Sequential Growth of Cs₃Bi₂I₉/BiVO₄ Direct Z-Scheme Heterojunction for Visible-Light-Driven Photocatalytic CO₂ Reduction

The high exciton binding energy and lack of a positive oxidation band potential restrict the photocatalytic CO₂ reduction efficiency of lead-free Bi-based halide perovskites Cs₃Bi₂X₉ (X = Br, I). In this study, a sequential growth method is presented to prepare a visible-light-driven (λ > 420 nm) Z-scheme heterojunction photocatalyst composed of BiVO₄ nanocrystals decorated on a Cs₃Bi₂I₉ nanosheet for photocatalytic CO₂ reduction coupled with water oxidation. The Cs₃Bi₂I₉/BiVO₄ Z-scheme heterojunction photocatalyst is stable in the gas–solid photocatalytic CO₂ reduction system, demonstrating a high visible-light-driven photocatalytic CO₂-to-CO production rate of 17.5 μmol/(g·h), which is approximately three times that of pristine Cs₃Bi₂I₉. The high efficiency of the Cs₃Bi₂I₉/BiVO₄ heterojunction was attributed to the improved charge separation in Cs₃Bi₂I₉. Moreover, the Z-scheme charge-transfer pathway preserves the negative reduction potential of Cs₃Bi₂I₉ and the positive oxidation potential of BiVO₄. This study offers solid evidence of constructing Z-scheme heterojunctions to improve the photocatalytic performance of lead-free halide perovskites and would inspire more ideas for developing lead-free halide perovskite photocatalysts.