Engineering BiOBr/TpBD-COF S-scheme heterointerface via phase transformation strategy for boosted photocatalytic hydrogen generation

The construction of heterojunction is an effective way to promote the photoinduced charge carrier separation in spatial, thus accelerating the photocatalytic reaction. However, the regulation of interface properties, as a crucial factor in affecting the charge carrier diffusion process, still remains a significant challenge. In this work, BiOBr/TpBD-COF heterojunction was successfully constructed via a novel phase transformation strategy. Specifically, perovskite Cs₃Bi₂Br₉ was first synthesized and then in-situ transformed into BiOBr during the preparation of TpBD-COF procedure, thus obtaining BiOBr/TpBD-COF heterojunction with favorable interface. According to the in-situ X-ray photoelectron spectroscopy (XPS) characterization and electron paramagnetic resonance (EPR) analysis, the photogenerated electrons with weak reduction power transfer from BiOBr to TpBD-COF driven by the internal electric field under irradiation, conforming to S-scheme charge transfer mode. As a result, the photogenerated electrons and holes with strong redox abilities are spatially located on TpBD-COF and BiOBr surface, respectively, endowing the strong driving force toward the water splitting reaction. The optimized 10%BiOBr/TpBD-COF displayed remarkably enhanced photocatalytic hydrogen evolution rate (16.17 mmol⋅g⁻¹⋅h⁻¹) in comparison with TpBD-COF (5.18 mmol⋅g⁻¹⋅h⁻¹). This study will provide some novel inspirations for developing efficient COF-based S-scheme heterojunction photocatalysts.