Carbon dioxide capture by new DBU ‐based DES : The relationship between ionicity and absorptive capacity

1,8‐Diazabicyclo[5.4.0]undec‐7‐ene (DBU)/imine, DBU/imide DESs were designed and synthesized as CO 2 trapping agents. Toward this end, the optimal absorption temperature and the maximum absorption capacity were determined. It was found that ionicity is a key factor to affect the absorption capacity of CO 2 . Combined with the ionicity calculation, a new CO 2 capture mechanism has been proposed. HBD in DES can be divided into two parts. One can undergo proton transfer, obeying anion 2:1 absorption, whereas the other, without proton transfer, is amine 1:1 absorption. The degree of proton transfer in DES determines the ionicity and affects the absorption performance. The DFT calculation results confirmed this mechanism by micro perspective. DBU/2‐Pyrrolidinone and DBU/Oxazolidinone were proved to be good CO 2 trapping agents with high absorption capacity, being 1.064 mol CO 2 /mol DES and 0.827 mol CO 2 /mol DES, respectively, and excellent recyclability when the mole ratio of HBA:HBD is 2:1.