X-ray Photoemission and Density Functional Theory Study of the Interaction of Water Vapor with the Fe3O4(001) Surface at Near-Ambient Conditions

Abstract

The interaction of water with the Fe3O4(001) surface was investigated in a combined ambient pressure X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) study. The uptake of molecular water and hydroxyl species on the (001) surface of a natural magnetite sample at near-ambient conditions was quantified using O 1s spectra taken in the p(H2O) range from 10–9 to 2 Torr. At low p(H2O) (≤10–4–10–5 Torr) and room temperature, we found that water does not adsorb dissociatively on the surface, except on defect sites. In contrast, progressive dissociation into surface hydroxyl species was observed between 10–4 and 10–2 Torr p(H2O). The onset of hydroxylation coincides with the increasing presence of molecular water species on the surface, which demonstrates the key role played by cooperative interactions between adsorbed water molecules, leading to dissociation and surface hydroxylation. The measured O 1s chemical shifts of hydroxyl and molecular water species from both isotherm and isobar d...