Isotopic effect on the formation kinetics of Pu(IV) intrinsic colloids
Résumé
Fundamental knowledge of the intrinsic colloids of plutonium is a major issue in predicting
their behavior in the environment.[1,2] It has been demonstrated that these species are
spherical nanoparticles measuring ca. 2 nm with a local structure similar to the one of bulk
PuO2.[3,4] Recent studies have questioned the contribution of small Pu clusters in the
formation mechanism of Pu(IV) intrinsic colloids.[5] The current work draws attention to this
issue by investigating an unprecedented kinetic isotopic effect (KIE) observed during the
preparation of Pu(IV) colloids in light (H2O) or heavy (D2O) water.
Plutonium colloids have been synthetized by the dilution of acidic Pu(IV) solutions in H2O
and D2O.Time dependent measurements carried out with UV-Vis absorption spectroscopy
demonstrated a much lower formation rate of the Pu(IV) colloids in D2O compared to H2O
(Figure 1a). The observed KIE was attributed to the difference in zero-point energies of OH and O-D bonds. This finding has confirmed that the formation of Pu(IV) colloids is limited
by the rupture of O-H bonds during hydrolysis and polymerization of Pu(IV) species. In
addition, formation of some unstable intermediate Pu(IV) species was observed during
colloid formation. A thorough investigation of this intermediate using synchrotron SAXS and
XAS techniques revealed the presence of an hexanuclear Pu(IV) cluster of quasi-spherical
shape measuring ca. 0.8 nm and agreeing with the literature (Figure 1b).[6,7]
Domaines
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