• Membrane Journal
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• v.14 no.4
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• pp.312-319
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• 2004

The porous SiO$_2$-B$_2$O$_3$ membrane was prepared from Si(OC$_2$$H_5$)$_4$-($CH_3$O)$_3$B-C$_2$$H_5$OH-$H_2O$ system by sol-gel method. In order to investigate the characteristics of this membrane, we examined that using BET, IR spectrophotometer, X-ray diffractometer, SEM and TEM. At $700^{\circ}C$, the surface area of SiO$_2$-B$_2$O$_3$ membrane was 354.398 $m^2$/, the median pore diameter was 0.0048 ${\mu}{\textrm}{m}$, and the particle size of SiO$_2$-B$_2$O$_3$ membrane was 7 nm. The separation properties of the gas mixture ($H_2$/$N_2$) through the SiO$_2$-B$_2$O$_3$ membrane was studied as a function of pressure. The real separation factor($\alpha$) of SiO$_2$-B$_2$O$_3$ membrane for $H_2$/$N_2$ gas mixture was 4.68 at 155.15 cmHg and $25^{\circ}C$. The real separation factor($\alpha$), head separation factor($\beta$) and tail separation factor((equation omitted)) were increased as the pressure of permeation cell increased.

• Journal of the Korean Electrochemical Society
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• v.7 no.3
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• pp.131-137
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• 2004

Sol-gel method which provides better electrochemical and physiochemical properties compared to the solid-state method was used to synthesize the material of $LiFe_yMn_{2-y}O_4$. Fe was substituted to increase the structural stability so that the effects of the substitution amount and sintering temperature were analyzed. XRD was used for the structural analysis of produced material, which in turn, showed the same cubic spinel structure as $LiMn_2O_4$ despite the substitution of $Fe^{3+}$. During the synthesis of $LiFe_yMn_{2-y}O_4$, as the sintering temperature and the doping amount of Fe(y=0.05, 0.1, 0.2)were increased, grain growth proceeded which in turn, showed a high crystalline and a large grain size, certain morphology with narrow specific surface area and large pore volume distribution was observed. In order to examine the ability for the practical use of the battery, charge-discharge tests were undertaken. When the substitution amount of $Fe^{3+}\;into\;LiMn_2O_4$ increased, the initial discharge capacity showed a tendency to decrease within the region of $3.0\~4.2V$ but when charge-discharge processes were repeated, other capacity maintenance properties turned out to be outstanding. In addition, when the sintering temperature was $800\~850^{\circ}C$, the initial capacity was small but showed very stable cycle performance. According to EVS(electrochemical voltage spectroscopy) test, $LiFe_yMn_{2-y}O_4(y=0,\;0.05,\;0.1,\;0.2)$ showed two plateau region and the typical peaks of manganese spinel structure when the substitution amount of $Fe^{3+}$ increased, the peak value at about 4.15V during the charge-discharge process showed a tendency to decrease. From the previous results, the local distortion due to the biphase within the region near 4.15V during the lithium extraction gave a phase transition to a more suitable single phase. When the transition was derived, the discharge capacity decreased. However the cycle performance showed an outstanding result.

• KSBB Journal
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• v.14 no.1
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• pp.82-90
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• 1999

In order to eventually fabricate an analytical system for infectious microorganisms, we synthesized major immunochemical components, utilized them for the construction of model system, and investigated an assay concept for bacterial whole cells. For the preparation of system components, a polyclonal antibody, against Salmonella thompson as model analyte, purified by immuno-affinity chromatography was used to chemically link to streptavidin or an enzyme, horseradish peroxidase(HRP). The antibody and streptavidin was modified with sulfosuccinimidyl 4-[N-maleimidomethyl]cyclohexane-1-carboxylate and N-succinimidyl-3-[2-pyridyldithio]propionate(subsequently activated by dithiotheritol), respectively. The modified components were reacted to synthesize antibody-streptavidin conjugates which were then purified on a two-layer chromatography column of diaminobiotin gel and Sephadex G-100. For antibody-HRP conjugates, HRP molecules were activated by $NalO_4$ oxidation and then coupled to immunoglobulin. After stabilizing with ($NaCNBH_3$, the conjugates were purified by size exclusion chromatography on Biogel A5M column. To devise a model system, such produced components were combined with a dot-blotter in which a nitrocellulose membrane($12{\mu}m$ pre size) with immobilized biotin was already located. The analyte (S. thompson cells) was reacted with the both antibody conjugates in a liquid phase, and the complexes formed were captured on the membrane surfaces by applying vacuum in the bottom compartment of the blotter to invoke biotin-streptavidin reaction. Under optimal conditions, the system enabled to identify the analytical concept for bacterial whole cells, and the lower limit of detection was approximately $1{\mu}g/m{\ell}$($10^5-10^6$ cells/m$m{\ell}$). The controlling factors were the concentrations of each antibody conjugate that caused agglutination in the presence of analyte as they increased.

