Reactivity and mechanism between ^[rad]OH and phenolic pollutants: Efficiency and DFT calculation

Phenolic pollutants (PPs) are regarded as hazardous pollutants, posing severe threats to humans. In this study, a vacuum ultraviolet (VUV) lamp was used to decay PPs with different functional groups, including phenol, paradioxybenzene (PDB), and p-nitrophenol (PNP). Results showed the removal rate for phenol, PDB, and PNP reached 99.78 %, 97.78 %, and 80.73 % within 60 min. Density functional theory (DFT) involving in quantum chemical descriptors (QCD), frontier molecular orbitals (FMO), thermochemical properties, and the Gibbs free energy was applied to reveal the reactivity and mechanism between ·OH and PPs with various functional groups. Results confirmed that PDB and phenol with the electron-donating group exhibited favorable reactivity, while PNP with an electron-withdrawing group presented a lower one. Furthermore, the oxidation mechanism between PPs and ·OH in the VUV system was also deeply investigated, mainly following four steps: photo-excitation, ·OH substitution, molecular rearrangement, and finally ring-opening. Among them, the required energy for the ring-opening was about 145 and 787-fold higher than that of ·OH substitution and molecular rearrangement. Results suggested that the formation of micro-fatty acids were the primary rate-controlling step.