A facile synthesis of trioctylphosphine oxide-based azole deep eutectic solvents: Efficient reversible CO2 capture

Capturing and recovering carbon dioxide (CO 2 ) from the combustion of fossil fuels is an effective way to reduce carbon emissions, as CO 2 is not only a threat to the environment but also an important C1 feedstock. In the current work, a series of trioctylphosphine oxide (TOPO)-based azole deep eutectic solvents (DESs) have been synthesized for the efficient absorption of CO 2 . The solid–liquid phase diagrams of the DESs were projected using the prediction data from COSMO-RS, and the experimental melting temperature was found to be lower than that of the prediction. These DESs exhibit satisfactory physical properties, including low viscosities (20–60 mPa·s) and high thermal decomposition temperatures (up to 192.5 °C). Furthermore, the CO 2 uptake process was carried out at 35 °C and 0.1 MPa, and the results demonstrated that the CO 2 uptake capacity was positively influenced by hydrogen bond donors (HBDs), mole fraction of HBDs, temperatures, and humidity. Among the DESs, TOPO-imidazole (1:1) was notable for its high absorption capacity of 0.062 mol CO 2 /mol DES, as well as its excellent recyclability. There was no discernible decline in the CO 2 uptake capacity after four absorption–desorption cycles. In this work, NMR and FT-IR investigations indicated the physical absorption mechanism of this system. The designed DESs have the potential to be effective absorbents for efficient reversible CO 2 capture.