• Carbon letters
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• v.18
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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.

• Electronic Materials Letters
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• v.14 no.6
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• pp.739-748
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• 2018

ZnS nanowalls, microspheres and rice-shaped nanoparticles have been successfully grown on graphene oxide (GO) sheets by the hydrothermal method. The morphologies, structures, chemical compositions and optical properties of the as-synthesized GO/ZnS have been characterized by X-ray power diffraction, energy dispersive spectrometer, scanning electron microscope, Raman spectra, photoluminescence spectroscopy and ultraviolet-visible absorption spectroscopy. It was found that the concentration of CTAB and the reaction temperature were important in the formation of GO/ZnS microstructures. The photocatalytic activity of the as-synthesized GO/ZnS was investigated through the photocatalytic degradation of textile dyeing waste. Results showed that the catalytic activity of the GO/ZnS porous spheres to methyl orange and methylene blue is higher than those of other samples. The degradation rates of methyl orange and methylene blue by porous spheres in 50 min were 97.6 and 97.1%, respectively. This is mainly attributed to the large specific surface area of GO/ZnS porous spheres and high separation efficiency between photogenerated electron and hole pairs.

• Applied Chemistry for Engineering
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• v.26 no.1
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• pp.99-103
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• 2015

We conducted reduction reactions of graphene oxide (GO) using three selected reductants. The conductivity and solubility of three kinds of the reduced graphene oxides (RGOs) were examined based on the degree of reduction. When the ethylene glycol (EG) was used as a reductant, the reduction reaction did not sufficiently progress and as a result the conductivity of RGOs was observed to be relatively low. For RGOs made by hydrazine (HZ) and thiourea dioxide (TU), we observed no significant differences in the degree of the reduction, conductivity and dispersity in water. However, RGO prepared by TU showed an exceptionally good solubility in N-methylpyrrolidone, and the solution was stable for more than 4 months.

• Bulletin of the Korean Chemical Society
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• v.35 no.5
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• pp.1349-1355
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• 2014

A three-dimensional (3D) $Co_3O_4$/mildly oxidized multiwalled carbon nanotubes (moCNTs)/reduced mildly oxidized graphene oxide (rmGO) ternary composite was prepared via a simple and green hydrolysishydrothermal approach by mixing $Co(Ac)_2{\cdot}4H_2O$ with moCNTs and mGO suspension in mixed ethanol/$H_2O$. As characterized by scanning electron microscopy and transmission electron microscopy, $Co_3O_4$ nanoparticles with size of 20-100 nm and moCNTs are effectively anchored in mGO. Cyclic voltammetry and galvanostatic charge-discharge measurements were adopted to investigate the electrochemical properties of $Co_3O_4$/moCNTs/rmGO ternary composite in 6 M KOH solution. In a potential window of 0-0.6 V vs. Hg/HgO, the composite delivers an initial specific capacitance of 492 $Fg^{-1}$ at 0.5 $Ag^{-1}$ and the capacitance remains 592 $Fg^{-1}$ after 2000 cycles, while the pure $Co_3O_4$ shows obviously capacitance fading, indicating that rmGO and moCNTs greatly enhance the electrochemical performance of $Co_3O_4$.

• Advances in concrete construction
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• v.12 no.6
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• pp.479-490
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• 2021

Present research is mainly focused on, microstructural and durability analysis of Graphene Oxide (GO) in Wollastonite (WO) induced cement mortar with silica fume. The study was conducted by evaluating the mechanical properties (compressive and flexural strength), durability properties (water absorption, sorptivity and sulphate resistance) and microstructural analysis by SEM. Cement mortar mix prepared by replacing 10% ordinary portland cement with SF was considered as the control mix. Wollastonite replacement level varied from 0 to 20% by weight of cement. The optimum replacement of wollastonite was found to be 15% and this was followed by four sets of mortar specimens with varying substitution levels of cementitious material with GO at dosage rates of 0.1%, 0.2%, 0.3% and 0.4% by weight. The results indicated that the addition of up to 15%WO and 0.3% GO improves the hydration process and increase the compressive strength and flexural strength of the mortar due to the pore volume reduction, thereby strengthening the mortar mix. The resistance to water penetration and sulphate attack of mortar mixes were generally improved with the dosage of GO in presence of 15% Wollastonite and 10% silica fume content in the mortar mix. Furthermore, FE-SEM test results showed that the WO influences the lattice framework of the cement hydration products increasing the bonding between silica fume particles and cement. The optimum mix containing 0.3% GO with 15% WO replacement exhibited extensive C-S-H formation along with a uniform densified structure indicating that calcium meta-silicate has filled the pores.

