High-valent ferryl intermediates generation, reactivity and kinetic characterization with contaminants of emerging concern via a facile photo-Fenton competition kinetic methodology

High-valent ferryl (Fe IV ) intermediates are important reactive species in biological oxidation and Fe-catalyzed advanced oxidation processes (Fe-AOPs). Notwithstanding notable progress has been made on Fe IV identification, the second-order reaction rate constants of Fe IV with contaminants of emerging concern (CECs) were rarely reported in literature, severely hindering understanding its reactivity and kinetics toward various CECs. To this end, we discovered a novel system, i.e., photo-Fenton reaction of peracetic acid with Fe 3+ -nitrilotriacetate complex, which enabled stable generation of Fe IV with steady-state concentrations at ∼10 −8 –10 −7 M at neutral pH, as evidenced by electron spin resonance (ESR) trapping detection, quenching experiments and probe testing. Notably, a facile competition kinetic methodology was developed by using methyl phenyl sulfoxide (PMSO) as a probe, which enabled to characterize the reactivity and kinetics of Fe IV with 12 target CECs (e.g., phenolic compounds, endocrine disruptor, herbicide, and pharmaceuticals). The measured second-order rate constants were in a range of 3.99 × 10 3 –4.75 × 10 5 M −1 s −1 , which were correlated to the ionization potential of the target CECs, owing to electrophilic attack by Fe IV . This achievement can fill a critical gap in uncovering the reactivity and kinetics of Fe IV toward CECs for promising environmental application.