Institute of Radiochemistry, Forschungszentrum Dresden-Rossendorf, Dresden, Germany.
Environ Sci Technol. 2009 Oct 15;43(20):7665-70. doi: 10.1021/es901256v.
The migration of hazardous neptunium is strongly affected by sorption processes at the solid-water interface. Up to now, almost no spectroscopic data are available to characterize Np(V) species on a molecular level. For the first time, at a micromolar concentration level the Np(V) speciation in aqueous solution and the sorption of Np(V) onto metal oxides were studied using NIR and in situ attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectroscopy. Reference data for future investigations of neptunyl(V) sorption processes on natural mineral phases under environmental conditions are provided. The obtained spectra of aqueous Np(V) solutions confirmed the predominance of the fully hydrated species NpO2(+) up to pH 7.7, predicted by the updated NEA thermochemical database. From the Np(V) sorption studies on TiO2, stable surface species of NpO2(+) are derived. The type of the sorbed species can be elucidated by a spectral shift (approximately 30 cm(-1)) to lower wavenumbers of the antisymmetric stretching vibration v3(NpO2(+)) compared to the aqueous species suggesting an inner-sphere complexation. Outer-sphere complexation is found to play a minor role due to the pH independence of the sorption species throughout the pH range 4-7.6. The comparative spectroscopic experiments of Np(V) sorption onto TiO2, SiO2 and ZnO indicate structurally similar bidentate surface complexes.
在固-水界面，锕系元素的迁移强烈地受到吸附过程的影响。到目前为止，几乎没有光谱数据可以在分子水平上对 Np(V)物种进行特征描述。本文首次采用近红外和原位衰减全反射傅里叶变换红外（ATR FT-IR）光谱法，在微摩尔浓度水平上研究了水溶液中 Np(V)的形态和 Np(V)在金属氧化物上的吸附。为今后在环境条件下研究天然矿物相中锕系元素(V)的吸附过程提供了参考数据。水溶液中 Np(V)溶液的获得的光谱证实，在更新后的 NEA 热化学数据库预测的 pH 值为 7.7 之前，完全水合的 NpO2(+)物种占主导地位。从 TiO2 上的 Np(V)吸附研究中，可以推导出 NpO2(+)的稳定表面物种。与水相物种相比，吸附物种的对称伸缩振动 v3(NpO2(+))的波数向低波数移动（约 30 cm(-1))，可以说明吸附物种的内配位络合。由于在整个 pH 值范围 4-7.6 内吸附物种的 pH 值不依赖，因此外配位络合作用的作用较小。Np(V)在 TiO2、SiO2 和 ZnO 上的吸附的比较光谱实验表明，它们具有结构相似的双齿表面络合物。
