• Carbon letters
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• v.16 no.1
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• pp.41-44
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• 2015

We report the preparation of sulfonated reduced graphene oxide (SRGO) by the sulfonation of graphene oxide followed by radiation-induced chemical reduction. Graphene oxide prepared by the well-known modified Hummer's method was sulfonated with the aryl diazonium salt of sulfanilic acid. Sulfonated graphene oxide (SGO) dispersed in ethanol was subsequently reduced by ${\gamma}$-ray irradiation at various absorbed doses to produce SRGO. The results of optical, chemical, and thermal analyses revealed that SRGO was successfully prepared by ${\gamma}$-ray irradiation-induced chemical reduction of the SGO suspension. Moreover, the electrical conductivity of SRGO was increased up to 2.94 S/cm with an increase of the absorbed dose.

• Steel and Composite Structures
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• v.31 no.5
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• pp.529-539
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• 2019

Current paper deals with thermoelastic static and free vibrational behaviors of axisymmetric thick cylinders reinforced with functionally graded (FG) randomly oriented graphene subjected to internal pressure and thermal gradient loads. The heat transfer and mechanical analyses of randomly oriented graphene-reinforced nanocomposite (GRNC) cylinders are facilitated by developing a weak form mesh-free method based on moving least squares (MLS) shape functions. Furthermore, in order to estimate the material properties of GRNC with temperature dependent components, a modified Halpin-Tsai model incorporated with two efficiency parameters is utilized. It is assumed that the distributions of graphene nano-sheets are uniform and FG along the radial direction of nanocomposite cylinders. By comparing with the exact result, the accuracy of the developed method is verified. Also, the convergence of the method is successfully confirmed. Then we investigated the effects of graphene distribution and volume fraction as well as thermo-mechanical boundary conditions on the temperature distribution, static response and natural frequency of the considered FG-GRNC thick cylinders. The results disclosed that graphene distribution has significant effects on the temperature and hoop stress distributions of FG-GRNC cylinders. However, the volume fraction of graphene has stronger effect on the natural frequencies of the considered thick cylinders than its distribution.

• Korean Journal of Materials Research
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• v.32 no.12
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• pp.522-527
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• 2022

Among efforts to improve techniques for the chemical vapor deposition of large-area and high-quality graphene films on transition metal substrates, being able to reliably transfer these atomistic membranes onto the desired substrate is a critical step for various practical uses, such as graphene-based electronic and photonic devices. However, the most used approach, the wet etching transfer process based on the complete etching of metal substrates, remains a great challenge. This is mainly due to the inevitable damage to the graphene, unintentional contamination of the graphene layer, and increased production cost and time. Here, we report the systematic study of an H₂ bubbling-assisted transfer technique for graphene films grown on Cu foils, which is nondestructive not only to the graphene film but also to the Cu substrate. Also, we demonstrate the origin of the graphene film tearing phenomenon induced by this H₂ bubbling-assisted transfer process. This study reveals that inherent features are produced by rolling Cu foil, which cause a saw-like corrugation in the poly(methyl methacrylate) (PMMA)/graphene stack when it is transferred onto the target substrate after the Cu foil is dissolved. During the PMMA removal stage, the graphene tearing mainly appears at the apexes of the corrugated PMMA/graphene stack, due to weak adhesion to the target substrate. To address this, we have developed a modified heat-press-assisted transfer technique that has much better control of both tearing and the formation of residues in the transferred graphene films.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.360-360
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• 2012

Graphene shows diverse novel physical properties arising from its peculiar electronic states, so called Dirac electrons. Especially, effect of magnetic field is very unique, exhibiting exotic Landau level (LL) splitting. LLs are substantially modified by spins of Dirac electrons and pseudo-spins. The degeneracy of LLs is lifted to show splitting by electron-electron interaction and by the Zeeman effect. We investigated the magneto-optical absorption of graphene subjected to ultra-high magnetic field. Samples were prepared by the CVD method deposited on GaAs and Quart substrate. We have confirmed existence of graphene on each substrate by the micro-Raman spectroscopy. Next, we conducted magneto-absorption measurements in magnetic field up to 120 T by the single-turn coil (STC) method. We could observe absorption peak at 65 T and 100 T, respectively, probably arising from the LL inter-band transitions.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.139.1-139.1
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• 2013

Graphene and graphene oxide (GO) have been modified with palladium nanoparticles (Pd NPs) to develop high performance catalysts for the Sonogashira cross coupling reaction. To understand catalytic performance of Pd NPs on graphene (Pd/G) and Pd NPs on GO (Pd/GO), we monitored their morphological and electronic structural changes before/after Sonogashira reaction using FT-IR, XRD, XPS, and XAFS. Here, we demonstrate that both Pd/G and Pd/GO show high catalytic efficiency toward the Sonogashira reaction, but only Pd/GO revealed excellent recyclability. The remarkable catalytic efficiency of both catalysts is attributed to the high degree of the Pd NP dispersions on supports and thus smaller Pd NPs can provide highly reactive low coordinated Pd atoms. However, we attributed the excellent recyclability of Pd/GO to the presence of oxygen functionalities on GO, which can provide nucleation sites for the detached Pd atoms during the Sonogashira reaction and prevent agglomeration of the Pd NPs since the oxygen functional groups are very reactive to mobile Pd adatoms.

