Protonation-assisted exfoliation synthesis of P-Doped g-C3N4 for the highly efficient photocatalytic degradation of levofloxacin

• Acid-mediated protonation followed by thermal exfoliation enables concurrent nanoarchitectural engineering and electronic structure tailoring of g-C3N4 through phosphorus doping. • The optimized P-CN-4.2 exhibits a specific surface area of 35.15 m2 g−1, a narrowed bandgap of 2.66 eV, and significantly enhanced charge-separation efficiency as evidenced by photoelectrochemical measurements. • Under visible-light irradiation, 99 % levofloxacin degradation is achieved within 45 min, corresponding to a rate constant 3.8-fold higher than that of pristine g-C3N4. • The catalyst maintains >90 % degradation activity over seven successive cycles without detectable phosphorus leaching, underscoring its outstanding stability and reusability. Phosphorus‑doped graphitic carbon nitride nanosheets (P-CN-4.2) were synthesized via a synergistic strategy combining phosphoric‑acid‑mediated protonation and thermal exfoliation. Under visible light, P-CN-4.2 exhibits optimal performance, achieving 99% degradation of levofloxacin within 45 min, with a photocatalytic rate constant 3.8 times that of pristine g‑C 3 N 4 . The enhanced activity originates from the combined effects of exfoliation‑induced morphological engineering and electronic structure tailoring by phosphorus doping. XRD, TEM, and UV‑Vis DRS characterizations confirm the transformation of bulk layered aggregates into ultrathin nanosheets while preserving the crystalline heptazine skeleton. Concurrently, lattice P‑N bonding narrows the bandgap from 2.76 eV to 2.66 eV, shifts the conduction band upward by 0.17 eV, prolongs carrier lifetime, and enhances visible‑light absorption. Furthermore, P-CN-4.2 retains >90% activity after seven consecutive cycles without detectable phosphorus leaching, underscoring its excellent stability and reusability. This work establishes a scalable synthesis of high‑efficiency metal‑free photocatalysts and delivers in‑depth mechanistic insights for the remediation of antibiotic‑contaminated water.