Shedding light on the nature of the catalytically active species in photocatalytic reactions using Bi2O3 semiconductor

The importance of discovering the true catalytically active species involved in photocatalytic systems allows for a better and more general understanding of photocatalytic processes, which eventually may help to improve their efficiency. Bi₂O₃ has been used as a heterogeneous photocatalyst and is able to catalyze several synthetically important visible-light-driven organic transformations. However, insight into the operative catalyst involved in the photocatalytic process is hitherto missing. Herein, we show through a combination of theoretical and experimental studies that the perceived heterogeneous photocatalysis with Bi₂O₃ in the presence of alkyl bromides involves a homogeneous Bi_nBr_m species, which is the true photocatalyst operative in the reaction. Hence, Bi₂O₃ can be regarded as a precatalyst which is slowly converted in an active homogeneous photocatalyst. This work can also be of importance to mechanistic studies involving other semiconductor-based photocatalytic processes.