Explaining the Enhanced Photocatalytic Activity of Degussa P25 Mixed-Phase TiO₂ Using EPR

TLDR

Previous proposals viewed rutile as a passive electron sink that hinders recombination in anatase, but this study highlights its active role in TiO₂ formulations. The study aims to elucidate the active role of rutile in mixed‑phase TiO₂ photocatalysts. EPR spectroscopy was used to probe charge separation in Degussa P25, revealing rapid electron transfer from rutile to anatase at phase transition points. Pure rutile is inactive due to rapid recombination, but in mixed‑phase P25, visible‑light–generated charges on rutile are stabilized by electron transfer to anatase, creating nanocluster interfaces that act as antennas and catalytic hot spots extending photoactivity into the visible range.

Abstract

Charge separation characteristics of a high-activity, mixed-phase titania photocatalyst (Degussa P25) are probed by EPR spectroscopy. While previous proposals consider rutile as a passive electron sink hindering recombination in anatase, this research details the critical and active role of rutile in TiO2 formulations. The inactivity of pure-phase rutile is due in part to rapid rates of recombination. Yet, in mixed-phase TiO2, charges produced on rutile by visible light are stabilized through electron transfer to lower energy anatase lattice trapping sites. These results suggest that within mixed-phase titania (P25) there is a morphology of nanoclusters containing atypically small rutile crystallites interwoven with anatase crystallites. The transition points between these two phases allow for rapid electron transfer from rutile to anatase. Thus, rutile acts as an antenna to extend the photoactivity into visible wavelengths and the structural arrangement of the similarly sized TiO2 crystallites creates catalytic "hot spots" at the rutile−anatase interface.