• Membrane Journal
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• v.28 no.1
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• pp.75-82
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• 2018

Forward osmosis (FO) desalination system has been highlighted to improve the energy efficiency and drive down the carbon footprint of current reverse osmosis (RO) desalination technology. To improve the trade-off between water flux and salt rejection of thin film composite (TFC) desalination membrane, thin film nanocomposite membranes (TFN), in which nanomaterials as a filler are embeded within a polymeric matrix, are being explored to tailor the separation performance and add new functionality to membranes for water purification applications. The objective of this article is to develop a graphene nanocomposite membrane with high performance of water selective permeability (high water flux, high salt rejection, and low reverse solute diffusion) as a next-generation FO desalination membrane. For advances in fabrication of graphene oxide (GO) membranes, layer-by-layer (LBL) technique was used to control the desirable structure, alignment, and chemical functionality that can lead to ultrahigh-permeability membranes due to highly selective transport of water molecules. In this study, the GO nanocomposite membrane fabricated by LBL dip coating method showed high water flux ($J_w/{\Delta}{\pi}=2.51LMH/bar$), water selectivity ($J_w/J_s=8.3L/g$), and salt rejection (99.5%) as well as high stability in aqueous solution and under FO operation condition.

• Journal of the Korean GEO-environmental Society
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• v.12 no.11
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• pp.51-57
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• 2011

The calcium hydroxide($Ca(OH)_{2}$) which is flowed into the deteriorated tunnel by groundwater is reacted with carbon dioxide($CO_{2}$) and the vehicle's exhaust gas ($SO_{3}$). So its by-products are precipitated at the drainage pipe and these cause the drainage clogging. Most by-products are composed of $CaCO_{3}$ with calcite from a chemical experiment. The purpose of this study is mainly focused on comparison of attachment on each material of drainage pipe (teflon-coated steel pipe, silicon-Oil coated pipe, acrylic pipe and PVC pipe). The test was progressed to disembogue the CaO aqueous solution and tunnel outflow into each of the pipes. The experimental results show that the most produced scale pipe is PVC material and the followings are Acrylic pipe, Silicon-Oil coating pipe and Teflon coating pipe. But the long-term test results showed that teflon-coated steel pipe had a problem with durability because soil which was contained in the tunnel outflow occurred detachment of coating and corrosion of the steel pipe.

• Journal of Biosystems Engineering
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• v.33 no.6
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• pp.404-409
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• 2008

Excessive presence of heavy metals in environment affects plants and fruits grown in the contaminated area. Rapid on-site monitoring of heavy metals can provide useful information for efficiently characterizing heavy metal-contaminated sites and for minimizing the exposure of the contaminated food crops to humans. This study reports on the evaluation of gold and glassy carbon (GC) electrodes with mercury or bismuth as a coating material for simultaneous determination of cadmium (Cd) and lead (Pb) in 0.1 M $HNO_3$ solution by anodic stripping voltammetry (ASV). The use of a square-wave voltammetric potential between a working electrode and a reference electrode caused Cd and Pb ions deposited on the electrode surface to be oxidized, thereby generating electric currents at different potentials. The mercury-coated gold electrode was not sensitive enough to detect the usable range of Cd concentrations (1 to 100 ppb). The GC electrodes with mercury or bismuth displayed well-defined, sharp and separate current peaks for Cd and Pb ions when the square-wave voltammetric potentials were applied. The peak currents measured with both mercury- and bismuth- coated GC electrodes were linearly proportional to Cd and Pb concentrations in the range of 1 to 200 ppb in 0.1 M $HNO_3$ with strong linear relationships between concentration and peak current ($R^2$ > 0.95), indicating that both of Cd and Pb ions could be quantitatively measured.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.10a
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• pp.43.2-43.2
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• 2011

