A sulfate radical based ferrous–peroxydisulfate oxidative system for indomethacin degradation in aqueous solutions

Abstract

The degradation of indomethacin (IM) by ferrous ion-activated potassium peroxydisulfate (Fe²⁺/PDS) was investigated. We aimed to determine the optimal conditions for the removal of IM under different concentrations of Fe²⁺and PDS, evaluate the effects of operational parameters (solution pH, humic acid (HA), N₂ bubbling and persulfate species), and propose the degradation mechanism of IM by the Fe²⁺/PDS system. The sequential addition of Fe²⁺ led to an improvement in the IM degradation and TOC removal efficiency. When the molar ratio of IM/PDS/Fe²⁺ was 1 : 1.5 : 2, the IM was almost completely degraded. Restrictions to the degradation efficiency of IM were caused by increasing the solution pH, bubbling with nitrogen, or through the addition of HA. A low concentration of Cl⁻ had no effect on the reaction, while a high concentration led to a dramatic inhibitory effect. In addition, quenching experiments revealed that SO₄˙⁻ was the major active radical for the degradation of IM by ferrous ion-activated peroxydisulfate. Based on the identification of transformation products by liquid chromatography-mass spectrometry (LC-MS/MS), the pathways of the ferrous–peroxydisulfate oxidative system for the degradation of IM were tentatively proposed.