功能化柱芳烃在离子液体中对镧锕离子的萃取分离研究

Highly efficient separation of lanthanides and actinides represents one of the urgent issues to address in the field of nuclear fuel cycle chemistry. Built on our previous work on pillar[5]arenes as extractants for separation of lanthanides and actinides, this project presents the design and synthesis of a class of heteroditopic pillar[5]arene (HDP5A) with unique molecular structures by introducing functional groups that could enable simultaneous complexation of both a cation and an anion. With well-preorganized chelating groups on the platform and concomitant binding of the ion pair, these ligands are able to achieve electron-neutral separation of lanthanides and actinides in ionic liquids (CnmimNTf2), thereby circumventing the loss of ionic liquids due to cation exchange and aqueous pollution in the course of extraction. The extractive mechanism will be explored by examining the relationship between preorganization/binding sites associated with functionalities and complexation/extraction behaviors, as well as by implementing X-ray structural analysis, EXAFS characterization, density functional theory (DFT) computation, and quantitative study on the coordinated structures of extractive complexes from the extraction system HDP5A/CnmimNTf2. The major factors and general trend of extraction and separation will be also probed by evaluating the extraction system from several aspects including coordination chemistry, acidity, extraction/stripping and radiation stability. The results from this project will pave the way for the application of pillararenes for the extraction of lanthanides and actinides in the field of ionic liquids.

镧锕离子的高效分离是当今核燃料循环领域亟待解决的课题之一。基于本课题组前期关于柱[5]芳烃作为萃取剂分离镧锕离子的工作，本项目设计在柱芳烃骨架上引入同时能络合阴阳离子对的功能基团，合成一类结构独特的异双位点型柱[5]芳烃配体（HDP5A）；借助平台的预组织性和配位基同时螯合阴阳离子对的作用，拟实现离子液体（CnmimNTf2）萃取体系对镧锕系离子的电中性萃取分离，从而减少或避免因离子交换引起的离子液体损失和水相污染问题。通过考察柱芳烃骨架的预组织性和配位基团作用位点与离子对络合行为及萃取分离的关系，借助单晶结构分析、EXAFS技术、计算化学以及对HDP5A/CnmimNTf2萃取体系中萃合物结构的定量研究，阐释其萃取机制，并从配位化学、酸度、萃取与反萃效率及辐射稳定性等方面对该萃取体系进行评价，探究萃取分离的主控因素和规律。本项目将为柱芳烃在离子液体镧锕离子萃取领域的应用研究奠定理论基础。

针对乏燃料后处理过程中镧锕离子的高效分离的难题，开展新型有机功能材料在放化分离中的应用研究至关重要。本项目利用柱[5]芳烃的预组织平台，依次将结构独特的三唑-氧化膦、吡啶酰胺、吡啶三唑等螯合基团引入柱[5]芳烃骨架，合成不同碳链长度、不同类型的9种柱芳烃萃取剂衍生物。另外，基于功能离子液体兼具离子液体和有机配体的双重优势，通过点击化学将吡啶三唑三齿氮配体修饰到离子液体的咪唑阳离子上，合成了一种新型的吡啶三唑功能离子液体。此外，还制备了联嘧啶二酰胺、菲咯啉-吡咯烷酮等氮杂环萃取剂。通过核磁共振氢谱、质谱、电感耦合等离子体-发射光谱/质谱（ICP-OES/MS）、γ活度测定仪、紫外-可见光谱UV-Vis和荧光光谱等方法研究萃取动力学、水相初始酸度、萃取剂浓度、温度、硝酸根浓度和离子液体C4mim·NTf2阴/阳离子浓度对镧锕系离子萃取性能的影响，还借助单晶结构分析、扩展X-射线吸收精细结构（EXAFS）技术和密度泛函理论DFT等手段研究萃合物配位模式，并从配位化学、酸度、萃取与反萃效率及辐射稳定性等方面对该萃取体系进行评价，揭示了超分子阳离子交换机理的萃取机理。实验发现萃取体系没有出现三相造成的水相污染问题，为进一步发展柱芳烃类萃取剂在镧锕离子分离领域的应用研究了提供新的方向和思路。