• Carbon letters
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• v.22
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• pp.60-69
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• 2017

Nitrogen-doped carbon nanosheets with a developed porous structure were prepared from polyurethane foams by hydrothermal carbonization following $ZnCl_2$ chemical activation. Scanning electron microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, solid state $^{13}C$ nuclear magnetic resonance (NMR) spectra and X-ray photoelectron spectroscopy were used to characterize the nitrogen-doped carbon nanosheet structure and composition. The removal of Cr(VI) by the N-doped carbon nanosheets was investigated. The results showed that the maximum removal capacity for chromium of 188 mg/g was found at pH=2.0 with PHC-Z-3. pH had an important effect on Cr(VI) removal and the optimal pH was 2.0. Moreover, amino groups and carboxyl groups in the nitrogen-doped carbon nanosheet played important roles in Cr(VI) removal, and promoted the reduction of Cr(VI) to Cr(III).

• Journal of Sensor Science and Technology
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• v.22 no.3
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• pp.207-211
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• 2013

In this research, the pH sensor was developed using CNT nanosheet with Nafion coating for the advanced medical sensor such as a blood gas analyzer. The CNT nanosheet was formed by dielectrophoresis and water-meniscus between cantilever-type electrodes. Then, the process of the heat annealing and the Nafion coating was conducted for reducing contact resistance and giving proton selectivity respectively. We measured the response of the pH sensor as the electrolyte-gated CNT-nanosheet field effect transistor. The sensor showed a linear current ratio in a similar range of the normal blood pH. A calibration method for decreasing of the response variation among sensors has also been introduced. Coefficient of variance of the pH sensor was decreased by applying the calibration method. A linear relation between the calibrated response of the sensors and pH variance was also obtained. Finally, the pH sensor with a high resolution was fabricated and we verify the feasibility of the sensor by applying the calibration method.

• Carbon letters
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• v.14 no.1
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• pp.51-54
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• 2013

In this study, polyaniline (PANI)/graphene nanosheet (GNS) composites were synthesized through chemical oxidation polymerization by changing the weight ratio of aniline monomers. To examine the morphological structure of the composites, scanning electron microscopy and transmission electron microscopy (TEM) were conducted. TEM results revealed that fibril-like PANI with a diameter of 50 nm was homogeneously coated on the surface of the GNS. The electrochemical properties of the composites were studied by cyclic voltammetry in 1 M $H_2SO_4$ electrolyte. Among the prepared samples, the PANI/GNS (having 40 wt% aniline content) showed the highest specific capacitance, 528 $Fg^{-1}$, at 10 $mVs^{-1}$. The improved performance was attributed to the GNS, which provides a large number of active sites and good electrical conductivity. The resulting composites are promising electrode materials for high capacitative supercapacitors.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.24 no.5
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• pp.207-212
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• 2014

An ultrathin sheet-like carbon nanostructure provides an important model of a two-dimensional graphite structure with strong anisotropy in physical properties. As an easy and cheap route for mass production, RF thermal plasma synthesis of freestanding carbon nanosheet from $CH_4$ (Methane) and $C_3H_8$ (Propane) is presented. Using vapor synthesis process with RF inductively thermal plasma, carbon nanosheets were obtained without catalysts and substrates. The synthesized carbon nanosheets were characterized using transmission electron microscopy (TEM), Raman spectroscopy, X-ray diffraction (XRD) and Brunauer-Emmett-Teller (BET) analysis. The carbon nanosheets synthesized using methane and propane generally showed 5~6 and 15~16 layers with a wrinkled morphology and size of approximately 100 nm.

• Carbon letters
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• v.10 no.4
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• pp.335-338
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• 2009

In this work, the effect of co-carbon fillers on the electrical and mechanical properties of epoxy nanocomposites was investigated. The graphite nanosheets (GNs) and multi-walled carbon nanotubes (MWNTs) were used as co-carbon fillers. The results showed that the electrical conductivity of the epoxy nanocomposites showed a considerable increase upon an addition of MWNTs when GNs were fixed at 2 wt.%. This indicated that low content GNs formed the bulk conductive network and then MWNTs added were intercalated between the GN layers, resulted in the formation of additional conductive pathway. Furthermore, the flexural strength of the epoxy nanocomposites was enhanced with increasing the MWNT content. It was probably attributed to the flexible MWNTs compared with rigid GNs, resulted in the enhancement of the mechanical properties.

• Korean Chemical Engineering Research
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• v.48 no.3
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• pp.292-299
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• 2010

Graphene is a two-dimensional nanosheet consisting of honeycomb lattices of $sp^2$ carbon atoms. It is one of promising active materials for the anode of lithium-ion battery and the electrode of supercapacitor, due to its large specific surface area(theoretically $2600m^2\;g^{-1}$), high electric conductivity(typically $8{\times}10^5S\;cm^{-1}$), and mechanical strength. In this review, the synthetic methods of graphene nanosheet and graphene-based nanocomposite are introduced. Also, the electrochemical properties obtainable when the graphene-based materials are adopted to the electrodes of lithium-ion battery and supercapacitor are discussed along with their nanostructures.

