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