• Membrane Journal
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• v.31 no.4
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• pp.268-274
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• 2021

One of the chronic problems in the issue of global warming is the emission of greenhouse gases. Carbon dioxide (CO₂), which accounts for the highest proportion of various greenhouse gases, has been continuously researched by humans to separate it. From this point of view, a poly(vinyl alcohol) (PVA)-based copolymer with acrylic acid monomer was utilized in a gas separation membrane in this study. We employed a free radical polymerization to fabricate PVA-g-PAA (VAA) graft copolymer. It was utilized in the form of a composite membrane on a polysulfone substrate. The proper amount of acrylic acid reduced the crystallinity of PVA and increased CO₂ solubility in separation membranes. In this perspective, we suggest the novel approach in CO₂ separation membrane area by grafting and solution-diffusion.

• Journal of Sensor Science and Technology
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• v.30 no.2
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• pp.94-98
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• 2021

In this study, pure and Co3O4/CoFe2O4-loaded Indium oxide (In2O3) nanofibers were synthesized by the electrospinning of an Indium/Polyvinylpyrrolidone precursor solution containing cobalt and iron bimetallic zeolitic imidazolate frameworks and subsequent heat treatment. The ethanol, toluene, p-xylene, benzene, carbon monodxide, and hydrogen gas sensing characteristics of the solution were measured at 250-400 ℃. 0.5 at%-Co3O4/CoFe2O4-loaded In2O3 nanofibers exhibited extreme response (resistance ratio - 1) to 5 ppm of ethanol (210.5) at 250 ℃ and excellent selectivity over the interfering gases. In contrast, pure In2O3 nanofibers exhibited relatively low responses to all the analyte gases and low selectivity above 250-400 ℃. The superior response and selectivity toward ethanol is explained by the catalytic roles of Co3O4 and CoFe2O4 in gas sensing reaction and the electronic sensitization induced by the formation of p (Co3O4/CoFe2O4)-n (In2O3) junctions.

• Journal of Energy Engineering
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• v.23 no.4
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• pp.141-149
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• 2014

In the present study, pure RHO zeolite was hydrothermally synthesized by using 18-crown-6 ether as a structure directing agent(SDA), and the small gases adsorption was investigated. Synthesized RHO zeolite was a cube shape particle of which average edge length was around $1.2{\mu}m$ and composed of primary crystallites having a diameter of around 100 to 200 nm. RHO zeolite structure was stable under 3h calcination at $600^{\circ}C$. Water adsorption data announced that RHO zeolite has a specific surface area of 483.32 m2/g and its micropore diameter was about 4 A. Gas adsorption was studied in the pressure range of 50 to 500 kPa for $CO_2$, $N_2$, $O_2$ and $H_2$. It was evident that RHO zeolite showed a strong $CO_2$ adsorption behavior. Especially, RHO zeolite showed a transient $CO_2$ adsorption behavior. The 3h $CO_2$ up-take at 50 kPa and 500 kPa was 1.283 and 3.357 mmol/g, respectively. The $CO_2/H_2$ selectivity was around 16 at 500 kPa. Compared with gas adsorption data for some representative microporous adsorbents, it was certain that RHO zeolite is a beneficial adsorbent for $CO_2/H_2$ separation.

• Journal of the Korean Ceramic Society
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• v.39 no.8
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• pp.789-794
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• 2002

In this study, nano-sized Si-C-N precursor powders were synthesized by Chemical Vapor Condensation Method(CVC) using TMS(Tetramethylsilane: $Si(CH_3)_4$), $NH_3$ and $H_2$ gases under the various reaction conditions of the reaction temperature, TMS/$NH_3$ ratio and TMS/$H_2$ ratio. XRD and FESEM were used to analysis the crystalline phase and the average particle size of the synthesized powders. It was found that the obtained powders under the considering conditions were all spherical amorphous powder with the particle size of 87∼130 nm. The particle size was decreased as the reaction temperature increased and TMS/$NH_3$ and TMS/$H_2$ ratio decreased. As the results of EA analysis, it was found that the synthesized powders had been formed the powders composed of Si, N, C and H. Through FT-IR results, it was found that the synthesized powders were Si-C-N precursor powders with Si-C, Si-N and C-N bonds.

