Comparative Study of the Photocatalytic Hydrogen Evolution over Cd 1−x Mn x S and CdS-β-Mn 3 O 4 -MnOOH Photocatalysts under Visible Light.

A series of solid solutions of cadmium and manganese sulfides, Cd_1−xMn_xS (x = 0–0.35), and composite photocatalysts, CdS-β-Mn₃O₄-MnOOH, were synthesized by precipitation with sodium sulfide from soluble cadmium and manganese salts with further hydrothermal treatment at 120 °C. The obtained photocatalysts were studied by the X-ray diffraction method (XRD), UV-vis diffuse reflectance spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and N₂ low temperature adsorption. The photocatalysts were tested in hydrogen production using a Na₂S/Na₂SO₃ aqueous solution under visible light (λ = 450 nm). It was shown for the first time that both kinds of photocatalysts possess high activity in hydrogen evolution under visible light. The solid solution Cd_0.65Mn_0.35S has an enhanced photocatalytic activity due to its valence and conduction band position tuning, whereas the CdS-β-Mn₃O₄-MnOOH (40–60 at% Mn) samples were active due to ternary heterojunction formation. Further, the composite CdS-β-Mn₃O₄-MnOOH photocatalyst had much higher stability in comparison to the Cd_0.65Mn_0.35S solid solution. The highest activity was 600 mmol g⁻¹ h⁻¹, and apparent quantum efficiency of 2.9% (λ = 450 nm) was possessed by the sample of CdS-β-Mn₃O₄-MnOOH (40 at% Mn). [ABSTRACT FROM AUTHOR]