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

Abstract

This paper presents an accelerated ferrate(VI) (FeO, Fe) oxidation of contaminants in 30 s by adding one-electron and two-electron transfer reductants (R and R). An addition of R (e.g., NHOH, As, Se, P, and NO, and SO) results in Fe initially, while Fe is generated with the addition of R (e.g., SO). R additives, except SO, 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 to Fe. Interestingly, addition of SO (i.e., R) also achieves the enhanced oxidation to 100%. Removal efficiency of TMP depends on the molar ratio ([R]:[Fe] or [R]:[Fe]). Most of the reductants have the highest removal at molar ratio of ∼0.125. A Fe-SO 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 and Fe as the oxidative species in the Fe-SO-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-SO systems. Significantly, elimination of SO from sulfonamide (i.e., SDM) is observed for the first time.

Preliminary Assessment of Ferrate Treatment of Metals in Acid Mine Drainage

“…It is also possible that Fe and Mn formed very small (<20 nm) particles that were operationally defined as dissolved. The oxidation–reduction pathways of Fe(VI) in the presence of acid are complex and an active area of research, including the “activation” of Fe(VI) by accelerating decay to oxidize recalcitrant organics by increasing formation of reactive Fe species (Feng et al, 2018). …”

Versatile Functionalization of Carbon Nanomaterials by Ferrate(VI)

“…With prolonged reaction time, the purple toluene layer faded and the aqueous phase gradually became yellowish transparent, indicating continuous oxidative transformation and increasing oxidation degree [47]. The product MS showed many ion clusters above m/z 720.004, clearly separated by multiples of 16 (Fig. S4).…”

“…Ferrate(VI) possesses powerful oxidizing ability, as revealed by its higher redox potentials (up to + 2.2 V in acidic conditions) than those of most traditional oxidants [9][10][11][12]. Together with the environmentally benign nature, ferrate(VI) compounds (commonly K 2 FeO 4 ) have been considered as promising oxidizing agents in several areas, including water remediation [13][14][15][16][17], organic synthesis [18][19][20][21], high-capacity battery [22][23][24] and O 2 evolution [25][26][27][28][29]. Recent years have witnessed an emerging role of ferrate(VI) in materials science [30][31][32][33][34], where ferrate(VI)-enabled oxidative functionalization/transformation of a target material is a key step toward functional applications.…”

Sulfite activation changes character of ferrate resultant particles

“…[9][10][11][12] However, some recalcitrant contaminants of emerging concern are not effectively oxidized by Fe(VI) at relevant dosages and pH values. 13 Oxidation with Fe(VI) can be improved by "activation" of Fe(VI) by common chemical reducing agents, 14 acids, 15 carbon nanotubes, ammonia, 16 and ultraviolet light. 17 Disagreement in the literature exists with respect to exact mechanisms of activation, and vary with activation approach; however, an important role of ephemeral iron species (e.g.…”