Degradation of diclofenac by H2O2 activated with pre-magnetization Fe0: Influencing factors and degradation pathways.

Diclofenac sodium (DCF) is frequently detected as a non-steroidal pharmaceutical in the aquatic environment. In this study, the degradation of DCF in two heterogeneous systems, pre-magnetization Fe0/H2O2 (Pre-Fe0/H2O2) and Fe0/H2O2 system, was comparably studied. Our findings proved that Pre-Fe0 could significantly improve the degradation and dechlorination of DCF due to the change of Fe0 characteristics after pre-magnetization. Compared with Fe0/H2O2 process, Pre-Fe0/H2O2 process has 2.1-7.0 times higher rate constant for DCF degradation at different H2O2 dosages (0.25-2.0 mM), initial pH (3.0-6.0) and Fe0 dosages (0.25-1.5 mM). The characterizations by X-ray Photoelectron Spectroscopy and Electron Paramagnetic Resonance confirmed that the enhancement attributed to the increase of Fe0 corrosion and fast generation of OH. In addition, preliminary degradation mechanism was elucidated by major products identification using UPLC-MS, through which the degradation intermediates, such as 4-hydroxy-diclofenac or 5-hydroxydiclofenac, 2,6-dichloroaniline, phenylacetic acid, 1,3-dichlorobenzene and 2-aminophenylacetic acid were identified. Hydroxylation, decarboxylation, CN bond cleavage and ring-opening involving the attack of OH or other substances, were the main degradation mechanism. Therefore, Pre-Fe0/H2O2 process, which does not need extra energy and costly reagents, is an efficient and environmental-friendly process to degrade DCF.