Unexpected tetracycline antibiotics degradation in the Fenton process under near-neutral pH conditions: Performance and mechanism

Fenton process is one of the widely used advanced oxidation processes, but its application is mainly limited by its narrow working pH range (pH 2.0–4.0). In this work, we observed the unexpected degradation of tetracyclines (TCs) in the Fenton process under near-neutral pH conditions without introducing extra energy or chemicals. We found that TCs could be effectively degraded in the Fenton process at pH 5.0–7.0, although other organic contaminants, such as phenol and acetaminophen, were hardly degraded under the same conditions. Multiple lines of evidence, including UV-spectra, ¹H NMR spectra, calculation of complexation constants, and analysis of transformation products, revealed that the complexation of Fe(II) with TCs played a crucial role in driving the degradation of TCs in this process and that the BCD ring of TCs was the key structure. Moreover, the degradation of TCs was attributed to the Fe(Ⅱ)-TCs complex-induced electron transfer between H₂O₂ and TCs during this process under near-neutral pH conditions. Additionally, the degradation of TCs in this process was not sensitive to interference from the water matrix. The findings of this study provide new insight into the development of wastewater treatment technologies based on the properties of organic contaminants.