固液界面处功能基团对铀酰离子吸附行为的调控机制

With the vigorous development of nuclear energy, it is an emergency task to recover uranium from aqueous solution. Functional materials based on functional group and specific substrates give a great opportunity for the U(Ⅵ) separation from aqueous solution. Single research method is hard to fully describe the adsorption behavior of ions at the solid-liquid interface due to the multi-scale structures. Towards on the design and development of functional materials for uranyl recovery from aqueous solution, this project puts forward the concept of combining calculation and surface complexation theory to study the adsorption of ions at the functional materials-water interface. DFT, high accuracy ab initio calculations, ab initio molecular dynamics, molecular mechanic calculation and XAFS will be used to study the impact of composition and structure of functional groups on the ion adsorption strength. The Diffusion Layer Model will be used to describe the electrical double layer structure at the functional materials-water interface. The mass action equations based on mole fraction will be used to describe chemical reactions. The Diffusion Layer Model, mass action equations together with the chemical reactions, the intrinsic acidity constant of functional groups and the complexing constant between functional groups and ions determined by calculation will be combined to construct the surface complexation model for the adsorption of ions at the functional materials-water interface. This study aims to reveal the response mechanism of ion adsorption strength to the compositions and structures of functional groups. The connection between microscopic molecular information and macro adsorption performance will be eventually established, which is essential to provide theoretical basis for the design and development of functional materials for the U(Ⅵ) separation from aqueous solution. Moreover, this study will provide ideas to connect molecular insights derived from calculations to macroscopic models and experiments.

在大力发展核电的背景下，开展水体中U(Ⅵ)的分离和富集已成为极为紧迫的任务，表面官能团化的介孔材料有望为U(Ⅵ)的分离带来广阔前景。研究体系涉及跨尺度结构，单一手段难以全面描述功能材料/水界面处离子的吸附行为。本项目创新地将模拟计算与专为(氢)氧化物/水界面处离子吸附发展起来的表面络合理论相结合，从功能基团构成单元入手，采用DFT、高精度从头算、AIMD、分子力学及XAFS相结合的方法研究功能基团组成、结构对吸附强度的影响；扩散层模型描述界面双电层结构，以摩尔分数为基础的质量作用方程描述化学反应，结合模拟计算确定的化学反应方程及相应的平衡常数建立可以描述功能材料/水界面处离子吸附行为的表面络合模型，项目预期揭示离子吸附强度对功能基团组成、结构的响应规律，建立模拟计算得到的微观分子信息到宏观吸附性能的联系，为功能吸附材料的开发提供理论基础，也为模拟计算结果与宏观模型及实验的结合提供思路。

本项研究以化工热力学和传递过程原理为基础，通过模拟计算、表征实验、模型化以及实验的手段，研究吸附材料界面处功能基团对目标离子U(VI)以及竞争离子的吸附及传递规律，建立了微观分子行为到宏观材料吸附性能的联系，为新型U(VI)富集材料的设计、制备与应用提供理论基础；研究一系列锕系镧系离子在熔盐中的配位结构和传递性质，为核燃料循环过程中锕系及镧系金属离子的分离提供基础。首先，对功能基团/离子间的本征相互作用进行分析，考察功能基团组成对U(VI)及竞争离子吸附强度的影响，发现功能基团对U(VI)的作用强度为偕胺肟基>羟基>羧酸基>膦酸基>硝酸基，供电子取代基有利于功能基团对U(VI)的吸附，吸电子取代基不利于功能基团对U(VI)的吸附，为功能基团的遴选和设计提供理论基础，考察了熔盐环境中U(Ⅲ)和Th(Ⅳ)等离子的微观结构及传递性质，首次在大范围内预测了U3+在氯盐体系中的扩散系数和体系黏度，解析了微观结构与体系宏观热力学性质之间的关系，为核燃料循环过程中锕系及镧系金属离子的分离提供基础；其次，将偕胺肟和羧酸基团锚固在聚乙烯链上，表征聚乙烯基功能吸附材料，计算功能基团的酸性常数，U(VI)的水解过程及U(VI)与功能基团络和过程的络和常数，将其作为表面络和模型的输入，结合实验制备的功能吸附材料中功能基团的含量，预测功能吸附材料对U(VI)宏观吸附结果，与实验结果进行比较；此外，制备功能化的聚乙烯纤维吸附材料，用于水溶液中U(VI)的吸附，与表面络和模型计算值对比，相较于实验结果，表面络和模型计算值高估了U(VI)吸附结果。综合上述成果，本研究对U(VI)富集材料以及镧锕分离材料的设计和开发提供了一定的理论基础。