Surpassing the Performance of Phenolate‐derived Ionic Liquids in CO2 Chemisorption by Harnessing the Robust Nature of Pyrazolonates

A series of pyrazolonate-derived superbase ionic liquids (SILs) have been developed towards efficient and stable carbon capture. High and tunable CO₂ uptake capacity was achieved by producing the carbonates via O−C bond formation. The enhanced CO₂ uptake and improved stability in long-term utilization were enabled by combining the strong interaction strength of oxygenate species with CO₂ and the involvement of aza-fused rings in the anions.

Abstract

Superbase-derived ionic liquids (SILs) are promising sorbents to tackle the carbon challenge featured by tunable interaction strength with CO₂ via structural engineering, particularly the oxygenate-derived counterparts (e. g., phenolate). However, for the widely deployed phenolate-derived SILs, unsolved stability issues severely limited their applications leading to unfavorable and diminished CO₂ chemisorption performance caused by ylide formation-involved side reactions and the phenolate-quinone transformation via auto-oxidation. In this work, robust pyrazolonate-derived SILs possessing anti-oxidation nature were developed by introducing aza-fused rings in the oxygenate-derived anions, which delivered promising and tunable CO₂ uptake capacity surpassing the phenolate-based SIL via a carbonate formation pathway (O−C bond formation), as illustrated by detailed spectroscopy studies. Further theoretical calculations and experimental comparisons demonstrated the more favorable reaction enthalpy and improved anti-oxidation properties of the pyrazolonate-derived SILs compared with phenolate anions. The achievements being made in this work provides a promising approach to achieve efficient carbon capture by combining the benefits of strong interaction strength of oxygenate species with CO₂ and the stability improvement enabled by aza-fused rings introduction.

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