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利用氩离子激光器4880激光照射UO_2(NO_3)_2—C_2H_5OH—HNO_3溶液体系,研究了在乙醇的作用下U(Ⅵ)—U(Ⅳ)的光化学还原行为。报告中计算了不同条件下光还原生成 U(Ⅳ)的量子产额,观察了各种因素对U(Ⅳ)初始生成速率和量子产额φ的影响。本实验条件下生成的U(Ⅳ)量与光照时间呈线性关系,光照时间延长则U(Ⅳ)生成速率减慢;激光功率改变对φ的影响不大。随着体系温度T的升高,φ值逐渐降低,T≥55℃,φ急剧下降,这与HNO_2量骤增有关。乙醇浓度低时,[C_2H_5OH]增加φ上升很快,[C_2H_5OH]≥1M,φ的变化很小。起始硝酸铀酰浓度对φ的影响不大。介质硝酸浓度的变化对φ的影响很大:低[HNO_3]时,随[HNO_3]提高φ明显增加;[HNO_3]～0.5M 时,φ值达到最大(～0.88);[HNO_3]继续提高,φ值降低,当[HNO_3]≥3M,φ值下降很快。φ值随[HNO_3]的变化较敏感是与 U(Ⅴ)的歧化、U(Ⅳ)的水解和氧化以及[HNO_3]较高时体系中 HNO_2的增加诸因素有关,并根据φ>0.5的事实以及低酸时 U(Ⅴ)的吸收谱推测了不同酸度区间可能的光化学反应历程。报告还提供了光还原生成 U(Ⅳ)稳定性的数据。最后讨论了提高量子产额的几个因素。
The photochemical reduction of U (Ⅵ) -U (Ⅳ) under the action of ethanol was studied by irradiating UO_2 (NO_3) _2-C_2H_5OH-HNO_3 with 4880 argon laser. The quantum yields of U (IV) photoreduced under different conditions were calculated and the effects of various factors on the initial formation rate of U (IV) and the quantum yield φ were observed. Under the experimental conditions, the amount of U (Ⅳ) produced has a linear relationship with the illumination time, and the generation rate of U (Ⅳ) slows down when the illumination time is prolonged. The change of laser power has little effect on φ. With the increase of the system temperature T, the value of φ gradually decreased, T≥55 ℃, φ decreased sharply, which was related to the sudden increase of the amount of HNO_2. When the ethanol concentration is low, the increase of [C 2 H 5 OH] increases very quickly, and the change of C 2 H 5 OH is more than 1 M and φ is small. The initial uranyl nitrate concentration has little effect on φ. The change of nitric acid concentration in media has a great influence on φ: the value of φ increases with [HNO_3] when [HNO_3] is low; the value of φ reaches the maximum (~0.88) when [HNO_3] ~0.5 M; The value of φ decreases. When [HNO_3] ≥3M, the value of φ decreases rapidly. The value of φ is more sensitive to the change of [HNO_3], which is related to the disproportionation of U (Ⅴ), the hydrolysis and oxidation of U (Ⅳ) and the increase of HNO_2 in the system with [HNO_3] And the absorption spectra of U (Ⅴ) at low acid concentrations suggest possible photochemical reaction processes in different acidity intervals. The report also provides data on the photoreduction of U (IV) to produce stability. Finally, several factors to improve quantum yield are discussed.