Magnetic MoS/FeO composite as an effective activator of persulfate for the degradation of tetracycline: performance, activation mechanisms and degradation pathways.

The activated persulfate (PS) process could produce sulfate radical (SO) and rapidly degrade organic pollutants. The application of FeO as a promising PS activator was limited due to the rapid conversion of Fe to Fe on its surface. Mo on MoS surface could be used as a reducing site to convert Fe to Fe, but the separation and recovery of MoS was complex. In this study, MoS/FeO was prepared to accelerate the Fe/Fe cycle on FeO surface and achieved efficient separation of MoS. The results showed that MoS/FeO was more effective for PS activation compared to FeO or MoS, with a removal efficiency of 91.8% for 20 mg·L tetracycline (TC) solution under the optimal conditions. Fe and Mo on MoS/FeO surface acted as active sites for PS activation with the generation of SO, •OH, •O, and O. Mo acted as an electron donor to promote the Fe/Fe cycling and thus improved the PS activation capability of MoS/FeO. The degradation pathways of TC were inferred as hydroxylation, ketylation of dimethylamino group and C-N bond breaking. This study provided a promising activated persulfate-based advanced oxidation process for the efficient degradation of TC by employing MoS/FeO as an effective activator.