阳离子MOFs的构筑及对高锝酸根离子吸附的研究

As one of the most important fission products in the nuclear fuel cycle, 99Tc has a long half-life and large inventory, thus posing a long-term potential radiation hazard. It exists in the form of oxo-anionic pertechnetate (TcO4-) with good stability and mobility in aqueous solution. It is a grand challenge in the field of environmental radiochemistry on how to separate TcO4- selectively from the nuclear waste solution and contaminated natural water systems. In this project, a series of cationic metallic organic frameworks (MOFs) will be designed based on the coordination of soft neutral imidazolyl organic ligands and transition metal cations. Free or weakly coordinated anions in the pore could effectively exchange with TcO4- through anion-exchange process. The effect of the graft length, hydrophobic groups, functional cardinal number of imidazolyl ligands, the pore size, positive charge density, and active sites of cationic MOFs will be systematically investigated. The adsorption behavior of cationic MOFs on TcO4- in aqueous solution will be studied, and the structure-property relationship will be established to provide new strategies and tools for the practical application of TcO4- removal from nuclear waste. With the aid of X-ray crystallography and density functional theory calculation, the sorption mechanism of TcO4- in cationic MOFs will be elucidated.

99Tc是核燃料循环中最重要的裂变产物之一，其半衰期长且库存量大，具有长期潜在的辐射危害。TcO4-是99Tc的主要存在形式，其稳定性高、随环境流动性强，在核废液中与大量常见阴离子共存。如何高效分离去除TcO4-仍然是环境放射化学领域亟待解决的难题。本项目设计了一系列由软中性咪唑基有机配体与过渡金属离子配位形成的阳离子金属有机骨架化合物（MOFs），孔道中游离或弱配位的阴离子可以有效与核废料中的TcO4-发生交换。通过调节咪唑基配体的接枝长度、疏水基团和功能基数目，有效地调控阳离子MOFs的孔洞尺度、正电荷密度以及活性位点。针对阳离子MOFs材料对核废液中TcO4-的吸附行为进行研究，建立构效关系，为核废料中去除TcO4-的实际应用提供新策略和新工具。结合X-射线单晶衍射和密度泛函数理论计算等手段，揭示阳离子MOFs材料对TcO4-的去除机制。

99Tc作为核燃料循环中最重要的裂变产物之一，半衰期长，库存大，具有长期的潜在辐射危害。它以高锝酸根(TcO4-)的形式存在，在水溶液中具有良好的稳定性和迁移率。如何从核废料溶液和受污染的天然水系统中选择性分离TcO4是环境放射化学领域面临的重大挑战。本课题基于软中性含氮有机配体与过渡金属阳离子的配位，设计合成了一系列阳离子金属有机框架(MOFs)。孔洞或片层之间的游离或弱配位阴离子可以通过阴离子交换过程与TcO4-进行有效的交换。另外，本课题还设计合成阳离聚合物材料，并研究了其对高锝酸根去除效果。研究阳离子型MOFs和阳离聚合物在水溶液中对TcO4-的吸附行为，建立其构效关系，为核废料中TcO4-的实际应用提供新的策略和工具。借助X射线晶体学和密度泛函理论计算，阐明了TcO4-在阳离子MOFs中的吸附机理。