功能化多级孔材料的辐射法制备及其对锕系元素分离性能研究

Most of the absorbents used in separation of actinides (An) in spent nuclear fuel reprocessing and high level liquid waste treatment nowadays are macroporous or unimodal mesoporous/microporous materials, which cannot take full advantages of porous materials. In this project, three types of functionalized hierarchically porous polymer and boron nitride materials will be synthesized by ionizing radiation technique, which possess structures of surficial mesoporous window-multihollow core, surficial open macropores-mesoporous wall, and hierarchically interpenetrating disorder pores. Subsequently, the above three types of hierarchically porous materials will be further functionalized by ligands with nitrogen-containing heterocyclic ring which can complex with An specifically. It is able to prepare separation materials for An possessing high adsorption rate and large adsorption capacity simultaneously. On one hand, ionizing radiation can initiate polymerization and crosslinking of monomer. So hierarchically porous polymeric microspheres will be obtained in combination of radiation polymerization and different pore formation mechanism including dynamic swelling, swelling-osmosis, and polymerization-induced phase separation. On the other hand, cleavage of chemical bonds in matrix will be occurred by direct effect of ionizing radiation, while highly reactive species will also generated by radiolysis of solvent molecules. So inert boron nitride hierarchically porous materials will also be modified by ionizing radiation. The mechanism of preparation of hierarchically porous materials by radiation will be illustrated in combination of study on the intermediate by pulse radiolysis technique, and steady-state characterization of material structure. In addition, the synthesis of hierarchically porous materials will be optimized according to the influence of physical and chemical structure on adsorption performance. The implementation of this project will not only open up a new way for the design of high performance separation materials for An, but also enrich the methods of preparation and functionalization of hierarchically porous materials and promote the development of related theories.

目前用于乏燃料和放射性废液中锕系元素（An）吸附分离的材料多为大孔或单一介孔/微孔材料，难以最大限度发挥多孔材料的优势。本项目拟利用电离辐射制备具有表面介孔窗口-内部中空大孔、表面开放大孔-内部介孔孔壁、无序贯穿多级孔三种结构的功能化交联聚合物及氮化硼多级孔材料，再使用能络合An的含氮杂环配体进一步功能化上述材料，制备出兼具高吸附速率和大吸附容量的An分离材料。电离辐射可引发单体聚合并交联，结合动态溶胀、溶胀-渗透、聚合诱导相分离等致孔机理便能制备多级孔聚合物微球；也可直接使基体断键及使溶剂辐解产生高活性物种，从而改性惰性的氮化硼多级孔材料。通过表征材料结构，结合脉冲辐解研究中间产物，揭示辐射法制备多级孔材料的机理，并根据材料物理、化学结构对An分离性能的影响，优化多级孔分离材料制备方法。本项目研究工作既能为An分离材料的设计开辟新思路，又能丰富多级孔材料的制备改性方法，推动相关理论发展。

为了最大限度发挥多孔材料的优势，实现大孔材料传质快和介孔/微孔材料比表面积大的优势互补，快速高效分离放射性废液中锕系元素（An）等放射性核素，除了要在吸附剂中构筑多级孔结构之外，还须合理设计孔道拓扑结构。.通过制备表面介孔窗口–内部大孔、表面开放大孔–孔壁微孔、表面开放大介孔–孔壁小介孔、无序贯穿多级孔等一系列不同孔道拓扑结构的吸附剂，我们建立了利用辐射技术调控多级孔聚合物微球孔道拓扑结构的方法：选用高辐射化学产额的亲水聚合物诱导微球表面交联，再结合聚合诱导相分离可构筑介孔窗口；反之，选用高辐射化学产额的疏水聚合物则可构筑表面开放大孔及其孔壁上的介孔/微孔孔道。同时我们也实现了化学惰性BN的辐射改性：伽马射线与BN作用产生的缺陷可与水辐解产生的·OH和·H等自由基结合，生成羟基和氨基等基团，为后续进一步功能化提供反应位点。.通过研究这些多级孔材料对An等放射性核素的吸附性能，我们阐明了孔道拓扑结构对吸附性能影响的规律。按照吸附质在吸附剂内的扩散过程，大尺寸孔道位于“前端”、小尺寸孔道位于“后端”的拓扑结构可促进多级孔内的传质。“前端”孔道只需大于10 nm便可满足离子快速扩散进入“后端”孔道的需求。而对于“后端”孔道，既可通过缩短其长度来减小颗粒内扩散阻力；也可通过修饰合适的基团来促进孔道内离子传输，从而提高吸附速率。.选择修饰基团时还需要平衡吸附速率和吸附选择性。使用能与An形成内层络合物的邻菲罗啉二酰胺和吡啶二酰胺等基团，可以提高选择性，但吸附位点与吸附质作用力过强，An难以脱附向“后端”孔道深处扩散，反而会降低吸附速率。而基于离子交换机理的双阳离子吡啶基团虽然选择性较差，但缩短两个阳离子位点间距，可使之在“后端”孔道内形成便于阴离子快速传输的微相区，实现硝酸铀酰络合物等放射性阴离子的快速去除。.本项目成果对于An及其它放射性离子分离材料的结构设计、性能优化具有重要参考价值。