Converting peracetic acid activation by Fe 3 O 4 from nonradical to radical pathway via the incorporation of L-cysteine.

Recently, peracetic acid (PAA) based Fenton (-like) processes have received much attention in water treatment. However, these processes are limited by the sluggish Fe(III)/Fe(II) redox circulation efficiency. In this study, L-cysteine (L-Cys), an environmentally friendly electron donor, was applied to enhance the Fe ₃ O ₄ /PAA process for the sulfamethoxazole (SMX) abatement. Surprisingly, the L-Cys incorporation was found not only to enhance the SMX degradation rate constant by 3.2 times but also to switch the Fe(IV) dominated nonradical pathway into the ^• OH dominated radical pathway. Experiment and theoretical calculation result elucidated -NH ₂ , -SH, and -COOH of L-Cys can increase Fe solubilization by binding to the Fe sites of Fe ₃ O ₄ , while -SH of L-Cys can promote the reduction of bounded/dissolved Fe(III). Similar SMX conversion pathways driven by the Fe ₃ O ₄ /PAA process with or without L-Cys were revealed. Excessive L-Cys or PAA, high pH and the coexisting HCO ₃ ^- /H ₂ PO ₄ ^- exhibit inhibitory effects on SMX degradation, while Cl ^- and humic acid barely affect the SMX removal. This work advances the knowledge of the enhanced mechanism insights of L-Cys toward heterogeneous Fenton (-like) processes and provides experimental data for the efficient treatment of sulfonamide antibiotics in the water treatment.
Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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