• Carbon letters
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• v.19
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• pp.66-71
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• 2016

The development of nanostructured functional materials derived from biomass and/or waste is of growing importance for creating sustainable energy-storage systems. In this study, nanoporous carbonaceous materials containing numerous heteroatoms were fabricated from waste coffee grounds using a top-down process via simple heating with KOH. The nanoporous carbon nanosheets exhibited notable material properties such as high specific surface area (1960.1 m² g⁻¹), numerous redox-active heteroatoms (16.1 at% oxygen, 2.7 at% nitrogen, and 1.6 at% sulfur), and high aspect ratios (>100). These unique properties led to good electrochemical performance as supercapacitor electrodes. A specific capacitance of ~438.5 F g⁻¹ was achieved at a scan rate of 2 mV s⁻¹, and a capacitance of 176 F g⁻¹ was maintained at a fast scan rate of 100 mV s⁻¹. Furthermore, cyclic stability was achieved for over 2000 cycles.

• Journal of Surface Science and Engineering
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• v.51 no.6
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• pp.365-371
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• 2018

1D core-shell nanostructures have attracted great attention due to their enhanced physical and chemical properties. Specifically, oriented single-crystalline $TiO_2$ nanorods or nanowires on a transparent conductive substrate would be more desirable as the building core backbone. However, a facile approach to produce such structure-based hybrids is highly demanded. In this study, a three-step hydrothermal method was developed to grow NiMn-layered double hydroxide-decorated $TiO_2$/carbon core-shell nanorod arrays on transparent conductive fluorine-doped tin oxide (FTO) substrates. XRD, SEM, TEM, XPS and Raman were used to analyze the obtained samples. The in-situ fabricated hybrid nanostructured materials are expected to be applicable for photoelectrode working in water splitting.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.60-60
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• 2015

Nanosheets of graphene and related 2D materials have attracted much attention due to excellent physical, chemical and mechanical properties. Single-layer graphene (SLG) was first synthesized by Blakely et al in 1974 [1]. Following his achievements, we initiated the growth and characterization of graphene and h-BN on metal substrates using surface segregation and precipitation in 1980s [2,3]. There are three important steps for nanosheet growth; surface segregation of dopants, surface reaction for monolayer phase, and subsequent 3-D growth (surface precipitation). Surface phase transition was clearly demonstrated on C-doped Ni(111) by in situ XPS at elevated temperatures [4]. The growth mode was clarified by inelastic background analysis [5]. The surface segregation approach has been applied to C-doped Pt(111) and Pd(111), and controllable growth of SLG has been demonstrated successfully [6]. Recently we proposed a promising method for producing SLG fully covering an entire substrate using Ni films deposited on graphite substrates [7]. A universal method for layer counting has been proposed [8]. In this paper, we will focus on the effect of competitive surface-site occupation between carbon and other surface-active impurities on the graphene growth. It is known that S is a typical impurity of metals and the most surface-active element. The surface sites shall be occupied by S through surface segregation. In the case of Ni(110), it is confirmed by AES and STM that the available surface sites is nearly occupied by S with a centered $2{\times}2$ arrangement. When Ni(110) is doped with C, surface segregation of C may be interfered by surface active elements like S. In this case, nanoscopic characterization has discovered a preferred directional growth of SLG, exhibiting a square-like shape (Fig. 1). Also the detailed characterization methodologies for graphene and h-BN nanosheets, including AFM, STM, KPFM, AES, HIM and XPS shall be discussed.

• Journal of Hydrogen and New Energy
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• v.29 no.5
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• pp.450-457
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• 2018

To design the practical core-shell electrocatalysts, combination of core and shell materials is important to meet catalytic activity and durability target. In general, Pd is considered as a good core material due to its best activity caused by strain/ligand effect. Preparing Pd nanoparticles can be a starting point in fabricating core-shell type electrocatalysts, much simplified Pd preparing process is suggested by using carbon monoxide (CO) as a reducing agent and/or capping agent. The solvent composition and reaction temperature can control to nanosheet, tetrahedron, and sphere without using additional stabilizer. Among them, Pd nanosheet which has mainly (111) plane showed about 3 times higher electrocatalytic activity for oxygen reduction reaction (ORR) to the spherical Pd nanoparticles. The enhanced ORR activity of Pd nanosheets can be attributed to the exposure of Pd (111) surface and the high electrochemical surface area. Therefore, we demonstrated that the shape of Pd nanomaterials is easily controlled via a facile reduction method using CO, and (111) plane-oriented Pd nanosheets can be a promising ORR catalysts and core material for polymer electrolyte fuel cells (PEFCs).