• Journal of the Korean Electrochemical Society
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• v.17 no.1
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• pp.18-25
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• 2014

A Pt nanoparticle-decorated multiwall carbon nanotube (Pt-MWNT) electrode was prepared on Nafion by a hot-pressing at relatively low temperature. This electrode exhibited an intricate entangled, nanoporous structure as a result of gathering highly anisotropic Pt-MWNTs. Individual Pt nanoparticles were confirmed to have a polycrystalline face-centered cubic structure with an average crystal size of around 3.5 nm. From the cyclic voltammograms for hydrogen redox reactions, the Pt-MWNT electrode was found to have a similar electrochemical behavior to polycrystalline Pt, and a specific electrochemical surface area of $2170cm^2mg^{-1}$. Upon exposure to hydrogen analyte, the Pt-MWNT/Nafion electrode demon-strated a very high sensitivity of $3.60{\mu}A\;ppm^{-1}$ and an excellent linear response over the concentration range of 100-1000 ppm. Moreover, this electrode was also evaluated in terms of response and recovery times, reproducibility, and long-term stability. Obtained results revealed good sensing performance in hydrogen detection.

• Bulletin of the Korean Chemical Society
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• v.33 no.10
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• pp.3191-3195
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• 2012

New silver nanoparticle (AgNP)-loaded amino acid based hydrogels were synthesized successfully from poly (vinyl alcohol) (PVA) and poly(acryl amide-co-acryloyl phenyl alanine) (PAA) by redox polymerization. The formation of AgNP in hydrogels was confirmed by using a UV-Vis spectrophotometer and XRD. The structure and morphology of silver nanocomposite hydrogels were studied by using a scanning electron microscopy (SEM), which demonstrated scattered nanoparticles, ca. 10-20 nm. Thermogravimetric analysis revealed large differences of weight loss (i.e., 48%) between the prestine hydrogel and silver nanocomposite. The antibacterial studies of AgNP-loaded PAA (Ag-PAA) hydrogels was evaluated against Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive) bacteria. These Ag-PAA hydrogels showed significant activities against all the test bacteria. Newly developed hydrogels could be used for medical applications, such as artificial burn dressings.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.218-218
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• 2013

We report a simple and cost-effective method to fabricate transparent superhydrophobic surface on various substrates. The surface was fabricated by coating hydrophobic PDMS (polydimethylsiloxane) film on the silica nanoparticle and subsequent fixing of the hydrophobic silica nanoparticles onto substrates. The water contact angle for the prepared surface was determined to be over $150^{\circ}$, whichindicates that the surface is highly repellent to water. The hierarchical structure and roughness of the surface were examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Additionally, transparency of the prepared surface was measured with UV-VIS spectrometer. The transmittance of the superhydrophobic surface was ~80%, which is lower than that without PDMS-coated silica by only 5 to 10%. It is also notable that the superhydrophobic surface fully recovers its original transmittance after self-cleaning process. Also the PDMS coating is stable under a wide range of pH conditions, UV radiation and salinity conditions, which is essential for the practical use. Moreover, our fabrication method is applicable in large scale production.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.239.1-239.1
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• 2011

Dye sensitized solar cells (DSC) are promising devices for inexpensive, nontoxic, transparent, and large-scale solar energy conversion. Generally thick $TiO_2$ nanoporous films act as efficient photoanodes with their large surface area for absorbing light. However, electron transport through nanoparticle networks causes the slowdown and the loss of electron transport because of a number of interparticle boundaries inside the conduction path. We have studied DSCs with precisely dimension-controlled $TiO_2$ nanotubes array as photoanode. $TiO_2$ nanotubes array is prepared by template-directed fabrication method with atomic layer deposition. Well-ordered nanotubes array provides not only large surface area for light absorbing but also direct pathway for electrons with minimalized grain boundaries. Large enlongated anatase grains in the nanotubes could enhance the conductivity of electrons, but also suppress the recombination with holes through defect sites during diffusion into the electrode. To study the effect of grain boundaries, we fabricated two kinds of nanotubes which have different grain sizes by controlling deposition conditions. And we studied electron conduction through two kinds of nanotubes with different grain structures. The solar cell performance was studied as a function of thickness and grain structures. And overall solar-to-electric energy conversion efficiencies of up to 7% were obtained.

• Journal of Industrial Technology
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• v.38 no.1
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• pp.15-19
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• 2018

In this study, hyaluronic acid (HA) was electro-spun to fabricate nanofibrous membranes for support materials. Because HA is very hygroscopic, it is difficult to obtain enough viscosity to apply electrospinning method. Therefore, we mixed HA with polyethylene oxide (PEO) to obtain proper viscosity and added adipic acid (ADH) to promote cross-linking of PEO/HA during electrospinning. The morphology of PEO/HA membrane was optimized according to PEO/HA concentration ratio and spinning rate. Finally, we fabricated gold-nanoparticle-embedded PEO/HA membranes and their catalyst activities were evaluated in tetramethylbenzidine (TMB) oxidation.

