Photocatalytic Activity of Radial Rutile Titanium(IV) Oxide Microspheres for Aerobic Oxidation of Organics.

Radial rutile TiO 2 nanorod homomesocrystals (TiO 2 -NR HOMCs) or the so-called "sea urchin-like TiO 2 microspheres" were synthesized by using a hydrothermal method. TiO 2 -NR HOMCs show photocatalytic activity for aerobic oxidative degradation of 2-naphthol under irradiation of UV- and visible light. Furthermore, extremely small iron oxide clusters were formed on the surface of TiO 2 -NR HOMCs (FeO x /TiO 2 -NR HOMCs) by the chemisorption-calcination technique to reduce the band gap. The FeO x -surface modification gives rise to drastic enhancement of the UV- and visible-light activity. Reversed double-beam photoacoustic spectroscopy measurements were performed for TiO 2 -NR HOMCs and FeO x /TiO 2 -NR HOMCs to obtain the ERDT (energy-resolved distribution of electron traps)/CBB (conduction-band bottom) patterns. The ERDT/CBB pattern of TiO 2 -NR HOMCs consists of two components derived from rutile (C1) and amorphous TiO 2 (C2). In the pattern, the surface electron traps in C2 exist near the CBB to be removed by the FeO x -surface modification. By taking this finding into consideration, the striking surface modification effect is ascribable to the electrocatalytic activity (or the action as an electron reservoir) of the FeO x clusters for multiple ORR, the suppression of recombination, and the increase in the visible-light harvesting efficiency.