Single-walled carbon nanotubes (SWCNT) are transparent in the visible and show conductivity comparable to copper, and are environmentally stable. SWCNT films have high flexibility, conductivity and transparency approaching that indium tin oxide (ITO), and can be prepared inexpensively without vacuum equipment. Transparent conducting Films (TCF) of SWCNTs has the potential to replace conventional transparent conducting oxides (TCO, e.g. ITO) in a wide variety of optoelectronic devices, energy conversion and photovoltaic industry. However, the sheet resistance of SWCNT films is still higher than ITO films. A decreased in the resistivity of SWCNT-TCFs would be beneficial for such an application. We fabricated SWCNT sheet with $KAuBr_4$ on PET substrate. Arc-discharge SWCNTs were dispersed in deionized water by adding sodum dodecyl sulfate (SDS) as surfactant and sonicated, followed by the centrifugation. The dispersed SWCNT was spray-coated on PET substrate and dried on a hotplate at $100^{\circ}C$. When the spray process was terminated, the TCF was immersed into deionized water to remove the surfactant and then it was dried on hotplate. The TCF film was then treated with AuBr4-, rinsed with deionized water and dried. The surface morphology of TCF was characterized by field emission scanning electron microscopy. The sheet resistance and optical transmission properties of the TCF were measured with a four-point probe method and a UV-visible spectrometry, respectively. $HNO_3$ treated SWCNT films with Au nano-particles have the lowest 61 ${\Omega}$/< sheet resistance in the 80% transmittance. Sheet resistance was decreased due to the increase of the hole concentration at the washed SWCNT surface by p-type doping of $AuBr_4{^-}$.

• Journal of Ocean Engineering and Technology
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• v.25 no.6
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• pp.60-65
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• 2011

A low temperature plasma carburizing process was performed on AISI 316L austenitic stainless steel to achieve an enhancement of the surface hardness without degradation of its corrosion resistance. Attempts were made to investigate the influence of the processing temperatures on the surface hardened layer during low temperature plasma carburizing in order to obtain the optimum processing conditions. The expanded austenite (${\gamma}_c$) phase, which contains a high saturation of carbon (S phase), was formed on all of the treated surfaces. Precipitates of chromium carbides were detected in the hardened layer (C-enriched layer) only for the specimen treated at $550^{\circ}C$. The hardened layer thickness of ${\gamma}_c$ increased up to about $65{\mu}m$ with increasing treatment temperature. The surface hardness reached about 900 $HK_{0.05}$, which is about 4 times higher than that of the untreated sample (250 $HK_{0.05}$). A minor loss in corrosion resistance was observed for the specimens treated at temperatures of $300^{\circ}C{\sim}450^{\circ}C$ compared with untreated austenitic stainless steel. In particular, the precipitation of chromium carbides at $550^{\circ}C$ led to a significant decrease in the corrosion resistance. A diamond-like carbon (DLC) film coating was applied to improve the wear and friction properties of the S phase layer. The DLC film showed a low and stable friction coefficient value of about 0.1 compared with that of the carburized surface (about 0.45). The hardness and corrosion resistance of the S phase layer were further improved by the application of such a DLC film.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.65-65
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• 2011

Single-well carbon nanotubes (SWNT) have been proposed as a promising candidate for various applications owing to their excellent properties. In particular, their fascinating electrical and mechanical properties could provide a new area for the development of advanced engineering materials. A transparent conductive thin film (TCF) has increased for applications such as liquid crystal displays, touch panels, and flexible displays. Indium tin oxide (ITO) thin films, which have been traditionally used as the TCFs, have a serious obstacle in TCFs applications. SWNTs are the most appropriate materials for conductive films for displays due to their excellent high mechanical strength and electrical conductivity. But, a bundle of CNTs has different electrical properties than their individual counterparts. In this work, the fabrication by the spraying process of transparent SWNT films and reduction of its sheet resistance on PET substrates is researched. Arc-discharge SWNTs were dispersed in deionized water by adding sodum dodecyl sulfate (SDS) as surfactant and sonicated, followed by the centrifugation. The dispersed SWNT was spray-coated on PET substrate and dried on a hotplate at $100^{\circ}C$. When the spray process was terminated, the TCF was immersed into deionized water to remove the surfactant and then it was dried on hotplate. The TCF film was then treated with ionic doping treatment, rinsed with deionized water and dried. The surface morphology of TCF was characterized by field emission scanning electron microscopy. The sheet resistance and optical transmission properties of the TCF were measured with a four-point probe method and a UV-visible spectrometry, respectively. Results, we show that 97 ${\Omega}$/> sheet resistance can be achieved with 81% transmittance at the wavelength of 550 nm. The changes in electrical and optical conductivity of SWNT film before and after ionic doping treatments were discussed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.5
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• pp.517-521
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• 2012

