Green synthesis of 3D core–shell SnS2/SnS-Cd0.5Zn0.5S multi-heterojunction for efficient photocatalytic H2 evolution

Abstract

Low charge carrier separation efficiency is one of the key factors restricting photocatalytic hydrogen evolution performance. It is an effective strategy to build heterojunctions to steer charge migration. Herein, a series of x-SnS₂/SnS-Cd_0.5Zn_0.5S (x-SS-CZS) nanosphere composites with varying mass ratios of SnS₂/SnS (SS) were prepared through in situ hydrothermal synthesis. Moreover, XRD, TEM, and XPS were used to characterize the 3D core–shell SS-CZS multi-heterojunction composite. The 5-SS-CZS heterojunction composite with 5 wt% content of SS exhibits a remarkable hydrogen evolution rate of 168.85 mmol g⁻¹ h⁻¹, which is 5.4 times higher than that of pristine twin CZS (31.08 mmol g⁻¹ h⁻¹) and 1.9 times higher than that of 5-SnS₂-CZS (88.21 mmol g⁻¹ h⁻¹). Furthermore, the composite catalyst showed excellent photostability after four cycles of reactions under visible light illumination. The apparent quantum yield at λ = 420 nm could reach up to 24.78%. The excellent hydrogen evolution performance of 5-SS-CZS nanospheres is ascribed to the following factors: (1) a core–shell catalyst with broad spectral absorption improves light utilization efficiency, (2) hybrid material with large surface area provides more active sites and shows the highest H₂ activity, (3) a multi-heterojunction composite extends the lifetime of photoinduced carriers and accelerates charge separation and migration, and (4) SS as a hole trapping agent enhances the photocatalytic stability performance. This work proposes a possible photocatalytic mechanism, while also providing a novel approach for the synthesis of highly active and stable photocatalysts.