功能化磁性纳米复合材料的设计制备及其对锕离子的吸附与分离研究

The development of nuclear energy is greatly dependent on nuclear fuel cycle, and spent fuel reprocessing is the key of nuclear fuel cycle, which is of great significance from point of the view of both nuclear safety and sustainable development of nuclear energy. Nano-materials, as a result of their unique properties, have recently received an ever-increasing amount of interest in separation of nuclides in spent fuel reprocessing. Functional design of nano-materials and their radiation effects, however, should be drew much attentions before the practical applications. This project will start an investigation by a combination of magnetic material and nano-material on design and synthesis of functionalized magnetic nano composite materials for sorption of nuclides. Effect ligand for binding actinide ions will be designed and screened by using quantum chemical calculation. The screened ligand will then be combined with mesoporous silica and magnetic nanoparticle to fabricate functionalized magnetic nano composite materials. The separation of nuclides such as U, Th, Pu, Np, Am, Eu by the prepared materials will be studied in detail, and the speciation and mechanism will be analyzed based on the characterization of the sorbed ions on the sorbent by synchrotron radiation technology in Beijing Synchrotron Radiation Facility (BSRF). In addition, the radiation stability of the prepared materials will be assessed by monitoring the change of nano framework and chemical structure of ligand during gamma irradiation, and by probing the influence of gamma irradiation on the nuclides sorption by the nano composite materials. Based on above investigation, a rationalization proposal will be provide for application of functionalized magnetic nano-materials in nuclear fuel reprocessing.

核能的发展离不开核燃料循环，而乏燃料后处理是核燃料循环的核心，对于核环境安全和核能的可持续发展意义重大。纳米材料因其独特的性质在乏燃料后处理核素分离方面具有广阔的潜在应用前景，而纳米材料的功能化设计及其辐射稳定性评价是其应用前的研究重点。本项目拟将磁性材料与纳米材料结合开展功能化磁性纳米复合材料的设计制备及其对锕离子的吸附与分离研究。采用量子化学计算方法设计筛选高效的锕离子结合配体；将得到的配体与介孔硅、磁性纳米颗粒复合，制备新型功能化磁性纳米吸附材料，用于U、Th、Pu、Np、Am、Eu等核素的吸附与分离。依托北京同步辐射大科学装置研究核素与材料的相互作用及其中的种态变化；同时，对所制备的功能化磁性复合材料进行辐射稳定性评价。研究γ辐照前后材料的骨架结构变化及功能基团的化学结构变化；考察γ辐照对材料吸附性能的影响。基于以上研究对功能化磁性纳米材料在乏燃料后处理中的实际应用给出合理化建议。

核素分离是核燃料后处理的主要和关键任务之一，对于核环境安全和核能的可持续发展意义重大。纳米多孔材料因其独特的物理化学性质在核素的吸附、富集与分离方面有着非常广阔的潜在应用前景，而多孔材料的功能化设计及其性能评估是其应用前的研究重点。本项目利用从头算和密度泛函理论，通过在分子水平上研究核素与常见有机配体之间的相互作用机制，筛选出了一系列具有锕系阳离子识别能力的有机配体。在此基础上，利用后嫁接法将所设计的锕系阳离子识别配体的关键片段或类似物修饰到介孔氧化硅材料表面，并通过磁性复合的方法成功构筑了一系列结构规则有序，形貌可控，对锕系阳离子具有良好吸附效果的新型功能化磁性介孔硅材料，包括：（1）具有核壳结构咪唑功能化磁性介孔硅。以300 nm单分散Fe3O4粒子为核，包覆无定型SiO2及MCM-41型介孔硅并后接二氢咪唑功能基团。（2）掺杂型胺基功能化磁性介孔硅。将10~20nm单分散Fe3O4粒子封装于MCM-41型介孔硅的硅壁中并后接胺丙基功能基团。（3）具有三维孔道结构胺基功能化磁性介孔硅。酸性条件下，将500~1000 nm耐酸性Fe3O4粒子封装于具有三维孔道结构和更大孔径的KIT-6型介孔硅的硅壁中并后接胺丙基功能基团。采用静态批式方法研究了常规条件下三类材料对U(VI)等的吸附行为。实验结果表明，这几类材料对U(VI)的吸附容量大，吸附速度快，选择性好。吸附实验后，通过施加外加磁场即可实现吸附剂与溶液的快速分离。同时，吸附后的U(VI)经过简单酸处理即能从吸附剂上脱附，并且经过吸附脱附后的吸附剂对U(VI)的吸附效率保持稳定，因此可循环使用。此外，考虑到金属有机骨架（MOF）材料独特的物理化学性质，本项目还探索性研究了磁性MOFs材料的设计制备及其对U(VI)、Th(IV)等核素的吸附行为。最后，以典型功能化介孔硅为代表，评估了所制备材料的gamma辐照稳定性。本研究工作充分显示了功能化磁性纳米复合材料在吸附分离锕系阳离子方面的巨大潜力，为基于磁性复合材料的乏燃料后处理方法的建立提供了必要的基础数据支撑。