Mechanistic insight into the degradation of ibuprofen in UV/H2O2 process via a combined experimental and DFT study

The study investigated the degradation kinetic and transformation mechanism of ibuprofen (IBP) in UV/H2O2 process from both experimental and theoretical aspects. Impacts of H2O2 dosage, solution pH, quenching agent, and concentration of nitrite (NO2-) on IBP degradation in UV/H2O2 process were evaluated. Both experimental results and theoretical calculations indicated that (OH)-O-center dot played an important role in the degradation of IBP and its transformation products. The second-order rate constants of (OH)-O-center dot and (NO2)-N-center dot with IBP were calculated as 3.93 x 10 9 M-1 s(-1) and 5.59 x 10(-3) M-1 s(-1), based on the transition state theory, which explained the phenomenon that addition of NOi. inhibited IBP degradation. Further, according to the results of ultra-high-resolution mass and density functional theory calculations, mechanisms of a detailed degradation pathway for IBP were clarified. Namely, the detailed mechanistic formation pathways for hydroxylated and keto-based products were proposed. Then, possible active sites of the keto-based products, as well as the corresponding subsequent products were predicted by Condensed Fukui Function. Our study can broaden the knowledge of the reactions of emerging contaminants with (OH)-O-center dot, and provide theoretical foundation for the optimization of UV/H2O2 process. (C) 2020 Elsevier Ltd. All rights reserved.