Single-Atom Cu-Induced Electronic Localization Enhances Charge Transfer in g-C₃N₄/PyBT S-Scheme Photocatalyst

Efficient singlet-oxygen-assisted photocatalytic oxidation requires both effective charge separation and well-controlled excited-state pathways, yet achieving both remains challenging in organic semiconductor heterojunctions. Herein, a Cu single-atom-engineered S-scheme heterojunction is developed by coupling Cu-modified graphitic carbon nitride (Cu─CN) with an imine-linked covalent organic framework (PyBT). The atomically dispersed Cu sites induce pronounced interfacial charge localization, strengthen the internal electric field (IEF), and accelerate directional charge transfer across the heterojunction. Quantitative analysis shows that the IEF intensity of Cu─CN/PyBT is enhanced to 1.97 times that of its Cu-free counterpart, enabling markedly improved spatial separation of photogenerated carriers. More importantly, the enhanced charge separation promotes intersystem crossing and boosts singlet oxygen generation. Consequently, the optimized heterojunction achieves 94.2% styrene conversion with 79.2% benzaldehyde selectivity under simulated sunlight. This work provides a feasible strategy for strengthening charge-transfer kinetics while activating singlet-oxygen chemistry in organic semiconductor heterojunction photocatalysts.