Locally Asymmetric BiOBr for Efficient Exciton Dissociation and Selective O2 Activation toward Oxidative Coupling of Amines

Two-dimensional (2D) layered photocatalysts with highly ordered out-of-plane symmetry usually display robust excitonic effects, thus being ineffective in driving catalytic reactions that necessitate unchained charge carriers. Herein, taking 2D BiOBr as a prototype model, we implement a superficial asymmetric [Br-Bi-O-Bi] stacking in the out-of-plane direction by selectively stripping off the top-layer Br of BiOBr. This local asymmetry disrupts the diagnostic confinement configuration of BiOBr to urge energetic exciton dissociation into charge carriers and further contributes to the emergence of a surface dipole field that powers the subsequent separation of transient electron-hole pairs. Distinct from the symmetric BiOBr, which activates O₂ into ¹O₂ via an exciton-mediated energy transfer, surface asymmetric BiOBr favors selective O₂ activation into ·O₂^- for a broad range of amine-to-imine conversions. Our work here not only presents a paradigm for asymmetric photocatalyst design but also expands the toolkit available for regulating exciton behaviors in semiconductor photocatalytic systems.