Confirmation of the surface structures of goethite (α-FeOOH) and phosphated goethite by infrared spectroscopy

Abstract

The infrared absorption spectrum of phosphate adsorbed on α-FeOOD and α-FeOOH establishes the presence of binuclear (FeO)2PO. OH groups, bridging adjacent Fe3+ ions on (100) faces of the crystals. Examination of D2O-exchanged surfaces shows the predicted three species of OD on the goethite surface, two on fluoridated goethite, and four (including POD) on phosphated goethite. The spectrum of adsorbed pyridine indicates that both goethite and phosphated goethite have Lewis acid sites on edge faces only; neither exhibit Brönsted acidity. These observations confirm a proposed model of the (100) face.