Physicochemical properties of uranium in lower oxidation states

Heterogeneous photocatalytic removal of U(VI) in the presence of formic acid: U(III) formation

“…4 was surely overlapped by the broad U(IV) band. Remarkably, an important increase in the absorbance in the 350-600 nm range was observed (see inset), together with a change of color in the suspension, from transparent to deep orange, which coincides with the reported absorbance of U(III) species [19,20,26,27], corresponding probably to a U(III)-HCOOH complex [28][29][30]. Other peaks corresponding to U(III) were not observed, surely due to a masking by the strong U(IV) signals [19,20].…”

“…The change of color of the suspension also confirmed U(III) formation. Interestingly, U(III) seems to have been formed also in the HP experiments with P25 at high HCOOH concentrations (pH 3) in QP, GP and QAN, as suggested by the brick red color developed in the suspension [27] which disappeared in air [19,27,60]. This contrasts with the 2-PrOH system [9], where this change of color was never appreciated, and neither U(IV) nor U(III) in solution was observed.…”

“…(13)) [27] is also negligible at the working pH, as U(III) half-life for this decay is at least 755 h [37].…”

“…(8)). Even U(II) might be generated, but its existence is still unclear [27,56] and it will not be considered here.…”

“…further reduction to other uranium oxidation states is not possible, according to the Latimer diagram (Scheme 1).Scheme 1.Latimer diagram for different uranium species vs. SHE[27,[39][40][41].…”