Changes in the molecular adsorption properties of pitch-based activated carbon fibres by air oxidation

Abstract

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.