Visible-Light-Active Iron Oxide-Modified Anatase Titanium(IV) Dioxide

Fe(acac)(3) is chemisorbed on the surfaces of anatase TiO2 via partial ligand exchange between the acetylacetonate and surface Ti-OH groups [Fe(acac)(2)/TiO2]. The postheating at 773 K in air forms iron oxide species on the TiO2 surface in a highly dispersed state at a molecular level ((FeOx)(m)/TiO2). As a result of the iron oxide surface modification, the band gap of TiO2 decreases, while the absorption due to the d-d transition clearly observed for the usual impregnation samples is very weak. (FeOx)(m)/TiO2 gives rise to a noticeable visible light activity concomitantly with a significant increase in UV light activity, whereas Fe(acac)(2)/TiO2 hardly responds to visible light. Valence-band X-ray photoelectron spectra of (FeOx)(m)/TiO2 showed that the band gap narrowing results from the rise in the valence band top with surface modification. Also, photoluminescence spectroscopy indicated that the surface iron oxide species rapidly capture the excited electrons in the conduction band of TiO2 to suppress recombination via surface oxygen vacancy levels. Furthermore, the surface iron oxide species act as excellent mediators for electron transfer from TiO2 to O-2.