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Time-dependent changes of adsorption and wetting properties of pillared montmorillonites

¹ Department of Colloid Chemistry, University of Szeged and Nanostructured Materials Research Group of the Hungarian Academy of Sciences, Aradi Vt. 1, H-6720 Szeged, Hungary, ² Institute of Applied Chemistry, Berlin-Adlershof e. V., Richard-Willstätter-Str. 12, D-12484 Berlin, Germany, and ³ Institute of Inorganic Chemistry, University of Kiel, D-24098 Kiel, Germany

^* E-mail: h.mittag{at}email.uni-kiel.de

(Received 10 February 2000; revised 7 April 2000)

The changes of adsorption properties of uncalcined Al-pillared montmorillonite were studied. A soda-activated bentonite from Slovakia was reacted with polymeric hydroxoaluminium salt solutions. During storage in air at room temperature for three years, the basal spacing decreased by 0.15–0.2 nm; the specific surface area was reduced by 80% and the total pore volume by 40–60%. Adsorption experiments from ethanol-cyclohexane mixtures revealed the decreasing adsorption capacity and the increasing hydrophobicity. The changing surface character was also evident in the decrease in enthalpy of immersion in ethanol from 65.3 J/g to 8.3 J/g (sample B) and from 37.8 J/g to 5.2 J/g (sample C). The alteration probably arises from gradual formation of gibbsite-like interlayers and the redistribution of charges.

KEYWORDS: adsorption, enthalpy of immersion, hydrophobicity, pillared montmorillonites