• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.5
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• pp.463-469
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• 2015

In this study, we synthesized graphene oxide and developed novel spin-spray coating technology. The graphene oxide thin film was uniformly coated on amine-functionalized glass surfaces using spin-spray coating technology. We also stacked up to four layers of graphene oxide on glass substrates in a uniform manner. From the results, we infer that this spin-spray coating of graphene oxide thin film could be a powerful tool for various electronic display coating applications.

• Journal of the Korean Geosynthetics Society
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• v.20 no.4
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• pp.1-7
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• 2021

In response to the carbon emission reduction trends and the depletion of natural sand caused by the use of cement in construction works, graphene oxide and porous feldspar were applied as countermeasures in this study. By using (3-aminopropyl)trimethoxysilane-functionalized graphene oxide with enhanced bond characteristics, a concrete specimen was prepared with 5% less cement content than that in a standard mortar mix, and the compressive strengths of the specimens were examined. The compressive strengths of the specimen with (3-aminopropyl)trimethoxysilane-functionalized graphene oxide and porous feldspar and the specimen with standard mixing were 26MPa and 28MPa, respectively, showing only a small difference. In addition, both specimens met the compressive strength of cement mortar required for geotechnical structures. It is believed that a reasonable level of compressive strength was maintained in spite of the lower cement content because the high content of pozzolans, namely SiO₂ and Al₂O₃, in the porous feldspar enhanced the reactions with Ca(OH)₂ during hydration, the nano-sized graphene surface acted as a reactive surface for the hydration products to react actively, and the strong covalent bonding of the carboxyl functional group increased the bonding strength of the hydration products.

• Carbon letters
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• v.14 no.2
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• pp.117-120
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• 2013

In this study, an electro-catalyst of Pt nanoparticles supported by polypyrrole-functionalized graphene (Pt/PPy-reduced graphene oxide [RGO]) is reported. The Pt nanoparticles are deposited on the PPy-RGO composite by chemical reduction of H2PtCl6 using NaBH4. The presence of graphene (RGO) caused higher activity. This might have been due to increased electro-chemically accessible surface areas, increased electronic conductivity, and easier charge-transfer at polymer-electrolyte interfaces, allowing higher dispersion and utilization of the deposited Pt nano-particles. Microstructure, morphology and crystallinity of the synthesized materials were investigated using X-ray diffraction and transmission electron microscopy. The results showed successful deposition of Pt nano-particles, with crystallite size of about 2.7 nm, on the PPy-RGO support film. Catalytic activity for methanol electro-oxidation in fuel cells was investigated using cyclic voltammetry. The fundamental electrochemical test results indicated that the electro-catalytic activity, for methanol oxidation, of the Pt/PPy-RGO combination was much better than for commercial catalyst.

• Applied Chemistry for Engineering
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• v.29 no.5
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• pp.533-540
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• 2018

Graphene has been reported to be an excellent lubricant additive that reduces friction and wear when coated on the surface of various materials or when dispersed in lubricants as an atomic thin material with the low surface energy. In this study, alkyl functionalized graphene oxide (FGO) nanosheets for oil-based lubricant additives were prepared by using three types of alkyl chloride chemicals (butyl chloride, octyl chloride, and tetradecyl chloride). The chemical and structural properties of the synthesized FGOs were analyzed by Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscope (SEM), and transmission electron microscope (TEM). The synthesized FGOs were dispersed at 0.02 wt% in PAO-0W40 oil and its tribological characteristics were investigated using a high frequency friction/wear tester. The friction coefficient and the wear track width of poly alpha olefin (PAO) oil added with FGO-14 were tested by a ball-on-disk method, and the measured results were reduced by ~5.88 and ~3.8%, respectively compared with those of the conventional PAO oil. Thus, it was found that the wear resistance of PAO oil was improved. In this study, we demonstrated the successful functionalization of GO as well as the improvement of dispersion stability and tribological characteristics of FGOs based on various alkyl chain lengths.

• Polymer(Korea)
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• v.36 no.1
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• pp.22-28
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• 2012

Functionalized graphene/epoxy composites were prepared to miprove thermal conductivities of epoxy composites and to maintain electrical insulating property. Graphene oxide (GO) was prepared using Hummers method, and then GO was reacted with aluminum isopropoxide to functionalize $Al(OH)_3$ layer onto GO surface by a simple sol-gel method (Al-GO). GO and Al-GO were characterized by X-ray photoelectron spectroscopy, field emission scanning electron microscopy and transmission electron microscopy. The analyses confirm that GO was coated with a large and dense coverage of $Al(OH)_3$. GO and Al-GO (1 and 3 wt%) were embedded in bisphenol A (DGEBA) to investigate the effects of electrical insulating property. Electrical resistivity showed that Al-GO had better insulating property than GO. Further, the thermal conductivity of GO and Al-GO/epoxy composites was higher than that of neat epoxy resins. In particular, the thermal conductivity of Al-GO/bisphenol F (DGEBF) improved by 23.3% and Al-GO/DGEBA enhanced by 21.8% compared with pure epoxy resins.

