Photochromic Bi2WO6/BiOBr ultrathin nanosheet heterojunctions for the efficient photocatalytic synthesis of imine via toluene and aniline coupling

Abstract

The photocatalytic activation of inert C–H bonds, followed by cross-coupling reactions driven by semiconductors, represents an important strategy in organic synthesis. However, the photocatalytic synthesis of imines via toluene and aniline coupling over semiconductor photocatalysts remains a significant challenge owing to the high C–H bond dissociation energy of toluene and poor charge separation and transfer efficiency of photocatalysts. Herein, we report Bi₂WO₆/BiOBr ultrathin nanosheet heterojunctions (UNHs) with photochromic behaviors for the photocatalytic oxidation of toluene, followed by coupling with aniline to synthesize imines. The heterojunctions achieve a 99% imine yield, which is 7 and 5 times higher than that of pure Bi₂WO₆ (14%) and BiOBr (20%) nanosheets, respectively. The Bi₂WO₆/BiOBr UNHs exhibit outstanding photocatalytic performance owing to the synergistic effect of the photochromism-induced W⁶⁺/W⁵⁺ species and heterojunction engineering that expedites the separation and transfer of photogenerated charges, provides active sites for O₂ adsorption and activation to form superoxide radicals (O₂˙⁻), and promotes the photooxidation of toluene to benzaldehyde and then cross-coupling with aniline to produce imines under 405 nm light irradiation. The present investigation offers a promising approach to the development of high-performance photocatalysts via the combination of photochromism and heterojunction engineering.