Mixed oxidation of aqueous nonylphenol and triclosan by thermally activated persulfate: Reaction kinetics and formation of co-oligomerization products

Abstract

As two representative endocrine disrupting chemicals (EDCs), nonylphenol (NP) and triclosan (TCS) often coexist in water and wastewater. In this study, the mixed elimination of aqueous NP and TCS in thermally activated persulfate system was investigated in detail. The effects of the initial oxidant dosage, initial pH, and reaction temperature, as well as the presence of humic acid and coexisting anions and the water matrix on NP and TCS removal were evaluated. The results showed that the pseudo-first-order reaction rate constant of NP was higher than that of TCS in every case. In addition, the presence of TCS enhanced NP conversion, whereas the latter hindered the degradation of the former. A total of 23 intermediates were identified, and four pathways including hydroxylation, sulfate addition, cleavage of an ether bond and the single-electron coupling reaction were elucidated. Furthermore, numerous polymerization products formed by the self- and cross-coupling reactions of NP and TCS were discovered, and their abundance could be further improved under acidic conditions. Based on the density functional theory calculation, the energy barrier (ΔG) values of hydrogen atom extraction by OH from NP and TCS molecules to generate phenoxy radicals were just 4.37 and 12.70 kJ mol−1, respectively, which was significantly lower than those of the other reaction pathways. Combined with the results of quenching tests, we proposed a single-electron coupling reaction induced by OH as the dominant route in the mixed system. These findings can provide useful information for the elimination of mixed EDCs in water and wastewater.