Enhanced photoactivity and selectivity over BiOI-decorated Bi2WO6 microflower for selective oxidation of benzylamine: Role of BiOI and mechanism

The importance of developing effective and selective photocatalytic materials to realize efficient renewable energy-based organic synthetic processes, such as selective oxidation of benzylamines and its derivatives to the corresponding imines has become more apparent in recent years. Here we present the first reported BiOI/Bi2WO6 (BI/BW) microflower heterostructure as a visible-light-driven photocatalyst for such reactions. By decorating the hydrothermally prepared BW with BI via successive ionic layer adsorption and reaction (SILAR) method, benzylamine conversion is improved from 68 % to 92 % as compared to undecorated. Furthermore, selectivity to desired imine product is substantially increased from 59 % to 95 %. These outstanding performances are attributed to enhanced electron-hole separation and transfer efficiency as well as a greater preference for adsorption of benzylamine compared to the imine products and extended visible-light absorption range inherited from BI component as supported by competitive adsorption studies, ultraviolet–visible diffuse reflectance spectroscopy, and photoelectrochemical experiments. Possible mechanisms, band energy diagram, and decisive roles of O2−[rad] and h+ in the selective transformation of benzylamine were proposed based on Mott-Schottky, scavenging, and electron paramagnetic resonance radical trapping experiments. This work highlights a simple approach for improving photocatalytic activity and selectivity which are highly desirable in renewable energy-based chemical synthetic processes.