Ionic liquid-assisted preparation of a lead-free Cs3Bi2Br9 perovskite with high stability for selective photocatalytic oxidation of benzyl alcohol

Abstract

Metal halide perovskites (MHPs) stand out as photocatalysts because of their excellent optical property. However, the main drawbacks of MHPs are their instability resulting from their ionic nature and the toxicity of Pb in popular lead halide perovskites. To solve these problems, in this work, we chose Cs₃Bi₂Br₉ as a typical lead-free MHP and prepared Cs₃Bi₂Br₉ using the ionic liquid 1-decyl-3-methylimidazolium bromide ([Dmim]Br) as the surface ligand and bromine source through a ligand-assisted reprecipitation method. The prepared Cs₃Bi₂Br₉ nanocrystals (NCs) remained stable under moisture, light, and heat, which was attributed to the anchoring of the ionic liquid [Dmim]Br on the nanocrystalline surface to passivate harmful defects. Then, we selected the oxidation of benzyl alcohol as a representative model reaction and investigated the photocatalytic performance of Cs₃Bi₂Br₉ NCs. Under the illumination of visible light, it was found that benzyl alcohols could be transformed in the presence of the Cs₃Bi₂Br₉ NCs into corresponding aldehydes with near 100% selectivity and 99.64% conversion within 1 h. EPR measurements confirmed that the main active species responsible for the highly selective oxidation were singlet oxygen ¹O₂, which was proved to be generated from the transformation of superoxide radicals (·O₂⁻). This work is expected to provide insights for extending the design and photocatalytic applications of lead-free MHP NCs.