Molecular dynamics simulations of adsorption of organic compounds at the clay mineral/aqueous solution interface
by Yu, C. H.; Newton, S. Q.; Norman, M. A.; Schafer, L.; Miller, D. M.
Computational studies of the sorption of organic compounds at clay mineral surfaces are described. Molecular dynamics simulations were performed with a recently developed empirical force field for dioctahedral clays. The studies allow the identification of three general mechanisms of adsorption. In the absence of water, organic compounds adsorb to mineral surfaces in such a way that contact area is maximized. In the presence of a sufficient amount of water, some molecules can adsorb via a single functional group, while the bulk of the molecular structure is immersed in the aqueous phase. When many water molecules are present, they form a structured layer, excluding organic adsorbates from the mineral basal plane. A detailed description is given of the characteristic structure found for water layers in the interlayer space of clays. The calculated trends are reasonable, but we also expect that current dynamics simulations may overestimate the extent of the structuring of water because of the absence of polarization terms in the available empirical force fields.