Dual reaction pathways toward CO2 capture enabled by 1,5-diazabicyclo[4.3.0]non-5-ene in ternary deep eutectic solvents: Mechanistic insights and performance advantages

The development of efficient, low-viscosity, and environmentally friendly solvents is essential for sustainable CO 2 capture. In this study, a series of ternary deep eutectic solvents (DEAz-DESs) were synthesized using 1,5-diazabicyclo[4.3.0]non-5-ene (DBN) as the hydrogen bond acceptor, and ethylene glycol (EG) along with various azoles as hydrogen bond donors. These DESs exhibited excellent physicochemical properties, including low viscosity (7.83–41.41 mPa·s at 40 °C) and high thermal stability ( T d  = 112–133 °C). The low viscosities enabled rapid CO 2 mass transfer and absorption kinetics. Among them, the DBN/Pyrazole/EG (3:1:1) system demonstrated a high CO 2 uptake of 0.194 gCO 2 /gDES at 1 bar and 40 °C. Combined spectroscopic characterization and DFT calculations elucidated dual chemisorption mechanisms: carbamate formation through pyrazolate and carbonate formation mediated by DBN-activated EG, jointly accounting for the elevated CO 2 absorption capacity. Thermodynamic analysis yielded moderate absorption enthalpies (−38 to −63 kJ/mol), indicating favorable regeneration at mild temperatures. The DBN/Pyrazole/EG (3,1:1) DES retained over 90% of its absorption capacity after 10 cycles, demonstrating excellent reusability. Compared with other reported DESs, the DEAz-DESs presented in this work offer superior absorption performance and lower viscosities. These findings suggest that the ternary DBN/azole/EG systems are promising candidates for efficient and sustainable post-combustion CO 2 capture applications.