Bithiophene-engineered carbon nitride with boosted built-in electric field and n-π* transition for PMS activation and...

Carbon nitride (CN) shows great potential for photocatalytic water remediation, yet its real-world application is still hindered by inefficient charge separation-transport, insufficient visible-light absorption, and limited exposure of active sites. The widespread contamination of water bodies by persistent chlorinated phenols poses serious risks to ecosystems and human health. In this study, a bithiophene-functionalized graphitic carbon nitride (SCN-100) was synthesized via a one-step thermal copolymerization strategy for efficient visible-light-driven peroxymonosulfate (PMS) activation to degrade 2,4-dichlorophenol (2,4-DCP). The introduction of bithiophene rings not only induces a strong built-in electric field and promotes spatial charge separation, but also awakens the n-π* electronic transition and extends the optical absorption, as well as enhances the exposure of active sites. Compared with pristine CN, SCN-100 achieves complete 2,4-DCP removal within 60 min under visible light, and the rate constant of SCN-100/PMS/light system is 5.65 times of pure CN, 32 times of SCN-100/light and 3 times of SCN-100/PMS system. Comprehensive characterizations (XRD, FTIR, XPS, SEM, TEM, AFM, and BET) confirm that SCN-100 possesses an ultrathin, wrinkled nanosheet morphology with a larger specific surface area (144.6332 m² g^-1) and enhanced hydrophilicity. Photoelectrochemical analyses (PL, TR-PL, EIS, photocurrent and KPFM) demonstrate markedly improved charge separation and transfer efficiency. The dominant reactive species, degradation pathway and intermediate toxicity were systematically evaluated via radical quenching, ESR experiments, LC-MS and T.E.S.T. software. This work provides a promising metal-free photocatalyst for PMS-based water remediation, and advances the understanding of n-π* transition and built-in electric field synergy.