Nonradical pathway dominated activation of peroxymonosulfate by ZnFe₂O₄/C composites to eliminate tetracycline hydrochloride: Insight into the cycle of Zn/Fe and electron transfer

Magnetic ZnFe₂O₄ nanoparticles show promising as heterogeneous catalysts in peroxymonosulfate (PMS) activation because of their ease of separation and good reusability. However, the low catalytic activity and easy agglomeration in clusters or clumps limit the application of ZnFe₂O₄ nanoparticles. Herein, ZnFe₂O₄ nanoparticles embedding into carbon substrate are prepared. Owing to the anchoring effect of carbon substrate and the improved electron transfer for ZnFe₂O₄ nanoparticles, the as-prepared magnetic ZnFe₂O₄/C composites exhibit efficiently catalytic activity in PMS activation, in which 92.0% of tetracycline hydrochloride (TC) can be eliminated. Moreover, the composites show a wide pH adaptation range (3.04–10.99) and good stability. The catalytic oxidation of TC is mainly based on the nonradical pathways, including contributions of ¹O₂ and electron transport. The high performance of ZnFe₂O₄/C in PMS activation is mainly attributed to the accelerated redox cycles of Fe³⁺/Fe²⁺ and Zn²⁺/Zn⁺ and the improved electron transfer. Three possible TC degradation pathways were proposed, and the biotoxicity assessment results further confirm the high efficiency of the ZnFe₂O₄/C/PMS system. This work provides a simple strategy for the preparation of magnetic ZnFe₂O₄/C heterogeneous catalyst and a new insight into PMS activation, which promotes the application of spinel nanomaterials in environmental remediation.