Formation of persistent free radicals and reactive chlorine species during photochemical processes of Polychlorophenols: Effect of temperature, humidity and particles

Abstract

Persistent free radicals (PFRs) generated by polychlorophenol pollutions (CPs) have attracted widespread attention, while the hazards of reactive chlorine species (RCS) generated during the oxidation process of PFRs to environment and human health have been largely ignored. In this study, the PFRs and RCS generation pathways in gas and on Si3O10H8 cluster from 2,4,6-trichlorophenol (2,4,6-TCPs) and pentachlorophenol (PCPs) initiated by OH radical are investigated by quantum chemistry method. In the gas phase, 2,4,6-TCPs mainly undergoes H-abstraction reaction to generate PFRs, while on Si3O10H8 cluster, the OH-addition reaction at the phenolic hydroxyl site becomes dominant and the addition product is dehydrated into PFRs under the synergisticeffectof H2O and Si3O10H8 cluster. Conversely, PCPs mainly undergoes H-abstraction reaction both in the gas phase and on Si3O10H8 clusters to form PFRs. This is because the PCPs form strong hydrogen bonds with Si3O10H8 clusters and the (highest occupied molecular orbital) HOMO of PCPs moves to higher energy levels, which reduces the electron binding ability and promotes the electrophilic reaction of OH radical. Introducing a carbonyl group ortho to the carbonyl group of phenolate-type PFRs leads to spontaneous ring-opening and subsequent decomposition into a series of RCS that can react with Cl, NO2 and O2 to form phosgene, chloroformyl peroxynitrate and peroxychloroformyl radical, respectively. These generated chlorine-containing compounds are highly irritating to human eyes and skin and have potential environmental toxicity.