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

Molecular dynamics simulations have been performed to determine the partiti oning behaviour of organic compounds between water phases and inorganic sur faces. In the first of these sets of simulations the heat of adsorption of a single benzocarbazole molecule on water-wet kaolinite surfaces was determ ined. The results from these simulations show that the benzocarbazole isome rs have a slight preference for being adsorbed on the water-wet kaolinite m ineral 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 behavio ur of benzo[a]- or benzo[c]carbazole were found. In a second set of simulat ions the stabilities of four different configurations of a three-phase wate r/cyclohexane/kaolinite system were determined. The results from these simu lations show that a fully water-wet kaolinite is thermodynamically preferre d 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 su rface. The contrasting results from these two sets of simulations show that the phase behaviour of a single organic molecule in a water/mineral surfac e system is not necessarily related to the behaviour of an equivalent organ ic phase in the same system. (C) 2001 Elsevier Science Ltd. All rights rese rved.