Enhanced ferrate(VI) oxidation of micropollutants in water by carbonaceous materials: Elucidating surface functionality

This paper investigated ultraviolet A light-emitting diode (UVA-LED) irradiation to activate Fe(VI) for the degradation of micropollutants (e.g., sulfamethoxazole (SMX), enrofloxacin, and trimethoprim). UVA-LED/Fe(VI) could significantly promote the degradation of micropollutants, with rates that were 2.6–7.2-fold faster than for Fe(VI) alone. Comparatively, UVA-LED alone hardly degraded selected micropollutants. The degradation performance was further evaluated in SMX degradation via different wavelengths (365–405 nm), light intensity, and pH. Increased wavelengths led to linearly decreased SMX degradation rates because Fe(VI) has a lower molar absorption coefficient at higher wavelengths. Higher light intensity caused faster SMX degradation, owing to the enhanced level of reactive species by stronger photolysis of Fe(VI). Significantly, SMX degradation was gradually suppressed from pH 7.0 to 9.0 due to the changing speciation of Fe(VI). Scavenging and probing experiments for identifying oxidative species indicated that high-valent iron species (Fe(V)/Fe(IV)) were responsible for the enhanced degradation. A kinetic model involving target compound (TC) degradation by Fe(VI), Fe(V), and Fe(IV) was employed to fit the TC degradation kinetics by UVA-LED/Fe(VI). The fitted results revealed that Fe(IV) and Fe(V) primarily contributed to TC degradation in this system. In addition, transformation products of SMX degradation by Fe(VI) and UVA-LED/Fe(VI) were identified and the possible pathways included hydroxylation, self-coupling, bond cleavage, and oxidation reactions. Removal of SMX in real water also showed remarkable promotion by UVA-LED/Fe(VI). Overall, these findings could shed light on the understanding and application of UVA-LED/Fe(VI) for eliminating micropollutants in water treatments.

Section: Resultsmentioning

confidence: 99%

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

Yang

Mai

Cheng

et al. 2021

“…The order of reactivity of Fe VI with the pollutants differed from the trend of removal, as seen in Figure 1, indicating that the nature and reactivity of Fe V /Fe IV species, produced in the Fe VI −Fe(III)−pollutant system, varied with the structure of the pollutant to result in different removal efficiencies by the Fe VI −Fe(III) system. 12 Furthermore, the competitive reactions including self-decomposition of Fe V /Fe IV and the reactions of Fe V /Fe IV with pollutants would determine the overall trend of removal of target compound by the Fe VI −Fe(III) system.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…The processes of iron-based materials with oxidation states ranging from 0 to +6 have been shown to eliminate micropollutants. This includes zero-valent iron [Fe(0)] technology, Fenton and Fenton-like reactions [e.g., Fe(II)/Fe(III)–H 2 O 2 ], and ferrate(VI) (Fe VI O 4 2– or Fe VI ) oxidations. − …”

Section: Introductionmentioning

confidence: 99%

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

Zhang

Feng

Luo

et al. 2020

Self Cite

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.

“…Over the past decade, Fe(VI) has emerged as a novel oxidant to remove contaminants from water. , While numerous studies have been conducted to evaluate the performance of Fe(VI) in removing different contaminants, relatively limited efforts have been devoted to understanding the mechanisms of Fe(VI) oxidation reactions that involved iron intermediate species [i.e., Fe(V) and Fe(IV)] generated via one- or two-electron transfer pathways. , Recently, researchers have focused on the discovery of activated-Fe(VI) systems in which activators (e.g., ammonia, acid, , sulfite/thiosulfate, − bicarbonate, Fe(II)/Fe(III), Mn(II), and carbon nanotube) can enhance the degradation of substrates or even facilitate the removal of substrates resistant to Fe(VI) oxidation. However, the previous work heavily relied on qualitative analysis of possible reactive species formed in situ [radical vs Fe(V)/Fe(IV)] via quencher experiments and/or electron paramagnetic resonance spectroscopic techniques, and only limited studies , have attempted to quantitatively investigate the kinetic behaviors of Fe(V)/Fe(IV) for their self-decays versus oxidation of substrates.…”

Section: Introductionmentioning

confidence: 99%

Revelation of Fe(V)/Fe(IV) Involvement in the Fe(VI)–ABTS System: Kinetic Modeling and Product Analysis

Luo

Sadhasivan

Kim

et al. 2021

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To quantitatively probe iron intermediate species [Fe(V)/Fe(IV)] in Fe(VI) oxidation, this study systematically investigated the reaction kinetics of Fe(VI) oxidation of 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic)acid (ABTS) at different ratios of [ABTS]0/[Fe(VI)]0 (i.e., >1.0, =1.0, and <1.0) in pH 7.0 phosphate (10 mM)-buffered solution. Compared to the literature, a more comprehensive and robust kinetic model for the Fe(VI)–ABTS system including interactions between high-valent iron species [Fe(VI), Fe(V), and Fe(IV)], ABTS, and the ABTS•+ radical was proposed and validated. The oxidation of ABTS by Fe(VI) (k = (5.96 ± 0.9%) × 105 M–1 s–1), Fe(V) (k = (2.04 ± 0.0%) × 105 M–1 s–1), or Fe(IV) (k = (4.64 ± 13.0%) × 105 M–1 s–1) proceeds via one-electron transfer to generate ABTS•+, which is subsequently oxidized by Fe(VI) (k = (8.5 ± 0.0%) × 102 M–1 s–1), Fe(V) (k = (1.0 ± 40.0%) × 105 M–1 s–1), or Fe(IV) (k = (1.9 ± 17.0%) × 103 M–1 s–1), respectively, via two-electron (oxygen atom) transfer to generate colorless ABTSox. At [ABTS]0/[Fe(VI)]0 > 1.0, experimental data and model simulation both indicated that the reaction stoichiometric ratio of Fe(VI)/ABTS•+ increased from 1.0:1.0 to 1.0:1.2 as [ABTS]0 was increased. Furthermore, the Fe(VI)–ABTS–substrate model was developed to successfully determine reactivity of Fe(V) to different substrates (k = (0.7–1.42) × 106 M–1 s–1). Overall, the improved Fe(VI)–ABTS kinetic model provides a useful tool to quantitatively probe Fe(V)/Fe(IV) behaviors in Fe(VI) oxidation and gains new fundamental insights.