POROSITY OF SYNTHETIC SAPONITES WITH VARIABLE LAYER CHARGE PILLARED BY AL-13 POLYCATIONS

Saponites with variable layer charge (from 0.8 per unit cell to 1.5 per unit cell) were synthesized hydrothermally and pillared with Alla polycations following classical pillaring procedures. The amount of intercalated aluminum increases linearly with the layer charge up to 1.1 and remains constant for higher values. Characterization of the intercalated and pillared products reveals the presence of Al-13 polycations in the interlayer space. The microporosity of the samples was examined using quasi-equilibrium volumetric adsorption of carbon dioxide and classical nitrogen adsorption experiments. The Dubinin-Raduskhevich treatment applied to CO2 adsorption yields a microporous volume that is very close to a theoretical microporous volume derived from the amount of intercalated Alla moieties. It decreases with the layer charge. On the contrary, nitrogen BET surface areas increase with the layer charge suggesting that the characterization of aluminum pillared clays by nitrogen adsorption can lead to misleading results in terms of microporous volumes.