The relatively large pore sizes (typically around 1 nm) and the prevalence of defect sites make it challenging for covalent organic framework (COF) membranes to efficiently separate sub-nanometer scale ions. In this study, we customized four types of 2D Janus COF membranes using the acetic acid buffering interlayer interface method. By leveraging the design flexibility of COFs, we finely tuned the positioning of functional groups on the pore walls to achieve the preparation of 2D Janus COF membranes with enhanced synergistic coordination properties, which were then employed for the efficient separation of Sr and Y ions. The different relative positions of phenolic hydroxyl groups on the pore walls impart distinct coordination states with respect to Sr and Y ions, whereby COF membranes with ortho-hydroxyl configurations exhibit enhanced synergistic coordination capabilities compared to those with para-hydroxyl configurations. Screening experiments revealed that, with the same number of hydroxyl groups, the COF membranes featuring ortho-hydroxyl groups demonstrated a greater tendency to coordinate with Y (III) ions compared to those with para-hydroxyl groups, mainly due to the additional binding site provided by the ortho configuration. In the Sr/Y separation system, the selectivity of the COF membrane with synergistic coordination ability was as high as 99.7 % for Sr (II), maintaining selectivity above 95.8 % even after five repeated experiments. In contrast, the para-hydroxyl COF membranes exhibited a significantly lower selectivity for Sr (II), measuring only 66.4 %. This work provides valuable insights into the design and fabrication of high-performance ions separation membranes and Janus membranes.

中文翻译：

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增强 2D Janus 共价有机框架膜的协同配位，实现高效的 Sr/Y 离子分离


相对较大的孔径（通常约为 1 nm）和缺陷位点的普遍存在使得共价有机框架 （COF） 膜难以有效分离亚纳米级离子。在这项研究中，我们使用乙酸缓冲层间界面方法定制了四种类型的 2D Janus COF 膜。通过利用 COF 的设计灵活性，我们微调了官能团在孔壁上的位置，以制备具有增强协同配位特性的 2D Janus COF 膜，然后将其用于高效分离 Sr 和 Y 离子。酚羟基在孔壁上的不同相对位置赋予了关于 Sr 和 Y 离子的不同配位态，因此与具有对羟基构型的 COF 膜相比，具有邻羟基构型的 COF 膜表现出增强的协同配位能力。筛选实验表明，在羟基数量相同的情况下，与具有对羟基的 COF 膜相比，具有邻羟基的 COF 膜表现出更大的与 Y （III） 离子配位的倾向，这主要是由于邻位构型提供的额外结合位点。在 Sr/Y 分离系统中，具有协同配位能力的 COF 膜对 Sr （II） 的选择性高达 99.7 %，即使重复实验 5 次，选择性仍保持在 95.8 % 以上。相比之下，对羟基 COF 膜对 Sr （II） 的选择性显著降低，仅为 66.4 %。这项工作为高性能离子分离膜和 Janus 膜的设计和制造提供了有价值的见解。