• Journal of Electrochemical Science and Technology
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• v.8 no.4
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• pp.282-293
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• 2017

A new modified carbon paste electrode (CPE) was constructed based on nickel oxide nanoparticles (NiONPs) and graphene nanosheets (Gr) for simultaneous determination of paracetamol (PCM) and mefenamic acid (MFA) in aqueous media and pharmaceutical dosage forms. NiONPs were synthesized via a simple and inexpensive technique and characterized using X-ray diffraction method. Scanning electron microscopy was used for the characterization of the morphology of modified carbon paste electrode (NiONPs/Gr/CPE). Voltammetric studies suggest that the NiONPs and Gr provide a synergistic augmentation that can increase current responses by improvement of electron transfers of these compounds on the NiONPs/Gr/CPE surface. Using cyclic voltammetry, the NiONPs/Gr/CPE showed good sensitivity and selectivity for the determination of PCM and MFA in individually or mixture standard samples in the linear range of $0.1-30{\mu}g\;mL^{-1}$. The resulted limit of detection and limit of quantification were 20 and $60ng\;mL^{-1}$ for PCM, 24 and $72ng\;mL^{-1}$ for MFA, respectively. The analytical performance of the NiONPs/Gr/CPE was evaluated for the determination of PCM and MFA in pharmaceutical dosage forms with satisfactory results.

• Wind and Structures
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• v.32 no.1
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• pp.31-46
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• 2021

The current research deals with, stability/instability and cylindrical composite nano-scaled shell's resonance frequency filled by graphene nanoplatelets (GPLs) under various thermal conditions (linear and nonlinear thermal loadings). The piece-wise GPL-reinforced composites' material properties change through the orientation of cylindrical nano-sized shell's thickness as the temperature changes. Moreover, in order to model all layers' efficient material properties, nanomechanical model of Halpin-Tsai has been applied. A functionally modified couple stress model (FMCS) has been employed to simulate GPLRC nano-sized shell's size dependency. It is firstly investigated that reaching the relative frequency's percentage to 30% would lead to thermal buckling. The current study's originality is in considering the multifarious influences of GPLRC and thermal loading along with FMCS on GPLRC nano-scaled shell's resonance frequencies, relative frequency, dynamic deflection, and thermal buckling. Furthermore, Hamilton's principle is applied to achieve boundary conditions (BCs) and governing motion equations, while the mentioned equations are solved using an analytical approach. The outcomes reveal that a range of distributions in temperature and other mechanical and configurational characteristics have an essential contribution in GPLRC cylindrical nano-scaled shell's relative frequency change, resonance frequency, stability/instability, and dynamic deflection. The current study's outcomes are practical assumptions for materials science designing, nano-mechanical, and micromechanical systems such as micro-sized sensors and actuators.

• Elastomers and Composites
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• v.47 no.3
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• pp.238-245
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• 2012

Graphene oxide was synthesized from natural graphite, and its surface was modified using diisocyanatodicyclohexylmethane( $H_{12}MDI$). Isocyanate-graphene sheet(i-RGO) was obtained by reduction of surface modified GO. To select nanofiller having good dispersion with polyurethane, GO, i-RGO, natural graphite and thermal reduced graphite were analyzed, and then i-RGO was selected as a suitable nanofiller. PU/i-RGO nanocomposite was synthesized with various i-RGO contents to estimate effect of reinforcement on nanocomposite. Thermal stability, hardness, contact angle were increased with i-RGO contents due to i-RGO characteristic and crosslink bridge effect. But, tensile strength and elongation were decreased at i-RGO contents more than the 4 wt%. This phenomenon was interpreted by the excess formation of crosslink bridge.

• Carbon letters
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• v.13 no.1
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• pp.39-43
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• 2012

The size and the physical properties of graphene oxide sheets were controlled by changing the oxidation temperature of graphite. Graphite oxide (GO) samples were prepared at different oxidation temperatures of $20^{\circ}C$, $27^{\circ}C$ and $35^{\circ}C$ using a modified Hummers' method. The carbon-to-oxygen (C/O) ratio and the average size of the GO sheets varied according to the oxidation temperature: 1.26 and 12.4 ${\mu}m$ at $20^{\circ}C$, 1.24 and 10.5 ${\mu}m$ at $27^{\circ}C$, and 1.18 and 8.5 ${\mu}m$ at $35^{\circ}C$. This indicates that the C/O ratio and the average size of the graphene oxide sheets respectively increase as the oxidation temperature decreases. Moreover, it was observed that the surface charge and optical properties of the graphene oxide sheets could be tuned by changing the temperature. This study demonstrates the tunability of the physical properties of graphene oxide sheets and shows that the properties depend on the functional groups generated during the oxidation process.

• Applied Science and Convergence Technology
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• v.27 no.5
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• pp.90-94
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• 2018

The electron band structure of manganese-adsorbed graphene on an SiC(0001) substrate has been studied using angle-resolved photoemission spectroscopy. Upon introducing manganese atoms, the conduction band of graphene, that is observed in pristine graphene indicating intrinsic electron-doping by the substrate, completely disappears and the valence band maximum is observed at 0.4 eV below Fermi energy. At the same time, the slope of the valence band decreases by the presence of manganese atoms, approaching the electron band structure calculated using the local density approximation method. The former provides experimental evidence of the formation of nearly free-standing graphene on an SiC substrate, concomitant with a metal-to-insulator transition. The latter suggests that its electronic correlations are efficiently screened, suggesting that the dielectric property of the substrate is modified by manganese atoms and indicating that electronic correlations in grpahene can also be tuned by foreign atoms. These results pave the way for promising device application using graphene that is semiconducting and charge neutral.