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Destruction of pharmaceuticals excreted in urine can be an efficient approach to eliminate these environmental pollutants. However, urine contains high concentrations of chloride, ammonium, and bicarbonate, which may hinder treatment processes. This study evaluated the application of ferrate(VI) (FeVIO42-, Fe(VI)) to oxidize pharmaceuticals (carbamazepine (CBZ), naproxen (NAP), trimethoprim (TMP) and sulfonamide antibiotics (SAs)) in synthetic hydrolyzed human urine and uncovered new effects from urine’s major inorganic constituents. Chloride slightly decreased pharmaceuticals’ removal rate by Fe(VI) due to the ionic strength effect. Ammonium (0.5 M) in undiluted hydrolyzed urine posed a strong scavenging effect, but lower concentrations (≤ 0.25 M) of ammonium enhanced the pharmaceuticals’ degradation by 300 µM Fe(VI), likely due to the reactive ammonium complex form of Fe(V)/Fe(IV). For the first time, bicarbonate was found to significantly promote the oxidation of aniline-containing SAs by Fe(VI) and alter the reaction stoichiometry of Fe(VI) and SA from 4:1 to 3:1. In-depth investigation indicated that bicarbonate not only changed the Fe(VI):SA complexation ratio from 1:2 to 1:1, but provided stabilizing effect for Fe(V) intermediate formed in situ, enabling its degradation of SAs. Overall, results of this study suggested that Fe(VI) is a promising oxidant for the removal of pharmaceuticals in hydrolyzed urine.
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Photochemical and Photophysical Dynamics of the Aqueous Ferrate(VI) Ion
Ferrate(VI) has the potential to play a key role in future water supplies. Its salts have been suggested as “green” alternatives to current advanced oxidation and disinfection methods in water treatment, especially when combined with ultraviolet light to stimulate generation of highly oxidizing Fe(V) and Fe(IV) species. However, the nature of these intermediates, the mechanisms by which they form, and their roles in downstream oxidation reactions remain unclear. Here, we use a combination of optical and X-ray transient absorption spectroscopies to study the formation, interconversion, and relaxation of several excited-state and metastable high-valent iron species following excitation of aqueous potassium ferrate(VI) by ultraviolet and visible light. Branching from the initially populated ligand-to-metal charge transfer state into independent photophysical and photochemical pathways occurs within tens of picoseconds, with the quantum yield for the generation of reactive Fe(V) species determined by relative rates of the competing intersystem crossing and reverse electron transfer processes. Relaxation of the metal-centered states then occurs within 4 ns, while the formation of metastable Fe(V) species occurs in several steps with time constants of 250 ps and 300 ns. Results here improve the mechanistic understanding of the formation and fate of Fe(V) and Fe(IV), which will accelerate the development of novel advanced oxidation processes for water treatment applications.
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- Award ID(s):
- 2046383
- PAR ID:
- 10499335
- Publisher / Repository:
- ACS
- Date Published:
- Journal Name:
- Journal of the American Chemical Society
- Volume:
- 144
- Issue:
- 49
- ISSN:
- 0002-7863
- Page Range / eLocation ID:
- 22514 to 22527
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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null (Ed.)High-valent iron species are key intermediates in oxidative biological processes, but hexavalent complexes apart from the ferrate ion are exceedingly rare. Here, we report the synthesis and structural and spectroscopic characterization of a stable Fe(VI) complex ( 3 ) prepared by facile one-electron oxidation of an Fe(V) bis(imido) ( 2 ). Single-crystal x-ray diffraction of 2 and 3 revealed four-coordinate Fe centers with an unusual “seesaw” geometry. 57 Fe Mössbauer, x-ray photoelectron, x-ray absorption, and electron-nuclear double resonance (ENDOR) spectroscopies, supported by electronic structure calculations, support a low-spin ( S = 1/2) d 3 Fe(V) configuration in 2 and a diamagnetic ( S = 0) d 2 Fe(VI) configuration in 3 . Their shared seesaw geometry is electronically dictated by a balance of Fe-imido σ- and π-bonding interactions.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1021/jacs.2c08048
