Fe3O4@CQDs/dielectric barrier discharge plasma coupled system for enrofloxacin degradation: efficiency, influencing factors, and synergistic mechanism

The escalating residue of enrofloxacin (ENR) in aquatic environments exacerbates antibiotic resistance, necessitating efficient degradation technologies. Herein, a Fe₃O₄@CQDs/dielectric barrier discharge (DBD) plasma system was constructed to degrade ENR, with a focus on unraveling the synergistic mechanism. Fe₃O₄@CQDs are synthesized via the hydrothermal method and exhibit enhanced specific surface area, abundant surface functional groups (hydroxyl, carbonyl), and efficient Fe(III)/Fe(II) redox cycling performance. Optimal degradation of ENR was achieved at 20 kV discharge voltage, 0.3 g/L Fe₃O₄@CQDs dosage, with a 95% removal efficiency at 30 min and a synergistic factor of 2.66. The system showed robust anti-interference against pH fluctuation, Cl⁻, ${\text{CO}}_3^{2-}$, and humic acid. Degradation intermediates and density functional theory analysis revealed degradation pathways (defluorination, decarboxylation, demethylation) with intermediates of reduced toxicity. •OH, •$O_2^{-}$, ¹O₂, ONOO⁻, H₂O₂, and O₃ were confirmed key reactive species with e⁻ as the initiator. The primary synergistic mechanisms of Fe₃O₄@CQDs/DBD involve the plasma providing initial energy and active species, while Fe₃O₄@CQDs offers active sites. Additionally, Fe(III)/Fe(II) can drive the Fenton reaction for H₂O₂ generation and the conversion of O₃ to •OH, inhibiting e⁻-h⁺ recombination and enhancing oxidation. Besides, Fe₃O₄@CQDs retained 77% activity after 4 cycles. This study highlights the Fe₃O₄@CQDs/DBD synergism, offering a sustainable strategy for antibiotic degradation in complex matrices.