Uranium, a key nuclide in the nuclear industry, has substantially damaged the ecological environment and human health due to its high toxicity and radioactivity. Therefore, its efficient separation and extraction from water are of great significance for environmental safety. However, the low concentration of uranium in water requires capture materials with high adsorption affinity, which poses a severe challenge to conventional materials. Herein, we designed a novel covalent organic framework (COF-TpDd-AO₂) with two amidoxime groups in each structure unit, to provide multiple capture sites towards uranium, as the trap material. This COF exhibited different adsorption behaviors towards uranium with different concentrations, with a maximum affinity of 8.27 × 10⁵ mL g⁻¹, which was 6.82 and 9.81 times higher than those of the control sample COF-TpDb-AO with a single amidoxime group and the pristine COF-TpDd. The removal efficiency exceeded 99.2% with the initial uranium concentration of 0.5 mg L⁻¹. Mechanism studies showed that the chelation interaction between multi-site amidoxime groups and uranium acted as the dominant adsorption force. Moreover, with the increasing density of the amidoxime group in COF-TpDd-AO₂, the chelation effect changed from one single site to multiple sites, thus further enhancing the uranium affinity. This work suggested that the purposeful design of COFs with multi-site amidoxime groups could be an effective strategy to improve the adsorption affinity of COFs towards low-concentration uranium.

中文翻译：

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合理构建具有多位官能团的共价有机骨架，以高效去除水中的低浓度U（VI）

铀是核工业中的关键核素，由于其高毒性和放射性，已严重破坏了生态环境和人类健康。因此，从水中有效分离和提取对环境安全具有重要意义。然而，水中低浓度的铀需要具有高吸附亲和力的捕集材料，这对常规材料提出了严峻的挑战。在这里，我们设计了一个新颖的共价有机骨架（COF-TpDd-AO ₂），每个结构单元中都有两个a胺肟基，以提供多个捕获铀的捕获位点作为捕集材料。该COF对不同浓度的铀表现出不同的吸附行为，最大亲和力为8.27×10 ⁵ mL g ^-1分别是含with胺肟组和原始COF-TpDd的对照样品COF-TpDb-AO的6.82和9.81倍。初始铀浓度为0.5 mg L ^-1时，去除效率超过99.2％。机理研究表明，多位a胺肟基团与铀之间的螯合相互作用是主要的吸附力。此外，随着COF-TpDd-AO ₂中the肟肟基团密度的增加，螯合作用从一个位点变为多个位点，从而进一步增强了铀的亲和力。这项工作表明，针对多位a胺肟基的COF进行有目的的设计可能是提高COF对低浓度铀的吸附亲和力的有效策略。