Adsorption of nitrogen-heterocyclic compounds on oxide surfaces: Final report for the period September 1, 1984-November 31, 1986

The principal objective of this investigation is to develop scientific understanding of the surface reactions that effect the sorption of nitrogen-heterocyclic compounds onto natural minerals. Adsorption phenomena may significantly influence the transport and ultimate fate of organic compounds on land and in aquatic systems. The concepts developed in this study provide a basis for evaluating the surface and solution reactions that control the sorption of nitrogen-heterocyclic compounds in groundwater environments. This work also serves as a basis for design of additional experiments in follow-up studies on the interactions between aromatic solutes and mineral media. Because of compound ionization and electrostatic effects, simple models which emphasize ''hydrophobic'' interactions to describe sorption of organic compounds are not appropriate for the nitrogen-heterocyclic compounds investigated in this study. Ligand exchange models which interpret the specific adsorption (binding mechanisms other than coulombic) of organic ligands to hydrous oxide surfaces as ligand exchange reactions at reactive surface sites are more appropriate for ionizable nitrogen-heterocyclic compounds. In order to fully understand the behavior of nitrogen-containing aromatic organics in systems containing inorganic solid phases such as metal oxides, additional work is needed to characterize surface binding phenomena and chemical oxidation mechanisms. 40 refs., 23 figs., 10 tabs.