Density Functional Theory Investigations on the Structure and Reactivity of Aqueous Hematite (a-Fe₂O₃) Surfaces

Cynthia S. Lo and Anne M. Chaka

Physical and Chemical Properties Division

Chemical Sciences and Technology Laboratory

Building 222, Room A157, Mail Stop 8380

Tel: (301) 975-5478, Fax: (301) 975-3672

E-mail: cynthia.lo@nist.gov

Sigma Xi Member (2000)

January 14, 2005

The reactivity of a mineral surface depends on several factors, including the composition of the bulk material, crystallographic orientation, local coordination of the surface atoms, and topographic arrangement of the surface functional groups. In particular, the interaction of corundum-type metal oxide surfaces with water is not well understood, because the majority of experimental and theoretical data has been on the corresponding UHV-prepared or clean surfaces. These interactions play major roles in environmental processes, including contaminant sequestration, mobility, and remediation, and biogeochemical cycling of contaminants and nutrients.

We have focused our studies on investigating the structure/reactivity relationship of iron oxide surfaces under conditions encountered in environmental settings. We present density functional theory studies of the structure of clean and hydroxylated a-Fe₂O₃ (0001) and a-Fe₂O₃ (1-102), and the various H and metal coordinations leading to the lowest surface free energies. We also compare the stability of aqueous Fe to bulk Fe₂O₃. Finally, we compare our theoretical results to those from crystal truncation rod diffraction data.