Investigation on mechanisms of ammonia absorption in [Im][SCN]-based eutectic solvents using computational methods

Abstract

With the characteristics of high thermal stability, low cost, and strong solvation capacity, deep eutectic solvents (DESs) are recognized as promising absorbents for harmful gases, especially NH3. Unfortunately, the works from literatures rarely explore the molecular mechanism, which plays an essential and decisive factor in tailoring DESs for NH3 capture. Present study utilized molecular dynamics and quantum chemistry to systematically deduce NH3 absorption mechanisms in [Im][SCN]-based DESs. Results revealed the decisive role of competitive binding between HBD or [SCN]- and [Im]+ for promoting NH3 absorption. Upon NH3 dissolving into DESs, the initial small portion establishes strong hydrogen bonds with N–H of [Im]+ and –OH of EG, while the subsequent majority of NH3 interacts with EG via van der Waals forces. Even in NH3-saturated DES, the NH3-NH3 hydrogen bonds are not obvious. Elevated temperatures negatively affect the formation of hydrogen-bond between NH3 and DES, and result in the release of NH3 at 323.15 K. The research provides valuable and comprehensive insights on the absorption mechanism of NH3 at molecular level.