Adsorption interaction of water with microporous adsorbents. Part 3.—Dependence of adsorption–desorption hystereses on extent of activation

Abstract

The influence of extent of air and HNO₃ activation on the adsorption–desorption hysteresis behaviour of water vapour on activated porous carbon cloth has been investigated. Following Pierce and Smith (J. Phys. Chem., 1950, 54, 784) hysteresis is attributed to the formation of a continuous adsorbed layer when water-molecule clusters, initially formed on and around surface-oxide sites, coalesce into a more stable state. It is shown that when high surface-oxide concentrations exist, the continuous adsorbed phase is formed at low p/p₀ values so that the isotherm type is changed and hysteresis is not longer observed. Kinetically controlled hysteresis due to very small aperture size and the sorption of water molecules into exfoliated regions, formed during HNO₃ activation, are also considered.