Kaolinite hydrogen-bonded interactions

Hydrogen-Bonded Interactions of Surfaces of the Isolated Kaolinite Layer... 

The number and exact composition of the sheets is used to classify the phyllosilicates. The most important classification for our purposes is the distinction between 1 1 and 2 1-type minerals (Figure 2.1). In 1 1 minerals such as kaolinite, the basal oxygens of the tetrahedral sheet are free to interact with octahedral OH groups forming hydrogen bonds. In contrast, 2 1 minerals such as pyrophyllite or talc contain two tetrahedral sheets sandwiched around an octahedral sheet. These minerals have only basal oxygens exposed on the faces of the tetrahedral sheets and are linked by weak van der Waals forces. The weaker interaction of one 2 1 layer with a second 2 1 layer results in interlayer spaces which, depending on the particular mineral, may be available for contaminant intercalation. 

The periodic calculations show good agreement with results of cluster calculations, with small deviations in the geometry parameters of the intercalated molecules and in the distances of hydrogen bonds as a consequence of distinct mutual interactions of intercalated DMSO molecules or interactions between the DMSO molecules and the surface of kaolinite. 

Figure 12-4. Models for the surface interactions of kaolinite. In case (a) atomic symbols correspond to those used in Table 12-3. Numbers in cases (b), (c) and (d) give hydrogen bond distances obtained in the cluster calculations at the ONIOM(B3LYP/SVP PM3) level [73]...

The least reactive type of surface site found on clay minerals is the neutral siloxane surface. Features associated with this type of site include no charge, no permanent dipole moment, and weak interactions with the hydrogen-bonded network of water molecules. Hydrophobic surfaces occur on 2 1 phyllosilicates, where there is no isomorphic substitution (e.g., talc and pyrophyllite), and also on the siloxane side of the kaolinite 1 1 TO unit. There is currently some question about the structural microscopic hydrophilicity of talclike surfaces (43) however, from a... 

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