Enhanced CO2 capture driven by synergistic proton transfer via dual anionic and cationic active sites

Dual-active-site PIL-based phase-merging absorbent (TDPH) for efficient CO 2 capture. • High CO 2 loading (4.32 mol·kg −1 ) and rapid absorption via synergistic proton transfer. • Proton transfer mechanism revealed by NMR, titration and DFT calculations. • Regeneration energy reduced to 1.82 GJ·t −1 . During the CO 2 capture process with amine-based absorbents, proton transfer can effectively regulate the absorption performance, especially the absorption rate and the composition of the products. In this study, by using lysine anion (Lys − ) and 3-dimethylaminopropyl ammonium (DMAPAH + ) as the anion and cation of a protic ionic liquid (PIL), respectively, a biphasic system (TDPH) was constructed with aqueous solutions of N , N , N ′, N ′-tetramethyl-1,6-hexanediamine (TMHDA) and PIL, which presents a rich and effective proton transfer network for efficient CO 2 capture. Lys − and DMAPAH + jointly form a dual-active-site network, creating a rich proton-transfer microenvironment that facilitates proton migration, thereby achieving a high CO 2 loading (4.32 mol/kg). Moreover, during the absorption process, TMHDA accepts protons, inducing the original two phases to merge into one phase, thereby reducing the viscosity of the absorbent. Accordingly, compared to the single-active-site system, the CO 2 loading of TDPH is increased by 20.6%, while the absorption equilibrium time is reduced by 50.1%, with the regeneration energy consumption being only 1.82 GJ/ton CO 2 . NMR, titration and quantum chemical calculations confirm that Lys − and DMAPAH + synergistically participate in the proton transfer process toward TMHDA, forming multiple CO 2 binding sites, and enhancing phase merging during absorption and phase separation during desorption. This work demonstrates that the dual-active-site functionalization strategy is an effective approach for harnessing the potential of phase-transition ionic liquids and designing highly efficient, low-energy-consumption CO 2 absorbents.