Highly efficient CO2 capture from open air and dilute gas streams by tunable azolate ionic liquids based deep eutectic solvents

A series of functional deep eutectic solvents (DESs) forming from azolate ionic liquids (ILs) and ethylene glycol (EG) or succinonitrile (SN) were designed and synthesized for CO2 capture with ultra-high uptake from open air (420–430 ppm) or dilute gas streams (500 ppm–5 vol%). With the increase of pKa of azoles, the CO2 capacity of these azolate-based DESs increased linearly with R2 = 0.96. Compared with other DESs and ILs, the extremely high CO2 capture capacities of 14 wt% (3.18 mmol/g), 25 wt% (5.68 mmol/g), and 26 wt% (5.91 mmol/g) could be reached under open air / 500 ppm, 2 vol%, and 5 vol% CO2, respectively, via tuning the structures of DESs. In addition, spectroscopic investigations revealed that the anion-induced multi-site cooperations of O···CO2 and N···CO2 were the reason of ultrahigh CO2 capacities. To the best of our knowledge, these are the first examples of tuning amine-free functional DESs for the highly efficient CO2 capture from open air. The significant improvements made in this work on CO2 capture over conventional sorbents provide an alternative strategy for industrial gas capture and utilization via anion-induced multi-site cooperations.