Design of lateral and vertical Bi₄O₅I₂/BiOCl heterojunctions with different charge migration pathway for efficient photoredox activity

As 2D heterojunction photocatalysts, lateral heterojunctions (LHs) formed based on chemical bonding generally exhibit much higher photocarrier separation efficiency than vertical heterojunctions (VHs) formed by van der Waals bonds. However, little is known about the different detailed interfacial structures and photocarrier separation mechanisms of the two heterojunctions. Herein, 2D BiOCl and Bi₄O₅I₂ were selected as model building blocks to construct BiOCl/Bi₄O₅I₂ VHs and LHs. The LHs with direct charge carrier transport channels show stronger interfacial electric field and higher charge transfer efficiency than the VHs. The photogenerated charge carrier migration pathway in the LHs follows a Z-scheme model, while the VHs fits a type II model. As a result, the BiOCl/Bi₄O₅I₂ LHs exhibited higher redox performance than the VHs, which is 1.55, 1.56 and 2.1 times better for H₂ production, Cr(VI) photoreduction and phenol photodegradation, respectively. This study demonstrates a new approach to constructing highly efficient facet-dependent 2D heterojunction photocatalysts.