Direct Air Capture: Recyclability and Exceptional CO 2 Uptake Using a Superbase

Direct air capture (DAC) of CO2 presents challenges owing to its low concentration and the high humidity of ambient air. In this study, efficient and reversible CO2 capture from humid air was achieved using a liquid absorbent derived from a deep eutectic solvent (DES), composed of 1,5,7-triazabicyclo [4.3.0] non-6-ene (TBN) and benzyl alcohol. Unlike conventional superbases, TBN-containing DES exhibits an exceptional absorption capacity of 0.154 gCO2/gDES (3.5 mmol/g, 1.25 mol/mol) from untreated ambient air (humidity above 90%). The DES underwent 100 absorption–desorption cycles, retaining 74% of its CO2 capture capacity after 50 cycles and 50% after 100 cycles. High stability, low toxicity, very high capture capacity, recyclability, and moisture insensitivity characterize this outstanding sorbent, making it suitable for DAC. This absorbent desorbs CO2 at just 70 °C within 30 min, effectively addressing one of the most challenging steps in DAC. According to the literature survey, this unique DES outperforms all previously reported liquid absorbents for DAC in terms of recyclability, efficiency, and practicality.