Surface Properties of Smectites Exchanged with Mono- and Biprotonated 1,4-Diazobicyclo(2,2,2)-Octane

Abstract

Abstraet--Smectites exchanged to various degrees with mono-or biprotonated 1,4-diazobicyclo(2,2,2)-octane (Dabco) have a porous structure in which the organic molecule acts as a "pillar." Less Dabco z+ than Dabco '+ was necessary both to initiate and to complete expansion, whereas for both Dabco 1+ and Dabco 2+ the threshold for expansion increased with the charge density of the clay. Interstratification of 9.7-/~ and 14.5-/~ (Dabco 1+) or 14. l-/~ (Dabco 2+) layers was observed before full expansion occurred.Nitrogen sorption isotherms on partially exchanged Dabco '+-and Dabco~+-clays are of the BET II and Langmuir type respectively, whereas n-butane adsorbed according to BET type II for both cationic forms. The specific surface area was governed by the number of Dabco z+ pillars, irrespective of the inorganic cation, and increased with Dabco z+ content even beyond the composition where full expansion was reached and notwithstanding the increasing number of silicate layers in the c direction of the crystal units. This relationship is explained by an enhanced random interleaving of clay platelets in the stacking units conraining Dabco z+.

Internal Surface of Clays and Constrained Chemical Reactions

“…Mortland and Berkheiser (1976) and Shabtai et al (1977) also prepared pillared clays using large protonated molecules, such as Dabco (1,4 diazobicydo (2,2,2)-octane) (see also, Loeppert et aL, 1979). Surface areas of ~ 300 m2/g measured by N2 adsorption (BET method) were obtained with Dabco (2 + and 1 + cations) (see, e.g., Van Leemput et al, 1983), whereas the observed d(001) value was only 14.5/~. Similar surface areas have been measured for clays pillared with the Alia hydroxy-Alpolymer, despite the fact that the 001 spacing of this material is ~ 18/~.…”