Infrared studies of the adsorption of probe molecules onto the surface of goethite

Abstract

Infrared spectra are reported of pyridine, acetic acid, carbon dioxide, nitric oxide and trimethyl-chlorosilane adsorbed on the surface of goethite. Surface hydroxyl groups formed hydrogen bonds with pyridine molecules. Pyridine was also adsorbed onto Lewis acidic surface sites. Acetic acid was molecularly adsorbed onto Lewis acidic sites and was chemisorbed to give surface acetate species and water. Carbon dioxide was chemisorbed to give bicarbonate and several types of surface carbonate species. Similarly the adsorption of nitric oxide gave surface nitro and nitrato complexes. Possible configurations of the surface acetate, carbonate, nitro and nitrate species are discussed. Trimethylchlorosilane reacted with one type of surface hydroxyl group to give adsorbed trimethyl-siloxyl groups and hydrogen chloride. The latter was chemisorbed to give H₃O⁺ ions in the goethite surface.