Effect of post-treatments on the photocatalytic activity of Sm2Ti2S2O5 for the hydrogen evolution reaction

Abstract

The oxysulphide photocatalyst Sm₂Ti₂S₂O₅ was synthesized by sulphurizing an amorphous Sm₂Ti₂O₇ prepared using a polymerized complex method under a H₂S flow and was used as a H₂ evolution photocatalyst in the sacrificial H₂ evolution and Z-scheme water splitting reactions. The H₂ evolution activity of Rh-loaded Sm₂Ti₂S₂O₅ was improved by annealing with sulphur powder and etching with nitric acid. Characterization using XRD, SEM, DRS and XPS suggested that annealing with sulphur decreased the density of the reduced Ti species in Sm₂Ti₂S₂O₅ and etching with nitric acid removed the amorphous phases and excessive sulphur species on the surface. After the two post-treatments, platinized Sm₂Ti₂S₂O₅ combined with rutile-type TiO₂ and NaI showed activity for Z-scheme water splitting under UV irradiation. Although UV irradiation was necessary owing to the use of TiO₂, this work provided the first evidence that an oxysulphide photocatalyst was applicable to Z-scheme water splitting.