Euigyung Jeong

Effects of surface chemical properties of activated carbon modified by amino-fluorination for electric double-layer capacitor.

The surface of phenol-based activated carbon (AC) was seriatim amino-fluorinated with solution of ammonium hydroxide and hydrofluoric acid in varying ratio to fabricate electrode materials for use in an electric double-layer capacitor (EDLC). The specific capacitance of the amino-fluorinated AC-based EDLC was measured in a 1 M H(2)SO(4) electrolyte, in which it was observed that the specific capacitances increased from 215 to 389 Fg(-1) and 119 and 250 Fg(-1) with the current densities of 0.1 and 1.0 Ag(-1), respectively, in comparison with those of an untreated AC-based EDLC when the amino-fluorination was optimized via seriatim mixed solution of 7.43 mol L(-1) ammonium hydroxide and 2.06 mol L(-1) hydrofluoric acid. This enhancement of capacitance was attributed to the synergistic effects of an increased electrochemical activity due to the formation of surface N- and F-functional groups and increased, specific surface area, and mesopore volumes, all of which resulted from the amino-fluorination of the electrode material.

Preparation and Characterization of Electrospun TiO 2 -Activated Carbon Complex Fiber as Photocatalyst

In this study, -Activated carbon (AC) complex fibers were prepared by electrospinning for the synergetic effect of adsorption and degradation of organic pollutant. The average diameter of these fibers increased with increasing the amount of AC added, except for 1AC-TOF (AC =1/40 mass ratio). After calcinations at , long as-spun fibers were broken and their average diameter was slightly decreased. The resultant fibers after calcination had rough surface and sphere shapes like a peanut. From XRD results, it was confirmed that as-spun fibers were changed to anatase fiber after calcinations at . The prepared -AC complex fibers could remove procian blue dyes by solar light irradiation with high removal property of 94~99%. The PB dye was rapidly removed by adsorption during the initial 5 minutes. But after 5 minutes, dye removal was occurred by photodegradation. In this study, the most efficient AC/ ratio of -AC complex fibers was 5/40, showing the synergetic effect of adsorption and photodegradation. It is expected that the -AC complex fibers can be used to remove of organic pollutants in water system.

Hydrogen Adsorption of PAN-based Porous Carbon Nanofibers using MgO as the Substrate

In this study, porous electrospun carbon fibers were prepared by electrospinning with PAN and , as a MgO precursor. MgO was selected as a substrate because of its chemical and thermal stability, no reaction with carbon, and ease of removal after carbonization by dissolving out in acidic solutions. was mixed with polyacrylonitrile (PAN) solution as a precursor of MgO with various weight ratios of /PAN. The average diameter of porous electrospun carbon fibers increased from 1.3 to 3 , as the to PAN weight ratio increased. During the stabilization step, was hydrolyzed to MgOHCl by heat treatment. At elevated temperature of 823 K for carbonization step, MgOHCl was decomposed to MgO. Specific surface area and pore structure of prepared electrospun carbon fibers were decided by weight ratio of /PAN. The amount of hydrogen storage increased with increase of specific surface area and micropore volume of prepared electrospun carbon fibers.

Direct fluorination as a novel organophilic modification method for the preparation of Illite/polypropylene nanocomposites

This study reports the application of illite as a clay filler and direct fluorination as an organophilic modification for clays. Illite was also modified using conventional methods, with reagents such as 3-aminopropyltrimethoxysilane and hexadecyl-trimethoxysilane for comparison of the resultant illite/polypropylene (PP) composites with the fluorinated illite/PP composites. The thermal properties, flame retardancy, and mechanical properties of the resultant composites were also investigated. Fluorination of illite resulted in exfoliation and more thermally stable organophilic modification compared with the conventional silane treatment. When comparing two different silane-treated illite/PP composites with fluorinated illite/PP composites, fluorinated illite had better thermal stability and exfoliation after modification and more improved dispersion in PP matrix. This resulted in improved thermal stability, flame retardancy, and mechanical properties compared with the silane-treated illite/PP composites. The fluorinated illite/PP composite exhibited a 28% increase in thermal stability and a 50% increase in flame retardancy compared with neat PP. Fluorination of illite yielded at least 50% further improvement in the thermal stability and flame retardancy of the resulting illite/PP composites compared with the conventional silane treatments.

