• 한국결정성장학회지
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• 제32권6호
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• pp.239-245
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• 2022

환원그래핀옥사이드(rGO)는 우수한 전기 화학적 능력으로 많은 응용과 관심이 집중되고 있어, 이에 대한 구조 및 열분석을 통한 rGO의 표준화는 품질개선과 관리를 용이하게 하여 사용자가 효율성을 높이고 비용을 절감할 수 있도록 할 수 있다. rGO 및 그래핀 관련 재료의 경우 레이어 층수의 결정과 그에 따른 물성의 차이를 정의하는 것이 매우 중요하다. 본 연구에서는 하이드라진 환원공정을 통해 그래핀옥사이드(GO)로부터 3~4층의 rGO-1과 9~10층의 rGO-2를 얻었다. 이렇게 준비된 rGO에 대해 X선 회절(XRD) 패턴인 (002) 반사와 관련된 2θ≈25°에서 회절 피크를 얻어 층간 거리와 FWHM 값을 얻어 층수(layer number)를 결정하였다. 이때 XRD 데이터 분석은 회절분석용 표준물질들을 사용하여 각도 보정을 수행하였다. 정밀한 층간거리와 FWHM 값은, 각도 보정된 회절 데이터를 이용하여 OriginLab 및 오픈 소스 XRD 회절분석 프로그램들을 사용하여 결정하였다. rGO 샘플들의 추가적인 물성 표준화 분석을 위해 TG-DSC 열분석을 수행하였다.

• Carbon letters
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• 제14권4호
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• pp.251-254
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• 2013

In this study, poly(amic acid) was prepared via a polycondensation reaction of 3,3'-dihydroxybenzidine and pyromellitic dianhydride in an N-methyl-2-pyrrolidone solution; reduced graphene oxide/polybenzoxazole (r-GO/PBO) composite films, which significantly increased the electrical conductivity, were successfully fabricated. GO was prepared from graphite using Brodie's method. The GO was used as nanofillers for the preparation of r-GO/PBO composites through an in situ polymerization. The addition of 50 wt% GO led to a significant increase in the electrical conductivity of the composite films by more than sixteen orders of magnitude compared with that of pure PBO films as a result of the electrical percolation networks in the r-GO during the thermal treatment at various temperatures within the films.

• 공업화학
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• 제30권1호
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• pp.23-28
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• 2019

탄소 실의 표면에 코팅 된 3차원 다공성 그래핀으로 구성된 슈퍼커패시터 케이블 소자를 보고하고자 한다. 그래핀의 3D 다공성 구조는 그래핀옥사이드로 코팅된 탄소 실을 사용하여 마이크로웨이브 활성화 방법에 의해 제작하였다. 마이크로파 조사의 사용은 환원제 없이 그래핀옥사이드를 환원된 그래핀옥사이드로 전환시키고 그래핀 시트를 박리 및 다공성 그래핀 시트로 활성화시켰다. 두 개의 와이어 전극을 고분자 겔 전해질과 결합하여 성공적으로 케이블 구조 형태의 슈퍼커패시터 소자를 제작하였다. 슈퍼커패시터 케이블은 매우 유연하기 때문에 다양한 형태의 장치로 변형될 수 있고 섬유 품목으로 통합될 수 있다. 주사 속도 10 mV/s에서 38.1 mF/cm의 높은 정전용량이 얻어졌다. 이용량은 500 mV/s에서 원래 값의 88%를 유지하였다. 장수명특성은 구부러진 형태에서도 10,000회 동안 충전/방전 과정을 반복함으로써 96.5%의 높은 정전용량 유지율을 증명하였다.

• 마이크로전자및패키징학회지
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• 제27권4호
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• pp.25-37
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• 2020

본 연구에서는 그래핀 소재의 전기전도성 및 자기적 특성을 향상시키기 위해 산화그래핀 표면상의 산소를 포함한 기능기와 열처리 환원공정을 이용하여 환원그래핀과 금속소재를 하리브리드화 하였다. 산화 그래핀 표면의 -OH, -COOH 등의 산소 포함 기능기들을 열처리 환원시킴과 동시에 금속이온을 기능기와의 이온교환법에 의해 치환 합성하는 연구를 진행하였다. 하이브리드 소재 합성에 사용된 금속은 Fe, Ag, Ni, Zn, Fe/Ag이며 SEM, TEM 및 EDS를 통해 환원 그래핀 표면 위에 균일한 크기의 금속 입자가 비교적 구형 잘 분산되었음을 확인하였다. 그래핀 표면상의 금속입자들은 모두 산화물 형태의 구조를 가지고 있었다. 하이브리드 소재의 전기적 특성을 확인하기 위해 rGO-metal hybrid 시료를 PET film에 dip-coating 방법으로 후막 필름을 형성시킨 후 면저항을 측정하였고, SEM을 통해 시편의 두께를 측정하여 비저항을 계산한 결과, 비저항의 범위는 2.14×10-5 ~ 3.5×10-3 ohm/cm범위에 있음을 확인하였다.

