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 2 ) 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 2 g -1 ), excellent crystallinity, and high thermal stability. Moreover, the CO 2 uptake capacities of these COFs were excellent: up to 61 and 123 mg g -1 at 298 and 273 K, respectively. The high surface areas facilitated greater numbers of strong interactions with CO 2 molecules, leading to high CO 2 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.
Bibliographical noteFunding Information:
This study was supported financially by the Ministry of Science and Technology, Taiwan, under contracts MOST 106-2221-E-110-067-MY3, 105-2221-E-110-092-MY3, and 108-2218-E-110-013-MY3. This work was also performed in part at the Queensland node of the Australian National Fabrication Facility, a company established under the National Collaborative Research Infrastructure Strategy to provide nano and microfabrication facilities for Australia’s researchers.
© 2019 American Chemical Society.
All Science Journal Classification (ASJC) codes
- Materials Science(all)