• The Korean Journal of Food And Nutrition
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• v.13 no.4
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• pp.328-333
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• 2000

The spore of Aspergillus niger KCTC-6144 was immobilized on alginate gel beads. When pumpkin powder was used with glucose for a medium of citric acid fermentation by Aspergillus niger beads, the beaded Aspergilus niger grew up inside the bead and mycelia penetrated through the pore of the bead membrane. The bead size became largely from 2.0∼2.5mm to 6∼8mm after growing at 30$\^{C}$ for 4 days. Studies of optimum culture conditions on citric acid fermentation using Aspergillus niger beads on pumpkin medium (pumpkin powder 1% +glucose 7%, pH 6.0) were carried out in submerged cultures on 250m1 Erlenmeyer flask. As a result, it was found that to reinforce 12% as carbon source was good for citric acid production and that 1% pumpkin powder was good as nitrogen and mineral source in orbital shaker (150rpm) at 30$\^{C}$ for 5 days. The optimum initial pH on citric acid production was pH 6.0 and it was found that 100 beads of immobilized Aspergillus niger was adequate for citric acid production in a 250ml Erlenmeyer flask containing 50m3 of pumpkin medium solution with orbital shaker at 30$\^{C}$ for 5 days. We also found that maximal production of citric acid was 23.5g/ℓ at optimal condition (at 30$\^{C}$ for 5 days, pH 6.0, and 100 beads and medium containing 1% pumpkin powder plus 12% glucose).

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.8.1-8.1
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• 2011

Nanocrystalline titanium dioxide ($TiO_2$) materials have been widely used as an electron collector in DSSC. This is required to have an extremely high porosity and surface area such that the dye can be sufficiently adsorbed and be electronically interconnected, resulting in the generation of a high photocurrent within cells. In particular, their geometrical structures and crystalline phase have been extensively investigated as important issues in improving its photovoltaic efficiency. In this study, we present a new strategy to fabricate a photoelectrode having a periodic structured $TiO_2$ film templated from 1D or 3D polystyrene (PS) microspheres array. Monodisperse PS spheres of various radiuses were used for colloidal array on FTO glasses and two types of photoelectrode structures with different $TiO_2$ materials were investigated respectively. One is the igloo-shaped electrode prepared by $TiO_2$ deposition by RF-sputtering onto 2D microsphere-templated substrates. At the interface between the film and substrate, there are voids formed by the decomposition of PS microspheres during the calcination step. These holes might be expected to play the predominant roles as scattering spherical voids to promote a light harvesting effect, a spacious structure for electrolytes with higher viscosity and effective paths for electron transfer. Additionally the nanocrystalline $TiO_2$ phase prepared by the RF-sputtering method was previously reported to improve the electron drift mobility within $TiO_2$ electrodes. This yields solar cells with a cell efficiency of 2.45% or more at AM 1.5 illumination, which is a very remarkable result, considering its $TiO_2$ electrode thickness (<2 ${\mu}m$). This study can be expanded to obtain higher cell efficiency by higher dye loading through the increase of surface area or multi-layered stacking. The other is the inverse opal photonic crystal electrode prepared by titania particles infusion within 3D colloidal arrays. To obtain the enlargement of ordered area and high quality of crystallinity, the synthesis of titania particles coated with a organic thin layer were applied instead of sol-gel process using the $TiO_2$ precursors. They were dispersed so well in most solvents without aggregates and infused successfully within colloidal array structures. This ordered mesoporous structure provides the large surface area leading to the enough adsorption of dye molecules and have an light harvesting effect due to the photonic band gap properties (back-and-forth reflection effects within structures). A major advantage of this colloidal array template method is that the pore size and its distribution within $TiO_2$ photoelectrodes are determined by those of latex beads, which can be controlled easily. These materials may have promising potentials for future applications of membrane, sensor and so on as well as solar cells.

• Membrane Journal
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• v.4 no.3
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• pp.152-162
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• 1994

The photodegradation efficiency of formic acid on $TiO_2$ photocatalytic membranes was investigated. A new titania membrane reactors for purification of water combining microfiltration with photocatalytic degradation of organic compounds were developed. Titania membrane tubes(average pore size of $0.2\mu m$) were prepared by the slip casting, and porous thin films of $TiO_2$ were formed on the tube surface by the sol-gel process to increase the surface area, and consequently to increase photodegradation efficiency of organic compounds. The UV light with the wavelength of 365 nm was used as a light source for photocatalytic reactions. The photodegradation efficiency of the organic compounds was strongly dependent on the flux of the solution, the microstructure of the membrane (sol pH), and the amount of $O_2$ supplied. The effects of the primary oxidant such as $H_2O_2$ and dopants such as $Nb_2O_5$ on the photodegradation efficiency were also investigated. The results showed that more than 80% of formic acid could be degraded using membrane coated with a $TiO_2$ sol of pH 1.45. The photodegradation efficiency could be improved by about 20% when adding $H_2O_2$ in feed solution or doping $TiO_2$ membranes with $Fe_2O_3$.

