Green synthesis of 3D core-shell SnS₂/SnS-Cd_0.5Zn_0.5S multi-heterojunction for efficient photocatalytic H₂ evolution

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.