Sulfur vacancy-regulated interface charge transfer for boosting photocatalytic hydrogen evolution over Bi₂S_3−x@Cd_0.7Zn_0.3S hollow hexagonal nanocages

How to tailor the interface charge transfer in heterostructured photocatalysts via energy band engineering has been an important research topic in boosting photocatalysis and promoting its application in hydrogen evolution. In this study, we have developed Bi₂S_3−x@Cd_0.7Zn_0.3S (BS-Sv@CZS, Bi₂S_3−x with S vacancies labeled as BS-Sv) heterostructured photocatalysts, where the energy band structures of BS-Sv were continuously regulated via creating S vacancies in the lattice to realize manipulation of the interface charge transfer and boost the photocatalysis for H₂ generation. The BS-Sv@CZS photocatalysts are constructed into double-shell hollow hexagonal nanocages with BS-Sv coating on the outer surface of CZS nanocages. It is demonstrated that with increasing the S vacancy concentration in BS-Sv (i.e., elevating the energy band positions of BS-Sv), the interface electric field of BS-Sv@CZS gradually increases; and more importantly, the photoelectron transfer behavior from CZS to BS-Sv is tailored from conduction band (CB)-to-CB transfer to CB-to-CB/valence band (VB) transfer, and then to CB-to-VB transfer. The BS-Sv@CZS heterostructured photocatalysts are endowed with much improved photocatalysis for H₂ evolution; particularly, the BS-Sv2@CZS with CB-to-CB/VB photoelectron transfer displays the highest photocatalytic activity (H₂ generation rate: 2.56 mmol·g⁻¹·h⁻¹) that is 4.1 (or 8.0) times larger than that of CZS (or BS-Sv2). The photocatalytic enhancement mechanism was deeply elucidated via combined experimental and theoretical studies. This study highlights an important strategy for boosting photocatalytic H₂ evolution of heterostructured photocatalysts.