Ozonation of parabens in aqueous solution: Kinetics and mechanism of degradation

Computational consideration on advanced oxidation degradation of phenolic preservative, methylparaben, in water: mechanisms, kinetics, and toxicity assessments

“…The second-order rate constants for each route and total reaction (k total , the sum of rate constants of each route) were calculated (Table S2). At 298 K (room temperature), the calculated k total was 5.01 × 10 9 M −1 s −1 , which agreed well with the available experimental value 6.8 × 10 9 M −1 s −1 [19]. This indicates that our calculation values are reliable and particularly very important for those routes without experimental data.…”

“…The latter route was easier to occur than the former in the presence of O 2 , and the degradation products were HOO • and MPB-OH, in line with the experimental results [17,19]. This theoretical finding can further explain the experimental results as to why the O atom of O 2 cannot be incorporated into the degradation product through direct coupling between molecular O 2 and substrate-based radicals during AOPs [42].…”

“…Over past few years, various AOPs including photocatalysis [17,18], ozone oxidation [19], UV irradiation [20] with the in situ production of highly reactive hydroxyl radicals ( • OH), as the main oxidants, have been frequently employed to degrade MPB experimentally. However, some studies only optimized experimental conditions without considering MPB degradation mechanism [18,20,21].…”

“…However, some studies only optimized experimental conditions without considering MPB degradation mechanism [18,20,21]. Some proposed that • OH can attack both the alkyl chain and benzene ring of MPB based on experimental determination of intermediates [17,19]. However, the specific reaction sites in MPB and pathways involved are still unclear.…”

“…However, the specific reaction sites in MPB and pathways involved are still unclear. For example, a tentative reaction pathway reported that MPB is mainly attacked by • OH at -CH 3 and -H in the aromatic ring [17], hydroxylation at the aromatic ring and hydrogen abstraction were the degradation mechanism of MPB in ozonation [19]. Nevertheless, these studies on quantitative distribution and potential toxicities of products during MPB degradation using AOPs have not yet been concerned, even though this information is very important for environmental protection.…”