Explaining the enhanced photocatalytic activity of Degussa P25 mixed-phase TiO₂ using EPR

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.