• Journal of Powder Materials
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• v.23 no.6
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• pp.420-425
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• 2016

N-doped carbon nanofibers as catalysts for oxygen-reduction reactions are synthesized using electrospinning and carbonization. Their morphologies, structures, chemical bonding states, and electrochemical performance are characterized. The optimized N-doped carbon nanofibers exhibit graphitization of carbon nanofibers and an increased nitrogen doping as well as a uniform network structure. In particular, the optimized N-doped carbon nanofibers show outstanding catalytic activity for oxygen-reduction reactions, such as a half-wave potential ($E_{1/2}$) of 0.43 V, kinetic limiting current density of $6.2mAcm^{-2}$, electron reduction pathways (n = 3.1), and excellent long-term stability after 2000 cycles, resulting in a lower $E_{1/2}$ potential degradation of 13 mV. The improvement in the electrochemical performance results from the synergistic effect of the graphitization of carbon nanofibers and the increased amount of nitrogen doping.

• Korean Journal of Materials Research
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• v.25 no.3
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• pp.113-118
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• 2015

To improve the methanol electro-oxidation in direct methanol fuel cells(DMFCs), Pt electrocatalysts embedded on porous carbon nanofibers(CNFs) were synthesized by electrospinning followed by a reduction method. To fabricate the porous CNFs, we prepared three types of porous CNFs using three different amount of a styrene-co-acrylonitrile(SAN) polymer: 0.2 wt%, 0.5 wt%, and 1 wt%, respectively. A SAN polymer, which provides vacant spaces in porous CNFs, was decomposed and burn out during the carbonization. The structure and morphology of the samples were examined using field emission scanning electron microscopy and transmission electron microscopy and their surface area were measured using the Brunauer-Emmett-Teller(BET). The crystallinities and chemical compositions of the samples were examined using X-ray diffraction and X-ray photoelectron spectroscopy. The electrochemical properties on the methanol electro-oxidation were characterized using cyclic voltammetry and chronoamperometry. Pt electrocatalysts embedded on porous CNFs containing 0.5 wt% SAN polymer exhibited the improved methanol oxidation and electrocatalytic stability compared to Pt/conventional CNFs and commercial Pt/C(40 wt% Pt on Vulcan carbon, E-TEK).

• International Journal of Industrial Entomology and Biomaterials
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• v.48 no.1
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• pp.25-32
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• 2024

Soy protein isolate (SPI) has garnered researchers' attention due to its abundance, costeffectiveness, excellent biocompatibility, hemo-compatibility, and biodegradability. However, SPI faces limitations in application due to poor processability and weak mechanical strength. Substantial efforts have been made to address these challenges. In this preliminary study, glycerol and biofibers were added to SPI to improve the mechanical properties and film forming, and glyoxal was employed to crosslink SPI molecules. The microstructure and mechanical properties of the resulting SPI/composite films were evaluated. A 15% addition of glycerol proved sufficient for good film formation. Among the biofibers, short SF microfibers were the most effective in enhancing breaking strength, while TEMPO-oxidized CNF (cellulose nanofiber) excelled among CNFs. Crosslinking with glyoxal significantly enhanced the mechanical properties, with the type of biofiber minimally affecting the mechanical properties of the crosslinked SPI composite films.

• Polymer(Korea)
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• v.32 no.2
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• pp.131-137
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• 2008

We have fabricated polystyrene (PS) nanofibrous scaffold for hepatocyte culture by electrospinning method and subsequently coated with specific ligand of Poly[N-p-vinylbenzyl-O-$\beta$-D-galactopyranocyl-($1{\rightarrow}4$)-D-gluconamide](PVLA) to enhance hepatocytes attachment. Rat hepatocytes behavior on the PVLA-coated and non-coated PS nanofibrous matrices have been investigated. Electrospun PS nanofiber structures revealed randomly aligned fibers with average diameter of 500 nm. It is observed that PS nanofibrous matrix could incorporate many cells into the interior of the matrix probably due to the suitable pore size. Cell viabilities cultured on PVLA-coated PS nanofibrous mats were maintained for 3 weeks, while it was decreased rapidly on PVLA-coated PS dishes. High hepatic functions especially for albumin secretion and ammonia removal were maintained at least for 2 weeks on nanofibrous mats but rapidly decreased on flat PS dishes. These results indicate that nanofibrous structure enabled 3-D culture with high level of cell-cell contact results in providing cell-cell communications and subsequent long-term maintenance of specific cell functions.

• Applied Chemistry for Engineering
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• v.19 no.1
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• pp.80-85
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• 2008

Catalytic filter is capable of performing shallow bed dust filtration plus a catalytic reaction, promoted by a catalyst deposited in its inner structure. Such a feature may allow potential cost and space reduction in several environmental applications. Dust filtration and halogenated volatile organic compound (1,2-dichlorobenzene) destruction were carried out in a lab-scale reactor. $WO_3-V_2O_5/TiO_2$ supplied by MaGreen, which showed high catalytic acitivity at low temperature, was used as a catalyst. P-84 that can be operated under $250^{\circ}C$ was used as a felt. The catalytic activity and filtration efficiency of catalytic filters were investigated under the operating conditions, including temperature, face velocity, and dust concentration. The catalytic activity of catalytic filter increased with increasing temperature and the amount of catalyst loaded. The test results showed that the filtration efficiency was primarily affected by the face velocity. Pressure drop variations as a function of time were investigated for a variety of conditions. In case of virgin filter, a dramatic decrease in the pulse interval and a slightly increase in the base line pressure drop were observed. A relatively slow pressure drop build-up was recorded for the catalytic filter due to smooth and slippery surface characteristics of nanofiber. The catalytic filter indicated that high filtration efficiency over 99.98% and high catalytic activity over 90% at 1 m/min and $210^{\circ}C$.