• 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.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.165-165
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• 2014

In this study, we demonstrated that the soft lithographic patterning processing of chemical vapor deposition (CVD) graphene and rGO sheets as large scale, low cost, high quality and simplicity for future industrial applications. Recently, a previous study has reported that single layer graphene grown via CVD was patterned and transferred to a target surface by controlling the surface energy of the polydimethylsiloxane (PDMS) stamp [1]. Using this approach, the surface of a relief-patterned elastomeric stamp was functionalized with hydrophilic dimethylsulfoxide (DMSO) molecules to enhance the surface energy of the stamp and to remove the graphene-based layer from the initial substrate and transfer it to a target surface [2]. Further, we developed a soft lithographic patterning process via surface energy modification for advanced graphene-based flexible devices such as transistors or simple and efficient chemical sensor consisting of reduced graphene oxide (rGO) and a metallic nanoparticle composite. A flexible graphene-based device on a biocompatible silk fibroin substrate, which is attachable to an arbitrary target surface, was also successfully fabricated.

• Clean Technology
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• v.21 no.1
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• pp.62-67
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• 2015

We have developed a versatile method for the preparation of chemically linked graphene/multi-walled carbon nanotubes (MWNTs) hybrid materials via simple acid-catalyzed dehydration reaction between graphene oxide (GO) and amine-functionalized MWNTs (af-MWNTs). In this condition, ketone (-C=O) groups in GO and primary amine (-NH₂) moieties in af-MWNTs readily react to form imine (-C=N-) linkage. The chemical structures of graphene/MWNTs hybrid materials have been investigated using various microscopic and spectroscopic measurements. As a result of the synergetic effects of hybrid materials such as improved surface area and the superior structural restoration of graphitic networks, the hybrid materials demonstrate improved capacitance with excellent long-term stability. Furthermore, controlled experiments were conducted to optimize the weight ratio of graphene/MWNTs in hybrid materials. The highest capacitance of 132.4 F/g was obtained from the GM7.5 material, in which the weight ratio between graphene and MWNTs was adjusted to 7.5/1, in 1M KOH electrolyte at a scan rate of 100 mV/s.

• Composites Research
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• v.33 no.4
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• pp.177-184
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• 2020

Flame retardant(FR) clothes prohibit additional fire diffusion and make the personnel do their tasks without a hitch in a flammable environment. The existing FR clothes, however, are heavy and give high thermal fatigue. Therefore, it is strongly demanded to develop a light, convenient, and eco-friendly clothes. Recently, many works have been reported to make FR fabrics with phosphorus compounds, but their performance could not satisfy the specified criteria in appraisal standards of domestic and American FR clothes or combat uniforms. In this paper, two kinds of phosphorus compounds were applied to cotton fabric. Graphene oxide functionalized with a phosphorus-rich deep eutectic solvent and ammonium polyphosphate were coated on cotton fabric by eco-friendly padding procedure. The coated fabrics were analyzed with thermogravimetric analysis, vertical flame resistance test(ASTM D6413), cone calorimeter test(ISO 5660-1), and method of test for limited flame spread(ISO 15025). It was revealed that the as-made cotton with those two materials simultaneously had better flame resistance than the cottons with each one. Furthermore, an additional coating for hydrophobicity on the FR cotton was tried for better washing fastness.

• Membrane Journal
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• v.26 no.6
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• pp.480-489
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• 2016

In this study, the PVdF/MGO composite nanofiber membranes (PMGs) introducing Iron oxide-Graphene oxide ($Fe_3O_4/GO$, Metallic graphene oxide; MGO) was prepared via electrospinng method and its arsenic removal characteristics were investigated. The thermal treatment was carried out to improve the mechanical strength of nanofiber membranes and then the results showed that of outstanding improvement effect. However, in case of PMGs, the decreasing tendency of mechanical strength was indicated as increasing MGO contents. From the results of pore-size analysis, it was confirmed that the porous structured membranes with 0.3 to $0.45{\mu}m$ were prepared. For the water treatment application, the water flux measurement was carried out. In particular, PMG2.0 sample showed about 70% improved water flux results ($153kg/m^2h$) compared to that of pure PVdF nanofiber membrane ($91kg/m^2h$) under the 0.3 bar condition. In addition, the PMGs have indicated the high removal rates of both As(III) and As(V) (up to 81% and 68%, respectively). Based on the adsorption isotherm analysis, the adsorption of As(III) and As(V) ions were both more suitable for the Freundlich. From all of results, it was concluded that PVdF/MGO composite nanofiber membranes could be utilized as a water treatment membrane and for the Arsenic removal applications.