• Clean Technology
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• v.8 no.3
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• pp.119-128
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• 2002

In the present study the membrane filtration characteristics of a commercially available synthetic water-based cutting oil through two kinds of ultrafiltration membranes (HF1-45-CM50 and HF1-43-CM100) with molecular weight cut-offs of 50,000 and 100,000, respectively, have been investigated in detail. Among these membranes, the hydrophilic one (HF1-45-CM50) was found to show a satisfactory result for both the permeate flux and the permeability of oil components, whereas the permeate flux obtained with the hydrophobic membrane (HF1-43-CM100) appears to be significantly low, indicating that synthetic cutting oil was easily wetted on the hydrophobic membrane surface and induced more membrane fouling. The effect of material characteristics of the membrane on the filtration characteristics was found to be much more significant compared with the mean pore size of the membrane. Backflushing by nitrogen gas was applied to reduce the formation of a gel layer and membrane fouling. With the hydrophilic membrane, the backflushing was found to increase the permeate flux, whereas the backflushing resulted in a decrease in flux for the hydrophobic membrane. The flux recovery was observed to be highest when the membranes fouled with waste synthetic cutting oil were immersed into a cleaning solution for more than 72 hours and then backflushed by nitrogen gas.

• Polymer(Korea)
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• v.39 no.2
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• pp.323-328
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• 2015

Poly(${\varepsilon}$-caprolactone) (PCL) nanofibers and PCL/silica membranes were synthesized by sol-gel derived electrospinning and casting, respectively. Smooth PCL nanofibers were obtained from the precursor containing N,N-dimethylformamide (DMF). PCL/silica membranes were prepared by varying the tetraethyl orthosilicate (TEOS) contents from 0 to 40 vol% to investigate the effect of silica addition on mechanical properties and cytotoxicity of the membranes. Although the strength of the membranes decreased from 12 to 8 MPa with increasing the silica content, the strength remained almost constant 7 weeks after dipping in phosphate buffered saline solution (PBS). The strength reduction was attributed to the presence of a patterned surface pores and micro-pores present in the walls between pores. The crystal structure of the membranes was orthorhombic and the crystallite size decreased from 57 to 18 nm with increasing the silica content. From the agar overlay test, the PCL/silica membranes exhibited neither deformation and discoloration nor lysis of L-929 fibroblast cells.

• Clean Technology
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• v.14 no.1
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• pp.40-46
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• 2008

The dehumidifiers were prepared by the impregnation of the zeolites such as MCM 48, USY, beta on the silica ceramic paper. Their capacities for $H_2O$ absorption and regeneration of the bed were tested in a fixed bed reactor system. The $H_2O$ absorption capacities of the dehumidifiers impregnated with the zeolites were $1.5{\sim}2$ times higher than those without the zeolites. Especially, the humidifier using MCM 48 and colloidal silica showed an excellent capacity (42.1g $H_2O/g$ absorbent). It was found that the $H_2O$ absorption capacities of the dehumidifiers were improved because the amount of silica gel, the main component in absorbing $H_2O$, increased due to the large surface area and pore volume of the zeolites. In addition, $H_2O$ was easily desorbed from the dehumidifiers with zeolites at $80^{\circ}C$ of regeneration temperature and the desorption amount of $H_2O$ was the same as that absorbed. It was confirmed that the $H_2O$ absorption capacities of the dehumidifiers impregnated with zeolite were maintained without deactivation through the repeated cyclic experiments.

• Membrane Journal
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• v.29 no.1
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• pp.51-60
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• 2019

In order to improve gas separation properties of polymeric membranes which have been widely applied in the industry field, aluminosilicate hollow nanoparticles named as allophanes were synthesized by sol-gel method and formulated in Poly(dimethylsiloxane) (PDMS) matrix to investigate the gas separation properties of PDMS membrane. Transmission electron microscope (TEM), Energy dispersive X-ray analysis (EDX), X-ray diffractometer (XRD), Surface area and pore size analyzer (BET) and Fourier transform infrared spectrophotometer (FTIR) were carried out to characterize the synthetic allophanes. Then the PDMS mixed matrix membranes were prepared by adding different volume fraction of allophanes. To examine the effect of allophanes addition in PDMS matrix using unmodified allophane and modified ones, the gas permeation experiments were performed using oxygen, nitrogen, methane and carbon dioxide. As the volume fraction of modified allophane increased up to 4.05 Vol% the permeability of four test gases through PDMS mixed matrix membranes increased. Also, the selectivity of $O_2/N_2$ and $CO_2/CH_4$ increased with the contents of the modified allophane. Further improvement of gas separation properties of PDMS mixed matrix membranes containing higher volume percent of allophanes can be expected as long as well dispersion of allophanes in PDMS matrix can be achieved for better PDMS membranes.