Understanding and optimizing the sensitization of anatase titanium dioxide surface with hematite clusters

Abstract

The presence of hematite (Fe2O3) clusters at low coverage on titanium dioxide (TiO2) sur-
face has been observed to enhance photocatalytic activity, while excess loading of hematite is
detrimental. We conduct a comprehensive density functional theory study of Fe2O3 clusters
adsorbed on the anatase TiO2 (101) surface to investigate the effect of Fe2O3 on TiO2. Our
study shows that TiO2 exhibits improved photocatalytic properties with hematite clusters at
low coverage, as evidenced by a systematic study conducted by increasing the number of cluster
adsorbates. The adsorption of the clusters generates impurity states in the band gap improving
light absorption and consequently affecting the charge transfer dynamics. Furthermore, the
presence of hematite clusters enhances the activity of TiO2 in the hydrogen evolution reaction.
The Fe valence mixing present in some clusters leads to a significant increase in H2 evolution rate
compared with the fixed +3 valence of Fe in hematite. We also investigate the effect of oxygen
defects and find extensive modifications in the electronic properties and local magnetism of the
TiO2 -Fe2O3 system, demonstrating the wide-ranging effect of oxygen defects in the combined
system.