Photocatalytic Hydrogen Evolution on ZnS−CuInS₂−AgInS₂ Solid Solution Photocatalysts with Wide Visible Light Absorption Bands

Pt-loaded ZnS−CuInS 2 −AgInS 2 solid solutions showed photocatalytic activities for H 2 evolution from aqueous solutions containing SO 3 2 - and S 2 - as sacrificial reagents under visible light irradiation (λ ≥ 420 nm). The crystal structures of the solid solutions were either zinc blende or wurtzite, depending on the composition. The diffuse reflectance and photoluminescence spectra of the solid solutions were shifted monotonically to longer wavelengths as the ratio of MInS 2 (M = Cu and Ag) to ZnS increased, indicating that the energy band structure of the sold solution was controllable by the change in the composition. The ZnS−CuInS 2 −AgInS 2 solid solutions exhibited absorption bands that were longer in wavelength than those for the ZnS−CuInS 2 and ZnS−AgInS 2 solid solutions, which is probably due to interactions between the Cu 3d and Ag 4d orbitals. The photocatalytic activity for H 2 evolution was much improved by low-temperature synthesis (773−873 K) and the loading of Ru cocatalysts. The Ru-loaded Cu 0.25 Ag 0.25 In 0.5 ZnS 2 solid solution, which had a wide absorption band (band gap, 1.77 eV) in the visible light region, showed high activity for H 2 production, even under simulated solar irradiation (AM 1.5).