Kinetic and Mechanistic Insights into the Oxidative Transformation of Atrazine by Aqueous Fe(IV): Comparison with Hydroxyl and Sulfate Radicals

This study explored the oxidative transformation of atrazine (ATZ) by an aqueous iron(IV)–oxo complex (Fe(IV)) formed through ozonation of Fe(II) and compared it to ATZ oxidation by •OH and SO4•– generated by ultraviolet (UV) irradiation of H2O2 and peroxydisulfate (PDS), respectively. The second-order rate constant between Fe(IV) and ATZ was estimated to be greater than (5.18 ± 0.3) × 105 M–1 s–1 at pH 3, which was markedly higher than the reactivity of Fe(IV) toward various water matrices. Consequently, Fe(IV) achieved the most effective selective abatement of ATZ, compared with •OH- and SO4•–-mediated processes. Moreover, in the Fe(II)/O3 system, we identified six products of ATZ and grouped them into three types: dealkylation (desethyl-atrazine [DEA] and desisopropyl-atrazine), alkylic-oxidation (atrazine amide [CDIT] and 2-hydroxy-4-(2-hydroxy-ethylamino)-6-isopropylamino-s-triazine), and dechlorination-hydroxylation (N-(4-hydroxy-6-(isopropylamino)-1,3,5-triazin-2-yl) acetamide and deethylhydroxyatrazine) products. These products also constituted the primary outcomes of ATZ in the UV/H2O2 and UV/PDS systems. Mechanism analysis revealed that Fe(IV) and SO4•– triggered the dealkylation of ATZ by electron transfer, whereas •OH initiated dealkylation by H-atom abstraction, which resulted in the reactive oxidant nature-dependent distribution of specific ATZ oxidation products. Specifically, the [CDIT]/[DEA] ratio was quantified as 0.2, 0.7, and 2.3 in Fe(IV)-, •OH-, and SO4•–-mediated oxidation processes, respectively. Accordingly, this ratio was developed as a sensitive internal probe for evaluating the relative contribution of Fe(IV) and •OH/SO4•– during ATZ oxidative abatement.