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

Radial rutile TiO nanorod homomesocrystals (TiO -NR HOMCs) or the so-called "sea urchin-like TiO microspheres" were synthesized by using a hydrothermal method. TiO -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 -NR HOMCs (FeO /TiO -NR HOMCs) by the chemisorption-calcination technique to reduce the band gap. The FeO -surface modification gives rise to drastic enhancement of the UV- and visible-light activity. Reversed double-beam photoacoustic spectroscopy measurements were performed for TiO -NR HOMCs and FeO /TiO -NR HOMCs to obtain the ERDT (energy-resolved distribution of electron traps)/CBB (conduction-band bottom) patterns. The ERDT/CBB pattern of TiO -NR HOMCs consists of two components derived from rutile (C1) and amorphous TiO (C2). In the pattern, the surface electron traps in C2 exist near the CBB to be removed by the FeO -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 clusters for multiple ORR, the suppression of recombination, and the increase in the visible-light harvesting efficiency.