Selective Ion Transport in Two-Dimensional Ti₃C₂T Nanochannel Decorated by Crown Ether

Ion sieving is a critical process employed in various applications, such as desalination and ion extraction. Nevertheless, achieving rapid and accurate ion sieving remains an exceptionally difficult task. Drawing inspiration from the effective ion sieving capabilities of biological ion channels, we present the development of two-dimensional Ti₃C₂T ion nanochannels incorporating 4-aminobenzo-15-crown-5-ether molecules as specific ion binding sites. These binding sites had a significant influence on the ion transport process and improved ion recognition. Permeation of both Na⁺ and K⁺ was facilitated because their ion diameters are compatible with the cavity in the ether ring. Moreover, owing to the strong electrostatic interactions, the permeation rate for Mg²⁺ increased by a factor of 55 compared to that for the pristine channels, which was higher than those of all monovalent cations. Furthermore, the transport rate for Li⁺ was relatively lower than those of Na⁺ and K⁺, which was attributed to difficult binding of the Li⁺ to the oxygens in the ether ring. Consequently, the ion selectivities of the composite nanochannel were up to 7.6 for Na⁺/Li⁺ and 9.2 for Mg²⁺/Li⁺. Our work presents a straightforward approach to creating nanochannels exhibiting precise ion discrimination.