Mechanistic insights into Z-scheme Cs3Bi2Br9/Bi2WO6 for photocatalytic benzyl alcohol oxidation

The carbonyl compounds synthesized from benzyl alcohol by selective photocatalysis have a wide range of applications in the chemical, pharmaceutical and food industries, while the fine chemical synthesis remains challenged by inefficient carrier separation and inadequate redox potential control in conventional semiconductor systems. The stability and eco-friendly attribute of lead-free bismuth halide perovskites emerge as promising photocatalysts for practical applications. Herein, we design and synthesize a Z-scheme heterojunction between Cs 3 Bi 2 Br 9 and Bi 2 WO 6 by an anti-solvent method. The optimized Cs 3 Bi 2 Br 9 /Bi 2 WO 6 composite demonstrates enhanced photocatalytic performance for benzyl alcohol oxidation, achieving 95 % conversion efficiency with 99 % benzaldehyde selectivity under AM 1.5G irradiation. Systematic in situ characterizations, including electron spin resonance, X-ray photoelectron spectroscopy and diffuse reflectance infrared Fourier-transform spectroscopy, evidence the Z-scheme charge transfer mechanism in Cs 3 Bi 2 Br 9 /Bi 2 WO 6 , track key intermediates during the oxidation pathway, and mechanistically identify superoxide radicals (• O 2 - ) as the predominant active species. This study not only advances the understanding of photocatalytic mechanisms in Z-scheme organic transformations but also provides a foundational framework for the design of efficient photocatalytic systems.