Theoretical study of interaction of formamide with kaolinite

The interactions between small molecules and clay minerals have attracted more interest of scientists recently due to the wide use of them in the catalysts and environmental absorbents. In the clays, kaolinite as an important layered aluminosilicate presents a variety of physicochemical properties. In this paper, the clusters of Si6O18H12, Al6O24H30 and Si6Al6O42H42 were constructed for tetrahedral, octahedral layers and isolated kaolinite to investigate the microscopic properties of formamide (FA) on kaolinite layers by Density Function Theory (DFT) methods. All computations were performed at the B3LYP (Becke, three-parameter, Lee–Yang–Parr exchange–correlation functional) level using the 6-31G(d) basis set. The properties, such as the optimal structures, structural parameters, interaction energies, NBO (natural bond orbital) charge distributions, vibrational frequencies, electrostatic potential, were extracted from them. The results show that hydrogen bonds between FA and the surface hydroxyl groups of the octahedral layer or the basal oxygen atoms of the tetrahedral layer in kaolinite are formed. The absolute values of calculated interaction energies on the tetrahedral layer are smaller than those on the octahedral layer and the interaction energies of adsorbed systems are smaller than intercalated one, which indicate that the adsorption between FA and octahedral layer of kaolinite is stronger than that of FA on the tetrahedral layer of kaolinite, and the intercalation is more stable than the adsorption.