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Issue 21, 2020
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Temperature-dependent luminescence spectroscopic investigations of uranyl(vi) complexation with the halides F and Cl

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In the present study we have investigated the complexation of uranyl(VI) with chloride and fluoride using luminescence spectroscopy (TRLFS, time-resolved laser-induced fluorescence spectroscopy). At 25 °C (298.15 K), in the presence of 0–0.175 M fluoride, the first single-component emission spectra for all four uranyl(VI)-fluoride complexes, i.e. UO2F+, UO2F2, UO2F3, and UO2F42− could be extracted. Based on the aqueous speciation derived from the TRLFS data, log K* values at I = 1 M were calculated for all these complexes and extrapolated to infinite dilution using the SIT approach. In the case of chloride, however, quenching of the uranyl(VI)-luminescence hampered the experiments. Thus, uranyl(VI)-complexation was studied with TRLFS at liquid nitrogen temperatures. Samples were prepared at 25 °C (298.15 K) with chloride concentrations ranging from 0 to 1.0 M followed by instantaneous freezing and subsequent luminescence spectroscopic measurements at −120 °C (153.15 K). This allowed for the determination of the first luminescence spectra for the UO2Cl+ complex with the TRLFS method. The chloride quench reaction was further studied in the temperature range 1–45 °C (274.15–318.15 K) using Stern–Volmer analysis. By applying the Arrhenius and the Eyring equations we obtained the first thermodynamic parameters for the dynamic quench process, i.e. the activation energy (Ea = 55.0 ± 12.9 kJ mol−1), enthalpy (ΔH = 52.5 ± 13.0 kJ mol−1), and entropy (ΔS = 103.9 ± 42.8 J mol−1 K−1).

Graphical abstract: Temperature-dependent luminescence spectroscopic investigations of uranyl(vi) complexation with the halides F− and Cl−

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Supplementary files

Article information

20 Feb 2020
01 May 2020
First published
04 May 2020

Dalton Trans., 2020,49, 7109-7122
Article type

Temperature-dependent luminescence spectroscopic investigations of uranyl(VI) complexation with the halides F and Cl

M. Demnitz, S. Hilpmann, H. Lösch, F. Bok, R. Steudtner, M. Patzschke, T. Stumpf and N. Huittinen, Dalton Trans., 2020, 49, 7109
DOI: 10.1039/D0DT00646G

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