Mechanistic differences in ce-MoS₂ catalytic activation of peroxides: Pathway divergence and reactive species roles

Two-dimensional MoS₂-based advanced oxidation processes (AOPs) have recently shown significant promise in wastewater treatment. However, the activation of different oxidants leads to distinct degradation mechanisms and transformation pathways for organic pollutants. In this study, we explored the distinct mechanisms of chemical exfoliation (ce-MoS₂) in activating peroxymonosulfate (PMS), peroxydisulfate (PDS), and H₂O₂ for the degradation of roxarsone (ROX). The removal efficiency of ROX is in the order of ce-MoS₂/PMS > ce-MoS₂/PDS > ce-MoS₂/H₂O₂, with the highest total organic carbon (TOC) removal rate achieved by ce-MoS₂/PDS. The ce-MoS₂/PMS system primarily generates radicals (·OH, SO₄^·-) and oxidizes ROX to As(V), while PDS is weakly adsorbed onto the surface vacancies (SVs) to form surface complexes (PDS*), facilitating ROX removal through an electron transfer pathway rather than radical-mediated reactions. H₂O₂ is strongly adsorbed to SVs, directing the ce-MoS₂/H₂O₂ system to predominantly convert H₂O₂ into H₂O via a two-electron (2e^-) reduction pathway. The distinct activation pathways and types of reactive species led to differences in ROX removal efficiency, product transformation, and toxicity. This study clarifies the role of ce-MoS₂ in peroxide activation and offers guidance for the strategic design of MoS₂-based composites tailored to specific oxidants, aiming to improve wastewater treatment efficiency.