Is basicity the sole criterion for attaining high carbon dioxide capture in deep-eutectic solvents?

Area of Science:

• Chemical Engineering
• Materials Science
• Physical Chemistry

Background:

• Deep-eutectic solvents (DESs) are promising absorbents for carbon dioxide (CO2) capture.
• Understanding the fundamental properties governing CO2 solubility in DESs is crucial for optimizing their performance.
• Basicity, measured by Hammett basicity (H-) and aqueous basicity (pKa), has been proposed as a key factor influencing CO2 uptake.

Purpose of the Study:

• To critically analyze the correlation between different measures of basicity (H- and pKa) and CO2 weight-by-weight (w/w%) capacity in various DESs.
• To identify the primary interactions responsible for CO2 absorption in DESs.

Main Methods:

• A critical analysis of existing data on CO2 uptake in DESs.
• Evaluation of Hammett basicity (H-) and aqueous basicity (pKa) values for the studied DESs.
• Investigation of potential correlations between basicity parameters and CO2 w/w% capacity.

Main Results:

• Neither Hammett basicity (H-) nor aqueous basicity (pKa) showed a direct correlation with the CO2 w/w% capacity across the studied DESs.
• A strong correlation was observed between the "synergistic interactions" of donor and acceptor moieties within the DES and the CO2 w/w% capacity.
• These synergistic interactions appear to be the dominant factor governing CO2 absorption.

Conclusions:

• Traditional measures of basicity (H- and pKa) are not reliable predictors of CO2 uptake capacity in DESs.
• The interplay and synergistic interactions between the components of DESs are critical for effective CO2 absorption.
• Future research should focus on understanding and quantifying these synergistic interactions for rational DES design in CO2 capture applications.