Efficient non-radical Dominated activation of persulfate through magnetite nanoparticles for tetracycline oxidation in natural water systems: Mechanism Evaluation and DFT calculations

Antibiotic resistance has emerged in recent years, posing a threat to human health and the environment. There is promising evidence that Fe 3 O 4 nanomaterials can act as catalysts for the breakdown of antibiotics in aqueous systems. Herein, Fe 3 O 4 was synthesized using a hydrothermal technique, and its potential as a catalyst for tetracycline (TC) degradation in the persulfate (PS) system was explored. Highly crystalline (73.4 %) Fe 3 O 4 possessed a prominent octahedral and tetrahedral structure. After testing different combinations of Fe 3 O 4 dosage, PS concentration, pH, and temperature, the optimal conditions for removing about 86.7 % of the TC were 0.20 g/L Fe 3 O 4 , 8.0 mM PS, and pH around 8. In contrast to the more typically seen sulfate (SO 4 •− ) and hydroxyl (OH • ) radicals, quenching tests showed that the non-radical oxo-specie ( 1 O 2 ) predominated in TC degradation, which was also supported by density functional theory (DFT) calculations, when the O O bond was stretched, the free energy barrier of O O bond break (transition state) was 1.2 eV, followed by a thermodynamically favorable process to produce 1 O 2 . However, the reaction energy barrier (2.03 eV) for generating OH • and SO 4 •− on Fe 3 O 4 (4 4 0) was higher, making it difficult to trigger the reaction. Furthermore, electron spin resonance (ESR) tests validated the prominence of the 1 O 2 species in TC degradation. The stability experiments showed that the TC degradation efficiency remained at over 56 % after three cycles. Finally, natural water systems using lake and river water demonstrated that the Fe 3 O 4 catalyst was suitable for practical applications, with more than 70 % TC degradation. Based on these findings, Fe 3 O 4 nanomaterials showed non-radical dominant activation of PS as a potential candidate in practical applications for the degradation of organic pollutants in water systems.