Unidirectional and Selective Proton Transport in Artificial Heterostructured Nanochannels with Nano-to-Subnano Confined Water Clusters.

The construction of biological proton channel analogues has attracted substantial interest owing to their wide potential in separation of ions, sensing, and energy conversion. Here, metal-organic framework (MOF)/polymer heterogeneous nanochannels are presented, in which water molecules are confined to disordered clusters in the nanometer-sized polymer regions and to ordered chains with unique molecular configurations in the 1D sub-1-nm porous MOF regions, to realize unidirectional, fast, and selective proton transport properties, analogous to natural proton channels. Given the nano-to-subnano confined water junctions, experimental proton conductivities in the polymer-to-MOF direction of the channels are much higher than those in the opposite direction, showing a high rectification up to 500 and one to two orders of magnitude enhancement compared to the conductivity of proton transport in bulk water. The channels also show a good proton selectivity over other cations. Theoretical simulations further reveal that the preferential and fast proton conduction in the nano-to-subnano channel direction is attributed to extremely low energy barriers for proton transport from disordered to ordered water clusters. This study opens a novel approach to regulate ion permeability and selectivity of artificial ion channels.