Effect of oxygen plasma treatment on gas adsorption behavior and surface structure of carbon spheres derived from phenol
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Effect of oxygen plasma treatment on gas adsorption behavior and surface structure of carbon spheres derived from phenol resin M. Inagaki,a) M. Sunahara, A. Shindo, V. Vignal, and H. Konno Graduate School of Engineering, Hokkaido University, Kita-ku, Sapporo, 060-8628 Japan (Received 7 January 1999; accepted 30 April 1999)
Plasma treatment was applied on glasslike carbon spheres to modify their gas adsorption behavior. After the oxygen plasma treatment, a selective adsorption of CO2 gas was obtained, almost no nitrogen adsorption being detected, at low temperatures. Surface morphology observed by using field-emission scanning electron microscopy, atomic force microscopy, and scanning tunneling microscopy was found to be changed after the oxygen plasma treatment.
In our previous works,1–8 the spheres of glasslike carbon derived from phenol resin spheres have been used mainly because of their easy handling and activation. The fundamental researches on carbonization and activation of these carbon spheres were reported.3–5 On these carbon spheres, an irreversible adsorption of gases, particularly of CO2, was found, suggesting a preferential storage of CO2.1,2 With use of the same spheres, the analytical procedure for studying pore shape and size distribution from scanning tunneling microscopy (STM) images was developed,6 and the effect of oxidation on pore structure was discussed in relation to the gas adsorption7 and also trihalomethane adsorption.8 To understand the effect of surface microstructure on surface energy, plasma treatments in different atmospheres were conducted on carbon blacks9 and carbon fibers.10 In the present work, these activated carbon spheres were treated by oxygen plasma to modify their adsorption behavior of gases. After plasma treatment, a selective adsorption of CO2 gas at 201 K was obtained, almost no N2 adsorption at 77 K being measured. The surface morphology of the spheres was observed by using fieldemission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), and STM techniques. Carbon spheres with rather homogeneous size of ∼10 m in diameter were prepared from phenol resin spheres (AP, Unitica Co., Ltd.) by the carbonization at 900 °C for 1 h in high-purity Ar gas. Plasma treatment of these carbon spheres was conducted between two parallel plate electrodes for 20 min under a pressure of ∼102 Pa and a flow rate of ∼50 mL/min of either oxygen or argon
a)
Address all correspondence to this author. Present address: Aichi Institute of Technology, Department of Applied Chemistry, Yakusa, Toyota 470-0392, Japan.
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J. Mater. Res., Vol. 14, No. 8, Aug 1999 Downloaded: 16 Mar 2015
with different input powers of radio frequency to 200 W (model BP-I, SAMCO). The sample placed on the lower electrode was heated at 400 °C, according to the previous article,11 which reported that heating was effective to keep the effect of plasma treatment on carbon materials a long time. After the treatment, the low
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