Comparative investigation of diclofenac degradation by Fe2+/chlorine and Fe2+/PMS processes

Abstract

The degradation of diclofenac (DCF), a commonly used nonsteroidal anti-inflammatory drug, by Fe2+/chlorine and Fe2+/PMS processes was comparatively investigated. The influencing factors of pH, Fe2+ and oxidant dosage on DCF degradation efficiency were evaluated and optimized. Typically, with an initial solution pH of 5, an Fe2+ dosage of 70 μM, and a chlorine or PMS dosage of 70 μM, the degradation efficiency of DCF using the Fe2+/chlorine and Fe2+/PMS processes reached 94.2% and 79.7%, respectively, within 10 min. Quenching tests indicated the coexistence of •OH and RCS in the Fe2+/chlorine system, and both SO4●– and •OH were identified in the Fe2+/PMS system. In addition, Fe(IV) was also identified to participate in DCF degradation in two systems based on the oxidation of PMSO to PMSO2. The degradation products and pathways of DCF were elucidated by LC/TOF/MS analysis and DFT calculations. It was assumed that the degradation pathway of DCF involves hydroxylation, dechlorination, decarboxylation, cleavage of the C-N bond, and chlorine substitution. In addition, trichloromethane (TCM), dichloroacetaldehyde (DCAL), dichloroacetonitrile (DCAN) and trichloronitromethane (TCNM) were also detected in the Fe2+/chlorine process, and these chlorinated DBPs initially increased and then decreased with prolonged reaction time, indicating that Fe2+/chlorine is capable of controlling DBPs formation. Finally, the acute and chronic toxicity of DCF and its degradation products were evaluated by the ECOSAR program.