Synergistic activation of peroxymonosulfate by Fe 3 O 4 /diatomite composite for efficient tetracycline degradation: mechanistic insights from experiments and density functional theory

BACKGROUND Tetracycline (TC) is a persistent antibiotic contaminant in water; because conventional treatments cannot adequately remove it, its persistence raises concerns about antibiotic resistance. To enhance degradation, magnetic Fe 3 O 4 /diatomite (DT) composites were synthesized via hydrothermal methods using natural porous DT to prevent the aggregation of Fe 3 O 4 nanoparticles and improve the reusability of the catalyst. RESULTS Characterization confirmed the successful Fe 3 O 4 loading onto DT with uniform elemental distribution, preserved pore structure, redox‐active Fe sites, and high thermal stability. The composite with 10% Fe 3 O 4 (10‐FDT) exhibited superior catalytic activity compared to Fe 3 O 4 or peroxymonosulfate alone. Under optimized conditions (25 mg L −1 TC, 0.20 g L−1 10‐FDT, 2.5 mmol L −1 peroxymonosulfate, pH 4), 87.4% TC degradation was achieved in 3 h. Degradation efficiency improved with catalyst and oxidant dosage, moderate acidity, and elevated temperature, but was inhibited by chloride ions and humic acid, while carbonate and dihydrogen phosphate ions enhanced the performance of the system. Radical quenching and electron spin resonance analyses revealed hydroxyl and sulfate radicals, alongside a dominant non‐radical singlet oxygen pathway linked to oxygen vacancies in DT. Density functional theory showed that electron transfer from DT to Fe 3 O 4 promotes oxidant adsorption and lowers the activation barriers for the formation of singlet oxygen. Mass spectrometry and molecular orbital analyses indicated TC degradation via functional group loss and ring opening. CONCLUSION The 10‐FDT composite proves to be an effective and stable catalyst for advanced oxidation processes, retaining 68.4% of its catalytic activity after three cycles and maintaining over 75% degradation efficiency in real wastewater samples. This highlights its strong potential for practical, scalable wastewater treatment applications.