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

Abstract

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 played an important role in the degradation of IBP and its transformation products. The second-order rate constants of •OH and •NO2 with IBP were calculated as 3.93 × 109 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 NO2− 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/H2O2 process.