Quantum chemical study of the adsorption of water molecules on kaolinite surfaces

Kaolinite is a kind of layered aluminosilicate showing a large variety of physicochemical properties. In this research, various gas phase properties of interactions between the Si–O layer (Si6O18H12) or Al–O layer (Al6O24H30) cluster model of kaolinite and n water molecules (n = 1–3) have been systematically explored at the B3LYP [Becke’s three-parameter hybrid exchange functional (B3) and the correlation functional of Lee, Yang, and Parr (LYP)] level using the 6-31G(d) basis set. These gas phase properties include optimal structures, structural parameters, hydrogen bonds, interaction energies, natural bond orbital charge distributions, vibration frequencies, electron density characteristics and maps of electronic potential. The most stable structures of each system have been obtained when one, two and three water molecules are adsorbed on each surface. With an increasing number of water molecules, there are also hydrogen bonds between water molecules besides the hydrogen bonds between water and the kaolinite surface. The results show that the stabilization of hydrogen bonds is closely connected with the kaolinite surface type, surface structure, and position and orientation towards the surface of water molecules. Moreover, the Al–O/water system is more stable than the Si–O/water system. Simultaneously, the hydrogen bonds formed between water molecules are the strongest, followed by those between water and the Al–O layer and lastly those between water and the Si–O layer.