Hydrophobic deep eutectic solvents as green absorbents for hydrophilic VOC elimination

As a common hydrophilic volatile organic compound (VOC), acetone is known to harm human health and the atmospheric environment. Absorption is a typical technique applied to capture hydrophilic VOCs; however, the difficulty of separating and recovering absorbed hydrophilic VOCs (e.g., acetone) from aqueous absorbents has become one of the major challenges in practical applications. Hydrophobic deep eutectic solvents (DESs) have therefore been developed as novel green absorbents for capturing hydrophilic VOCs in the present work. The compiled results show that efficient hydrophilic VOC elimination can be accomplished by the proposed hydrophobic DESs through high absorption capacity and thermodynamically favorable gas-to-liquid mass transfer. Among the explored DESs, the hydrophobic DES containing thymol [Thy] and decanoic acid [DecA] with a molar ratio of 1:1 has achieved the highest absorption capacity of acetone, i.e., 6.57 mg acetone per g DES at 20 °C and 1480 ppm acetone. The oxygen of acetone interacts favorably with the hydrogen atom of [Thy] upon absorption, rendering hydrogen bonding interaction surpassing polarity as the key factor in attaining superior solubility of acetone in DESs. Moreover, the absorbed acetone can be easily removed from Thy-based DESs, realizing an effective hydrophilic VOC elimination process with economic and ecological benefits.