• Composites Research
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• v.29 no.4
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• pp.173-178
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• 2016

Graphene oxide (GO) was concurrently reduced and functionalized using long alkyl chain dodecyl amine (DA). The DA functionalized GO (DA-G) was assumed to disperse homogenously in linear low density polyethylene (LLDPE). Subsequently, DA-G was used to fabricate DA-G/LLDPE composites by melt mixing technique. Fourier transform infrared spectra analysis was performed to ascertain the simultaneous reduction and functionlization of GO. Field emission scanning electron microscopy analysis was performed to ensure the homogenous distribution and dispersion of DA-G in LLDPE matrix. The enhanced storage modulus value of the composites validates the homogenous dispersion of DA-G and its good interfacial interaction with LLDPE matrix. An increased in tensile strength value by ~ 64% also confirms the generation of good interface between the two constituents, through which efficient load transfer is possible. However, no significant improvement in glass transition temperature was observed. This simple technique of fabricating LLDPE composites following industrially viable melt mixing procedure could be realizable to developed mechanically strong graphene based LLDPE composites for future applications.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.431-431
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• 2011

Graphene, two dimensional sheet of sp2-hybridized carbon, has attracted an enormous amount of interest due to excellent electrical, chemical and mechanical properties for the application of transparent conducting films, clean energy devices, field-effect transistors, optoelectronic devices and chemical sensors. Especially, graphene is promising candidate to detect the gas molecules and biomolecules due to the large specific surface area and signal-to-noise ratios. Despite of importance to the disease diagnosis, there are a few reports to demonstrate the graphene- and rGO-FET for biological sensors and the sensing mechanism are not fully understood. Here we describe scalable and facile fabrication of rGO-FET with the capability of label-free, ultrasensitive electrical detection of a cancer biomarker, prostate specific antigen/${\alpha}1$-antichymotrypsin (PSA-ACT) complex, in which the ultrathin rGO sensing channel was simply formed by a uniform self-assembly of two-dimensional rGO nanosheets on aminated pattern generated by inkjet printing. Sensing characteristics of rGO-FET immunosensor showed the highly precise, reliable, and linear shift in the Dirac point with the analyte concentration of PSA-ACT complex and extremely low detection limit as low as 1 fg/ml. We further analyzed the charge doping mechanism, which is the change in the charge carrier in the rGO channel varying by the concentration of biomolecules. Amenability of solution-based scalable fabrication and extremely high performance may enable rGO-FET device as a versatile multiplexed diagnostic biosensor for disease biomarkers.

• Korean Chemical Engineering Research
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• v.54 no.1
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• pp.127-134
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• 2016

A series of Ce-doped ZnO (Ce/ZnO) nanostructures were fabricated using the co-precipitation method, then a simply nontoxic hydrothermal approach was proposed for preparation of reduced graphene oxide (rGO)-Ce/ZnO composites. The synthesized composites were investigated by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), photoluminescence spectroscopy (PL), electrochemical impedance spectroscopy (EIS), UV-vis diffuse reflectance spectroscopy (DRS) techniques and Raman pattern. The as-synthesized rGO-Ce/ZnO composites showed high photodecomposition efficiency in comparison with the rGO-ZnO, Ce/ZnO, pure ZnO under UV, visible-light and sunlight irradiation. The degradation of methylene blue (MB) (10 mg/L, 100ml) by 95.8% within 60 min by using rGO-2 (10 mg) under sunlight irradiation was observed. The repeated use of the rGO-2 was investigated, and the results showed almost no decay in the catalytic activity.

• Microbiology and Biotechnology Letters
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• v.41 no.4
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• pp.456-461
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• 2013

Using the different adsorption properties of ssDNA and dsDNA to GO, this study used a real time and efficient fluorescence assay to detect the enzymatic activity of the Klenow fragment with the adsorbed DNA to GO. Results showed that adsorption of fluorescein-tagged ssDNA to GO resulted in fluorescence quenching and DNA was released from GO by adding complementary DNA. In addition, fluorescence restoration was increased through a polymerization reaction by the Klenow fragment in the presence of a fluorescein-attached template, GO, and primer. Gel electrophoresis was conducted to confirm the hybridization and DNA polymerization reactions on GO.

• KEPCO Journal on Electric Power and Energy
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• v.2 no.1
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• pp.127-131
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• 2016

Polymer electrolyte membrane for unitized regenerative fuel cells requires high proton conductivity, high dimensional stability, low permeability, and low cost. However, DuPont's Nafion which is a commercial polymer electrolyte membrane has high permeability, high cost, and decreasing proton conductivity and dimensional stability over $80^{\circ}C$. To address these problems, sulfonated poly ether ether ketone (sPEEK) which is a low cost hydrocarbon polymer is selected as matrix polymer for the preparation of polymer electrolyte membrane. In addition, composite membrane with improved proton conductivity and dimensional stability is prepared by introducing sulfonated graphene oxide (sGO). The fundamental properties of polymer electrolyte membranes are analyzed by investigating membrane's water content, dimensional stability, proton conductivity, and morphology. The cell test is conducted to consider the possibility of application of sPEEK/sGO composite membrane for an unitized regenerative fuel cell.