Insights into Lead-Free Bismuth-Based Halide Perovskites Toward Alcohol Oxidation Under Blue LED Illumination

In recent years, lead halide perovskite materials have been explored as photocatalysts for various organic transformations. However, the toxicity of "lead" has directed further research toward lead-free halide perovskites. Herein, two bismuth-based lead-free halide perovskites with the chemical compositions Cs₃Bi₂Br₉ and Cs₃Bi₂Br₆I₃ were synthesized via a modified antisolvent-assisted precipitation method, which resulted in a hexagonal morphology of the synthesized materials. Cs₃Bi₂Br₉ was observed to have a higher bandgap (E_g = 2.5 eV) than Cs₃Bi₂Br₆I₃ (E_g = 2.0 eV). The photocatalytic activity of both materials was studied. Both photocatalysts were employed to oxidize 1-phenylethanol to acetophenone under the irradiation of blue LEDs (light-emitting diodes, λ = 427 nm). The oxidation reaction with Cs₃Bi₂Br₉ provided 100% conversion after 8 h of illumination. However, only 23% conversion was observed for Cs₃Bi₂Br₆I₃ even after 14 h of illumination. Cs₃Bi₂Br₉ has a deep-lying valence band (VB) with a higher oxidation potential of the photogenerated holes and a conduction band (CB) with a higher reduction potential of photogenerated electrons than Cs₃Bi₂Br₆I₃, giving a better yield for alcohol (1-phenylethanol) oxidation. Furthermore, impedance spectroscopy and BET analysis have been studied to gain critical insights into the photocatalytic activity of the two materials.