Abstract
Abstract Studies on complexation of uranium with organophosphorous ligands in aquatic systems are important from point of view of mobility of uranium in environment. In the present paper, we report the results of complexation of U(VI) by a model ligand for organophosphorus functionalities in humic substances (HS), that is, phenylphosphonic acid (PPA), using electro analytical techniques. The UO2 2+ has been found to form 1:1 and 1:2 complexes with mono-protonated PPA (HPhPO3 −) and 1:1 complex with non-protonated PPA, (PhPO3)2−, with the latter complex (UO2PhPO3) dominating over the other two species. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were used to investigate the redox behavior of UO2PhPO3 species and to explore the kinetics of its reduction by evaluating heterogeneous electron-transfer kinetic (D, k s and α) parameters. The diffusion coefficient (D) value was found to be 6.76×10−5 cm2 s−1 and 5.03×10−5 cm2 s−1 at pH 5 and 3, respectively, with rate constant, k s=0.304×10−3 cm/s. Using the DeFord and Hume formalism the stability constant (log β) of UO2PhPO3 was calculated to be (6.98±0.12), which is in agreement with the literature data. Electrospray ionization mass spectrometry (ESI-MS) studies corroborated the existence of UO2PhPO3 complex.
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