Quenching Mechanism of Uranyl(VI) by Chloride and Bromide in Aqueous and Non-Aqueous Solutions

Abstract

A major hindrance in utilizing uranyl­(VI) luminescence as a standard analytical tool, for example, in environmental monitoring or nuclear industries, is quenching by other ions such as halide ions, which are present in many relevant matrices of uranyl­(VI) speciation. Here, we demonstrate through a combination of time-resolved laser-induced fluorescence spectroscopy, transient absorption spectroscopy, and quantum chemistry that coordinating solvent molecules play a crucial role in U­(VI) halide luminescence quenching. We show that our previously suggested quenching mechanism based on an internal redox reaction of the 1:2-uranyl–halide-complex holds also true for bromide-induced quenching of uranyl­(VI). By adopting specific organic solvents, we were able to suppress the separation of the oxidized halide ligand X2 · – and the formed uranyl­(V) into fully solvated ions, thereby “reigniting” U­(VI) luminescence. Time-dependent density functional theory calculations show that quenching occurs through the outer-sphere complex of U­(VI) and halide in water, while the ligand-to-metal charge transfer is strongly reduced in acetonitrile.

Ultrastrong Electron‐Phonon Coupling in Uranium‐Organic Frameworks Leading to Inverse Luminescence Temperature Dependence

“…In KIT‐U‐1, the uranyl units are highly symmetric coordinated by the six oxygen atoms from the BTC linker in the equatorial plane [25b,27] . To our knowledge, the KIT‐U‐1 thin film presented here exhibited the largest ratio (>40 %) of the hot band to the main emission band at 503 nm (S 10 –S 01 ) among all uranyl‐based MOFs [6,28] …”

Spectroscopic characterization of europium binding to a calmodulin-EF4 hand peptide–polymer conjugate

“…PARAFAC is a routine analysis used to deconvolute multidimensional emission spectra. 25,30–36 In the PARAFAC analysis, fitting the data with a two-species-model yielded for both ligands the best result.…”

Efficient and durable uranium extraction from uranium mine tailings seepage water via a photoelectrochemical method

“…The absence of spectral patterns of either U(VI) or U(IV) shows that the PEC extracted U was pentavalent, consistent with the CV characterization. Although some previous studies on the homogeneous photoreduction of U(VI) showed that the photosensitization of aqueous U(VI) may lead to the formation of U(V) ( Tsushima et al., 2010 ; Haubitz et al., 2021 ; Li et al., 2019d ), upon illumination aqueous U(V) is very unstable and prone to re-oxidation if halide ions and/or dissolved oxygen are present in the reaction solution ( Haubitz et al., 2021 ; Tsushima et al., 2010 ). We examined the UV-vis absorption spectra of the reaction solution before and after illumination, and no characteristic peaks of U(V) were observed, suggesting no formation of stable U(V) via the homogeneous photosensitization pathway.…”