Efficient Photocatalytic Hydrogen Production over NiS-Modified Cadmium and Manganese Sulfide Solid Solutions

In this work, new photocatalysts based on Cd1−xMnxS sulfide solid solutions were synthesized by varying the fraction of MnS (x = 0.4, 0.6, and 0.8) and the hydrothermal treatment temperature (T = 100, 120, 140, and 160 °C). The active samples were modified with Pt and NiS co-catalysts. Characterization was performed using various methods, including XRD, XPS, HR TEM, and UV-vis spectroscopy. The photocatalytic activity was tested in hydrogen evolution from aqueous solutions of Na2S/Na2SO3 and glucose under visible light (425 nm). When studying the process of hydrogen evolution using an equimolar mixture of Na2S/Na2SO3 as a sacrificial agent, the photocatalysts Cd0.5Mn0.5S/Mn(OH)2 (T = 120 °C) and Cd0.4Mn0.6S (T = 160 °C) demonstrated the highest activity among the non-modified solid solutions. The deposition of NiS co-catalyst led to a significant increase in activity. The best activity in the case of the modified samples was shown by 0.5 wt.% NiS/Cd0.5Mn0.5S (T = 120 °C) at the extraordinary level of 34.2 mmol g−1 h−1 (AQE 14.4%) for the Na2S/Na2SO3 solution and 4.6 mmol g−1 h−1 (AQE 2.9%) for the glucose solution. The nickel-containing samples possessed a high stability in solutions of both sodium sulfide/sulfite and glucose. Thus, nickel sulfide is considered an alternative to depositing precious metals, which is attractive from an economic point of view. It worth noting that the process of photocatalytic hydrogen evolution from sugar solutions by adding samples based on Cd1−xMnxS has not been studied before

Comparative Study of the Photocatalytic Hydrogen Evolution over Cd1−xMnxS and CdS-β-Mn3O4-MnOOH Photocatalysts under Visible Light

A series of solid solutions of cadmium and manganese sulfides, Cd1−xMnxS (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 Cd0.65Mn0.35S 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 Cd0.65Mn0.35S 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)