흡착성능을 나타냈다. 등온흡착 데이터분석을 통해 Langmuir 등온선의 일치도가 높아 단분자층 흡착임을 확인하였으며, 동역학적 분석에서는 유사 1차 반응 보다 유사 2차 반응의 일치도가 높아 화학흡착임을 확인하였다. 또한, 자성 마이크로겔의 회수와 겔표면에 흡착된 염료의 탈착을 통한 재사용 성능을 평가하였는데, 흡착성능은 흡·탈착 5회동안 70% 이상의 성능을 유지하는 것으로 나타났다.

• Carbon letters
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• 제18권
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• pp.24-29
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• 2016

High pollutant-loading capacities (up to 319 times its own weight) are achieved by three-dimensional (3D) macroporous, slightly reduced graphene oxide (srGO) sorbents, which are prepared through ice-templating and consecutive thermal reduction. The reduction of the srGO is readily controlled by heating time under a mild condition (at 1 10⁻² Torr and 200℃). The saturated sorption capacity of the hydrophilic srGO sorbent (thermally reduced for 1 h) could not be improved further even though the samples were reduced for 10 h to achieve the hydrophobic surface. The large meso- and macroporosity of the srGO sorbent, which is achieved by removing the residual water and the hydroxyl groups, is crucial for achieving the enhanced capacity. In particular, a systematic study on absorption parameters indicates that the open porosity of the 3D srGO sorbents significantly contributes to the physical loading of oils and organic solvents on the hydrophilic surface. Therefore, this study provides insight into the absorption behavior of highly macroporous graphene-based macrostructures and hence paves the way to development of promising next-generation sorbents for removal of oils and organic solvent pollutants.

• Coupled systems mechanics
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• 제3권4호
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• pp.329-344
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• 2014

In this work, quantum molecular dynamics simulations (QMD) are preformed to study the hydrogen molecules in three types of carbon nanostructures, $C_{60}$ fullerene, (5,5) and (9,0) carbon nanotubes and graphene layers. Interactions between hydrogen and the nanostructures is of importance to understand hydrogen storage for the development of hydrogen economy. The QMD method overcomes the difficulties with empirical interatomic potentials to model the interaction among hydrogen and carbon atoms in the confined geometry. In QMD, the interatomic forces are calculated by solving the Schrodinger's equation with the density functional theory (DFT) formulation, and the positions of the atomic nucleus are calculated with the Newton's second law in accordance with the Born-Oppenheimer approximation. It is found that the number of hydrogen atoms that is less than 58 can be stored in the $C_{60}$ fullerene. With larger carbon fullerenes, more hydrogen may be stored. For hydrogen molecules passing though the fullerene, a particular orientation is required to obtain least energy barrier. For carbon nanotubes and graphene, adsorption may adhere hydrogen atoms to carbon atoms. In addition, hydrogen molecules can also be stored inside the nanotubes or between the adjacent layers in graphite, multi-layer graphene.