N2 adso~tion studies indicate that activated carbon fibers (ACF) contain a uniform micropore system, while the pores in granulated activated carbons usually show a broad pore size distribution, from micro to macropores. ACF also have better adsorption capacity and show better adsorption than granular activated carbons. The properties of ACF have been extensively investigated both from the practical and fundamental points of view [l-5]. For instance, measurements of N2 adsorption show clear differences in the micropore structures of different ACF 161. Also, vapor adsorption depends strongly on irregularities in the micropore structure [7] and surface modification of ACF with iron or copper oxides enchances the micropore filling by a super C&~&II aas. NO M-101. The investigation of ACF. bv other methods, is required to further Understand the adsorption ch~a~te~stics.
The micropore wall of the ACF is considered to consist of elementary microcrystalhtes of graphite, but graphitic microcrystallites are stacked together in a random o~entation [ 111. When adsorbed molecules fill the micropores and press on the micropore-walls, the structure of the graphitic carbons should be distorted. In this letter, the change in the graphitic crystallites of the ACF with desorption of water and benzene by use of in situ X-ray diffraction is described.
Cellulose-based ACF (Toyobo, KF1500) was used in this experiment. a-FeGOH dispersed ACF (a-ACF} was obtained in the same way as reported earlier [8]. The specific surface areas of ACF and a-Am are 1400 and 1470 mz/g, respectively; the micropore volume of ACF is 0.61 ml/g and that of a-ACF 0.62 mVg. In situ X-ray diffraction experiments were carried out with an automatic powder diffractometer (Rigaku 2028) combined with a specially designed diffraction cell which has a double framed wall made of stainless steel with Kapton windows. The radiation was Nickel filtered from CuKa operated at 35 kV and 10 mA. The accuracy in reflection angle obtained was examined by use of Grafoil. This apparatus can give a di~action diagram in the 26 range from 50 to 800. The ACF, ground after drying at 383 K for 2 h, was immersed in water or benzene, compacted to a pellet, and mounted in the A study combining in situ small angle X-ray scattering and precise N2 adsorption in addition to the in situ X-ray diffraction is necessary for the elucidation of the real micropore structure of the ACF.