Protic ionic liquids with low viscosity for efficient and reversible capture of carbon dioxide.

• Three low viscous protic ionic liquids were synthesized for CO 2 absorption. • The ionic liquids with larger basicity show higher CO 2 absorption capacity. • Addition of H 2 O influences greatly the CO 2 absorption performance of [TMGH][Im]. • Different products were obtained in [TMGH][Im] and [TMGH][Im]-H 2 O systems. Protic ionic liquids (PILs) are considered as potential solvents for CO 2 capture due to their simple synthetic routes and unique properties. In this work, three low viscous PILs, tetramethylgunidinium imidazole ([TMGH][Im]), tetramethylgunidinium pyrrole ([TMGH][Pyrr]) and tetramethylgunidinium phenol ([TMGH][PhO]) were synthesized and the effect of anions, temperature, CO 2 partial pressure and water content on CO 2 absorption performance of PILs was also systematically studied. It was found that the PILs with larger basicity show higher CO 2 absorption capacity, and [TMGH][Im] simultaneously shows relatively high absorption rate and CO 2 absorption capacity of 0.154 g CO 2 /g IL at 40 °C, 1 bar. The addition of H 2 O has a positive effect on gravimetric absorption capacity of CO 2 at the range of 0–20 wt% H 2 O, and the highest capacity of 0.186 g CO 2 /g IL was achieved as the water content was 7 wt%. In situ FTIR, ¹³C NMR and theoretical calculations verified that more stable bicarbonate are produced during CO 2 absorption by [TMGH][Im]-H 2 O system. However, neat [TMGH][Im] can react with CO 2 to form the reversible carbamate, leading to excellent recyclability after four absorption-desorption cycles. The results implied that neat [TMGH][Im] shows great potentials in CO 2 absorption applications. [ABSTRACT FROM AUTHOR]