Engineered ionic liquid-covalent organic framework composites for high-capacity CO₂ capture: Mechanism insights and process optimization

This work demonstrates a strategic fabrication of high-performance CO 2 adsorbents by impregnating three conventional ionic liquids (ILs: [BMIM][NTf 2 ], [EMIM][NTf 2 ] or [EMIM][SCN]) with a covalent organic framework (COF) for carbon dioxide (CO 2 ) capture under simulated flue gas streams (1 bar, 15 vol% CO 2 , 60 ℃). Through the systematical assessment of the effects of IL structural features (different anions and cations), adding ratios (15–95 wt%), and operational temperatures (30–90 °C), it was shown that the adsorbent modified by [EMIM][SCN] in an appropriate amount (35 wt%) achieves the remarkable CO 2 adsorption capacity (5.273 mmol·g −1 at 60 ℃), representing a 3.7-fold enhancement compared to the original COF (1.419 mmol·g −1 ) due to its optimal combination of small molecular weight, short alkyl chain cation, and high CO 2 affinity anion. FTIR analysis revealed the potential adsorption mechanisms: the amine of COF chemisorbs CO 2 through carbamate formation, while the ILs enhance both chemisorption and physisorption of CO 2 via the thiocyanate nucleophilicity, the [NTf 2 ] - electronic redistribution, and hydrogen bonding of imidazolium, which is dominated by anion. The optimum CO 2 adsorption temperature (45–60 ℃) matches post-desulfurization flue gas conditions in coal-fired plants. With excellent performance and robust stability, these innovative adsorbents show practical potential for CO 2 capture in real post-combustion flue gas scenarios.