Reaction Pathway Tuning between Electron Transfer-Mediated Degradation and Polymerization in Fe-MoS 2 -Based Persulfate Activation System

Persulfate-based advanced oxidation processes for organic pollutant removal have been reported to proceed through both an electron transfer-based degradation pathway and a polymerization reaction. However, there is an insufficient understanding of the effect of oxidant dosage on the reaction pathway, and the tuning of the reaction pathway between mineralization and polymerization has not yet been reported. In this study, we report an Fe-doped MoS2/peroxydisulfate (PDS) system for phenolic compounds (PCs) removal. This system undergoes a high-valent iron pathway and has a faster reaction rate when oxidizing PC with a higher electron donating capability. More importantly, we elucidate that a polymerization reaction exists in the Fe-MoS2/PDS system, and the oxidant dosage significantly affects the reaction pathway. Low oxidant dosage facilitates the polymerization reaction process, and high oxidant dosage normally leads to electron transfer-based degradation. It is also found that 2,6-dimethylphenol (DMP), 4-methoxy-phenol (MOP), p-cresol (MP), methylparaben (MeP), and nitrophenol (NP) have a high degree of polymerization trend among the 11 tested PCs, which stems from their polymer products being more easily adsorbed on the catalyst surface. This study demonstrates the wide presence of the polymerization process in the PDS activation system and verifies the impact of oxidant dosage and type of PCs on the transformation of the reaction pathway.