The interconversion chemistry of amine-to-imine sites in a covalent organic framework (COF) was developed for the redox-based separation of uranium. Compared to traditional approaches using sacrificial reagents or material decomposition for the reduction and separation of uranium, amine-COF served as the electron donor and was regenerated repeatedly following the oxidation and uranium reduction/separation. The amine-COF, PI-3-AR, was formed from the sodium borohydride (NaBH₄) reduction of the imine-linked COF, PI-3, prepared from the solvothermal synthesis of 1,3,5-triformyl benzene (TFB) and 4,4′,4″-(1,3,5-triazine-2,4,6-triyl)trianiline (TTA). PI-3-AR could be converted back to PI-3 via oxidative amination using an excess of the oxidant iodine, I₂, or in the photochemical reduction of uranyl ions (UO₂²⁺). In consecutive photochemical uranium reduction and separation cycling experiments, the reduced amine COF, PI-3-AR, underwent: (i) oxidation alongside uranium photoreduction and deposition; (ii) acid treatment and uranium extraction; and (iii) NaBH₄ reduction and material recovery. The COF, PI-3-AR, and novel separation process involving amine-to-imine interconversion effectively removed uranium (maximum adsorption = 278 mg U/g COF) and maintained >98% uranium recovery over five recycling steps at pH 4.0.

中文翻译：

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用于可持续铀氧化还原分离的共价有机框架中的可逆胺至亚胺化学

共价有机骨架（COF）中胺-亚胺位点的互变化学是为了基于氧化还原的铀分离而开发的。与使用牺牲试剂或材料分解来还原和分离铀的传统方法相比，胺-COF作为电子供体，并在氧化和铀还原/分离后反复再生。胺-COF（PI-3-AR）是由硼氢化钠（NaBH ₄）还原亚胺连接的COF（PI-3）形成的，而PI-3是通过1,3,5-三甲酰苯（TFB）的溶剂热合成制备的和4,4',4"-(1,3,5-三嗪-2,4,6-三基)三苯胺(TTA)。 PI-3-AR 可以通过使用过量氧化剂碘 I _{2的氧化胺化或在铀酰离子 (UO 2} ²⁺ )的光化学还原中转化回 PI-3 。在连续的光化学铀还原和分离循环实验中，还原胺COF，PI-3-AR经历了：（i）氧化同时铀光还原和沉积； (二) 酸处理和铀提取； (iii) NaBH ₄还原和材料回收。 COF、PI-3-AR 和涉及胺-亚胺相互转化的新型分离工艺可有效去除铀（最大吸附量 = 278 mg U/g COF），并在 pH 4.0 的五个回收步骤中保持 >98% 的铀回收率。