Tuning of Microenvironment in Covalent Organic Framework via Fluorination Strategy promotes Selective CO2 Capture

Abstract

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 CO₂ adsorption capacity and also CO₂ /N₂ selectivity. Compared to the non-fluorinated PD-COF (BET surface area 805 m² 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 m² g^-1 , total pore volume 0.2978 ccg^-1 ). This fact leads to an enormous decrease in the CO₂ adsorption capacity and CO₂ /N₂ selectivity of TF-COF, though it shows stronger affinity towards CO₂ with a Qst of 37.76 KJ/mol. The more CO₂ 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 CO₂ /N₂ selectivity of 16.8, higher than that of TF-COF (CO₂ /N₂ selectivity 13.4).

Keywords: CO2 adsorption; CO2/N2 selectivity; Covalent organic framework; Fluorination.