Formation of excited uranyl in oxidation of tetravalent uranium with oxygen in HClO4 aqueous solutions: IV. Enhancement of the chemiluminescent reaction in the presence of Fe2+

Abstract

Experimental data that support the hypothesis on the determining role of •OH radicals in the emergence of luminescence during the oxidation of U(IV) with atmospheric oxygen in aqueous HClO4 solutions have been obtained using the H2O2-FeSO4 system as a source of OH radicals. It has been found that brighter chemiluminescence (CL) is observed in the presence of 10−5 mol/l Fe2+ in a 5 × 10−4 mol/l U(IV) solution in 0.1 mol/l HClO4 compared with the FeSO4-free solution. The CL yield in the presence of Fe2+ (ηCL = 3.9 × 10−8) is 2.8 times that in the solution without iron (ηCL = 1.4 × 10−8). These results can be regarded as a further piece of evidence for the idea that the elementary event of the formation of a CL emitter—electronically excited uranyl ion *(UO22+)—in radical chain U(IV) oxidation reactions is electron transfer from the uranoyl ion (UO2+) to the oxidant, the •OH radical. Thus, one of the main prerequisites for light emission during U(IV) oxidation reactions is a high generation efficiency of •OH radicals and their easy access to the uranoyl UO2+ ion.