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In a recent paper published in Nature Communications, Prof. Timothy Noël and co-workers at the University of Amsterdam's Van 't Hoff Institute for Molecular Chemistry (HIMS) present the true nature of the catalytically active species in photocatalytic reactions using bismuth oxide semiconductor. Bi2O3 is a popular photocatalyst for light-induced organic transformations that provide a sustainable alternative for more traditional synthetic pathways.

Two reaction mixtures
Left: Initial reaction mixture. Right: Resultant reaction solution. Image: HIMS / Nature.

The researchers describe their investigation upon observing a remarkable phenomenon where the initially heterogeneous reaction mixture turned homogeneous after a while. They were able to trace this back to the formation of a catalytically active homogeneous bismuth species which is the true photocatalyst. Their findings were supported by DFT theoretical calculations performed at the Institute of Chemical Research of Catalonia, Spain (ICIQ).

Bi2O3 has become a popular photocatalyst to drive light-induced organic transformations as a 'green' alternative for traditional synthetic pathways. It combines a response to visible light with non-toxicity, a solid state nature, high availability and a low price. In some cases, it can replace the use of metal complexes based on expensive and non-abundant ruthenium and iridium photocatalysts.

Abstract

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 BinBrm 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.

Paper

Paola Riente, Mauro Fianchini, Patricia Llanes, Miquel Pericàs & Timothy Noël: Shedding light on the nature of the catalytically active species in photocatalytic reactions using Bi2O3 semiconductor. Nat. Comm. 12, 625 (2021). DOI: 10.1038/s41467-020-20882-x

Links

News item ICIQ: Brightening the future of semiconductor-based photocatalytic processes
Chemistry Views: What Is the Active Species in Reactions using Bi2O3 as a Photocatalyst?
Website research group Prof. Timothy Noël: Noël Research Group