Band engineering of single-halogen layered Sillén oxyhalide, BaBiO2X (X = Cl, Br, and I): The role of lone-pair effect in photocatalysts

Band structure engineering is an effective way to improve the performance of photocatalysis. Herein, layered oxyhalides, BaBiO2X (X = Cl, Br, and I), with single halogen layers were synthesized by using molten salt synthesis method. Density functional theory (DFT) calculation reveals that the valance band maximum (VBM) of BaBiO2X mainly consists of O 2p orbitals, not halogen p orbitals (Cl-3p, Br-4p, and I-5p), which means that this X1 oxyhalide owns the stability against self-degradation by photogenerated holes during the photocatalytic process. Simultaneously, with the increasing of atomic number from BaBiO2Cl to BaBiO2I, the band gap (Eg) decreases from 3.523 eV to 2.777 eV. Eventually, BaBiO2I exhibits the highest photocatalytic RhB degradation performance among all samples, mostly owning to the enhanced light absorption and improved separation and migration efficiency of photogenerated carriers. This study provides a new idea for designing bismuth-based photocatalysts by band engineering to solve environmental pollution. •The Sillen, BaBiO2X (X = Cl, Br, and I), were successfully synthesized.•BaBiO2I nanoplates show superior visible light photocatalytic activity.•Halogen substitution regulates the band structure of BaBiO2X.•Possible photocatalytic mechanisms have been discussed.