• Journal of the Korean Ceramic Society
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• v.39 no.8
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• pp.783-788
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• 2002

In this study, nano-sized Si-C-N precursor powders were synthesized by Chemical Vapor Condensation Method(CVC) using TMS(Tetramethylsilane: Si($CH_3)_4$), $NH_3$ and $H_2$ gases under the various reaction conditions of the reaction temperature, TMS/$NH_3$ ratio and TMS/$H_2$ ratio. XRD and FESEM were used to analysis the crystalline phase and the average particle size of the synthesized powders. It was found that the obtained powders under the considering conditions were all spherical amorphous powder with the particle size of 87∼130 nm. The particle size was decreased as the reaction temperature increased and TMS/$NH_3$ and TMS/$H_2$ ratio decreased. As the results of EA analysis, it was found that the synthesized powders had been formed the powders composed of Si, N, C and H. Through FT-IR results, it was found that the synthesized powders were Si-C-N precursor powders with Si-C, Si-N and C-N bonds.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.127-127
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• 2009

The most important part of the fabrication solar cells is the anti-reflection coating when excludes the kinds of silicon substrates (crystalline, polycrystalline, or amorphous), patterns and materials of electrodes. Anti-reflection coatings reduce the reflection of sunlight and at last increase the intensity of radiation to inside of solar cells. So, we can obtain increase of solar cell efficiency about 10% using anti-reflection coating. There are many kinds of anti-reflection film for solar cell, such as SiN, $SiO_2$, a-Si, and so on. And, they have two functions, anti-reflection and passivation. However such materials could not perfectly prevent reflection. So, in this work, we investigated the anti-reflection coating with the columnar structure ZnO thin film. We synthesized columnar structure ZnO film on glass substrates. The ZnO films were synthesized using a RF magnetron sputtering system with a pure (99.95%) ZnO target at room temperature. The anti-reflection coating layer was sputtered by argon and oxygen gases. The angle of target and substrate measures 0, 20, 40, 60 degrees, the working pressure 10 mtorr and the 250 W of RF power during 40 minutes. The confirm the growth mechanism of ZnO on columnar structure, the anti-reflection coating layer was observed by field emission scanning electron microscopy (FE-SEM). The optical trends were observed by UV-vis and Elleso meter.

• Journal of the Korean Ceramic Society
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• v.45 no.8
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• pp.477-481
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• 2008

$Eu^{2+}$ and $Dy^{3+}$ co-doped strontium aluminate, $SrAl_2O_4$ long phosphorescent phoshor was fabricated and its photoluminescence was characterized. The phosphor, $SrAl_2O_4:Eu^{2+},Dy^{3+}$ was synthesized by a coprecipitation in which metal salts of $Sr(NO_3)_2$, $Al(NO_3)_3{\cdot}9H_2O$, were dissolved in $(NH_4)_2CO_3$ solution with adding $Eu(NO_3)_3{\cdot}5H_2O$ and $Dy(NO_3)_3{\cdot}5H_2O$ as a activator and co-activator, respectively. The coprecipitated products were separated from solution, washed, and dried in a vacuum dry oven. The dried powders were then mixed with 3 wt% $B_2O_3$ as a flux and heated at $800{\sim}1400^{\circ}C$ for 3 h under the reducing ambient atmosphere of 95%Ar+$5%H_2$ gases. For the synthesized $SrAl_2O_4:Eu^{2+},Dy^{3+}$, properties of photoluminescence such as emission, excitation and decay time were examined. The emission intensity increased as the annealing temperature increased and showed a maximum peak intensity at 510 nm with a broad band from $400{\sim}650\;nm$. Monitored at 520 nm, the excitation spectrum showed a maximum peak intensity at $315{\sim}320\;nm$ wavelength with a broad band from $200{\sim}500\;nm$ wavelength. The decay time of $SrAl_2O_4:Eu^{2+},Dy^{3+}$ increased as the annealing temperature increased.

