Effect of Metal Ions on Oxidation of Micropollutants by Ferrate(VI): Enhancing Role of Fe^IV Species

Abstract

This paper investigated the oxidation of recalcitrant micropollutants [i.e., atenolol (ATL), flumequine, aspartame, and diatrizoic acid] by combining ferrate(VI) (Fe VI O 4 2− , Fe VI ) with a series of metal ions [i.e., Fe(III), Ca(II), Al(III), Sc(III), Co(II), and Ni(II )]. An addition of Fe(III) to Fe VI enhanced the oxidation of micropollutants compared solely to Fe VI . The enhanced oxidation of studied micropollutants increased with increasing [Fe(III)]/[Fe VI ] to 2.0. The complete conversion of phenyl methyl sulfoxide (PMSO), as a probe agent, to phenyl methyl sulfone (PMSO 2 ) by the Fe VI −Fe(III) system suggested that the highly reactive intermediate Fe IV /Fe V species causes the increased oxidation of all four micropollutants. A kinetic modeling of the oxidation of ATL demonstrated that the major species causing the increase in ATL removal was Fe IV , which had an estimated rate constant as (6.3 ± 0.2) × 10 4 M −1 s −1 , much higher than that of Fe VI [(5.0 ± 0.4) × 10 −1 M −1 s −1 ]. Mechanisms of the formed oxidation products of ATL by Fe IV , which included aromatic and/or benzylic oxidation, are delineated. The presence of natural organic matter significantly inhibited the removal of four pollutants by the Fe VI −Fe(III) system. The enhanced effect of the Fe VI −Fe(III) system was also seen in the oxidation of the micropollutants in river water and lake water.

UVA-LED-Assisted Activation of the Ferrate(VI) Process for Enhanced Micropollutant Degradation: Important Role of Ferrate(IV) and Ferrate(V)

“…In the aforementioned discussion, the UVA-LED/Fe­(VI) process could remarkably promote SMX degradation. During this process, the possible decomposition products of Fe­(VI) (e.g., Fe­(III) and H 2 O 2 ) participated in the micropollutant degradation. , Recent findings showed that the newly added Fe­(III) from the FeCl 3 solution played a catalytic role in the Fe­(VI) oxidation of micropollutants . The role of Fe­(III) was explored by adding Fe­(III) that was prepared via the Fe­(VI) decay under UVA-LED irradiation after 30 min into the reaction.…”

Generation of Iron(IV) in the Oxidation of Amines by Ferrate(VI): Theoretical Insight and Implications in Oxidizing Pharmaceuticals

“…Furthermore, the oxidation of amines will eliminate one of the precursors in water that generate DBPs during chlorination; ,, therefore, the amount of chlorinated DBPs would decrease in the use of Fe­(VI) as a preoxidant before chlorination. Fe­(VI) has been demonstrated to be an effective disinfectant and coagulant. ,− Therefore, application of Fe­(VI) has a potential to have multiple advantages in treatment processes.…”

“…24,26 The Fe IV /Fe V species are present at low steady-state concentrations and only for time scales in the range from microseconds to milliseconds. 30,32,33 approaches to identify Fe IV /Fe V species in an aqueous environment were not successful. 30,32 The demonstration of the intermediate Fe IV /Fe V species is restricted to a nonaqueous (or organic) solvent in which the central iron is complexed by bulky organic ligands such as porphyrins and 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane.…”

“…Many researchers, including us, applied a chemical probe molecule, i.e., methyl phenyl sulfoxide (PMSO), to demonstrate the formation of Fe IV /Fe V intermediates during the oxidations by Fe­(VI). Studies did not establish which of the two intermediates dominated during Fe­(VI) oxidations. , The Fe IV /Fe V species are present at low steady-state concentrations and only for time scales in the range from microseconds to milliseconds. ,, Therefore, attempts of spectroscopic approaches to identify Fe IV /Fe V species in an aqueous environment were not successful. , The demonstration of the intermediate Fe IV /Fe V species is restricted to a non-aqueous (or organic) solvent in which the central iron is complexed by bulky organic ligands such as porphyrins and 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane. ,, In other words, the direct experimental evidence of the high-valent iron intermediate in the oxidative chemistry of Fe­(VI) requires overcoming of limitations imposed by the inherent instability of Fe IV /Fe V species and their trapping in aqueous solutions.…”

Three Kinetic Patterns for the Oxidation of Emerging Organic Contaminants by Fe(VI): The Critical Roles of Fe(V) and Fe(IV)

“…These findings have profound implication in Fe­(VI) technologies for mitigation of EOCs in water and wastewater industries. Given that Fe­(V) and Fe­(IV) are much more reactive than Fe­(VI), ,, the generation of more Fe­(V) and Fe­(IV) from Fe­(VI) is one of the promising approaches for more efficient destruction of EOCs in Fe­(VI) applications. If the in situ production of Fe­(V) and Fe­(IV) can be well harnessed, better EOCs removals and lower Fe­(VI) dosages are expected in practices for improving the efficiency of Fe­(VI) treatment and saving the operation costs associated with water treatment.…”