Visible-Light Activation of Strontium Titanate by the Surface Modification with Iron(III) Oxide Nanoclusters

Tris(acetylacetonato)iron(III) (Fe(acac)(3)) is chemisorbed on strontium titanate (SrTiO3) via partial ligand-exchange between the acac ligand and the surface Ti-OH group. Postheating at 773 K in the air yields extremely small iron(III) oxide clusters on SrTiO3 (Fe2O3/SrTiO3). The Fe2O3 loading amount per unit surface area of SrTiO3 (Gamma/Fe ions nm(-2)) was controlled by the Fe(acac)(3) concentration. The surface modification gives rise to visible-light activity for the oxidation of 2-naphthol used as a model water pollutant simultaneously with the UV-light activity significantly boosted. The visible-light activity is sensitive to Gamma to reach a maximum at Gamma approximate to 0.36. Valence band-X-ray photoelectron spectroscopy (VB-XPS) and electrochemical measurements indicated that the surface modification by the Fe2O3 nanoclusters (NCs) generates new vacant surface levels below the conduction band minimum of SrTiO3, while the VB maximum level is invariant. The band energy diagram of Fe2O3/SrTiO3 suggested that the visible-light activity can be induced by the photo excitation of the electrons in the VB of SrTiO3 to the vacant surface levels or the bulk-to-surface interfacial electron transfer (IFET) in contrast to the visible-light-driven surface-to-bulk IFET in Fe2O3/TiO2. Eventually, the high visible-light activity of Fe2O3/SrTiO3 stems from the effective charge separation and the electrocatalytic activity of the Fe2O3 NCs for the oxygen reduction reaction.