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

Abstract

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% (3.18mmol/g), 25 wt% (5.68 mmol/g), and 26 wt% (5.91mmol/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.