Adsorption mechanism of water molecules on hematite (1 0 4) surface and the hydration microstructure

Abstract

The interactions between water and oxide surfaces play an important role in many fields. In this work, the adsorption mechanism of water molecules on hematite (104) surface and the hydration microstructures were systematically investigated by means of FT-IR spectroscopy, X-ray photoelectron spectroscopy, and DFT calculations. The XPS measurements confirmed that water molecules can be chemically adsorbed on hematite surface, and the peak position of Fe3+ in the Fe 2p3/2 splitting peak is shifted to a high binding energy after hydration, which was confirmed by the computational results of partial density of state (PDOS) that the adsorption of water molecules can improve the energy of Fe 3d state in the surface approaching to that in the bulk. FT-IR analysis showed that the peak of OH bending vibration was almost disappeared and the intensity of the OH stretching vibration peak was significantly weakened after dehydration. The DFT calculations further indicated that about 30 water molecules can be well adsorbed on the hematite surface per unit nm2 area, resulting in hydroxyl hydration layer, the primary hydration layer, and the secondary hydration layer. This work sheds some new lights on the interface hydration of oxidized mineral.