Tuning of Microenvironment in Covalent Organic Framework via Fluorination Strategy promotes Selective CO 2 Capture.

Herein, we have designed and synthesized two heteroatom (N, O) rich covalent organic frameworks (COF), PD-COF and TF-COF, respectively, to demonstrate their relative effect on CO 2 adsorption capacity and also CO 2 /N 2 selectivity. Compared to the non-fluorinated PD-COF (BET surface area 805 m 2  g -1 , total pore volume 0.3647 ccg -1 ), a decrease in BET surface area and also pore volume have been observed for fluorinated TF-COF due to the incorporation of fluorine to the porous framework (BET surface area 451 m 2  g -1 , total pore volume 0.2978 ccg -1 ). This fact leads to an enormous decrease in the CO 2 adsorption capacity and CO 2 /N 2 selectivity of TF-COF, though it shows stronger affinity towards CO 2 with a Qst of 37.76 KJ/mol. The more CO 2 adsorption capacity by PD-COF can be attributed to the large specific surface area with considerable amount of micropore volume compared to the TF-COF. Further, PD-COF exhibited CO 2 /N 2 selectivity of 16.8, higher than that of TF-COF (CO 2 /N 2 selectivity 13.4).