Homogeneous Gas-Phase Formation Mechanism of Emerging Organic Pollutants Polyfluorinated Dibenzo-p-dioxins and Dibenzofurans from 2-Fluorophenol

The emerging organic pollutants polyfluorinated dibenzo-p-dioxins and dibenzofurans (PFDD/ Fs) have attracted wide attention in environmental and toxicological effects. Here, based on the results of density functional theory (DFT) calculations, we present detailed insight into the formation mechanism of polyfluorinated dibenzo-p-dioxins and dibenzofurans. Fluorophenols are recognized as precursors of polyfluorinated dibenzo-p-dioxins and dibenzofurans. Using the simple structure 2-fluorophenol as model precursor, the formation mechanism of polyfluorinated dibenzo-p-dioxins and dibenzofurans was investigated. Thermodynamic and kinetic analysis suggested that only the pathways with no C-F bond breaking are thermodynamically favorable. The possible formation mechanism is compared with formation mechanism of polychlorinated dibenzo-p-dioxin/dibenzofurans and polybrominated dibenzo-p-dioxins and dibenzofurans in the previous literature. The rate constants and their temperature dependence of the crucial elementary reactions are calculated by canonical variation transition-state theory with the small curvature tunneling contribution over the temperature range of 600-1200 K. The calculated results may help to improve our understanding for the formation mechanism of polyfluorinated dibenzo-p-dioxins and dibenzofurans and be informative to environmental scientists.