• Carbon letters
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• 제11권2호
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• pp.90-95
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• 2010

Carbon materials such as graphite and graphene exhibit high electrical conductivity. We examined the electrical conductivity of synthetic and natural graphene powders after the chemical reduction of synthetic and natural graphite oxide from synthetic and natural graphite. The trend of electrical conductivity of both graphene (synthetic and natural) was compared with different graphite materials (synthetic, natural, and expanded) and carbon nanotubes (CNTs) under compression from 0.3 to 60 MPa. We found that synthetic graphene showed a marked increment in electrical conductivity compared to natural graphene. Interestingly, the total increment in electrical conductivity was greater for denser graphite; however, an opposite behavior was observed in nanocarbon materials such as graphene and CNTs, probably due to the differing layer arrangement of nanocarbon materials.

• Applied Microscopy
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• 제46권1호
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• pp.37-44
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• 2016

In this study $TiO_2$/reduced graphene oxide ($TiO_2/rGO$) bipyramid with tunable nanostructure was fabricated by two-step solvothermal process and subsequent heat-treatment in air. The as-synthesized anatase $TiO_2$ nanocrystals possessed morphological bipyramid with exposed dominantly by (101) facets. Polyethylenimine was utilized during the combination of $TiO_2$ and graphene oxide (GO) to tune the surface charge, hindering the restack of graphene during solvothermal process and resulting in 1 to 5 layers of rGO wrapped on $TiO_2$ surface. After a further calcination, a portion of carbon quantum dots (CQDs) with a diameter about 2 nm were produced owing to the oxidizing and cutting of rGO on $TiO_2$. The as-prepared $TiO_2/rGO$ hybrid showed a highly photocatalytic activity, which is about 3.2 and 7.7 times enhancement for photodegradation of methyl orange with compared to pure $TiO_2$ and P25, respectively. We assume that the improvement of photocatalysis is attributed to the chemical bonding between rGO/CQDs and $TiO_2$ that accelerates photogenerated electron-hole pair separation, as well as enhances light harvest.

• Carbon letters
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• 제26권
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• pp.81-87
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• 2018

Morphological differences in multi-layered graphene flakes or graphene nanoplatelets prepared by oxidative (rGO-NP, reduced graphene oxide-nanoplatelets) and non-oxidative (GIC-NP, graphite intercalation compound-nanoplatelets) routes were investigated with various analytical methods. Both types of NPs have similar specific surface areas but very different structural differences. Therefore, this study proposes an effective and simple method to identify structural differences in graphene-like allotropes. The adsorptive potential peaks of rGO-NP attained by the density functional theory method were found to be more scattered over the basal and non-basal regions than those of GIC-NP. Raman spectra and high resolution TEM images showed more distinctive crystallographic defects in the rGO-NP than in the GIC-NP. Because the R-ratio values of the edge and basal plane of the sample were maintained and relatively similar in the rGO-NP (0.944 for edge & 1.026 for basal), the discrepancy between those values in the GIC-NP were found to be much greater (0.918 for edge & 0.164 for basal). The electrical conductivity results showed a remarkable gap between the rGO-NP and GIC-NP attributed to their inherent morphological and crystallographic properties.

• ETRI Journal
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• 제40권2호
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• pp.275-282
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• 2018

Flash reduction of graphene oxide is an efficient method for producing high quality reduced graphene oxide under room temperature ambient conditions without the use of hazardous reducing agents (such as hydrazine and hydrogen iodide). The entire process is fast, low-cost, and suitable for large-scale fabrication, which makes it an attractive process for industrial manufacturing. Herein, we present a simple fabrication method for a flexible in-plane graphene micro-supercapacitor using flash light irradiation. All carbon-based, monolithic supercapacitors with in-plane geometry can be fabricated with simple flash irradiation, which occurs in only a few milliseconds. The thinness of the fabricated device makes it highly flexible and thus useful for a variety of applications, including portable and wearable electronics. The rapid flash reduction process creates a porous graphene structure with high surface area and good electrical conductivity, which ultimately results in high specific capacitance ($36.90mF\;cm^{-2}$) and good cyclic stability up to 8,000 cycles.

• 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.

• Carbon letters
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• 제15권3호
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• pp.171-179
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• 2014

An attempt was made to investigate the effect of the preparation temperature on the electrocapacitive performance of polypyrrole (PPY)/graphene oxide (GO) nanocomposites (PNCs). For this purpose, a series of PNCs were prepared at various temperatures by the cetyltrimethylammonium bromide-assisted dilute-solution polymerization of pyrrole in presence of GO (wt%) ranging from 1.0 to 4.0 with ferric chloride as an oxidant. The formation of the PNCs was ascertained through Fourier-transform infrared spectrometry, X-ray diffraction spectra, scanning electron microscopy and simultaneous thermogravimetric-differential scanning calorimetry. The electrocapacitive performance of the electrodes derived from sulphonated polysulphone-bound PNCs was evaluated through cyclic voltammetry with reference to Ag/AgCl at a scan rate (V/s) ranging from 0.2 and 0.001 in potassium hydroxide (1.0 M). The incorporation of GO into the PPY matrix at a reduced temperature has a pronounced effect on the electrocapacitive performance of PNCs. Under identical scan rates (0.001 V/s), PNCs prepared at $10{\pm}1^{\circ}C$ render improved specific conductivity (526.33 F/g) and power density (731.19 W/Kg) values compared to those prepared at $30{\pm}1^{\circ}C$ (217.69 F/g, 279.43 W/Kg). PNCs prepared at $10{\pm}1^{\circ}C$ rendered a capacitive retention rate of ~96% during the first 500 cycles. This indicates the excellent cyclic stability of the PNCs prepared at reduced temperatures for supercapacitor applications.