• Laser Solutions
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• v.15 no.4
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• pp.1-5
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• 2012

We demonstrate that reduced graphene oxide (rGO) coated thin aluminum film is an effective optoacoustic transmitter for generating high pressure and high frequency ultrasound previously unattainable by other techniques. The rGO layer of different thickness is deposited between a 100 nm-thick aluminum film and a glass substrate. Under a pulsed laser excitation, the transmitter generates enhanced optoacoustic pressure of 64 times the aluminum-alone transmitter. A promising optoacoustic wave generation is possible by optimizing thermoelasticity of metal film and thermal conductivity of rGO in the proposed transmitter for laser-induced ultrasound (LIUS) applications.

• Carbon letters
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• v.15 no.4
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• pp.282-289
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• 2014

Blends of poly(vinyl alcohol) (PVA), polyethyleneimine (PEI), and graphene oxide (GO) were prepared by solution casting method. Calorimetric thermal properties of the blends were investigated. The $T_gs$ of PVA/PEI blends were higher than the $T_gs$ of either of the component polymers at low concentrations of PEI. These abnormal increases of $T_gs$ may be due to the negative entropy of mixing which is associated with strong hydrogen bonding between PVA and PEI. The degree of depression of $T^0_ms$ was not reduced by the negative entropy of mixing, since strong hydrogen bonding also causes an increase in the magnitude of negative ${\chi}$ between PVA and PEI. The $T_g$ of PVA was increased significantly by adding 0.7 wt.% GO into PVA. The magnitude of negative ${\chi}$ was increased by adding GO into the blends of PVA and PEI.

• Journal of Industrial and Engineering Chemistry
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• v.67
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• pp.417-428
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• 2018

In this study, we fabricated hierarchically self-assembled thin films composed of graphene oxide (GO) sheets and gold nanoparticles (Au NPs) using the Langmuir-Blodgett (LB) and Langmuir-Schaefer (LS) techniques and investigated their gas-sensing performance. First, a thermally oxidized silicon wafer ($Si/SiO_2$) was hydrophobized by depositing the LB films of cadmium arachidate. Thin films of ligand-capped Au NPs and GO sheets of the appropriate size were then sequentially transferred onto the hydrophobic silicon wafer using the LB and the LS techniques, respectively. Several different films were prepared by varying the ligand type, film composition, and surface pressure of the spread monolayer at the air/water interface. Their structures were observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM), and their gas-sensing performance for $NH_3$ and $CO_2$ was assessed. The thin films of dodecanethiol-capped Au NPs and medium-sized GO sheets had a better hierarchical structure with higher uniformity and exhibited better gas-sensing performance.

• Advances in nano research
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• v.5 no.3
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• pp.231-244
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• 2017

Graphene oxide (GO) was prepared by modified Hummer's method to produce reduced graphene oxide (RGO) following standard thermal and chemical reduction processes. Prepared RGO colloids were utilized to fabricate RGO films over glass and FTO coated glass substrates through drop-coating. A systematic study was performed to evaluate the effect of reduction degree on the optical and electrical properties of the RGO film. We demonstrate that both the reduction process (thermal and chemical) produce RGO films of similar optical and electrical behaviors. However, the RGO films fabricated using chemically reduced GO colloid render better performance in dye sensitized solar cells (DSSCs), when they are used as counter electrodes (CEs). It has been demonstrated that RGO films of optimum thicknesses fabricated using RGO colloids prepared using lower concentration of hydrazine reducer have better catalytic performance in DSSCs due to a better catalytic interaction with redox couple. The better catalytic performance of the RGO films fabricated at optimal hydrazine concentration is associated to their higher available surface area and lower grain boundaries.

• Bulletin of the Korean Chemical Society
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• v.35 no.6
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• pp.1799-1805
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• 2014

In this article, we described about the preparation and electrochemical properties of a flexible energy storage system based on a plastic polyethylene terephthalate (PET) substrate. The PET treated with UV/ozone was fabricated with multilayer films composed of 30 polyaniline (PANi)/graphene oxide (GO) bilayers using layer-by-layer assembly of positively charged PANi and negatively charged GO. The conversion of GO to the reduced graphene oxide (RGO) in the multilayer film was achieved using hydroiodic acid vapor at $100^{\circ}C$, whereby PANi structure remained nearly unchanged except a little reduction of doping state. Cyclic voltammetry and charge/discharge curves of 30 PANi/RGO bilayers on PET substrate (shorten to PANi-$RGO_{30}$/PET) exhibited an excellent volumetric capacitance, good cycling stability, and rapid charge/discharge rates despite no use of any metal current collectors. The specific capacitance from charge/discharge curve of the PANi-$RGO_{30}$/PET electrode was found to be $529F/cm^3$ at a current density of $3A/cm^3$, which is one of the best values yet achieved among carbon-based materials including conducting polymers. Furthermore, the intrinsic electrical resistance of the PANi-$RGO_{30}$/PET electrodes varied within 20% range during 200 bending cycles at a fixed bend radius of 2.2 mm, indicating the increase in their flexibility by a factor of 225 compared with the ITO/PET electrode.