• Transactions of the Korean hydrogen and new energy society
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• v.16 no.2
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• pp.136-141
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• 2005

Li-doped NiO was synthesized by molten salt method. $LiNO_3$-LiOH flux was used as a source for Li doping. $NiCl_2$ was added to the molten Li flux and then processed to make the Li-doped NiO material. Li:Ni ratios were maintained from 5:1 to 30:1 during the synthetic procedure and the Li doping amount of synthesized materials were found between 0.086-0.190 as a Li ion to Ni ion ratio. Li doping did not change the basic cubic structural characteristics of NiO as evidenced by XRD studies, however the lattice parameter decreased from 0.41769nm in pure NiO to 0.41271nm as Li doping amount increased. Hydrogen gas sensors were fabricated using these materials as thick films on alumina substrates. The half surface of each sensor was coated with the Pt catalyst. The sensor when exposed to the hydrogen gas blended in air, heated up the catalytic surface leaving rest half surface (without catalyst) cold. The thermoelectric voltage thus built up along the hot and cold surface of the Li-doped NiO made the basis for detecting hydrogen gas. The linearity of the voltage signal vs $H_2$ concentration was checked up to 4% of $H_2$ in air (as higher concentrations above 4.65% are explosive in air) using Li doped NiO of Li ion/Ni ion=0.111 as the sensor material. The response time T90 and the recovery time RT90 were less than 25 sec. There was minimum interference of other gases and hence $H_2$ gas can easily be detected.

• Korean Journal of Materials Research
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• v.23 no.6
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• pp.299-303
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• 2013

In this study, a micro gas sensor for $NO_x$ was fabricated using a microelectromechanical system (MEMS) technology and sol-gel process. The membrane and micro heater of the sensor platform were fabricated by a standard MEMS and CMOS technology with minor changes. The sensing electrode and micro heater were designed to have a co-planar structure with a Pt thin film layer. The size of the gas sensor device was about $2mm{\times}2mm$. Indium oxide as a sensing material for the $NO_x$ gas was synthesized by a sol-gel process. The particle size of synthesized $In_2O_3$ was identified as about 50 nm by field emission scanning electron microscopy (FE-SEM). The maximum gas sensitivity of indium oxide, as measured in terms of the relative resistance ($R_s=R_{gas}/R_{air}$), occurred at $300^{\circ}C$ with a value of 8.0 at 1 ppm $NO_2$ gas. The response and recovery times were within 60 seconds and 2 min, respectively. The sensing properties of the $NO_2$ gas showed good linear behavior with an increase of gas concentration. This study confirms that a MEMS-based gas sensor is a potential candidate as an automobile gas sensor with many advantages: small dimension, high sensitivity, short response time and low power consumption.

• Journal of the Korean Chemical Society
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• v.46 no.2
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• pp.164-168
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• 2002

SrGa$_2$S$_4$ : Eu is a green emitting phosphor which is applied for field emission display, and cathodoluminescence. Conventionally, SrGa$_2$S$_4$ : Eu is synthesized by solid state reaction, in which a mixture of SrCO$_3$, Ga$_2$O$_3$, and Eu$_2$O$_3$ is fired at high temperatures under flowing H$_2$S and Ar gases. In this study,SrGa$_2$S$_4$ : Eu phosphor is synthesized by using a decomposition method, where SrS, Eu complex, and Ga com-plex are used. The advantage of this method is that toxic H$_2$S gas and Ar gas are not used. The synthetic con-ditions and luminescent properties of SrGa$_2$S$_4$ : Eu phosphor are also investigated.