Seung-Kon Ryu

Effect of modification with HNO3 and NaOH on metal adsorption by pitch-based activated carbon fibers

Abstract Pitch-based activated carbon fibers (ACFs) were modified with nitric acid and sodium hydroxide. Their physicochemical properties were investigated in terms of N 2 adsorption, mass titration, FTIR and metal adsorption. The specific surface area of the ACFs decreased after oxidation with 1 M nitric acid, but the total acidity increased three times compared to the untreated ACFs, resulting in an improved ion-exchange capacity of the ACFs. The points of zero charge of the ACFs that affect the selectivity for the ionic species changed from pH 6 to pH 4 by 1 M nitric acid and to pH 10 by 1 M sodium hydroxide treatment. Upon oxidation of the ACFs with nitric acid, surface oxide groups were observed in the FTIR spectra by absorption peaks at 1750–1400 cm −1 . The carboxyl groups of ACFs decreased, while the lactone groups increased after the sodium hydroxide treatment. The adsorption capacity of copper and nickel ion is mainly influenced by the lactone groups on the carbon surface pH zpc , and by the total acidic groups at pH>pH zpc .

Gelatin nanofibrous membrane fabricated by electrospinning of aqueous gelatin solution for guided tissue regeneration

The electrospinning of gelatin aqueous solution was successfully carried out by elevating the spinning temperature. The effects of spinning temperature and solution concentration were investigated on the morphology of gelatin nanofibers in the current study. To improve the stability and mechanical properties in moist state, the gelatin nanofibrous membrane was chemically crosslinked by 1-ethyl-3-dimethyl-aminopropyl carbodiimide hydrochloride and N-hydroxyl succinimide. The concentration of crosslinker was optimized by measuring the swelling degree and weight loss. Nanofibrous structure of the membrane was retained after lyophilization, although the fibers were curled and conglutinated. Tensile test revealed that the hydrated membrane becomes pliable and provides predetermined mechanical properties. Periodontal ligament cells cultured on the membrane in vitro exhibited good cell attachment, growth, and proliferation. Gelatin nanofibrous membrane can be one of promising biomaterials for the regeneration of damaged periodontal tissues.

Studies on pore structures and surface functional groups of pitch-based activated carbon fibers

The present study concerns the physical activation and chemical oxidation of pitch-based activated carbon fibers (ACFs) as ways to improve the adsorption properties. The surface oxides of the ACFs studied were determined by Boehms titration and the pore structures were studied by the BET method with N(2)/77 K adsorption. Also, the adsorption properties of the ACFs were investigated with chromium ion adsorption by different adsorption models. As a result, it was observed that carboxyl groups were largely created after nitric acid treatment on ACFs. The affinity for chromium ions increases with increasing specific surface area, micropore volume, and surface functionalities of ACFs as the activation time increases.

Electrochemical treatment on activated carbon fibers for increasing the amount and rate of Cr(VI) adsorption

The present study concerns anodic oxidation of activated carbon fibers (ACFs) in order to introduce the surface functional groups onto ACF surfaces. The surface oxides of ACFs were measured using titration and FT-IR spectrometry. As a result, it was observed that the amount of adsorption and the adsorption rate of Cr(VI) increase with increases in the surface oxide groups of ACFs, even though both the specific surface area and the micropore volume do not significantly change as with anodic oxidation treatments on ACFs.

Filler-elastomer interactions: Influence of oxygen plasma treatment on surface and mechanical properties of carbon black/rubber composites

Abstract In this work, the influence of oxygen plasma treatment on the surface and adsorption properties of carbon blacks was investigated using X-ray photoelectron spectroscopy (XPS), ζ -potential, and BET isotherms. Then the mechanical properties [tensile strength and tearing energy ( G IIIC )] of carbon black/acrylonitrile butadiene rubber (NBR) composites were measured. As a result, it was found that oxygen plasma treatment generated oxygen-containing functional groups, such as, carboxyl, hydroxyl, lactone, and carbonyl groups, on the carbon black surfaces, resulting in a decrease in the equilibrium spreading pressure or London dispersive component of surface free energy. The tearing energy of the carbon black/NBR composites improved as the oxygen-containing functional groups on the carbon black surfaces increased. This revealed that there is a relatively high degree of interaction between the polar NBR and the oxygen-functional groups of carbon blacks.

