Experimental And Theoretical Study On The Oxidative Degradation Of Typical PPCPs Contaminants In Aqueous Environments

Pharmaceutical and personal care products (PPCPs) have received increasing attention in recent years for their persistent input and potential threat to ecological environment and human health. As typical PPCPs, Ibuprofen, Ketoprofen and Aspirin were selected as target contaminants and this work aimed to realize the oxidative degradation mechanisms of PPCPs in aqueous environments. Density Functional Theory (DFT) study can provide accurate predictions for the reaction mechanism by calculating the energies and can generate kinetic data of key elementary reaction steps.In this paper, the writer has done the following works:(1) The OH-initiated Advanced Oxidation Processes (AOPs) degradation mechanism and its subsequent reaction mechanism of IBP were studied at the M06-2x/6-311++G(2d, p)//M06-2x/6-31+G(d,p) level. The frontier electron density and bond dissociation energy were analyzed. In addition, profiles of the potential energy surface were constructed and all the possible pathways were discussed.H-atom ion is the most important mechanism. The dominant products were IBAP,2-[4-(1-hydroxyisobutyl)phenyl]propionic acid and 1 -(4-isobutylphenyl)-1 -ethanol,which were in good agreement with the experimental results.(2) The OH-initiated transformation as well as the hydrolysis of a typical PPCPs,aspirin, was investigated using density functional theory (DFT) calculations and laboratory experiments. For DFT calculations, the frontier electron densities and bond dissociation energies were analyzed. Profiles of the potential energy surface were constructed, and all the possible pathways were discussed. Additionally, rate constants for each pathway were calculated with transition state theory (TST) method. Fenton experiments of aspirin were performed and degradation intermediates were identified by UPLC-MS-MS analysis. Different findings from previous experimental works were reported that the H-abstraction pathways at methyl position were dominated and OH-addition pathways on benzene ring were also favored. Meantime, hydroxyl ASA was confirmed as the main stable intermediate. Moreover, it was the first time to use DFT method to investigate the hydrolysis mechanisms of organic ester compound.(3) The OH-initiated transformation as well as the hydrolysis of a typical PPCPs,aspirin, was investigated using density functional theory (DFT) calculations and laboratory experiments. For DFT calculations, the frontier electron densities and bond dissociation energies were analyzed. Profiles of the potential energy surface were constructed, and all the possible pathways were discussed. Additionally, rate constants for each pathway were calculated with transition state theory (TST) method. UV/H2O2 experiments of aspirin were performed and degradation intermediates were identified by UPLC-MS-MS analysis. Different findings from previous experimental works were reported that the H-abstraction pathways at methyl position were dominated and OH-addition pathways on benzene ring were also favored. Meantime, hydroxyl ASA was confirmed as the main stable intermediate. Moreover, it was the first time to use DFT method to investigate the hydrolysis mechanisms of organic ester compound.