New Application of Clay Filler for Carbon/Carbon Composites and Improvement of Filler Effect by Clay Size Reduction

To investigate new potential application of a clay material for C/C composites, illite added C/C composites were prepared with various illite contents. The improvement of filler effect by illite size reduction was also investigated using wet ballmilling by evaluating illite/phenolic resin infiltration using bulk density and porosity measurements, chemical structural changes of the composites using XRD, and thermal oxidation stability in air of the composites using TGA. The size reduction of illite resulted in narrower particle size distribution and improved illite infiltration into carbon preform. And the resultant C/ C composites prepared with illite had even more improved thermal oxidation stability in air, showing more increased IDTs up to 100oC, compared to those of the C/C composites with pristine illite, due to the SiC formation through carbothermal reduction between illite and carbon materials. The illite induced delay in oxidation of the illite-C/C composites was also observed and the delayed oxidation behavior was attributed to the layered structure of illite, which improved illite/phenol resin infiltration. Therefore, the potential use of illite as filler to improve oxidation stability of C/C composite can be promising. And the size reduction of illite can improve its effect on the desired properties of illite-C/C composites even more.

Density functional theory study of CH4and CO2adsorption by fluorinated graphene

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Effects of heat-treatment temperature on carbon-based composites with added illite

To investigate new applications for illite as an additive for carbon-based composites, the com- posites were prepared with and without illite at different heat-treatment temperatures. The ef- fects of the heat-treatment temperature on the chemical structure, microstructure, and thermal oxidation properties of the resulting composites were studied. As the heat-treatment tempera- ture was increased, silicon carbide SiC formation via carbothermal reduction increased until all the added illite was consumed in the case of the samples heat-treated at 2,300°C. This is attributed to the intimate contact between the SiO2 in the illite and the phenol carbon precur- sor or the carbon fibers of the preform. Among composites prepared at all temperatures, those with illite addition exhibited fewer pores, voids, and interfacial cracks, resulting in larger bulk densities and lower porosities. A delay of oxidation was not observed in the illite-containing composites prepared at 2,300°C, suggesting that the illite itself absorbed energy for exfolia- tion or other physical changes. Therefore, if the illite-containing C/C composites can reach a density generally comparable to that of other C/C composites, illite may find application as a filler for C/C composites. However, in this study, the illite-containing C/C composites exhibited low density, even when prepared at a high heat-treatment temperature of 2300°C, although the thermal oxidation of the resulting composites was improved.

Applications of Carbon Materials for Ferroelectric and Related Materials

Ferroelectricity is spontaneous electric polarization of a material without an external electric field and the polarization can be reversed by applying an external electric field as shown in Fig.1 (Kanzig, 1957; Lines & Glass, 1979). Because the spontaneous polarization of the material is changed by an external stimulus, ferroelectric materials are also piezoelectric and pyroelectric, when the stimuli are force and heat, respectively. Ferroelectric materials have non-linear polarization; thus, they can be used as capacitors with tunable capacitance. Moreover, the hysteresis effect of the spontaneous polarization of ferroelectric materials enables the application of ferroelectric random-access memories (RAMS) for computers and radio-frequency identification (RFID) cards (Buck, 1952). In addition, piezoelectric materials are used for high voltage power source, sensors, and actuators. In these systems, it is evident that ferroelectric and related materials are not used alone. For complete systems, other materials are required to compensate for the poor properties, such as the low conductivity of piezoelectric concrete, or to enhance their performance (Shifeng, 2009; Ishiwara 2009).

Application and evaluation of boron nitride-assisted liquid silicon infiltration for preparing C f /SiC composites

C/SiC composites were prepared by boron nitride (BN)-assisted liquid silicon infiltra tion (LSI), and their anti-oxidation and mechanical properties were investigated. The microstructures, bulk densities, and porosities of the C/SiC composites demonstrated that the infiltration of liquid silicon into the composites improved them, because the layered-structure BN worked as a lubricant. Increasing the amount of BN improved the anti-oxidation of the prepared C/SiC composites. This synergistic effect was induced by the assistance of BN in the LSI. More thermally stable SiC was formed in the composite, and fewer pores were formed in the composite, which reduced inward oxygen diffusion. The mechanical strength of the composite increased up to the addition of 3% BN and decreased thereafter due to increased brittleness from the presence of more SiC in the composite. Based on the anti-oxidation and mechanical properties of the prepared composites, we concluded that improved anti-oxidation of C/SiC composites can be achieved through BN-assisted LSI, although there may be some degradation of the mechanical properties. The desired anti-oxidation and mechanical properties of the composite can be achieved by optimizing the BN-assisted LSI conditions.