Recognizing multiple kinds of ions specifically by ultrathin polymeric membranes with aligned angstrom pores for energy-efficient lithium extraction

Abstract Generally, it is common for the selective porous membrane to separate one specific ion from the mixture solution, which widely applied in water-treatment, energy storage systems, nuclear waste management and so on. However, it is still rare to recognize several ions simultaneously for a single selective membrane, analogous to ion chromatography systems. Here, we could recognize multi-kinds of ions simultaneously using one single ultrathin polymeric membrane with aligned angstrom pores by applying micro-voltages specifically, and finally realize ultralow energy-efficiency of lithium extraction. The ultrathin membrane is facile to be obtained by superspreading the organic solution of polymer bearing porphyrin rings onto the water substrate. Applied an ultralow electric field at micro-voltage scale, accurate ion sieving could be simply achieved in order of ion valences. And ions with same valence could also be finely recognized and sieved with micro-voltages independently. This is attributed to the low internal tortuosity for the ultrathin thickness. Therefore, the slight difference between the ion dehydration binding energy and the absorption barrier with the porphyrin ring for each ion could be retained. This phenomenon is highly dependent on the ionic concentration and each ion tends to feature unique voltage. Simulation results revealed that Li+ with small ionic radius and relatively low hydration free energy exhibits affinity for the porphyrin ring. Therefore, the significant voltage difference between Li⁺ and other ions makes it easy to extract Li⁺ at micro-scale voltage. Such ultralow voltage and separation efficiency guarantees an unprecedented energy efficiency (1.1×10-⁴ Wh/gLi) of lithium extraction, which reduces 1,000 times of cost compared to that of conventional electrodialysis methods. This strategy preparing aligned pore structure holds great promise in industrial energy-intensive and high-value industries requiring separations, with direct implications for sustainable resource recovery and next-generation membrane technologies.