Peroxydisulfate degradation of diclofenac sodium activated by nZVI@MoS2: Key roles of superoxide radicals in the free radical pathway and electron transfer in the nonradical pathway

Abstract

Diclofenac sodium (DCF) has potential biological toxicity and is difficult to degrade through conventional methods; therefore, there is a pressing imperative to develop an approach to address this environmental predicament. In this work, nZVI@MoS2 was synthesized via liquid-phase reduction to activate peroxydisulfate (PDS) for the degradation of DCF. The results demonstrated efficient degradation of DCF within 30 min with the nZVI@MoS2/PDS system. Quenching experiments, electron paramagnetic resonance (EPR) spectroscopy, steady-state concentration calculations, and electrochemical experiments demonstrated that DCF predominantly underwent degradation through an O2−-dominated free radical pathway and an electron transfer-dominated nonradical pathway. The nZVI@MoS2 composite promoted the Fe2+/Fe3+ cycle, generated O2− and showed exceptional electrochemical performance in enhancing electron transfer. The paths for DCF degradation were revealed via HPLC–MS analyses. Toxicological assessment software revealed reduced toxicity of DCF. This study presents a novel approach for the degradation of wastewater containing pharmaceuticals and personal care products (PPCPs).