DFT study on the interaction of H2O and O2 with α-Fe2O3 (001) surface

The interactions of H2O and O2 with α-Fe2O3 (001) surface were studied using density functional theory (DFT). The surface structures of α-Fe2O3 changed a lot after H2O and O2 molecules adsorption, and the O–Fe bonds of α-Fe2O3 surface are weakened. The oxygen atom of H2O molecule are bonded to iron atom of α-Fe2O3 surface, and one H–O bond is broken to form hydroxyl group (−OH). Two oxygen atoms of O2 molecule are bonded the same iron atom of α-Fe2O3 surface. The adsorption energy of O2 on the α-Fe2O3 surface is −170 kJ/mol, which is larger than that of H2O on the α-Fe2O3 surface (−130 kJ/mol). The charge transfers occur from H2O molecule to α-Fe2O3 surface during H2O molecule adsorption, while from α-Fe2O3 surface to O2 molecule for O2 molecule adsorption. The value of charge transfer from α-Fe2O3 surface to O2 molecule (−0. 47 e) is larger than that from H2O to α-Fe2O3 surface (+0.06 e). This study provides a microcosmic explanation for the effect of H2O and O2 on α-Fe2O3 surface, and thus on the photocatalytic mechanism, which has important guiding significance for the industrial application of α-Fe2O3 as a photocatalyst.