Physical properties of silver-containing pitch-based activated carbon fibers

Abstract Silver-containing pitch-based carbon fibers were prepared and activated in steam. SEM and TEM were used to investigate the surface morphology and the behavior of the silver particles in fibers. Physical properties such as density, tensile strength, and electrical resistivity were measured. The SEM photos of fibers containing silver (at initial concentrations of 1000 and 10 000 ppm) were similar to those of non-activated carbon fibers at high level burn-off. Silver particles accelerate the activation rate. However, the specific surface areas of silver-containing activated carbon fibers were similar to those of non-silver containing activated carbon fibers. The apparent density and the tensile strength of the 10 000 ppm silver-containing carbon fibers were 1.677g/cm3 and 24 kgf/mm2, and these decreased to 0.795 g/cm3 and 6 kgf/mm2, respectively, at 69% burn-off. The electrical resistivity of isotropic pitch-based carbon fiber was 97 μΩ m. By comparison, as the initial silver content of the fiber was increased to 1000 and 10 000 ppm, the resistivity decreased to 69 and 57 μΩ m, respectively. These resistivities depended on the total pore volume and increased exponentially with increasing specific surface area of fibers.

Scanning tunnelling microscopy study of activated carbon fibres

Scanning tunnelling microscopy (STM) has been used to study isotropic pitch-based carbon fibres before and after steam activation. The results show that the present carbon fibre precursor exhibits a particulate surface which is very favourable for the formation of activated carbon fibre. After activation, the carbon fibre surface becomes much more porous and rougher, and the mesopores are evidently present on the surface. Because the scale is down to atomic resolution, the STM observations offer direct evidence for the existence of micropores on the surface of the activated carbon fibres. In addition, the surface textures of both fibres are presented and discussed.

Unique charge/discharge properties of carbon materials with different structures

Abstract The electrochemical properties of isotropic and anisotropic carbon fibers were studied using the two-electrode method in a 1 M LiPF6 electrolyte solution dissolved in a 1:1 volume mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC). Isotropic carbon fiber had a larger irreversible capacity than that of the other carbon fibers and might have many sites for the electrolyte decompositon and residual lithium ions. Active carbon fibers prepared from isotropic carbon fibers by steam gasiformation at 850 °C showed large specific surface areas. After steam gasiformation, the active carbon fibers changed into a more crystalline state and had electrochemical characteristics similar to the anisotropic carbon fibers. Impedance profiles of the carbon fibers were fitted by equivalent analogs of a three-resistance—capacitance (RC) circuit in series and the thickness of passivation layers in the carbon fibers was calculated.

Nucleation of thiourea adduct crystals with cyclohexane-methylcyclopentane system

To study the homogeneous nucleation of thiourea adducts, the metastable zone widths for the thiourea adducts formed with guests of cydohexane, methylcyclopentane (MCP) and their mixtures were determined. The influence of moderate agitation rate and saturation temperature on the maximum allowable undercooling (i.e., metastable zone width) was studied. The metastable zone width is markedly affected by the cooling rate and the agitation rate. MCP in guests roles to retard the nucleation rate of cyclohexane-MCP-thiourea adducts by causing k2 to decrease. The order of the nucleation in the nucleation process of thiourea adducts is in the range between 3 and 6, and appears to be dependent on the saturation temperature and the guest concentration. The nucleation rate constant (i.e., frequency factor (k2/Nobs) has shown to exclusively depend on the concentration of guest and the temperature. The retarding effect of MCP in the thiourea adduction was found to be caused by, not only the increase of surface energy, b...

Preparation and structural studies of organotin(IV) complexes formed with organic carboxylic acids

Performance tests of silver ion-exchanged zeolite (AgX) adsorbent for the control of radioiodine gas generated from a high-temperature process were carried out using both non-radioactive and a radioactive methyl iodide tracers. From the identification of SEM-EDAX analysis, an experimental result of silver ion-exchanged ratio containing 10-30 wt% of Ag was fit to that calculated by the weight increment, and it was confirmed that the silver was uniformly distributed inside the pores of the adsorbent. Demonstration test of AgX-10 adsorbent using radioactive methyl iodide tracer was performed. The removal efficiency of radioiodine with AgX-10 in the temperature ranges of 150 to 300 °C was in the ranges of 99.9% to 99.99%, except for 300 °C. The influence of the long-term weathering and the poisoning with NO2 gas (200 ppm) on adsorption capacity of AgX-10 was also analyzed. The removal efficiency of radioactive methyl iodide by AgX-10 weathered for 14 weeks was 99.95%. Long-term poisoning test showed that the adsorption efficiency of methyl iodide started to decrease after 10 weeks, and the removal efficiency of radioiodine by AgX-10, poisoned for 16 weeks, was 99% (DF=100).