Synthesis and Photocatalytic Activity of La5Ti2Cu(S1-xSex)5O7 Solid Solutions for H2 Production under Visible Light Irradiation

The effects of substituting selenide for sulfide ions in La5Ti2CuS5O7 were studied, with the aim of developing visiblelight-driven photocatalysts with longer absorption edge wavelengths. La5Ti2Cu(S1-xSex)(5)O-7 (LTCS1-xSexO) solid solutions were obtained over the composition range of 0 <= x <= 1 by a solidstate 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 LTCS1-xSexO series follow Vegards' law. With increases in the Se2- content, the LTCS1-xSexO 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 Na2S and Na2SO3 as electron donors under visible- light irradiation ( lambda > 420 nm) after surface modification with in situ precipitated NiS. Comparatively higher H2 evolution was observed for LTCS1-xSexO 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.