• Transactions of the Korean hydrogen and new energy society
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• v.27 no.4
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• pp.329-334
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• 2016

Hydrogen is eco-friendly alternative energy source and the photoelectrochemical water splitting is believed to be one of the promising methods for hydrogen production. Many researchers have studied several potential photocatalysts to increase the photoelectochemical performance efficiency for hydrogen conversion. In this study, the GO (graphene oxide) was prepared by Tour's method and was dispersed in precursor solutions of $WO_3$ and $BiVO_4$. Those precursor solutions were spin-coated on FTO glass and several photocatalyst thin films of $WO_3$, $BiVO_4$ and $WO_3/BiVO_4$ were prepared by calcination. The morphologies of prepared photocatalyst thin films were measured by scanning electron microscope. The photoelectrochemical performances of photocatalyst thin films with rGO (reduced graphene oxide) and without rGO were analyzed systematically.

• Polymer(Korea)
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• v.38 no.2
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• pp.232-239
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• 2014

Poly(lactic acid)(PLA) nanocomposites containing various nanofillers were synthesized using the solution intercalation method. Organically modified bentonite clay (NSE), octadecylamine-graphene oxide (ODA-GO), and an NSE/ODA-GO complex were utilized as nanofillers in the fabrication of PLA hybrid films. PLA hybrid films with varying nanofiller contents in the range of 0-10 wt% were examined and compared in terms of their thermomechanical properties, morphologies, and oxygen permeabilities. Transmission electron microscopy (TEM) confirmed that most of the NSE and ODA-GO nanofillers were dispersed homogeneously throughout the PLA matrix on the nanoscale, although some agglomerate NSE/ODA-GO complex particles were also formed. Among the three nanofillers for PLA hybrid films, the NSE/ODA-GO complex showed the best improvement in film thermal stability. In contrast, NSE and ODA-GO exhibited the best improvement in tensile mechanical properties and oxygen barrier properties of the PLA hybrid films, respectively.

• Applied Chemistry for Engineering
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• v.26 no.3
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• pp.331-335
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• 2015

We prepared films by a bar-coating of various graphene oxide (GO) pastes by varying pH with amine compounds. The thermal treatment of films at $150^{\circ}C$ and measurement of surface resistances exhibited that the pH variation does not significantly affect the surface resistance. We, however, found that the addition of amines reduced the surface resistance by approximately 10 times and N,N-dimethylethanolamine (DMEA) showed the most significant effect among all amines investigated. XPS studies demonstrated that the addition of DMEA accelerated the reduction reaction of GO, and finally enhanced the electrical properties of GO films.

• Carbon letters
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• v.14 no.4
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• pp.251-254
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• 2013

In this study, poly(amic acid) was prepared via a polycondensation reaction of 3,3'-dihydroxybenzidine and pyromellitic dianhydride in an N-methyl-2-pyrrolidone solution; reduced graphene oxide/polybenzoxazole (r-GO/PBO) composite films, which significantly increased the electrical conductivity, were successfully fabricated. GO was prepared from graphite using Brodie's method. The GO was used as nanofillers for the preparation of r-GO/PBO composites through an in situ polymerization. The addition of 50 wt% GO led to a significant increase in the electrical conductivity of the composite films by more than sixteen orders of magnitude compared with that of pure PBO films as a result of the electrical percolation networks in the r-GO during the thermal treatment at various temperatures within the films.

• Applied Chemistry for Engineering
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• v.30 no.3
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• pp.324-330
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• 2019

Petal-like nickel cobaltite ($NiCo_2O_4$)/reduced graphene oxide (rGO) composites with different $rGO-to-NiCo_2O_4$ weight ratios were synthesized using a simple hydrothermal method and subsequent thermal treatment. In the $NiCo_2O_4/rGO$ composite, the $NiCo_2O_4$ 3-dimensional nanomaterials contributed to the improvement of electrochemical properties of the final composite material by preventing the restacking of the rGO sheet and securing ion movement passages. The composite structure was examined by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and Fourier-transform infrared (FT-IR) spectroscopy. The FE-SEM and TEM images showed that petal-like $NiCo_2O_4$ was supported on the rGO surface. Cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS) were used for the electrochemical analysis of composites. Among the prepared composites, $0.075g\;rGO/NiCo_2O_4$ composite showed the highest specific capacitance of $1,755Fg^{-1}$ at a current density of $2Ag^{-1}$. The cycle performance and rate capability of the composite material were higher than those of using the single $NiCo_2O_4$ material. These nano-structured composites could be regarded as valuable electrode materials for supercapacitors that require superior performance.