CO 2 capture by 1,2,3-triazole-based deep eutectic solvents: the unexpected role of hydrogen bonds.

Herein, tetraethylammonium 1,2,3-triazolide ([Et 4 N][Tz]), 1,2,3-triazole (Tz), and ethylene glycol (EG) are used to form DESs for CO 2 capture. Surprisingly, [Et 4 N][Tz]-EG DESs can react with CO 2 , but [Et 4 N][Tz]-Tz cannot react with CO 2 , although both of the two systems contain the same anion [Tz] - . Unexpectedly, with the addition of EG to [Et 4 N][Tz]-Tz, the formed ternary DESs [Et 4 N][Tz]-Tz-EG can react with CO 2 , although neither EG nor [Et 4 N][Tz]-Tz can react with CO 2 before the combination of them. NMR, FTIR and theoretical calculation results disclose that the surprise CO 2 absorption behavior mainly depends on the strength of hydrogen bonds (H-bonds) between the anion [Tz] - and H-bond donors (EG or Tz). The strength of the H-bond between [Tz] - and Tz is much stronger than that between [Tz] - and EG. The strong H-bond between [Tz] - and Tz in [Et 4 N][Tz]-Tz greatly reduces the basicity of [Tz] - , rendering the anion [Tz] - unreactive to CO 2 . In [Et 4 N][Tz]-Tz-EG ternary DESs, EG competes with Tz to form a H-bond with [Tz] - , which weakens the strength of the H-bond between [Tz] - and Tz. Moreover, H-bonds also impact the desorption behavior. [Et 4 N][Tz] : EG (1 : 2) is regenerated at 60 °C, whereas the chemisorbed CO 2 by [Et 4 N][Tz] : Tz : EG (1 : 2 : 2) can be released even down to 30 °C.