• Journal of the Korean Ceramic Society
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• v.47 no.4
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• pp.343-352
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• 2010

A zirconia gel/polymer hybrid nanofiber was produced in a nonwoven fabric mode by electrospinning a sol derived from hydrolysis of zirconium butoxide with a polyvinyl butyral. Results indicated that the hydroxyl groups on the vinyl alcohol units in the backbone of the polymer were involved in the hydrolysis as well as grafting the hydrolyzed zirconium butoxide. In addition, use of acetic acid as a catalyst resulted in further hydrolysis and condensation in the sol, which led to the growth of -Zr-O-Zr- networks among the polymer chains. These networks gradually transformed into a crystalline zirconia structure upon heating. The as-spun fiber was smooth but partially wrinkled on the surface. The average fiber diameter was $690{\pm}110\;nm$. The fiber exhibited a strong but broad blue photoluminescence with its maximum intensity at a wavelength of ~410 nm at room temperature. When the fiber was heat-treated at $400^{\circ}C$, the fiber diameter shrunk to $250{\pm}60\;nm$. Nanocrystals which belonged to a tetragonal zirconia phase and were ~5 nm in size appeared. A strong white photoluminescence was observed in this fiber. This suggests that oxygen or carbon defects associated with the formation of the nanocrystals play a role in generating the photoluminescence. Further heating to $800^{\circ}C$ resulted in a monoclinic phase beginning to form In the heat-treated fibers, coloring occurred but varied depending on the heating temperature. Crystallization, coloring, and phase transition to the monoclinic structure influenced the photoluminescence. At $600^{\circ}C$, the fiber appeared to be fully crystallized to a tetragonal zirconia phase.

• Polymer(Korea)
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• v.32 no.5
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• pp.409-414
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• 2008

The fabrication of gelatin nanofibers by electro spinning has been examined using the TFE/DW co-solvent system. It has been found that no beads-on-string structure was formed for the solution containing ionic salts. The resulting fibers exhibited a uniform diameter ranging from 110 to 125 nm. As the concentration of ionic salts increases, the beads become smaller and more spindle like, due to the increase of viscosity and conductivity. The addition of ionic salts induces a higher charge density on the surface of ejected jet during spinning, leading that higher elongation forces are applied to the jet. The higher enhancement of viscosity and conductivity was observed in gelatin solutions by the use of divalent salt. However, the concentration of ionic salts scarcely affected the variation of fiber diameter. While very low crystallinity was observed from XRD pattern for the sample containing no ionic salt, which increased with increasing the concentration of ionic salts.

• Applied Chemistry for Engineering
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• v.22 no.3
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• pp.243-248
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• 2011

Pt deposited porous carbon nanofibers was prepared as a highly sensitive material of hydrogen gas sensor operating at room temperature. Nanofibers was obtained by electrospinning method using polyacrylonitrile as a carbon precursor and then thermally treated for carbon nanofibers. Chemical activation of carbon nanofibers was carried out to enlarge specific surface area up to $2093m^2/g$. Sputtered Pt layer was uniformly distributed keeping the original shape of carbon nanofibers. The hydrogen gas sensing time and sensitivity were improved based on effects of high specific surface area, micropore structure and deposited Pt catalyst.

• Clean Technology
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• v.30 no.3
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• pp.258-266
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• 2024

Rechargeable Li-SnO₂ batteries suffer from issues such as poor electronic/ionic conductivity and huge volume changes. In order to overcome these inherent limitations, this study designed a cell with a unique hierarchical structure, denoted as SnO₂@PCNF. The SnO₂@PCNF cell design incorporates in-situ generated SnO₂ nanoparticles strategically positioned within N-doped porous carbon nanofibers (PCNF). The in-situ generated SnO₂ nanoparticles can alleviate strains during cycling and shorten the pathway for the ions and electrons, improving the utilization of active materials. Moreover, the N-doped PCNF establishes a continuously conductive network to further increase the electrical conductivity and also buffers the significant volume changes that occur during charging and discharging. The resulting SnO₂@PCNF cell exhibits outstanding electrochemical performance and stable cycling characteristics. Notably, a reversible capacity of 520 mAh g^-1 was achieved after 100 cycles at 70 mA g^-1. Even under a higher current density of 1 A g^-1, the cell maintained a capacity retention of 393 mAh g^-1 after 1,000 cycles. These results highlight the SnO₂@PCNF cell's exceptional cycling stability and superior rate capability.

• Clean Technology
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• v.30 no.3
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• pp.267-275
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• 2024

Lithium-ion batteries (LIBs) have attracted significant attention as potential energy storage solutions due to their high energy density, minimal self-discharge, extended cycle life, and absence of memory effects. However, conventional LIBs use graphite as the anode material and as a result struggle to meet the increasing demand for higher energy density because of the low theoretical capacity of graphite. In order to enhance Li storage capacity and address the current limitations of LIBs, this study designed and analyzed SnO₂ nanoflakes/CNF, which is an advanced anode material with a unique hierarchical structure synthesized via a facile method involving incipient wetness followed by annealing. The in-situ formed SnO₂ nanoflakes improve the electrolyte accessibility and shorten the ion and electron transport pathways, thereby enhancing the reaction kinetics. Additionally, the CNF matrix enhances the electrical conductivity, accelerates electron transport, and mitigates volume changes. The integrated SnO₂ nanoflakes/CNF cell demonstrated outstanding cycling performance and excellent rate capability, achieving a notable reversible capacity of 636 mAh g^-1 after 100 cycles at 0.1 C. This study provides valuable insights into the design of high-efficiency anode materials for the advancement of high-performance LIBs.