Gilson Sara E, Sadergaski Luke R, Parkison Adam J
Radioisotope Science and Technology Division, Oak Ridge National Laboratory, 1 Bethel Valley Road, Oak Ridge, Tennessee 37830, United States.
ACS Omega. 2025 Jul 17;10(29):32486-32495. doi: 10.1021/acsomega.5c05359. eCollection 2025 Jul 29.
Numerous areas of nuclear processing, such as radioisotope production, nuclear waste remediation, and separations, depend upon the speciation of f-elements in the solution state. However, fundamental knowledge of the actinidesparticularly Nplags behind most of the elements on the periodic table. Despite the importance of Np-(VI) chemistry in separations and nuclear processing, its speciation in HNO remains uncertain. This work addresses some of these gaps by investigating the effect of HNO concentration and temperature on the spectra and speciation of the Np-(VI) nitrate system. Six samples of Np in 1 to 10 M HNO were prepared and treated with (NH)[Ce-(NO)] to stabilize the hexavalent oxidation state. The absorbance spectrum of the 10 M HNO is drastically different from the spectra of the other samples; the 10 M spectrum indicates coordination of nitrate ligands to the Np-(VI)-O ion to form a complex with high symmetry. Additionally, absorbance spectra were recorded over the temperature range of 15 to 40 °C, and systematic increases and decreases in certain spectral features of the ultraviolet-visible (UV-vis)-near-infrared (NIR) spectra are present in the spectra. The difference in spectral features suggests that Np-(VI) nitrate speciation depends on temperature. Dilution studies of this sample were monitored with UV-vis-NIR and Raman spectroscopies. Spectral data indicate the presence of multiple complexes with different symmetries, including a high-symmetry complex with an inversion center. As samples are diluted and aquo ligands replace nitrate ligands bound to the Np-(VI) neptunyl cation, changes in spectroscopic signals indicate a decrease in the high-symmetry nitrate complex and an increase in the lower-symmetry aquo complex. Additionally, the Raman band associated with the Np-(VI)-O symmetric stretch broadens with dilution and is fitted with two peaks. These peaks are assigned to Np-(VI) aquo and nitrato complexes, indicating that this vibrational mode is sensitive to the coordination environment of the Np-(VI) neptunyl cation and that contributions from these two Np-(VI) complexes can be distinguished. This unique experimental data could be used to advance computational models describing the electronic transitions of complex actinyl ions.
许多核处理领域，如放射性同位素生产、核废料修复及分离等，都依赖于溶液态f元素的形态。然而，锕系元素（尤其是镎）的基础知识落后于元素周期表上的大多数元素。尽管Np(VI)化学在分离和核处理中很重要，但其在硝酸中的形态仍不确定。这项工作通过研究硝酸浓度和温度对Np(VI)硝酸盐体系光谱和形态的影响，填补了其中一些空白。制备了6个含有1至10 M硝酸的镎样品，并用(NH)[Ce-(NO)]处理以稳定六价氧化态。10 M硝酸样品的吸收光谱与其他样品的光谱有很大不同；10 M的光谱表明硝酸根配体与Np(VI)-O离子配位，形成具有高对称性的络合物。此外，在15至40°C的温度范围内记录了吸收光谱，紫外可见（UV-vis）-近红外（NIR）光谱的某些光谱特征出现了系统性的增减。光谱特征的差异表明Np(VI)硝酸盐的形态取决于温度。用UV-vis-NIR和拉曼光谱监测了该样品的稀释研究。光谱数据表明存在多种具有不同对称性的络合物，包括具有对称中心的高对称性络合物。随着样品的稀释，水合配体取代与Np(VI)镎酰阳离子结合的硝酸根配体，光谱信号的变化表明高对称性硝酸络合物减少，低对称性水合络合物增加。此外，与Np(VI)-O对称伸缩相关的拉曼带随着稀释而变宽，并拟合为两个峰。这些峰被归属于Np(VI)水合和硝酸根络合物，表明这种振动模式对Np(VI)镎酰阳离子的配位环境敏感，并且可以区分这两种Np(VI)络合物的贡献。这些独特的实验数据可用于推进描述复杂锕酰离子电子跃迁的计算模型。
