An atomic insight into BiOBr/La2Ti2O7 p–n heterojunctions: interfacial charge transfer pathway and photocatalysis mechanism

Abstract

Novel p–n heterojunction BiOBr/La₂Ti₂O₇ nanocomposites were synthesized through a hydrothermal method and applied to photocatalytic NO removal. The reaction course of visible light photocatalytic NO removal was dynamically monitored by in situ FT-IR, and free radicals were captured by electron spin resonance (ESR). The reaction mechanism of photocatalytic NO oxidation on BiOBr/La₂Ti₂O₇ was revealed. Density functional theory (DFT) calculations show that when BiOBr comes into contact with La₂Ti₂O₇ to form a p–n heterojunction, the charge could transfer from the La atom of La₂Ti₂O₇ to the O atom of BiOBr, leading to the accumulation of negative charge in the BiOBr region. When the Fermi levels of BiOBr and La₂Ti₂O₇ are in equilibrium, an internal electric field (IEF) from La₂Ti₂O₇ to BiOBr is established simultaneously. Under visible light illumination, the photogenerated electrons (e⁻) in the conduction band (CB) of BiOBr would migrate to the CB of La₂Ti₂O₇ with the assistance of the IEF, and the holes (h⁺) are gathered on the valence band (VB) of BiOBr. With this IEF, the charge carrier separation on BiOBr/La₂Ti₂O₇ was highly promoted and thus the visible light photocatalytic NO removal performance was enhanced. This work provides a new perspective on the understanding of the construction mechanism of p–n type heterostructures and the mechanism of gas–solid phase photocatalytic reactions.