铀酰离子光化学研究  Ⅲ.Ar~+激光对UO_2(NO_3)_2-HCOOH-HNO_3体系U(Ⅵ)的光化学还原

STUDIES ON THE PHOTOCHEMISTRY OF URANYL ION Ⅲ.PHOTOCHEMICAL REDUCTION OF U(Ⅵ)IN UO_2~(2+)-HCOOH-HNO_3 SYSTEM WITH AN ARGON ION LASER

摘要: 用Ar~+激光器的4880A单色光较详细地研究了UO_2(NO_3)_2)-HCOOH-HNO_3水溶液体系中UO_3~(2+)的光化学行为。结果表明,在此体系中吸收光物质主要是甲酸铀酰络合物,甲酸铀酰络合物首先还原生成U(Ⅴ),随后歧化生成U(Ⅳ)、U(Ⅵ)。生成U(Ⅳ)的量子产额Φ主要取决于溶液中甲酸铀酰络合物的生成度α。温度升高,Φ先是增大,而后降低。在低浓度范围,U(Ⅳ)生成速率分别与UO_2~(2+)浓度或HCOO-浓度成正比。所假设的反应机理能较好地符合一些实验结果。

Abstract: The photochemical reduction of uranyl ion by formic acid is investigated using an argon ion laser at wavelength 4880 A. The effects of concentration of the formic acid, formate, nitric acid, nitrate, uranylion and of temperature on quantum yield 0 of U(Ⅳ) formed are studied. Experimental results indicate that U(Ⅵ) can be reduced photochemically to U(Ⅴ), which disproportionates to U(Ⅳ) and U(Ⅵ). Φdepends mainly on the degree of complex formation of uranyl formate a in solution. Φ increases with the increase of α. Φ reaches 0.5 when a is close to 1. The rate of U(Ⅳ) formed is proportional to HCOO-1.08 at low concentration of formate and to UO2 2+ 1.01 at low concentration of uranyl ion respectively.