Peracetic acid concentration-driven active species switching in sulfur-modified iron-doped graphitic carbon nitride for adaptive degradation of organics.

Herein, a sulfur-modified iron-doped g-C₃N₄ composite (FSCN) was synthesized to activate peracetic acid (PAA) for organic micropollutant degradation. The FSCN/PAA system demonstrated exceptional catalytic performance surpassing control catalysts, achieving effective removal of multiple contaminants containing diverse electron-donating and -withdrawing functional groups. The results of quenching experiments and spectroscopic characterization analyses revealed concentration-dependent active species generation: hydroxyl radicals (HO^•) predominated at low PAA concentrations (25 μM), whereas high-valent iron species (Fe(IV/V)) became dominant at elevated PAA levels (400 μM). This distinctive switching behavior stems from the dual catalytic functionality of FSCN, which simultaneously activates PAA to generate Fe(IV/V) while catalyzing H₂O₂ decomposition to produce HO^•. The practicability of FSCN/PAA system was systematically validated through real wastewater treatment and continuous flow operation, and the results indicate that the system showed robust environmental compatibility. This work establishes a novel concentration-dependent active species regulation strategy through rational catalyst design and PAA dosage control, providing fundamental insights and technological advancement for advanced oxidation processes in water remediation.