Water-driven boost in the visible light photocatalytic performance of Cs2AgBiBr6 double perovskite nanocrystals

In recent years, the focus on lead-free halide perovskite nanocrystals (NCs) has now been shifted to their utilization as photocatalysts due to their strong light absorption and tunable photo-responsive range. Current studies have promised Cs2AgBiBr6 NCs to be a born photocatalytic material that will self-passivate to generate BiOBr when it encounters water. In this work, a unique Cs2AgBiBr6/BiOBr composite was found in water-soaked Cs2AgBiBr6 NCs, which was further diagnosed as a Z-type heterojunction to enhance the photocatalytic process. Meanwhile, variations in the structure and photocatalytic behavior of Cs2AgBiBr6 NCs in RhB solution with different water contents were investigated in detail. Results showed that appropriate water content could accelerate the visible-light-driven degradation of RhB by almost 1.5 times, but excessive water (more than 50 vt%) may result in weak or negative enhancement. Accordingly, the bandgap matching, carrier separation and the resultant photocatalytic mechanism of water-soaked Cs2AgBiBr6 NCs were discussed and proposed. This research will offer a new idea for the application of halide perovskite in a water-involved photocatalytic system.