Degradation Efficiency and Mechanism of Antibiotics by Sodium Hydroxide-Activated Hydrogen Peroxide Driven by Alkaline Environment

School of Inner Mongolia Normal University, Hohhot, 011517, China

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Abstract

Ciprofloxacin (CIP), a typical fluoroquinolone antibiotic, exhibits strong environmental persistence, easy accumulation and biological toxicity. Its long-term residual in aquatic environments may induce microbial drug resistance and threaten the safety of ecological systems. Aiming at the problem that traditional Fenton/photo-Fenton reactions are limited to acidic pH, this study developed a high-efficiency novel photo-Fenton system based on Cu-C₃N₅ catalyst activating hydrogen peroxide (H₂O₂) under alkaline conditions for the degradation of CIP in water. By systematically investigating the effects of key parameters such as pH, H₂O₂ concentration and catalyst dosage, it was found that a strong alkaline environment (pH 10.3) could significantly accelerate the degradation kinetic rate of CIP. Under the optimal conditions of catalyst dosage 0.3 g·L-1, CIP concentration 0.5 mg·L-1, H₂O₂ concentration 20 mM and pH 10.3 (adjusted by 0.1 mL NaOH), the reaction showed the highest normalized rate constant. Mechanism studies indicated that the alkaline environment played a dual regulatory role. On the one hand, it induced the deprotonation of CIP molecules, altered the local electron cloud distribution of the target pollutant, and reduced the cleavage energy barrier of key chemical bonds, making them easier to break. On the other hand, OH^- contributed an additional negative charge (about 8%) to the hydrogen bond network of water, which significantly enhanced the interfacial electron transfer efficiency. This process synergistically promoted the activation of the O-O bond in H₂O₂ to form a high-energy transition state, extended the lifetime of reactive oxygen species such as singlet oxygen, and drove the directional collision of reaction molecules. This work not only reveals the key regulatory mechanism of alkaline microenvironment in heterogeneous Fenton-like reactions, but also breaks the dependence of traditional Fenton systems on acidic conditions. It provides a new theoretical basis and regulatory strategy for the development of universal advanced oxidation technologies suitable for neutral to alkaline wastewater, and has important scientific significance for promoting the efficient treatment of refractory pollutants in complex water bodies.