Time-resolved infrared spectroscopic investigation of roles of valence states of Cr in (La,Cr)-doped SrTiO3 photocatalysts

The kinetics of photogenerated electrons in SrTiO3(La,Cr) pretreated with either H2 or O2 were studied using time-resolved infrared spectroscopy. The X-ray photoelectron and Raman spectra showed that the Cr cations in the sample reduced with H2 were all in Cr3+, whereas those oxidized with O2 were in mixed of Cr3+ and Cr6+. Electrons excited with 355 and 532 nm light pulses showed the absorption of mid-IR light, and this was traced as a function of the time delay in a microsecond domain. The time-resolved results revealed that the decay rate of the photoinduced electrons with Cr3+ was slower than that with Cr6+, implying that trivalent Cr contributed more to retarding recombination of photoinduced electrons and holes, and enhanced photocatalytic H2 production activity.

Graphical abstractThe Cr valence state plays an important role in H2 production under irradiation in the visible light region. Electrons are quickly trapped by Cr6+ ions and cannot contribute to H2 production.Figure optionsDownload full-size imageDownload as PowerPoint slide