Built-in electric field enables photocatalytic molecular oxygen activation into singlet oxygen over single-unit-cell...

Singlet oxygen (¹O₂)-dominated non-radical oxidation offers an ideal strategy for the selective elimination of pharmaceuticals and personal care products. However, activating the charge-transfer pathway for efficient ¹O₂ generation remains a great challenge due to rapid charge recombination. Herein, we synthesized single-unit-cell BiOI nanosheets (UBOI) (∼0.9-1.0 nm) featuring abundant surface oxygen vacancies (OVs) to create a built-in electric field (BIEF) that is ∼13.1 times stronger than in pristine multilayered BiOI. Such a significantly enhanced BIEF facilitates superior exciton dissociation and charge migration, driving molecular oxygen (O₂) activation from a conventional superoxide radical (•O₂^-)-dominated radical pathway to a ¹O₂-dominated non-radical pathway, achieving a ¹O₂ yield of 2.69 μmol L^-1. Crucially, the OVs are shown not to dictate the reaction pathway itself. Instead, they serve a dual role, facilitating charge separation and acting as the key catalytic sites for the charge transfer-mediated ¹O₂ evolution. As a result, UBOI achieves the complete degradation of acetaminophen within 60 min under visible light, exhibiting a reaction rate constant ∼11 times that of its bulk counterpart and ensuring a selective degradation with reduced intermediate toxicity. This work provides new insights into modulating charge dynamics and ROS selectivity in highly polarized photocatalytic systems.