Oxidation of Pharmaceuticals by Ferrate(VI)–Amino Acid Systems: Enhancement by Proline

Abstract

The occurrence of micropollutants in water threatens public health and ecology. Removal of micropollutants such as pharmaceuticals by a green oxidant, ferrate(VI) (Fe VI O 4 2− , Fe(VI)) can be accomplished. However, electron-deficient pharmaceuticals, such as carbamazepine (CBZ) showed a low removal rate by Fe(VI). This work investigates the activation of Fe(VI) by adding nine amino acids (AA) of different functionalities to accelerate the removal of CBZ in water under mild alkaline conditions. Among the studied amino acids, proline, a cyclic AA, had the highest removal of CBZ. The accelerated effect of proline was ascribed by demonstrating the involvement of highly reactive intermediate Fe(V) species, generated by one-electron transfer by the reaction of Fe(VI) with proline (i.e., Fe(VI) + proline → Fe(V) + proline • ). The degradation kinetics of CBZ by a Fe(VI)−proline system was interpreted by kinetic modeling of the reactions involved that estimated the rate of the reaction of Fe(V) with CBZ as (1.03 ± 0.21) × 10 6 M −1 s −1 , which was several orders of magnitude greater than that of Fe(VI) of 2.25 M −1 s −1 . Overall, natural compounds such as amino acids may be applied to increase the removal efficiency of recalcitrant micropollutants by Fe(VI).

Revisiting the Electron Transfer Mechanisms in Ru(III)-Mediated Advanced Oxidation Processes with Peroxyacids and Ferrate(VI)

“…Compared with radicals, high-valent metals generally have a higher steady-state concentration and better selectivity toward micropollutants due to targeting their electron-rich moieties. − Furthermore, high-valent metal species may resist the influence of matrices in the treatment of real water samples. High-valent iron (Fe­(IV)/Fe­(V), ferrate­(VI) (Fe VI O 4 2– )) species usually selectively react with contaminants with phenolic, − nitrogen-containing, − or sulfur-containing functional groups , while exhibit low reactivity toward merely aliphatic or aromatic compounds. For instance, benzoic acid, a commonly used probe compound and typical structure in natural organic matter, is inert to high-valent iron but susceptible to oxidation by nonmetallic radicals, including HO • , SO 4 •– , and Cl • . ,, In addition, unlike radicals susceptible to scavenging by halides, , ferrate­(VI) exhibits relatively low reactivity to bromide and almost no reactivity to chloride, hence mitigating the formation of toxic halogenated byproducts. ,− …”

“… 11 − 13 Furthermore, high-valent metal species may resist the influence of matrices in the treatment of real water samples. High-valent iron (Fe(IV)/Fe(V), ferrate(VI) (Fe VI O 4 2– )) species usually selectively react with contaminants with phenolic, 14 − 16 nitrogen-containing, 17 − 20 or sulfur-containing functional groups 18 , 21 while exhibit low reactivity toward merely aliphatic or aromatic compounds. For instance, benzoic acid, a commonly used probe compound and typical structure in natural organic matter, is inert to high-valent iron but susceptible to oxidation by nonmetallic radicals, including HO • , SO 4 •– , and Cl • .…”