构建基于超极化含氧酸盐的新颖晶体骨架材料实现锝99、硒79、碘129、铯135的选择性分离

A multitude of nuclear-fission relevant isotopes are present in used nuclear fuel and generated from nuclear fuel reprocessing. Among these isotopes 99Tc, 79Se, 129I, and 135Cs are particularly important because they are highly mobile in the environment due to their high solubility in the form of oxo-anions or cations. They are more environmentally persistent compared to some other radionuclides as they hold much longer half time of decay. Consequently, it is critical to develop materials with high efficiency, stability, and selectivity, to remove these radionuclides from contaminated water. We will undertake studies of synthesizing ion-exchangeable materials building from oxyanions with high hyperpolarizabilities. The reason why hyperpolarizable oxyanions are chosen is that these ligands can adopt multiple geometries and polymerize to form complicate structure, making them attractive candidates for synthesizing open-frameworks or layered topologies. One of the strategies of selective ion-exchange is based on the pore size or layer distance of ion-exchange materials, which can be fine-tuned by the ionic radii of the counterions. Selecting counterions with same charges as and similar coordination geometries to the target radionuclides enables selective absorption from competitive ions. By combining techniques of single crystal X-ray diffraction and X-ray absorption fine structure spectroscopy, the mechanisms of absorption or ion-exchange could be elucidated at molecular level, which would shed light on the improvement of materials with better performance in efficiency, stability, and selectivity.

我国核能产业高速发展的同时也伴随着放射性核素导致的环境污染风险。半衰期长的第二类裂变产物锝-99、硒-79、碘-129、铯-135，极容易溶解于水体，造成环境近乎永久性的放射性污染。因此迫切需要高效、稳定、有选择性的吸附材料，分离固化上述核素。本项目拟利用超极化无机含氧酸根配体结构多样和易聚合形成复杂拓扑结构的特点，设计合成具有微孔框架结构和层状结构的无机晶体材料，以离子交换的方式选择性分离上述放射性核素。通过微调参与电荷平衡离子的半径来调控晶体骨架材料孔径/层间的物理尺寸，以及通过筛选平衡离子的电荷数及拓扑结构，达到以物理尺寸和结构匹配为主导作用的选择性吸附效果。本项目结合X射线单晶衍射和X射线吸收精细结构谱技术，对新颖晶体骨架材料的吸附机理从分子层面进行深入研究，进而通过调控晶格材料的基本单元、合成方法实现材料的拓扑结构、功能的优化，在特异性、吸附效果、实用性等方面寻求改进和突破。

我国核工业高速发展，但是裂变产物导致的环境放射性污染风险也与日俱增。半衰期长的第二类裂变产物锝99、碘129等核素极易在环境中迁移，造成环境的近乎永久性的放射性污染。因此开发高效的裂变产物吸附材料对于环境放射性污染防治具有重要的意义。本课题开发了一系列具有高化学稳定性和耐辐照的无机含氧酸根晶格材料和金属有机框架材料，用于锝、碘等裂变产物的高效、选择性吸附。基于无机含氧酸根晶格体系，研究了酸度、抗衡离子对无机含氧酸盐材料结构维度、骨架电荷以及金属离子团簇聚合度的影响。在此基础上，进一步开发了一系列钍基金属有机框架材料，利用容易获得高质量钍基MOFs单晶的特性和钍离子配位结构的多样、特殊性，系统研究了MOFs孔隙率、孔径尺寸、比表面积、取代基团及结构穿插和放射性核素吸附性能之间的构效关系。此外，利用X射线单晶衍射和X射线吸收谱等技术，对放射性核素的吸附机理从分子层面进行了阐释。本项目还进一步研究了簇基晶格材料结构和化学、辐照稳定性之间的构效关系，获得了多例具有较高化学稳定性和耐高剂量辐照性能的簇基晶格材料。本项目共发表了SCI论文30篇，培养了研究生10名，同时极大提高了项目参与人员的科研素养和学术水平。在本项目的支持下开发的放射性核素吸附材料在乏燃料后处理和放射性核素污染应急处置领域具有较好的应用前景。开展的放射性核素吸附分离构效关系研究为后续进一步研发具有更优吸附材料提供了理论依据