The adsorption of [Au(HS)2]- on kaolinite surfaces:: Quantum chemistry calculations

Electronic structure and energies of the system of [Au(HS)(2)](-) adsorbed on an atomic cluster of kaolinite were calculated using the self-consistent-field discrete-variation (SCF-X-alpha-DV) method. A hexagonal ring Of SiO4 tetrahedra with three At octahedra, including 38 atoms, was used to model the flake of kaolinite. Calculations were per-formed on all possible systems with [Au(HS)(2)](-) adsorbed at different sites. The energy calculations show that the systems with lower total energy are those in which [Au(HS)(2)](-) is adsorbed on edge surfaces, adsorption of [Au(HS)(2)](-) at the edges is thus more stable than adsorption on the basal plane. The bond-order calculations suggest that significant shifts in atomic charge and the overlapping of electron clouds between Au+ of the [Au(HS)(2)](-) and the surface ions of kaolinite would take place in the systems with [Au(HS)(2)](-) adsorbed on the edges. especially at the site near At octahedra. The interaction between [Au(HS)(2)](-) ion and kaolinite is expected to be strong. This kind of adsorption can be regarded as the formation of a surface complex.