MoS₂-assisted Fe²⁺/peroxymonosulfate oxidation for the abatement of phenacetin: efficiency, mechanisms and toxicity evaluation

Abstract

In this study, molybdenum disulfide (MoS₂) was chosen as a co-catalyst to enhance the removal efficiency of phenacetin (PNT) in water by a ferrous ion-activated peroxymonosulfate (Fe²⁺/PMS) process. Operating parameters, such as the initial solution pH and chemical dose on PNT degradation efficiency were investigated and optimized. Under an initial pH of 3, an Fe²⁺ dose of 25 μM, a PMS dose of 125 μM and a MoS₂ dose of 0.1 g L^-1, the degradation efficiency of PNT reached 94.3%, within 15 min. The presence of common water constituents including Cl^-, HCO₃ ^-, SO₄ ^2- and natural organic matter (NOM) will inhibit degradation of PNT in the MoS₂/Fe²⁺/PMS system. Radical quenching tests combined with electron paramagnetic resonance (EPR) results indicated that in addition to free radical species (˙OH, SO₄˙^- and O₂˙^-), nonradical reactive species (¹O₂) were also crucial for PNT degradation. The variations in the composition and crystalline structure of the MoS₂ before and after the reaction were characterized by XPS and XRD. Further, the degradation pathways of PNT were proposed according to the combined results of LC/TOF/MS and DFT calculations, and primarily included hydroxylation of the aromatic ring, cleavage of the C-N bond of the acetyl-amino group, and cleavage of the C-O bond of the ethoxy group. Finally, toxicity assessment of PNT and its products was predicted using the ECOSAR program.