Department of Materials and Optoelectronic Science, Center of Crystal Research , National Sun Yat-Sen University , Kaohsiung 80424 , Taiwan.
Chemistry Department, Faculty of Science , Assiut University , Assiut 71516 , Egypt.
ACS Appl Mater Interfaces. 2019 Mar 6;11(9):9343-9354. doi: 10.1021/acsami.8b21867. Epub 2019 Feb 21.
Covalent organic frameworks (COFs) are a family of crystalline porous networks having applications in various fields, including gas and energy storage. Despite respectable progress in the synthesis of such crystalline materials, examples of the use of template-free methods to construct COFs having hollow nano- and microstructures are rare. Furthermore, all reported methods for synthesizing these hollow structural COFs have involved [4 + 2] and [3 + 2] condensations. Herein, we report the synthesis of hollow microspherical and microtubular carbazole-based COFs through template-free, one-pot, [3 + 3] condensations of the novel triamine 9-(4-aminophenyl)-carbazole-3,6-diamine (Car-3NH) and triformyl linkers with various degrees of planarity. Depending upon the monomer's planarity, a unique morphological variety was observed. A time-dependent study revealed that each COF formed through an individual mechanism depended on the degree of planarity of the triformyl linker; it also confirmed that the hollow structures of these COFs formed through inside-out Ostwald ripening. Our COFs exhibited high Brunauer-Emmett-Teller surface areas (up to ca. 1400 m g), excellent crystallinity, and high thermal stability. Moreover, the CO uptake capacities of these COFs were excellent: up to 61 and 123 mg g at 298 and 273 K, respectively. The high surface areas facilitated greater numbers of strong interactions with CO molecules, leading to high CO uptake capacities. Moreover, the prepared COFs exhibited redox activity because of their redox-active triphenylamine and pyridine groups, which can be utilized in electrochemical energy storages. Accordingly, such hollow COFs having high surface areas appear to be useful materials for industrial and biological applications.
共价有机骨架（COFs）是一类具有晶体多孔网络的物质，在气体和能量存储等各个领域都有应用。尽管在合成这种晶体材料方面取得了相当大的进展，但使用无模板方法构建具有纳米和微观空心结构的 COFs 的例子却很少。此外，所有报道的合成这些空心结构 COFs 的方法都涉及[4+2]和[3+2]缩合反应。在此，我们报告了通过无模板、一锅法、新型三胺 9-(4-氨基苯基)-咔唑-3,6-二胺（Car-3NH）和具有不同程度平面性的三醛基连接剂的[3+3]缩合反应，合成了空心微球和微管型咔唑基 COFs。根据单体的平面性，可以观察到独特的形态多样性。时间依赖性研究表明，每个 COF 通过单独的机制形成，这取决于三醛基连接剂的平面性程度；它还证实了这些 COFs 的空心结构是通过内部向外的奥斯特瓦尔德熟化形成的。我们的 COFs 具有高比表面积（高达约 1400 m g）、优异的结晶度和高热稳定性。此外，这些 COFs 的 CO 吸收能力非常出色：在 298 K 和 273 K 下分别达到 61 和 123 mg g。高比表面积促进了与 CO 分子的更多强相互作用，从而导致高 CO 吸收能力。此外，由于其具有氧化还原活性的三苯胺和吡啶基团，这些制备的 COFs 表现出氧化还原活性，可用于电化学储能。因此，具有高比表面积的这种空心 COFs 似乎是工业和生物应用的有用材料。
