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

This paper presents an accelerated ferrate(VI) ((FeO42-)-O-VI, 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 w 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, similar to 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 y and Fe w 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.