Comparative Study of the Photocatalytic Hydrogen Evolution over CdMnS and CdS-β-MnO-MnOOH Photocatalysts under Visible Light.

A series of solid solutions of cadmium and manganese sulfides, CdMnS (x = 0-0.35), and composite photocatalysts, CdS-β-MnO-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 N low temperature adsorption. The photocatalysts were tested in hydrogen production using a NaS/NaSO 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 CdMnS has an enhanced photocatalytic activity due to its valence and conduction band position tuning, whereas the CdS-β-MnO-MnOOH (40-60 at% Mn) samples were active due to ternary heterojunction formation. Further, the composite CdS-β-MnO-MnOOH photocatalyst had much higher stability in comparison to the CdMnS solid solution. The highest activity was 600 mmol g h, and apparent quantum efficiency of 2.9% (λ = 450 nm) was possessed by the sample of CdS-β-MnO-MnOOH (40 at% Mn).