Heteroatom-modified spinel ferrite MnFe2O4 for enhanced degradation of tetracycline via PMS/H2O2 activation

Tetracycline (TC) persistence in aquatic systems poses significant ecological and human health risks, due to its toxicity and resistance to conventional biodegradation. In this study, sulfur and nitrogen modification strategies were employed to enhance the catalytic performance of spinel ferrite MnFe 2 O 4 for TC degradation via H 2 O 2 and peroxymonosulfate (PMS) activation. The catalysts were characterized using SEM, XRD, VSM, CV, and ICP-OES to elucidate the effects of heteroatom modification on morphology, crystal structure, magnetic separability, and metal leaching behavior. S modification markedly enhanced both H 2 O 2 and PMS activation capabilities. The optimized S/MnFe 2 O 4 -5/H 2 O 2 system removed 82 % TC (50 mg/L) within 20 min, an eightfold increase in the reaction rate compared to the unmodified MnFe 2 O 4 /H 2 O 2 . This system maintained high efficiency across a broad pH range (3–11). In contrast, nitrogen modification selectively improved PMS activation, with the optimal N/MnFe 2 O 4 -3/PMS system degrading 74 % TC in 30 min, twice the degradation rate of MnFe 2 O 4 /PMS, and exhibiting minimal metal leaching with excellent recyclability. Scavenger studies confirmed that ·OH constitutes the dominant reactive oxygen species (ROS) in S/MnFe 2 O 4 -5/H 2 O 2 systems, while both ·OH and ·SO 4 - contribute significantly in N/MnFe 2 O 4 -3/PMS systems. Sulfur species act as electron mediators, facilitating the Fe/Mn redox cycle and enhancing ROS generation, whereas zero valence iron (Fe 0 ) formed during nitrogen modification serves as an efficient electron donor to activate PMS. Degradation pathway analysis and toxicity predictions confirmed a substantial reduction of TC environmental hazards. This work provides fundamental insights into the structure–activity relationships of heteroatom-modified MnFe 2 O 4 catalysts, and establishes practical design principles for robust advanced oxidation process catalysts in antibiotic remediation.