Efficient degradation of bisphenol S by ultraviolet/persulfate oxidation in fresh and saline waters: Effects of operating conditions and reaction mechanism

Abstract

Abstract Bisphenol S (BPS) is considered an emerging concern as an alternative to bisphenol A. In this study, the degradation of BPS by PS, UV, and UV/PS was comprehensively examined in fresh and saline waters. UV/PS can effectively degrade BPS, and the observed first-order rate constant, kobs, increased from 0.021 to 0.382 s− 1 with increasing PS concentration from 100 to 1000 mΜ. The addition of humic acid (HA) would inhibit the degradation of BPS, and 1/kobs was directly proportional to the concentration of HA. Eighteen degradation products, including β-scission, sulfate addition, quinone type, ring-opening, cross-coupling, were identified using high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Two possible pathways were proposed: (i) the initial step was considered to be an electron-transfer reaction from BPS to SO4•−, leading to the formation of a phenyl radical cation R1, and then phenol radical R4, 4-hydroxybenzenesulfonate cation R5, phenoxyl radical R3, resonant-type carbon-centered radical R2, and their secondary products; (ii) another pathway was the sulfate addition and hydroxylation. These primary reaction sites were further verified by theoretical calculation. This study highlights the effectiveness of UV/PS as a promising strategy for the remediation of BPS and other endocrine-disrupting chemicals in fresh and saline waters.