WATER-ADSORPTION PROPERTIES OF ALUMINA PILLARED CLAY

Interlayers of montmorillonite were pillared with aluminum oxide and the water adsorption isotherms were measured on the samples calcined at temperatures ranging from 200 to 600°C. Although the nitrogen adsorption isotherms on the same samples were of the extreme Type I for Brunauer classification, the water adsorption isotherms did not fit either the Langmuir or the BET adsorption equations. The unusual shape of the isotherms can be interpreted in terms of hydrophobicity of the alumina pillared clays. The t-plot analysis of the adsorption isotherms revealed that the micropore filling with water was suppressed in the very low pressure region. From the t-plots, the slitwidth of the interlayer pores was estimated to be 7-8 Å, in good agreement with the pillar height obtained from the basal spacing. The low BET c-constant and the small isosteric heats of adsorption of water also suggest that the alumina pillared clays have hydrophobic properties. © 1990.