Metal-Free Nitrogen-Doped Carbon Derived from g-C3N4/Glucose Composites for Singlet Oxygen-Dominated PMS Activation Toward Enrofloxacin Degradation

Enrofloxacin (ENR), a widely used veterinary fluoroquinolone, persists in the environment and resists conventional treatment. A metal-free nitrogen-doped carbon catalyst (N@C) was synthesized from graphitic carbon nitride (g-C3N4) and glucose via hydrothermal compositing and carbonization at 900 °C, and used to activate peroxymonosulfate (PMS) for ENR degradation. TEM, XRD, XPS, Raman spectroscopy, and N2 physisorption revealed a hierarchically porous architecture with a specific surface area of 578.6 m2 g−1 and 10.2 at% nitrogen. The N@C/PMS system removed over 99.9% of ENR in 20 min ([ENR]0 = 20 mg L−1, [PMS] = 0.2 mM, [N@C] = 5 mg L−1, 25 °C), with a rate constant of 0.4389 min−1. TOC removal reached 40% within 30 min at 1.0 mM PMS, and post-reaction XPS and XRD showed a preserved framework. Quenching tests, DPA probing, solvent isotope effects, and electron spin resonance (ESR) spectroscopy indicate a non-radical pathway dominated by singlet oxygen (1O2), initiated by heterolytic cleavage of the PMS peroxide bond at graphitic N sites. The catalyst retained >95% of its activity after four cycles and >93% removal in tap, river, and lake water. These findings provide a mechanistic basis for designing metal-free, matrix-tolerant persulfate activation systems for fluoroquinolone wastewater treatment.