We successfully clarified the mechanisms of visible-light-driven photocatalytic reactions of Fe(III)-grafted TiO 2 (Fe/TiO 2 ) and Fe(III)-grafted Ru-doped TiO 2 (Fe/ Ru:TiO 2 ). ESR spectroscopy revealed that the visible-light response of the Fe/TiO 2 photocatalyst resulted in the direct charge transfer from the valence band of TiO 2 to the grafted Fe ions. For the Fe/Ru:TiO 2 photocatalyst, acceptor levels were formed by doping Ru ions in the lattice of TiO 2 , and the electrons at the acceptor levels excited on visible-light irradiation readily transfer to Fe ions. Since a longer wavelength light generated the conduction band electrons, we also proposed a two-step electron excitation from valence band to the conduction band through defect levels such as oxygen vacancy. As a result, a part of photogenerated electrons in the conduction band transfer to the grafted Fe ions. Therefore, the Fe/Ru:TiO 2 photocatalyst showed a higher activity because such two kinds of indirect charge transfer to the grafted Fe ions occurred in addition to the direct interfacial charge transfer observed for Fe/TiO 2 . Moreover, chemiluminescence photometry confirmed that the grafted Fe ions function as a promoter to reduce O 2 into H 2 O 2 via two-electron reduction. Therefore, the acceleration in the reduction of O 2 with doping Ru and grafting Fe ions allows a larger number of holes to oxidize organic compounds, resulting in the higher photocatalytic activity.
A rhodium(III)
ion (Rh3+)-modified TiO2 (Rh3+/TiO2) photocatalyst, prepared by a simple adsorption
method and exhibiting high levels of photocatalytic activity in degradation
of organic compounds, was investigated by using X-ray absorption fine
structure (XAFS) measurements, (photo)electrochemical measurements,
double-beam photoacoustic (DB-PA) spectroscopic measurements, and
photoluminescence measurements. Based on the results, the features
of the Rh3+ modifier and the working mechanism of the Rh3+/TiO2 photocatalyst are discussed. XAFS measurements
revealed that the Rh3+ species were highly dispersed and
almost atomically isolated on TiO2. The (photo)electrochemical
measurements, DB-PA spectroscopic measurements, and photoluminescence
showed a unique bifunction of the Rh3+ modifier as a promoter
for O2 reductions and an electron injector to the conduction
band of TiO2 for response to visible light. The reasons
for the Rh3+/TiO2 photocatalyst exhibiting higher
levels of photocatalytic activity than those of TiO2 photocatalysts
modified with other metal ions are also discussed on the basis of
obtained results.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.