CHANGES IN THE MOLECULAR ADSORPTION PROPERTIES OF PITCH-BASED ACTIVATED CARBON-FIBERS BY AIR OXIDATION

Pitch-based activated carbon fibres (ACFs) have been oxidized at 373-1173 K for 1 h under an ambient atmosphere. The weight loss was measured and the change in the microporosity with the oxidation temperature was examined by N2 adsorption measurements. No change, even in the ACF oxidized at 1173 K was observed by scanning electron microscopy. The adsorption activities of the oxidized pitch-based ACFs for NH3, H2O and SO2 at 303 K (at 273-323 K in the case of NH3 adsorption) was determined. The relationship between the adsorption activity and the microporosity was discussed. The pitch-based ACF oxidized at 773 K showed the greatest adsorptivities for H2O and NH3 without a decrease in the micropore volume; also a slight enhancement of the isosteric heat of adsorption for SO2 was observed for the sample oxidized at 773 K. This behaviour could be caused by transformation of strong acidic groups such as -CO2H to weaker ones.