Imine-linked covalent organic frameworks with stable and microporous structure for effective carbon dioxide and iodine uptake

In recent years, many environmental problems including global warming and climate change have emerged due to the excessive emission of carbon dioxide. Covalent organic frameworks (COFs) exhibit good porosity and excellent stability. They can be constructed into uniform channel and tunable skeleton which are ideal for gas uptake. Here, we designed two new imine-linked COFs (ESM-COF-1 and ESM-COF-2) by condensation of two C3 symmetrical monomers. Interestingly, ESM-COF-1 and ESM-COF-2 displayed microporous features because of short length building units employed, the pore size, which is much smaller than most two-dimensional (2D) imine COFs. This virtue is good for gas adsorption via pore surroundings. Furthermore, rich methoxy units as electron-donate units on the walls delocalized electronic clouds from building units to the imine bond through π-conjugation interaction, indicating outstanding stability in harsh conditions. High-density active units from walls (triphenylamine and methoxy groups) to the imine linkage also improved the gas adsorption via the weak interaction. Interestingly, ESM-COFs exhibited stability, microporous features, and active units from walls to linkage to give a high carbon dioxide uptake at 4.64 mmol g−1, which is the excellent one among the reported 2D COFs.