Uranyl-Se(IV) interaction in aqueous acid solutions studied by time-resolved laser-induced fluorescence spectroscopy (TRLFS) and UV-Visspectrophotometry

Abstract

The uranyl-selenium(IV) interaction was studied by time-resolved laser-induced fluorescence spectroscopy in aqueous perchloric acid solutions containing 1 × 10⁻⁴ M U(VI) and Se(IV) at different concentrations (from 0 up to 0.3 M) at pH 1 and 2. The quenching of uranyl fluorescence is observed. HSeO₃⁻ is demonstrated to be responsible for the fluorescence quenching. Stern–Volmer analysis gives the dynamic quenching rate constant value (k_q) (5.0 ± 0.4) × 10⁹ L M⁻¹ s⁻¹ at ionic strength (μ) 0.05 M. The bimolecular excited-state process is shown to be diffusion-controlled as k_q is practically identical to the diffusion rate constant as calculated for uranyl and hydroselenite charged species. With an increase of HSeO₃⁻ concentration, static quenching occurs in addition to the dynamic quenching. The hypothesis of the formation of a weak fluorescent ground state complex between uranyl and HSeO₃⁻ is supported. The logarithm of the stability constant value (β) is found to be 3.35 ± 0.12 (μ= 0.05 M) and 3.32 ± 0.15 (μ = 0.2 M). These constants are confirmed by UV-Vis spectrophotometry. The modelling factor analysis of absorption spectra gives logβ = 3.35 ± 0.17 (μ = 0.035 M). Extrapolation to μ = 0 by the specific ion interaction theory (SIT) gives logβ° = 3.62 ± 0.15 at 20 °C.