Well-dispersed Au co-catalyst deposited on a rutile TiO2 photocatalyst via electron traps

We deposited Au nanoparticles as a co-catalyst onto a TiO₂ photocatalyst by reducing [AuCl₄]^- using electrons trapped in the oxygen vacancies of TiO₂. The dispersibility and hydrogen production ability of the Au co-catalyst are higher than those prepared using the conventional photodeposition method.

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

Radial rutile TiO₂ nanorod homomesocrystals (TiO₂ -NR HOMCs) or the so-called "sea urchin-like TiO₂ microspheres" were synthesized by using a hydrothermal method. TiO₂ -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 TiO₂ -NR HOMCs (FeO_x /TiO₂ -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 TiO₂ -NR HOMCs and FeO_x /TiO₂ -NR HOMCs to obtain the ERDT (energy-resolved distribution of electron traps)/CBB (conduction-band bottom) patterns. The ERDT/CBB pattern of TiO₂ -NR HOMCs consists of two components derived from rutile (C1) and amorphous TiO₂ (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.

Combined Spectroscopic Methods of Determination of Density of Electronic States: Comparative Analysis of Diffuse Reflectance Spectroelectrochemistry and Reversed Double-Beam Photoacoustic Spectroscopy

The diffuse reflectance spectroelectrochemistry (SE-DRS) and reversed double-beam photoacoustic spectroscopy (RDB-PAS) provide unique, complementary information on the density of electronic states (DOS) in the vicinity of the conduction band bottom. The measurements are performed under quite different conditions, representing the solid/liquid and solid/gas interfaces in SE-DRS and RDB-PAS, respectively. DOS profiles obtained from both types of measurements can be considered as unique "fingerprints" of the tested materials. The analysis of DOS profiles recorded for 16 different TiO₂ samples confirms that both methods similarly describe the shapes of DOS profiles around the conduction band edges. The states characterized by energy higher than VBT (valence-band top) + E_g can be considered as electronic states within the conduction band. Recognition of the potential of the conduction band bottom allows one to classify the electronic states as deep or shallow electron traps or conduction band states, which play different roles in photocatalysis. The comparative analysis shows that both methods provide very useful information which can be used in understanding and predicting the photo(electro)catalytic reactivity of semiconductors.