• Smart Structures and Systems
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• v.8 no.5
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• pp.471-486
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• 2011

Various types of strain sensors have been developed and widely used in the field for monitoring the mechanical deformation of structures. However, conventional strain sensors are not suited for measuring large strains associated with impact damage and local crack propagation. In addition, strain sensors are resistive-type transducers, which mean that the sensors require an external electrical or power source. In this study, a gold nanoparticle (GNP)-based polymer composite is proposed for large strain sensing. Fabrication of the composites relies on a novel and simple in situ GNP reduction technique that is performed directly within the elastomeric poly(dimethyl siloxane) (PDMS) matrix. First, the reducing and stabilizing capacities of PDMS constituents and mixtures are evaluated via visual observation, ultraviolet-visible (UV-Vis) spectroscopy, and transmission electron microscopy. The large strain sensing capacity of the GNP-PDMS thin film is then validated by correlating changes in thin film optical properties (e.g., maximum UV-Vis light absorption) with applied tensile strains. Also, the composite's strain sensing performance (e.g., sensitivity and sensing range) is also characterized with respect to gold chloride concentrations within the PDMS mixture.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.445.1-445.1
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• 2014

Dye-sensitized solar cells (DSSCs) have been widely investigated as a next-generation solar cell because of their simple structure and low manufacturing cost. The $TiO_2$ film with thickness of $8{\sim}10{\mu}m$, which consists of nanoparticles, acts as both a scaffold with a high surface-to-volume ratio for the dye loading and a pathway to remove the electrons. However, charge carriers have to move across many particle boundaries by a hopping mechanism. So, one dimensional nanostructures such as nanotubes, nanorods and nanowires should improve charge carrier transportation by providing a facile direct electron pathway and lowering the diffusion resistance. However, the efficiencies of DSSCs using one dimensional nanostructures are less than the $TiO_2$ nanoparticle-based DSSCs. In this work, the patterned $TiO_2$ film with thickness of $3{\mu}m$ was deposited using photolithography process to decrease of electron pathway and increase of surface area and transmittance of $TiO_2$ films. Properties of the patterned $TiO_2$ films were investigated by various analysis method such as X-ray diffraction, field emission scanning electron microscopy (FESEM) and UV-visible spectrophotometer.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.318.1-318.1
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• 2014

Metal nano-crystals have been received much attentions owing to their excellent catalytic property and surface plasmon effect. In the last decade, many studies on synthesizing well-dispersive nanoparticles and on understanding their distinct physical properties have been performed. There were tremendous reports revealing the electrochemical activities and enhancement of surface plasmonic effect were dependent mainly on the size, shape, and composition. So far, most fabrication methods have been based on vacuum based deposition techniques, such as chemical vapor deposition and electron-beam evaporation, and then annealed them to transform into the nanoparticles. Recently, there were several reports regarding to the photoinduced nano-crystal synthesis as an effective way to produce the metal nanoparticles. In this study, we report synchrotron x-ray mediated synthesis of Au nanoparticles on ZnO nanowires. ZnO nanowires were fabricated by hydrothermal method, and then they were dip into a solution having Au clusters. Detailed structural evolution of Au nanoparticles was investigated using scanning electron microscopy and photoluminescence measurements. The results on formation of well-dispersive Au nanoparticles on ZnO nanowires will be presented.

• 한국신재생에너지학회:학술대회논문집
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• 2011.11a
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• pp.53.2-53.2
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• 2011

Dye-sensitized solar cells(DSSCs) have been recognized as an alternative to the conventional p-n junction solar cells because of their simple fabrication process, low production cost, and transparency. A typical DSSC consists of a transparent conductive oxide (TCO) electrode, a dye-sensitized oxide semiconductor nanoparticle layer, liquid redox electrolyte, and a Pt-counter electrode. In dye-sensitized solar cells, charge recombination processes at interfaces between coducting glass, $TiO_2$, dye, and electrolyte play an important role in limiting the photon-to-electron conversion efficiency. A layer of ZTO thin film less than ~200nm in thickness, as a blocking layer, was deposited by DC magnetron sputtering method directly onto the anode electrode to be isolated from the electrolyte in dye-sensitized solar cells(DSCs). This is to prevent the electrons from back-transferring from the electrode to the electrolyte ($I^-/I_3^-$). The presented DSCs were fabricated with working electrode of Ga-doped ZnO glass coated with blocking ZTO layer, dye-attached nanoporous $TiO_2$ layer, gel electrolyte and counter electrode of Pt-deposited GZO glass. The effects of blocking layer were studied with respect to impedance and conversion efficiency of the cells.

• Journal of the Korean Ceramic Society
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• v.42 no.12 s.283
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• pp.821-826
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• 2005

Gadolinia-doped ceria nanopowder was prepared by glycine-nitrate combustion method with different glycine/nitrate mixing ratio. The characteristics of the synthesized powder were investigated by X-ray diffraction method, transmission electron microscopy, thermal gravity, differential thermal analysis and thermo-mechanical analysis. The smallest powder was obtained with glycine/nitrate ratio 1.00 and the lowest organic and water vapor contained powder was made with glycine/nitrate ratio 1.75. According to dilatometry, fast densification was occurred around $1000^{\circ}C$ and shows full density over $1300^{\circ}C$. Finally near-fully dense ceria electrolyte was fabricated with conventional sintering technique. Glycine-nitrate process yields fine nanopowders which enable low temperature sintering and fabrication of fully dense and nanostructured oxide electrolyte.