• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.290.1-290.1
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• 2016

Grapehen, a single atomic layer of graphite, has been in the spotlight and researched in vaious fields, because its fine mechanical, electrical properties, flexibility and transparence. Synthesis methods for large-area graphene such as chemical vaper deposition (CVD) and mechanical, chemical exfoliation have been reported. In particular, chemical exfoliation method receive attention due to low cost process. Chemical exfoliation method require reduction of graphene oxide in the process of exfoliation such as chemical reduction by strong reductant, thermal reduction on high temperature, and optical reduction via ultraviolet light exposure. Among these reduction methods, optical reduction is free from damage by strong reductant and high temperature. However, optical reduction is economically infeasible because the high cost of short-wavelength ultraviolet light sorce. In this paper, we make graphene-oxide and lanthanoid ion mixture aqueous solution which has highly optical absorbency in selective wevelength region. Sequentially, we synthesize reduced graphene oxide (RGO) using the solution and visible laser beam. Concretely, graphene oxide is made by modified hummer's method and mix with 1 ml each ultraviolet ray absorbent Gd3+ ion, Green laser absorbent Tb3+ ion, Red laser absorbent Eu3+ ion. After that, we revivify graphene oxide by laser exposure of 300 ~ 800 nm layser 1mW/cm2 +. We demonstrate reproducibility and repeatability of RGO through FT-IR, UV-VIS, Low temperature PL, SEM, XPS and electrical measurement.

• Journal of the Korean institute of surface engineering
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• v.54 no.2
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• pp.77-83
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• 2021

In this study, we investigated various coating methods of graphene oxide on the surface of a petri dish made of polystyrene and analyzed the physical and chemical properties of the coated surface. For coating, spinning, spraying and pressing methods were attempted. The coated surface was characterized by SEM, Raman Spectroscopy, AFM, FT-IR, UV-Vis Spectroscopy and Contact Angle measurement. By spin coating and spray coating, well distributed graphene oxide in the form of multiple islands on the plastic surface with an average size of 5 to 20㎛ are observed by SEM, and high binding energy between graphene oxide and plastic surface is measured by AFM. In case of hand press coating, graphene oxide of 10㎛ or more was observed, and low surface energy was measured. By FT-IR and Raman Spectroscopy analysis, surface coating of graphene oxide was confirmed.

• Carbon letters
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• v.21
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• pp.1-7
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• 2017

The effects of ammonia-treated graphene oxide (GO) on composites based on epoxy resin were investigated. Ammonia solutions of different concentrations (14-28%) were used to modify GO. Nitrogen functional groups were introduced on the GO surfaces without significant structural changes. The ammonia-treated GO-based epoxy composites exhibited interesting changes in their mechanical properties related to the presence of nitrogen functional groups, particularly amine ($C-NH_2$) groups on the GO surfaces. The highest tensile and impact strength values were 42.1 MPa and 12.3 J/m, respectively, which were observed in an epoxy composite prepared with GO treated with a 28% ammonia solution. This improved tensile strength was 2.2 and 1.3 times higher than those of the neat epoxy and the non-treated GO-based epoxy composite, respectively. The amine groups on the GO ensure its participation in the cross-linking reaction of the epoxy resin under amine curing agent condition and enhance its interfacial bonding with the epoxy resin.

• Proceedings of the Materials Research Society of Korea Conference
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• 2012.05a
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• pp.68.1-68.1
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• 2012

The best part of graphene is - charge-carriers in it are mass less particles which move in near relativistic speeds. Comparing to other materials, electrons in graphene travel much faster - at speeds of $10^8cm/s$. A graphene sheet is pure enough to ensure that electrons can travel a fair distance before colliding. Electronic devices few nanometers long that would be able to transmit charge at breath taking speeds for a fraction of power compared to present day CMOS transistors. Many researches try to check a possibility to make it a perfect replacement for silicon based devices. Graphene has shown high potential to be used as interconnects in the field of high frequency electrical devices. With all those advantages of graphene, we demonstrate characteristics of electrical and optical properties of graphene such as the effect of graphene geometry on the microwave properties using the measurements of S-parameter in range of 500 MHz - 40 GHz at room temperature condition. We confirm that impedance and resistance decrease with increasing the number of graphene layer and w/L ratio. This result shows proper geometry of graphene to be used as high frequency interconnects. This study also presents the optical properties of graphene oxide (GO), which were deposited in different substrate, or influenced by oxygen plasma, were confirmed using different characterization techniques. 4-6 layers of the polycrystalline GO layers, which were confirmed by High resolution transmission electron microscopy (HRTEM) and electron diffraction analysis, were shown short range order of crystallization by the substrate as well as interlayer effect with an increase in interplanar spacing, which can be attributed to the presence of oxygen functional groups on its layers. X-ray photoelectron Spectroscopy (XPS) and Raman spectroscopy confirms the presence of the $sp^2$ and $sp^3$ hybridization due to the disordered crystal structures of the carbon atoms results from oxidation, and Fourier Transform Infrared spectroscopy (FTIR) and XPS analysis shows the changes in oxygen functional groups with nature of substrate. Moreover, the photoluminescent (PL) peak emission wavelength varies with substrate and the broad energy level distribution produces excitation dependent PL emission in a broad wavelength ranging from 400 to 650 nm. The structural and optical properties of oxygen plasma treated GO films for possible optoelectronic applications were also investigated using various characterization techniques. HRTEM and electron diffraction analysis confirmed that the oxygen plasma treatment results short range order crystallization in GO films with an increase in interplanar spacing, which can be attributed to the presence of oxygen functional groups. In addition, Electron energy loss spectroscopy (EELS) and Raman spectroscopy confirms the presence of the $sp^2$ and $sp^3$ hybridization due to the disordered crystal structures of the carbon atoms results from oxidation and XPS analysis shows that epoxy pairs convert to more stable C=O and O-C=O groups with oxygen plasma treatment. The broad energy level distribution resulting from the broad size distribution of the $sp^2$ clusters produces excitation dependent PL emission in a broad wavelength range from 400 to 650 nm. Our results suggest that substrate influenced, or oxygen treatment GO has higher potential for future optoelectronic devices by its various optical properties and visible PL emission.

