海水提铀是一种重要的非常规铀资源开发途径，对于保障国家能源安全具有战略意义。基于辐照诱导接枝聚合（RIGP）制备偕胺肟聚合物材料并用于吸附分离铀被证明是具有前景的海水提铀方法。然而，由于RIGP对偕胺肟聚合物链段的组成和结构缺乏有效调控，材料的吸附效率并不理想，并且高能辐照过程会损伤聚合物机械强度和结构稳定性。近年来兴起的光控活性自由基聚合技术为海水提铀聚合物的可控、低能耗制备带来了新的契机。光控活性自由基聚合保留了经典可控/活性自由基聚合对高分子组成和结构的精确控制，能够合成分子量可设计、链段长度均一的聚合物，同时，光调控机制的引入能实现对自由基引发和链段生长过程的良好控制。基于此，本论文围绕光控活性自由基聚合制备高性能海水提铀材料展开探索性研究，结合碳量子点、磷酸银等光催化体系建立了可控、低能耗的光致电子转移-可逆加成断裂链转移（PET-RAFT）聚合方法，制备出具有特定组成和结构的海水提铀聚合物，并研究了其对铀的吸附行为和构效关系。同时，结合微流控技术建立了连续流光控聚合方法，为提铀材料的连续化合成奠定了基础。论文的创新性成果包括：第一，建立了S、P掺杂碳量子点催化的PET-RAFT聚合方法，实现了在低能耗可见光和太阳光下可控合成分子量可控、链段长度均一的聚合物。第二，利用Ag3PO4光催化过程原位生成纳米Ag的局域表面等离子共振（LSPR）效应，建立了一种可被近红外光子驱动、具备耐氧性的PET-RAFT聚合方法，实现了多种海水提铀材料单体高效、可控的聚合。第三，结合PET-RAFT聚合和静电纺丝技术成功制备了嵌段聚合物型海水提铀材料，基于其优化的链段构象和扩散传质环境，大幅度提升了对铀的吸附性能。第四，结合微流控技术分别建立了单相流和两相流的连续化PET-RAFT聚合方法，实现了海水提铀聚合物的快速合成。本论文的研究一方面为可控合成海水提铀聚合物提供了两种高效、低能耗的光控聚合方法，能够利用广泛的单体合成出具有特定组成和结构的海水提铀材料，另一方面也为从分子水平上研究材料吸附铀的构效关系，揭示聚合物链段构象、扩散传质动力学等因素对吸附铀能力的影响规律奠定了基础。同时，连续流光控聚合反应工艺的建立为未来海水提铀材料的规模化制备提供了保障。
Uranium extraction from seawater as an important way to explore unconventional uranium resources is of strategic significance for the security of national energy supply. Developing amidoxime-containing polymer materials by radiation-induced graft polymerization (RIGP) for uranium extraction from seawater has been proven to be a promising method in this field. However, due to the poor control over the composition and structure of polymer segments, the polymer sorbents prepared by RIGP exhibit unsatisfactory adsorption efficiency. Moreover, the energy-intensive radiation process generally compromises the mechanical strength and structural stability of the polymer sorbents. In recent years, the emergence of photo-regulated living radical polymerization (PLRP) has brought new opportunities for the controllable and energy-efficient preparation of polymer sorbents for uranium extraction from seawater. PLRP, like classical controlled/living radical polymerization (CLRP), can precisely control macromolecular compositions and structures, so it can synthesize polymers with a designable molecular weight and uniform segment length. Meanwhile, the introduction of light regulation achieves good control of free radical initiation and segment growth. On this basis, this dissertation is dedicated to the fundamental research on PLRP methods for preparation of high-performance polymer sorbents for uranium extraction from seawater. Taking advantage of carbon quantum dots (CDs) and silver phosphates based photocatalytic systems, controllable and energy-efficient photo-induced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization methods were established. Polymer sorbents for seawater uranium extraction with specific compositions and structures were prepared, and their uranium adsorption capability and structure-activity relationship were studied. Meanwhile, a continuous-flow PLRP process was established in combination with microfluidic technology, which paved the way for the continuous synthesis of uranium sorbents. Innovative achievements of this dissertation include:Firstly, a new PET-RAFT polymerization method catalyzed by S- and P-doped CDs was established, which facilitated the synthesis of polymers with controllable molecular weight and uniform segment length under visible light and sunlight with low energy consumption. Secondly, by exploiting the localized surface plasmon resonance (LSPR) effect of Ag nanoparticles in-situ generated during the photocatalytic process of Ag3PO4, a near-infrared-photon driven PET-RAFT polymerization method with oxygen resistance was established, achieving efficient and controlled polymerization of a variety of monomers of polymer sorbents for seawater uranium extraction. Thirdly, a block polymer sorbent for seawater uranium extraction was successfully prepared by combining PET-RAFT polymerization and electrostatic spinning technology. Based on optimized segment conformation of polymer chains and diffusion environment, uranium adsorption performance was greatly improved. Finally, single- and dual-phase continuous-flow PET-RAFT polymerization processes were established in combination with microfluidic technology, allowing rapid synthesis of polymer sorbents for uranium extraction from seawater.This dissertation provides two high-efficiency PLRP methods with low energy consumption for controllable synthesis of polymer sorbents with specific compositions and structures from a wide range of monomers for seawater uranium extraction. On the other hand, the research in this dissertation would promote further studies on the structure-activity relationship of uranium adsorption on the molecular level, which is expected to reveal the influence of factors such as polymer segment conformation, mass transfer kinetics on uranium adsorption capacity. Moreover, the establishment of the continuous-flow PLRP technology will benefit scalable synthesis of sorbents for seawater uranium extraction in the future.
