Theoretical study of interactions of dickite and kaolinite with small organic molecules

Intercalates and adsorbates of two minerals of the kaolin group (kaolinite and dickite) with formamide (FA), N-methyl-formamide (MFA) and dimethylsulfoxide (DMSO) were investigated using the B3LYP/3-21G* method of representative cluster models. Geometry optimisation of interacting molecules as well as of outer -OH groups of the octahedral sheet of the dickite and kaolinite layer was performed. Positions of molecules with respect to mineral layers were found. Formations and orientations of hydrogen bonds between intercalated or adsorbed molecules and layers were indicated. Interaction energies of intercalates and adsorbates were calculated and corrected to the basis set superposition error (BSSE). Intercalation energies are significantly larger than adsorption ones, thus showing the importance of additional stabilisation of the intercalated molecule in the interlayer space. The order of the stabilisation of intercalates is dickite-FA > dickite-MFA > kaolinite-DMSO. The same order is also observed for adsorbed systems. (C) 2002 Elsevier Science B.V. All rights reserved.