An insight into the surface properties of calcined kaolinitic clays: The grinding effect

The present work aimed characterizing in a systematic way the surface of metakaolinitic materials produced by calcination of a kaolinitic clay at different temperatures and to study the effect of grinding on the surface properties of metakaolinitic materials. Using X-ray photoelectron spectroscopy, it was found for all materials a Si/Al atomic ratio close to 1, confirming the presence of the 1:1 clay structure. By inverse gas chromatography, an increase of the Lewis basic properties of the surfaces of metakaolinitic materials in comparison to the original clay was found, which was due to the condensation of hydroxyl groups in the structure of the clay. The grinding of the metakaolinitic materials afforded a decrease of the dispersive component of the surface energy ( γ s d ) as well as an increase of the specific interaction with sterically hindered molecules, caused by the diminishing of the materials surface nanoroughness. The Lewis basic properties of the materials surface also increased with grinding. Noticeably, for all studied materials a good inverse relation could be found between the γ s d and the specific interaction of trichloromethane (but not with dichloromethane), showing the importance of surface nanoroughness on the adsorption process of bulky molecules.