Synthesis and Photocatalytic Activity of La 5 Ti 2 Cu(S 1− x Se x ) 5 O 7 Solid Solutions for H 2 Production under Visible Light Irradiation

The effects of substituting selenide for sulfide ions in La 5 Ti 2 CuS 5 O 7 were studied, with the aim of developing visible‐light‐driven photocatalysts with longer absorption edge wavelengths. La 5 Ti 2 Cu(S 1− x Se x ) 5 O 7 (LTCS 1− x Se x O) solid solutions were obtained over the composition range of 0≤ x ≤1 by a solid‐state reaction, and their physical properties and photocatalytic activities during the H 2 evolution reaction in aqueous solutions were assessed. Structural refinements revealed that the lattice constants and cell volumes of the LTCS 1− x Se x O series follow Vegards’ law. With increases in the Se 2− content, the LTCS 1− x Se x O absorption edge shifts monotonically toward longer wavelengths, to a maximum of 820 nm for LTCSeO ( x= 1). Those materials for which x ≤0.8 generated H 2 from aqueous solutions containing Na 2 S and Na 2 SO 3 as electron donors under visible‐light irradiation ( λ >420 nm) after surface modification with in situ precipitated NiS. Comparatively higher H 2 evolution was observed for LTCS 1− x Se x O with lower Se 2− levels, although the sample for which x= 0.2 generated H 2 under visible light at wavelengths longer than 640 nm, whereas the LTCSO did not.