Interfacial charge modulation in porphyrin-based COF/C3N5 S-scheme heterojunction for efficient metal-free peroxymonosulfate photoactivation

The efficacy of peroxymonosulfate (PMS) activation is critically dependent on interfacial charge dynamics in photocatalytic systems. While covalent organic frameworks (COFs) show promise, their performance is often limited by suboptimal charge separation. Herein, we construct a metal-free S-scheme heterojunction by integrating TphDha COF with C 3 N 5 to achieve precise interfacial charge modulation. This unique architecture, stabilized by intramolecular hydrogen bonds, establishes a built-in electric field that drives the directed migration and spatial separation of photogenerated carriers, thereby preserving their high redox potential. The optimized heterostructure exhibits significantly enhanced visible-light absorption and charge separation efficiency, which synergistically boosts the activation of PMS. Under visible light irradiation, the system achieves a superior tetracycline degradation efficiency of 96.9% and maintains over 90% efficiency after multiple cycles, demonstrating remarkable catalytic stability and reusability. The interfacial charge transfer mechanism was elucidated through in-situ characterization and theoretical calculations. Furthermore, the degradation pathways, toxicity evolution of intermediates, and the system's efficacy in continuous-flow operation, real water matrices, and complete bacterial inactivation were comprehensively investigated, underscoring its practical potential for environmental remediation. This work provides profound insights into interface engineering for designing efficient metal-free catalytic systems.