• Journal of Korean Society on Water Environment
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• v.32 no.1
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• pp.46-51
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• 2016

In this study, we synthesized a combination of graphene oxide (GO) and titanium dioxide (TiO₂) and confirm that GO can be used for CO₂ photoreduction. TiO₂ exhibited highly efficient combination with other conventional electric charges generated by these paration phenomenon for suppression of hole-electron recombination. This improved the efficiency of CO₂ photoreduction. The synthetic form of GO-TiO₂ used in this study was agraphene sheet surrounded by TiO₂ powder. Efficiency and stability were enhanced by combination of GO and TiO₂. In a CO₂ photoreduction experiment, the highest CO conversion rate was 0.652 μmol/g·h in GO10-TiO₂ (2.3-fold that of pure TiO₂) and the highest CH₄ production rate was 0.037 μmol/g·h in GO0.1-TiO₂ (2.4-fold that of pure TiO₂). GO enhances photocatalytic efficiency by functioning as a support and absorbent, and enabling charge separation. With increasing GO concentration, the CH₄ level decreases to~45% due to decreased transfer of electrons. In this study, TiO₂ together with GO yielded a different result than the normal doping effect and selective CO₂ photoreduction.

• Applied Chemistry for Engineering
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• v.27 no.1
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• pp.45-49
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• 2016

In the presence of poly(4-styrene sulfonate) (PSS) and excess amount of graphene oxide (GO), we conducted in-situ polymerization of 3,4-ethylenedioxythiophene (EDOT) without an oxidant. XPS and IR spectroscopies of the product (GO-P) showed that PEDOT/PSS was successfully synthesized by oxidative polymerization of EDOT and hybridized with GO. GO-P displayed a stable aqueous suspension, however, the high content (42%) of GO in GO-P diminished electrical conductivity down to $15S{\cdot}m^{-1}$. Annealing of GO-P films at $200^{\circ}C$ for 8 hr induced partial reduction of GO and finally enhanced electrical conductivity up to $212S{\cdot}m^{-1}$.

• Membrane and Water Treatment
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• v.9 no.4
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• pp.211-220
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• 2018

Incorporating nano-materials in thin-film composite (TFC) membranes has been considered to be an approach to achieve higher membrane performance in various water treatment processes. This study investigated the rejection efficiency of three target compounds, i.e., reserpine, norfloxacin and tetracycline hydrochloride, by TFC membranes with different graphene oxide proportions. Graphene oxide (GO) was incorporated into the polyamide active layer of a TFC membrane via an interfacial polymerization (IP) reaction. The TFC membranes were characterized with FTIR, FE-SEM, AFM; in addition, the water contact angle measurements as well as the permeation and separation performance were evaluated. The prepared GO-TFC membranes exhibited a much higher flux ($3.11{\pm}0.04L/m2{\cdot}h{\cdot}bar$) than the pristine TFC membranes ($2.12{\pm}0.05L/m2{\cdot}h{\cdot}bar$) without sacrificing their foulant rejection abilities. At the same time, the GO-modified membrane appeared to be less sensitive to pH changes than the pure TFC membrane. A significant improvement in the anti-fouling property of the membrane was observed, which was ascribed to the favorable change in the membrane's hydrophilicity, surface morphology and surface charge through the addition of an appropriate amount of GO. This study predominantly improved the understanding of the different PA/GO membranes and outlined improved industrial applications of such membranes in the future.

• Carbon letters
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• v.26
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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.

• Journal of the Korean Ceramic Society
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• v.56 no.1
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• pp.65-70
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• 2019

Simple fabrication of a powdered Ge-reduced graphene oxide (Ge-rGO) composite via spray pyrolysis and reduction is introduced herein. Successful incorporation of the rGO nanosheets with Ge hindered the aggregation of Ge and conferred enhanced structural stability to the composite by alleviating the mechanical stress associated with drastic volume changes during repeated cycling. The Li-ion storage performance of Ge-rGO was compared with that of powdered Ge metal. The reversible discharge capacity of Ge-rGO at the $200^{th}$ cycle was $748mA\;h\;g^{-1}$ at a current density of $1.0A\;g^{-1}$ and Ge-rGO showed a capacity of $375mA\;h\;g^{-1}$ even at a high current density of $5.0A\;g^{-1}$. The excellent performance of Ge-rGO is attributed to the structural robustness, enhanced electrical conductivity, and formation of open channels between the rGO nanosheets, which facilitated electrolyte penetration for improved Li-ion diffusion.

• Membrane and Water Treatment
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• v.14 no.3
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• pp.107-114
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• 2023

Graphene oxide (GO) membranes have attracted extensive attention in water treatment and related fields. However, GO films are unstable and have low permeability, which have hindered their further development. In this paper, a simple and effective method was used in which GO and single-layer graphene (GN) were mixed, and the layer spacing was effectively controlled by accurately controlling the ratio of GO to GN. GO-GN composite membranes have excellent stability, salt rejection (95.4%), and water flux (26 L m^-2 h^-1 bar^-1). This unique design structure can be used for precise and effective regulation of the layer spacing in GO, improving the rejection rate, and increasing water flux via the enhancement of low-friction capillary action. The rational development and use of this unique composite membrane provides a reference for the water treatment field.