In recent years, research into crystalline materials with nano-sized pores in academia and industry has attracted much attention. This is because these materials are capable of various properties and applications of materials such as gas adsorption and storage, catalyst, energy conversion, optoelectronic devices. The porous materials have a regular structure, which constitutes a highly crystalline whole network. Among the porous materials, Covalent organic frameworks (COFs) are crystalline organic materials in which organic building blocks are formed with strong covalent bonds. The COFs are very light and have strong covalent bond, so they have low density and excellent thermal stability. They also have permanent pores, large surface area, and orderly crystallinity, which corresponded to a regular structure of the framework. These properties have attributed to the application of the COFs, specifically the field of gas sorption. Especially, the 3D COFs have highly attracted as a strong candidate in the field because their surface area and pore size are larger than 2D COFs. In the field of the COFs, H2, CH4, CO2 and NH3 gas adsorption are generally reported, however the study of SO2 gas sorption with COFs has not been reported yet.
In part 1, I optimized the SO2 capturing COFs with imide backbone and amine functional groups. Removing sulfur dioxide (SO2) from exhaust flue gases of fossil fuel power plants is an important issue given the toxicity of SO2 and subsequent environmental problems. To address this issue, we successfully developed a new series of imide-linked covalent organic frameworks (COFs) that have high mesoporosity with large surface areas to support gas flowing through channels; furthermore, we incorporated 4-[(dimethylamino)methyl]aniline (DMMA) as the modulator to the imide-linked COF. We observed that the functionalized COFs serving as SO2 adsorbents exhibit outstanding molar SO2 adsorption capacity, i.e., PI-COF-m10 record 6.30 mmol SO2 g-1 (40 wt%). To our knowledge, it is firstly reported COF as SO2 sorbent to date. We also observed that the adsorbed SO2 is completely desorbed in a short time period with remarkable reversibility. These results suggest that channel-wall functional engineering could be a facile and powerful strategy for developing mesoporous COFs for high-performance reproducible gas storage and separation.