Carbon nanotubes (CNTs) have been regarded as a promising material for the fabrication of flexible conductors such as transparent electrodes, flexible heaters, and transparent speakers. In this study, a multiwalled carbon nanotube (MWCNT) film was deposited on a polyethylene terephthalate (PET) substrate using a spraying technique. MWCNTs were dispersed in water using sodium dodecyl sulfate (SDS). To evaluate the effect of the weight ratio between SDS and MWCNTs on the electromechanical properties of the film, direct tensile tests and optical strain measurement were conducted. It was found that the CNT film hardly affected the mechanical behavior of CNT/PET composite films, while the electrical behavior of the CNT film was strongly affected by the SDS concentration in the CNT film. The electrical resistance of CNT/PET films gradually increased with the strain applied to the PET substrate, even up to a large strain that ruptured the substrate.

• Bulletin of the Korean Chemical Society
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• v.32 no.7
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• pp.2178-2182
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• 2011

Recently, the synthesis of ordered macroporous materials has received much attention due to its potential use as photonic band gap materials.$^1$ In this study, we have used the three-dimensional (3D) latex array template impregnated with benzenesulfonic acid (BSA), which is capable of catalyzing the reaction using tetraethyl orthosilicate (TEOS) as a precursor and distilled water. The polystyrene (PS) templates were reacted with TEOS in $scCO_2$ at 40 $^{\circ}C$ and at 80 bar. In the reactor, TEOS was filtrated into the PS particle lattice. After the reaction, porous silica materials were obtained by calcinations of the template. The stability test of the PS template in pure $CO_2$ was conducted before the main experiment. Scanning electron microscopy (SEM) images showed that the reaction in $scCO_2$ takes place only on the particle surface. This new method using $scCO_2$ has advantages over conventional sol-gel processes in its capability to control the fluid properties such as viscosity and interfacial tension. It has been found that the reaction in $scCO_2$ occurs only on the particle surface, making the proposed technique as more rapid and sustainable method of synthesizing inverse opal materials than conventional coating processes in the liquid phase and in the vapor phase.

• Journal of the Korean Vacuum Society
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• v.13 no.4
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• pp.175-181
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• 2004

We investigated the stability of the DLC film coated on 304 stainless steel substrate by Radio frequency assisted chemical vapor deposition method. Fracture and spallation behaviour of the coating was observed during micro-tensile test of the fil $m_strate composite. As the tensile deformation progressed, the cracks of the film were observed in the perpendicular direction to the tensile axis. Further deformation resulted in the plastic deformation with $45^{\circ}$ slip bands on the substrate surface. Spallation of the film occurred with the plastic deformation, which was initiated at the cracks of the film and was aligned along the slip directions. We found that both the cracking and the spallation behaviors are strongly dependent on the pre-treatment condition, such as Ar plasma pre-treatment. The spallation of the film was considerably suppressed in an optimized condition of the substrate cleaning by Ar glow discharge. We observed the improved stability with increasing duration of Ar plasma pre-treatment.nt.

• Membrane Journal
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• v.24 no.4
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• pp.332-339
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• 2014

In this study, an anion-exchange ionomer solution was developed by employing poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) as the base material for the improvement of the capacitive deionization (CDI) performances. It was found that prepared quaternized PPO (QPPO) exhibited excellent ion conductivity superior to that of a commercial anion-exchange membrane (AMX, Astom Corp., Japan) and also the electrochemical properties were shown to be comparable with each other. The CDI tests were conducted by employing the porous carbon electrode coated with the ionomer solution and the result showed the high salt removal efficiency of about 94.9%. By comparing the desalination efficiencies in conventional CDI, membrane CDI (MCDI) with a commercial anion-exchange membrane, and coated CDI (CCDI) employing the porous carbon electrode coated with QPPO, it was confirmed that CCDI shows the high salt removal performance improved by 52.1% and 18.3% compared with those of conventional CDI and MCDI, respectively.