ADSORPTION OF ORGANIC-COMPOUNDS POSSESSING LIGAND DONOR GROUPS AT THEOXIDE WATER INTERFACE

A diffuse-layer model is used to demonstrate that the effects of pH an d ionic strength on organic ligand adsorption are a direct consequence of (i) stoichiometry of surface complex formation; (ii) mass balance equations for ligands, protons, and surface sites; and (iii) Poisson-B oltzmann terms which relate ion concentrations at the oxide/water inte rface to concentrations in bulk solution. Experiments examining the ad sorption of 2,4-dinitrophenol, 2-pyridinemethanol, and several substit uted 2-aminophenols onto TiO2, Al2O3, and FeOOH are used to illustrate the application of this approach. Once oxide surface protonation equi libria are properly accounted for, ligand adsorption can be modeled ef fectively in most instances through the choice of a single reaction st oichiometry and a single fitting parameter, the surface complex format ion constant.