Enhanced degradation of tetracycline over FeS-based Fenton-like process: Autocatalytic decomposition of HO and reduction of Fe(III).

This study constructed a FeS-based Fenton-like process to explore the degradation of TTC in the presence of copper ions. The acidic condition of pH 3 was more favorable to the HO decomposition and TTC degradation, and it was slightly enhanced by Cu(II). The production of •OH from HO was revealed through radical scavenging and benzoic acid probe experiments, and the ratio of HO decomposition to •OH production was about 1-1.5, which is comparatively consistent with the theoretical ratio. FeS-based Fenton process was proved to be a homogenous system, the slow release of Fe(II) source and the autocatalytic cycle of Fe(III) to Fe(II) resulting from the reductive species of TTC and dissolved S(-II) improved the production of •OH and the degradation of TTC, which was proved by comparing TTC degradation, TOC removal, HO decomposition and Fe(II) concentration with different iron sources (FeS, Fe(II) and Fe(III)) and external addition of dissolved S(-II). The possible degradation pathways of TTC were subsequently inferred according to the detected products by LC-MS. Understanding these autocatalytic processes is essential to reveal the transformation of redox-active substances in environments and may have potential significance in applying FeS-based Fenton-like process for the treatment of wastewater containing reductive organic matters.