Defect-activated and thermally exfoliated under N2 flow g-C3N4 photocatalysts for the degradation of ciprofloxacin as a model emerging aquatic pollutant

Defective and exfoliated graphitic carbon nitride (g-C 3 N 4 ) photocatalysts with nitrogen vacancies and cyanogroups were synthesized via single-step thermal polymerization of urea (CNU 2 ), followed by one and two-step exfoliation (UEX1, and UEX2) under a nitrogen atmosphere. The materials were extensively characterized using XRD, SEM-EDS, ATR-FT-IR, Raman, UV-Vis DRS, PL spectroscopy, TRPL, N 2 porosimetry, elemental analysis, and contact angle measurements to confirm defects and correlate structure and surface properties to photocatalytic efficiency towards ciprofloxacin (CIP) degradation in various aqueous matrices under simulated solar and visible light. The optimal photocatalyst (UEX1) achieved complete CIP degradation in very short times about 10 min (k = 0.605 min⁻¹), and total mineralization in 120 min in ultra-pure water matrix. Under realistic conditions—including varying pH, tertiary treated wastewater, mineral ions, and humic acids—complete CIP degradation occurred in 5 min (k = 0.712 min⁻¹). Thirteen transformation products were identified by UHPLC-LTQ-Orbitrap-MS, revealing pathways involving defluorination, quinolone ring oxidation, hydroxylation, and piperazine ring dealkylation/oxidation. Toxicity assessment using Aliivibrio fischeri indicated 35.89% bioluminescence inhibition, while ECOSAR predicted only two TPs as highly toxic to Daphnia . Mineralization was confirmed via TOC and ion analyses, showing complete release of F⁻, NO 2 ⁻, NO 3 ⁻, and total organic carbon removal. These findings demonstrate that nitrogen-deficient g-C 3 N 4 photocatalysts efficiently degrade and mineralize CIP, providing mechanistic insight and environmental safety assessment for pharmaceutical wastewater remediation. • Nitrogen-defective g-C 3 N 4 with -NHx, -CN groups were synthesized and exfoliated under N 2 • One-step exfoliated g-C 3 N 4 showed the optimum photocatalytic properties • Bulk and exfoliated g-C 3 N 4 exhibited fast ciprofloxacin degradation/mineralization • Dominant oxidant species were O 2 •- and secondarily hydroxyl radicals ( • OH). • Null toxicity on Aliivibrio fischeri and complete degradation of TPs after 2 h treatment.