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

Abstract

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.

Size‐Based Cationic Molecular Sieving through Solid‐State Nanochannels

“…This case constitutes a significant experimental and theoretical extension of our recent work. [45] 2. 1 Figure 1 shows the current (I)-voltage (V) curves and conductances after the addition of a fixed concentration (25 × 10 -3 m) of the crown ethers (12C4, 15C5, and 18C6) in 100 × 10 -3 m alkali salt (LiCl, NaCl, and KCl) solutions; see Scheme 1.…”

Construction of Metal‐Organic Frameworks (MOFs)–Based Membranes and Their Ion Transport Applications

“…In addition, Wang and co‐workers reported MOF/polymer heterostructured nanochannels with nano‐to‐subnano asymmetric architectures via a contra‐diffusion growth method, which realized biomimetic unidirectional, fast, and selective proton conduction properties (Figure 4b(i)). [ 73 ] Notably, after filling the MOFs on one side of the PET nanochannel, the I–V curve of the MIL‐121/PET channel became highly rectified, exhibiting unidirectional proton transport (Figure 4b(ii)), with a rectification ratio of ≈500. The MIL‐121/PET heterostructured channels exhibited good proton selectivity over other cations (Figure 4b(iii)).…”

Metal–Organic Framework‐Based Ion‐Selective Membranes

“…MOF/polymer heterostructured nanochannels with nano-tosubnano asymmetric architectures were constructed by hydrothermal contra-diffusion growth of MOFs (e.g., MIL-121, MIL-53(Al), and MIL-53(Al)-NH 2 ) of 1D sub-1-nm channels into one side of the hourglass-shaped PET nanochannel membranes (Figure 3a). [38] Through ion-track-etching, the single hourglass nanochannels with BDC linkers on the inner surface were fabricated, [39] which were used as supports to facilitate the asymmetric growth of MOFs into one side of the nanochannel. The metal ion solution and the organic ligand solution were transferred into an interfacial reaction holder with a singlenanochannel PET membrane placing vertically between the two cells, followed by a hydrothermal reaction to prepare MOF crystals.…”

“…The development of efficient monovalent metal ions selective separation membranes is key to addressing the increasing demand for energy storage materials, such as lithium or sodium ion for [38] Copyright 2020, Wiley-VCH. b) Contra-diffusion of ZIF-8 MOF layers onto AAO supported ZIF-8/GO substrate to fabricate ZIF-8 membranes.…”