Crown-Ether Crystal Channel Membranes with Subnanometer Pores for Selective Na + Transport.

Emulating biological sodium ion channels to achieve high selectivity and rapid Na + transport is important for water desalination, energy conversion, and separation processes. However, the development of artificial ion channels, especially multichannels, to achieve high ion selectivity, remains a challenge. In this work, we demonstrate the fabrication of ion channel membranes utilizing crown-ether crystals (DA18C6-nitrate crystals), which feature extremely consistent subnanometer pores. The polyethylene terephthalate (PET) membranes were initially subjected to amination, followed by the in situ growth of DA18C6-nitrate crystals to establish ordered multichannels aimed at facilitating selective Na + conductance. These channels allow rapid Na + transport while inhibiting the migration of other ions (K + and Ca 2+ ). The Na + transport rate was 2.15 mol m -2 h -1 , resulting in the Na + /K + and Na + /Ca 2+ selectivity ratios of 6.53 and 12.56, respectively. Due to the immobilization of the crown-ether ring, when the size of the transmembrane ion exceeded that of the crown-ether ring's cavity, the ions had to undergo a dehydration process to pass through the channel. This resulted in the ions encountering a higher energy barrier upon entering the channel, making it more difficult for them to permeate. However, the size of Na + was compatible with the cavity of the crown-ether ring and was able to displace the hydrated layer effectively, facilitating selective Na + translocation. In summary, this research offers a promising approach for the future development of functionalized ion channels and efficient membrane materials tailored for high-performance Na + separation.