ABSTRACT:Kaolin clays are layer aluminosilicates showing a large variety of physicochemical properties. The most common clay mineral, kaolinite, has been widely studied and it crystallizes in space group P1. We used the ab initio method in order to study kaolinite structure. The RHF calculations were performed at different basis set levels and pseudopotentials (3-21G*, 6-31G, DZP, TZV, CEP-31G, LANL2DZ, and SHC). The two-layer Oniom calculation was applied. The RHF and B3LYP at the 3-21G* basis set level were used for the high-layer Oniom and the Dreiding force field was used for the low-layer Oniom. The hydrogen positions were completely optimized. The geometry of cluster models is taken from the crystallographic data. Vibrational frequencies of hydrogen stretching are also reported.

ONIOM calculations using CCSD theory have been performed to study the dissociation of hydrogen and water molecules on ZnO surface. Three different cluster models were used to study the influence of ONIOM layer size at the interaction energies and optimized geometries. The geometric results indicate a near tetrahedral geometry for the interaction of zinc and oxygen sites of dissociated water. The interaction energies are larger for the water dissociation. The ONIOM layer size has more influence on the interaction energies when compared with the geometric parameters and mainly for water dissociation. © 2012 Wiley Periodicals, Inc.

Clay minerals represent a growing research area in the development of new materials. Clay and clay-based materials have been widely investigated in efforts to design adsorbents. Furthermore, adsorption has been applied in order to remove organics and as an important strategy to remediate soils and groundwater contaminated with petroleum hydrocarbons. Among clays, kaolinite, Al 2 Si 2 O 5 (OH) 4 , is a layered aluminosilicate of 1:1 clay minerals family. Therefore, we have performed semi-empirical AM1 and ab initio RHF/3-21G* calculations in order to investigate the benzene interaction on kaolinite surface. The cluster model method was employed. Benzene structure was fully optimized. Molecular orbitals and electrostatic potential was also analyzed. The ab initio and semiempirical results shows the benzene molecule largely tilted in relation to the hydroxyl layer. The π orbital of benzene has changed slightly indicating the interaction through the hydroxyl and benzene π orbital.

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