Ionic liquid-based supported liquid membranes for enhanced cesium continuous separation via crown-ether facilitated transport

The global high-tech industry is experiencing a consistent rise in the demand for cesium. Consequently, it is essential to establish a continuous and energy-efficient method for the recovery of Cs + from aqueous solutions. In this study, a novel supported ionic liquid membrane (SILM) was engineered by incorporating a crown ether-ionic liquid extraction system into the pores of a crown ether-based porous membrane, which was synthesized from 18-crown-6 ether-based polyimide (CE-PI) through non-solvent induced phase separation (NIPS). The findings indicate that the Cs + permeation rate in the SILM system containing free crown ether with a concentration of 0.12 mol/L achieved 3.36 μm/s, representing a 24-fold increase compared to that of the SILM system without free crown ether. When the feed phase comprised mixed ions (K + /Cs + /Rb + ) at a concentration of 50 ppm each, and 0.5 mol/L HCl was used as a stripping phase, the Cs + permeation flux of the SILM system reached 0.233 μg m −2  s −1 , which is substantially greater than that of the competing ions K + (0.001 μg m −2  s −1 ) and Rb + (0.005 μg m −2  s −1 ). The corresponding separation factors (SF) for Cs/K and Cs/Rb in the SILM system were determined to be 10.10 and 7.44, respectively. The high performance of the SILM system is attributed to the ion transport channels established by the free crown ether and ionic liquid within the membrane pores. DFT calculations and MD simulations demonstrated that the free crown ethers in the ionic liquid are instrumental in selectively complexing Cs + owning to their unique chelation interaction (E Cs  = −288.5 kJ/mol), thereby promoting the transport of Cs + within the SILM system.