Hydroxylation of some emerging disinfection byproducts (DBPs) in water environment: Halogenation induced strong pH-dependency

In this work, the hydroxylation mechanisms and kinetics of some emerging disinfection byproducts (DBPs) have been systematically investigated through theoretical calculation methods. Five chlorophenols and eleven halo-genated pyridinols were chosen as the model compounds to study their pH-dependent reaction laws in UV/H2O2 system. For the reactions of HO center dot with 37 different dissociation forms, radical adduct formation (RAF) was the main reaction pathway, and the reactivity decreased with the increase of halogenation degree. The kapp values (at 298 K) increased with the increase of pH from 0 to 10, and decreased with the increase of pH from 10 to 14. Compared with phenol, the larger the chlorination degree in chlorophenols was, the stronger the pH sensitivity of the kapp values; compared with chlorophenols, the pH sensitivity in halogenated pyridinols was further enhanced. As the pH increased from 2 to 10.5, the degradation efficiency increased at first and then decreased. With the increase of halogenation degree, the degradation efficiency range increased, the pH sensitivity increased, the optimal degradation efficiency slightly increased, and the optimal degradation pH value decreased. The ecotoxicity and bioaccumulation of most hydroxylated products were lower than their parental

Automated summary

The hydroxylation mechanisms and kinetics of emerging disinfection byproducts (DBPs) were systematically investigated using theoretical calculation methods. The pH-dependent reaction laws in the UV/H2O2 system were studied for five chlorophenols and eleven halogenated pyridinols. Radical adduct formation (RAF) was the main reaction pathway for the reactions of HO center dot with 37 different dissociation forms, and the reactivity decreased with increased halogenation degree. The kapp values (at 298 K) increased with increasing pH from 0 to 10 and decreased with increasing pH from 10 to 14. The higher the chlorination degree in chlorophenols, the stronger the pH sensitivity of the kapp values, and this pH sensitivity was further enhanced in halogenated pyridinols. The degradation efficiency increased initially and then decreased as pH increased from 2 to 10.5. With increased halogenation degree, the degradation efficiency range and pH sensitivity increased, while the optimal degradation efficiency slightly increased and the optimal degradation pH value decreased. The ecotoxicity and bioaccumulation of most hydroxylated products were lower than their parental compounds.