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/H 2 O 2 process from both experimental and theoretical aspects. Impacts of H 2 O 2 dosage, solution pH, quenching agent, and concentration of nitrite (NO 2 − ) on IBP degradation in UV/H 2 O 2 process were evaluated. Both experimental results and theoretical calculations indicated that • OH played an important role in the degradation of IBP and its transformation products . The second-order rate constants of • OH and • NO 2 with IBP were calculated as 3.93 × 10 9  M −1  s −1 and 5.59 × 10 −3  M −1  s −1 , based on the transition state theory, which explained the phenomenon that addition of NO 2 − 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, and provide theoretical foundation for the optimization of UV/H 2 O 2 process.