Formation of excited uranyl in oxidation of tetravalent uranium with oxygen in HClO_4 aqueous solutions: IV. Enhancement of the chemiluminescent reaction in the presence of Fe~(2+)

摘要

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 HClO_4 solutions have been obtained using the H_2O_2-FeSO_4 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 Fe~(2+) in a 5 × 10~(-4) mol/l U(IV) solution in 0.1 mol/l HClO_4 compared with the FeSO_4-free solution. The CL yield in the presence of Fe~(2+) (η_(CL) = 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*(UO _2~(2+))-in radical chain U(IV) oxidation reactions is electron transfer from the uranoyl ion (UO ~(2~+) 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 UO _2~+ ion.