Adsorption of two phenoxyacid compounds on a clay surface: a theoretical study

Using density functional theory methods, we studied the adsorption of (4-chloro-2-methylphenoxy)acetic acid (MCPA) and 2-(4-chlorophenoxy)-2-methylpropanoic acid, therapeutically used under the name of clofibric acid (CA), two commonly detected water pollutants, both in neutral and ionized form on a model surface of muscovite. We report the geometries of the adsorbed species and discuss their interaction with the surface. It was found that the ionized adsorbates interact more strongly with the surface than do their neutral forms particularly for MCPA when compared with CA, which points to the same direction of previous experimental findings. Changes on the electron density due to adsorption has been studied by means of Bader charges analysis and it was found that electronic density is transferred from the anions to the surface and less significantly from the surface to the neutral molecules on adsorption.