SURFACE-ACIDITY OF PILLARED TAENIOLITES IN TERMS OF THEIR PROTON AFFINITY DISTRIBUTIONS

Potentiometric titration data obtained for taeniolite samples pillared with hydroxyaluminum and hydroxyaluminum-zirconium polycations are analyzed using a stable numerical method for the solution of the adsorption integral equation. The samples studied were gradually heated before the experiment to impose changes in their acidic character. The acidic properties of modified minerals are characterized by their pK spectra. The relationship between these properties and the coordination and the chemical structure of cations in the pillaring species and the changes in the mineral layers due to heat treatment are discussed. The results obtained are also compared with the pK distributions for pure compounds used as pillars heated to the same temperatures as the pillared minerals. It is shown that heat treatment enhances the acidity of the pillared taeniolites which may be the results of the rearrangement of pillars (dehydroxylation) and possible protonic attack on SiO4 tetrahedra in the layers. The approach used enables one to assess both qualitatively and quantitatively the number and strength of acidic sites present on the surface of pillared taeniolites.