In-situ construction of BiOBr/Bi2WO6 S-scheme heterojunction nanoflowers for highly efficient CO2 photoreduction: Regulation of morphology and surface oxygen vacancy

The improvements of charge transfer efficiency and CO2 capture ability are of particular importance to the photocatalytic CO2 reduction activity of semiconductor photocatalysts. Herein, a BiOBr/Bi2WO6 S-scheme heterojunction with intimate interfacial contact is in-situ synthesized by a facile one-step hydrothermal method. The nanoflower morphology of the heterojunction is elaborately regulated based on the "allometric growth" mechanism, while the concentration of surface oxygen vacancies (SOVs) is readily tuned by low-temperature calcination duration. Due to the unique nanoflower morphology and rich SOVs, the CO2 capture ability is significantly enhanced, confirmed by the CO2 adsorption isotherms and density functional theory (DFT) calculations. The construction of S-scheme heterojunction and the introduction of SOVs also lead to the remarkably improved efficiency of charge separation and transfer. The BiOBr/Bi2WO6 heterojunction exhibits excellent photocatalytic CO2 reduction activity with a CO production rate of 55.17 mu mol.g(-1).h(-1) without using any sacrificial agent and cocatalyst, surpassing most reported photocatalysts. In addition, the formation of key intermediate *COOH during CO2 photoreduction on the photocatalyst surface is determined by in-situ FT-IR spectra. This work not only provides a new strategy for the construction of highly efficient S-scheme heterojunctions, but also sheds light on the optimization of photocatalytic performance through defect and morphology engineering.