Inorganic chemistry Z 0100Chemiluminescence in the Reactions of Uranium and Lanthanides -[8 refs.]. -(KAZAKOV, V. P.; OSTAKHOV, S. S.; KAZAKOV, D. V.; MAMIKIN, A. V.; ANTIPIN, V. A.; KLIMINA, S. N.; KHAZIMULLINA, L. N.; KOCHNEVA, O. A.; Biolumin.
Unusually strong influence of the solution acidity on the chemiluminescence intensity (I cl ) in U(IV) oxidation with xenon difluoride was found. Although the intensity of uranyl photoluminescence (I fl ) increases by a factor of 3 with increasing HClO 4 concentration from 0.5 to 2 M, under these conditions the maximal I cl in U(IV) oxidation with XeF 2 decreases by a factor of 8 and the quantum yield of CL (h cl ) decreases by a factor of 4.6. This strong influence of pH of the solution on I cl and h cl is likely due to deceleration of hydrolysis of U(V) intermediate to form uranyl(V) ion. Uranium(IV) is readily oxidized with a series of conventional oxidizing agents. Some of these reactions are chemiluminescent. In particular, strong luminescence is observed in U(IV) oxidation with XeF 2 [1, 2]High intensity and high efficiency of chemiluminescence (CL) of reaction (1) is caused by the high quantum yield (h lum ) of luminescence of the emitter, uranyl ion, with, in turn, depends on its complexation with anions, pH of the solution, presence of quenchers, temperature, etc. The higher is h lum of the emitter, the stronger is the CL intensity (and hence CL yield).We found that the maximal intensity and quantum yield of CL of reaction (1) decrease with increasing acidity of the solution, but not increase as we expected from the increase in h lum . EXPERIMENTALWe used a chemiluminometer consisting of a lighttight chamber with an FEU-140 photoelectron photomultiplier (sensitivity range 200 3 650 nm) which can register luminous fluxes with intensities as low as 1.5 0 10 4 photons s 31 . The chemiluminometer was calibrated with a standard radioluminescent source, liquid scintillator (a toluene solution of diphenyloxazole and diphenyloxazolylbenzene) containing acetic acid labeled with 14 C.Perchloric acid of chemically pure grade was distilled in a vacuum. A 12.4 M azeotrope with the optical density D < 0.1 (l = 210 nm, 5-cm cell) was taken. Working HClO 4 solutions (0.0132 M) were prepared by dilution of purified perchloric acid with double-distilled water.Uranium(IV) perchlorate was prepared by electrolytic reduction of uranyl perchlorate on a platinum cathode in 1 M HClO 4 . The reaction completion was determined spectrophotometrically. Electrolysis was stopped when the U(IV) absorption at 648 nm reached the maximal value. RESULTS AND DISCUSSIONThe lifetime of excited uranyl increases from 1 to 58 ms with increasing HClO 4 concentration from 0.01 to 10 M [3,4]. As a result, the photoluminescence (PL) intensity of uranyl ion increases. The dependence of PL intensity of uranyl ion on the HClO 4 concentration is shown in Fig. 1, curve 1. It is directly proportional to the HClO 4 concentration. In the presence of~10 32 M XeF 2 , I PL of uranyl decreases with an Fig. 1. Photoluminescence intensity of uranyl ion as a function of HClO 4 concentration: (1) [UO 2 2+ ] = 6.7 0 10 !4 M (l exc = 315 nm), (2) the same in the presence of 0.8 010 !2 M XeF 2 , and (3) the same in the presence of 0.2 010 !2 M NaF.
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