微孔芳香骨架MOF/聚吡咯复合膜的制备及吸附去除水中放射性碘机理研究

The use of metal-organic framework (MOF) materials to construct composite membranes with iodine adsorption is expected to overcome the limitations of traditional polymer membranes and make a breakthrough in the fields of treatment radioactive iodine wastewater. This project takes the microporous aromatic framework MOF as the research object, starting from the functional modification of ligands, the effects of electron-donating functional groups and non-polar functional groups on the iodine adsorption performance and water stability of MOF will be investigated. A MOF composite membrane will be prepared by seed crystal secondary growth coupling post-polymerization modification method. Through the in-depth study of in-situ crystallization of MOF induced by poly(4-vinylpyridine) and optimization of secondary growth conditions, the effective control of the microstructure of MOF membrane will be achieved, and then, the MOF membrane will be modified by pyrrole polymerization to improve its iodine adsorption capacity and hydrophobicity. Through various characterization techniques, the evolution law of MOF material structure and membrane structure in the process of water filtration will be studied, and the ways to improve the water stability of the MOF membrane will be explored. The adsorption behavior of iodine in water by MOF composite membrane will be thoroughly investigated, and the correlation between MOF materials, composite membrane structure and iodine removal efficiency will be established, the mechanism of adsorption removal of iodine from water by MOF composite membrane will be revealed. This project will open up a new field for the application of MOF composite membrane and provide an example for the preparation of new separation membranes for the removal of radionuclide in water.

利用金属有机骨架(MOF)材料构建具有碘吸附功能的复合膜，有望克服传统聚合物膜的局限，在含碘核素废水处理领域取得突破。本项目以微孔芳香骨架MOF为研究对象，从配体功能化修饰入手，探究供电子官能团、非极性官能团分别对MOF吸附碘性能及水稳定性的影响；提出晶种二次生长耦合聚合后修饰法制备MOF复合膜，通过对聚4-乙烯基吡啶诱导调节MOF原位晶化、二次生长条件优化的深入研究，实现对MOF膜微结构的有效调控，尝试利用吡咯聚合后修饰MOF膜以提高其碘吸附容量和疏水性；运用各种表征技术，重点研究水过滤过程中MOF材料结构与膜结构的演变规律，探索提高MOF膜水稳定性的途径；深入研究MOF复合膜对水中碘的吸附行为，建立MOF材料、复合膜结构与碘脱除效率之间的关联性，揭示MOF复合膜吸附脱除水中碘核素的机理。项目的实施将开拓MOF复合膜在水处理领域的应用，为去除水体中放射性核素的新型膜吸附技术研发提供实例。

放射性碘被认为是辐射效应最危险的核素之一，对水体中碘核素的高效捕集一直是放射性废水污染控制领域的前沿课题。本项目利用柱层式双壁MOF（{[Zn3(DL-lac)(pybz)2]·2.5DMF}n，简称为lac-Zn）为膜材料，将其制备成吸附膜并用于捕集水溶液中碘离子。具体研究内容及重要结果包括：（1）利用二次生长法在聚四氟乙烯载体上制备了lac-Zn多晶膜。研究发现，lac-Zn多晶膜的断裂伸长率达到79.3%。60Co辐照后lac-Zn 膜的化学、晶相和形貌结构均未发生明显变化。（2）研究了lac-Zn膜吸附去除水溶液中碘离子性能。研究结果发现，对pH = 6或7的碘水溶液，lac-Zn 膜对碘离子的去除效率达到92.9％。当碘水溶液中同时存在Cl-时，lac-Zn 膜对碘离子的去除率下降到68.6％。当碘水溶液中分别存在CO32-、SO42-、NO3-或Br-时，lac-Zn 膜对碘离子的去除率都小于58.9%。（3）探究了吡咯对lac-Zn 膜原位修饰。实验结果表明，lac-Zn@PPy 复合膜对碘离子的饱和吸附容量达到397 mg·g-1，明显高于lac-Zn膜（183 mg·g-1）。在经历5次循环吸附后，lac-Zn@PPy 复合膜对碘离子的去除率保持为65%。在动态吸附实验中，lac-Zn：PPy 复合膜在吸附26 h 被穿透，而lac-Zn 膜在吸附14.5 h被穿透。通过对lac-Zn@PPy复合膜吸附碘离子机理研究发现，首先，lac-Zn晶体中受限的纳米通道和较大的孔体积为碘离子提供了充足的吸附位点；其次，lac-Zn自身带有的芳香共轭体系增强了膜对碘离子的吸附能力；最后，lac-Zn@PPy膜表面的吡咯对碘离子也具有很好的吸附性能。项目的实施将拓展MOF复合膜在水处理领域的应用，为去除水体中放射性碘核素的新型吸附膜技术研发提供实例。