Artificial Monovalent Metal Ion-Selective Fluidic Devices Based on Crown Ether@Metal-Organic Frameworks with Subnanochannels.

Precise regulation of ion transport through nanoscale pores will profoundly impact diverse fields from separation to energy conversion but is still challenging to achieve in artificial ion channels. Herein, inspired by the exquisite ion selectivity of biological Na+ channels, we have successfully fabricated hierarchically grown metal-organic frameworks (MOFs) on an asymmetrical substrate assisted by atomically thin nanoporous graphene. Efficient separation of monovalent metal ions is realized by encapsulating 18-crown-6 into MOF crystals. The resulting 18-crown-6@ZIF-67/ZIF-8 device, with subnanochannels and specific K+ binding sites, shows an ultrahigh Li+ conductivity of 1.46 × 10-2 S cm-1 and selectivities of 9.56 and 6.43 for Li+/K+ and Na+/K+, respectively. The Li+ conductivity is around 1-2 orders of magnitude higher than reported values for the other MOF materials. It is the first time that MOFs with subnanochannels realize selective transport of Na+ (ionic diameter of 1.9 Å) over K+ (2.6 Å) based on subangstrom differences in their ionic diameter. Our work opens new avenues to develop crown ether@MOF platforms toward efficient ion transistors, fluidic logic devices, and biosensors.