Molecular dynamics investigation into the adsorption of organic compounds on kaolinite surfaces

Molecular dynamics simulations have been performed to determine the partitioning behaviour of organic compounds between water phases and inorganic surfaces. In the first of these sets of simulations the heat of adsorption of a single benzocarbazole molecule on water-wet kaolinite surfaces was determined. The results from these simulations show that the benzocarbazole isomers have a slight preference for being adsorbed on the water-wet kaolinite mineral surfaces over being desorbed in the water phase (about -1.5 kcal/mol for the kaolinite alumina surfaces and about -4 kcal/mol for the kaolinite silica surface). No significant differences between the adsorption behaviour of benzo[a]- or benzo[c]carbazole were found. In a second set of simulations the stabilities of four different configurations of a three-phase water/cyclohexane/kaolinite system were determined. The results from these simulations show that a fully water-wet kaolinite is thermodynamically preferred over a fully cyclohexane-wet kaolinite system and that the silica-surface of kaolinite has a higher affinity for the water-phase than the alumina surface. The contrasting results from these two sets of simulations show that the phase behaviour of a single organic molecule in a water/mineral surface system is not necessarily related to the behaviour of an equivalent organic phase in the same system. (C) 2001 Elsevier Science Ltd. All rights reserved.