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

Abstract

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 SO 4•− generated by ultraviolet (UV) irradiation of H 2 O 2 and peroxydisulfate (PDS), respectively. The second-order rate constant between Fe(IV) and ATZ was estimated to be greater than (5.18 ± 0.3) × 10 5 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 SO 4•− -mediated processes. Moreover, in the Fe(II)/O 3 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-(2hydroxy-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/H 2 O 2 and UV/PDS systems. Mechanism analysis revealed that Fe(IV) and SO 4•− 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 SO 4•− -mediated oxidation processes, respectively. Accordingly, this ratio was developed as a sensitive internal probe for evaluating the relative contribution of Fe(IV) and • OH/SO 4•− during ATZ oxidative abatement.