DFT Study of Interactions of Water on Kaolinite and Goethite Surfaces

摘要

Quantum-chemical DFT based simulations (relaxation and/or molecular dynamics) have been performed on models of surfaces of kaolinite and goethite minerals. Various structural models of surface sites, which are active in adsorption processes, have been investigated. Chemical activities of these sites have been estimated on the base of calculated interaction energies of water. It has been shown that hydrogen bonds represent a dominant mechanism in the formation of surface complexes with polar molecules. If the surface is formed from hydroxyl groups (the octahedral surface of kaolinite and the (110) surface of goethite) these OH groups are very flexible and are able to act as proton donors or acceptors in hydrogen bonds. On the other hand, if the surface is formed only from basal oxygen atom (the tetrahedral surface of kaolinite) only weak hydrogen bonds are formed with polar molecules. It has been possible to estimate energy of hydration for kaolinite on the base of calculated averaged energies from molecular dynamics for kaolinite surfaces covered wit a water layer. It has been shown that the goethite (110) surface offers several adsorption sites for the water molecules. The computed interaction energies for the goethite surface sites are larger (in absolute value) than for the octahedral kaolinite surface.