Accelerated Oxidation of Organic Contaminants by Ferrate(VI): The Overlooked Role of Reducing Additives

摘要

This paper presents an accelerated ferrate(VI) (Fe^VIO4²⁻, Fe^VI) oxidation of contaminants in 30 s by adding one-electron and two-electron transfer reductants (R(1) and R(2)). An addition of R(2) (e.g., NH2OH, As^III, Se^IV, P^III, and NO2⁻, and S2O3²⁻) results in Fe^IV initially, while Fe^V is generated with the addition of R(1) (e.g., SO3²⁻). R(2) additives, except S2O3²⁻, show the enhanced oxidation of 20–40% of target contaminant, trimethoprim (TMP). Comparatively, enhanced oxidation of TMP was up to 100% with the addition of R(1) to Fe^VI. Interestingly, addition of S2O3²⁻ (i.e., R₍₂₎) also achieves the enhanced oxidation to 100%. Removal efficiency of TMP depends on the molar ratio ([R₍₁₎]:[Fe^VI] or [R₍₂₎]:[Fe^VI]). Most of the reductants have the highest removal at molar ratio of ∼0.125. A Fe^VI–S₂O₃²⁻ system also oxidizes rapidly a wide range of organic contaminants (pharmaceuticals, pesticides, artificial sweetener, and X-ray contrast media) in water and real water matrices. Fe^V and Fe^IV as the oxidative species in the Fe^VI–S₂O₃²⁻-contaminant system are elucidated by determining removal of contaminants in oxygenated and deoxygenated water, applying probing agent, and identifying oxidized products of TMP and sulfadimethoxine (SDM) by Fe^VI–S₂O₃²⁻ systems. Significantly, elimination of SO₂ from sulfonamide (i.e., SDM) is observed for the first time.