Synergistic Vacancy-Doping Engineering in Porous C₃N₅ Nanosheets for Efficient Exciton Dissociation and ROS Generation

Polymeric C₃N₅ is a promising visible-light-responsive photocatalyst, yet its photocatalytic activity is limited by low specific surface area, high exciton binding energy, and sluggish oxygen activation kinetics. To address these limitations, porous C₃N₅ nanosheets co-modified with nitrogen vacancies and oxygen dopants (CN‑x) are constructed through acid-hydrothermal intercalation followed by thermal restructuring. The optimal sample, CN‑580, achieves a specific surface area of 66.95 m²/g (6.5 times that of pristine C₃N₅), and the porous architecture shortens charge migration distances. Experimental and density functional theory (DFT) studies reveal that oxygen doping induces local charge polarization, creating a built‑in electric field that lowers the exciton binding energy from 62.91 to 47.42 meV. Nitrogen vacancies provide favorable sites for O₂ adsorption and activation, thereby facilitating ROS generation. Consequently, CN‑580 delivers degradation rate constants for rhodamine B, methylene blue, and tetracycline that are 15.5‑fold, 6.0‑fold, and 8.9‑fold higher than those of pristine C₃N₅, respectively, and exhibits potent antibacterial activity against drug‑resistant bacteria. Electron paramagnetic resonance, radical trapping, and DFT calculations support a synergistic O₂ activation pathway in which ·O₂ ^- and ¹O₂ are the dominant ROS. This work presents a heterojunction-free design strategy for high-performance polymer photocatalysts by jointly regulating bulk charge separation and surface reaction kinetics.