How does pH influence ferrate(VI) oxidation of fluoroquinolone antibiotics?

This study investigated the impact of pH on the efficiency of ferrate (Fe(VI), K₂FeO₄) toward fluoroquinolone antibiotics, built kinetic models of Fe(VI) oxidation, and elucidated the involved active species during Fe(VI) oxidation at acidic and alkaline conditions. It was found that the second-order reaction rate constants (k_app, M⁻¹ s⁻¹) of Fe(VI) with three fluoroquinolone antibiotics (i.e., enroxacin, ofloxacin, and norfloxacin) were strongly dependent on pH, and k_app reached its maximum at pH about 6.5. The reactions between HFeO₄^-/H₂FeO₄ and neutral/protonated fluoroquinolone antibiotics (X and XH⁺) were the major ones. Moreover, the reactive species were identified as high-valent iron species, i.e., Fe(VI), Fe(V), and Fe(IV), in alkaline solution, while hydroxyl radicals was generated through Fenton or Fenton-like processes at acidic condition with limited contribution.