Engineering Polymeric Nanofluidic Membranes for Efficient Ionic Transport: Biomimetic Design, Material Construction, and Advanced Functionalities

Abstract

Design elements extracted from biological ion channels guide the engineering of artificial nanofluidic membranes for efficient ionic transport and spawn biomimetic devices with great potential in many cutting-edge areas. In this context, polymeric nanofluidic membranes can be especially attractive because of their inherent flexibility and benign processability, which facilitate massive fabrication and facile device integration for large-scale applications. Herein, the state-of-the-art achievements of polymeric nanofluidic membranes are systematically summarized. Theoretical fundamentals underlying both biological and synthetic ion channels are introduced. The advances of engineering polymeric nanofluidic membranes are then detailed from aspects of structural design, material construction, and chemical functionalization, emphasizing their broad chemical and reticular/topological variety as well as considerable property tunability. After that, this Review expands on examples of evolving these polymeric membranes into macroscopic devices and their potentials in addressing compelling issues in energy conversion and storage systems where efficient ion transport is highly desirable. Finally, a brief outlook on possible future developments in this field is provided.

Engineering solid nanochannels with macrocyclic host–guest chemistry for stimuli responses and molecular separations

“…15,16 To date, it should be noted that several groups have reported integrating host-guest systems for the creation of biomimetic gates. [17][18][19][20] As a result of the cooperative effect and directionality of the noncovalent interactions, host-guest chemistry-based nanochannels are beneficial for merging advantages and achieve applications in the field of membrane separation and smart devices.…”

The role of ion‐membrane interactions in fast and selective mono/multivalent ion separation with hierarchical nanochannels

“…6,7 To date, most regular IEMs with low permselectivities have not met the requirements for practical industrial applications. [8][9][10] Selective transport of a specific component, such as the permselectivity for monovalent cations over multivalent cations in a mixed salt solution, determines the separation efficiency, ensuring high purity of the target cations and high energy sustainability. 11,12 However, the intrinsic transportation mechanism cannot be fully explained.…”

“…Ion exchange membranes (IEMs) have been widely implemented in electrodialysis (ED), 3 reverse electrodialysis, 4 redox flow batteries, 5 and proton‐exchange membrane fuel cells 6,7 . To date, most regular IEMs with low permselectivities have not met the requirements for practical industrial applications 8–10 . Selective transport of a specific component, such as the permselectivity for monovalent cations over multivalent cations in a mixed salt solution, determines the separation efficiency, ensuring high purity of the target cations and high energy sustainability 11,12 .…”

Steric Hindrance-Induced Dehydration Promotes Cation Selectivity in Trans-Subnanochannel Transport

“…, lithium in salt-lake brines), reutilization of wastewater ( i.e. , N and P recovery), and desalination for fresh water. − Understanding the principles for transport or hindrance of ions is beneficial to improving membrane-based techniques and developing novel membrane materials for precise solute–solute selectivity. − Ions are hydrated by a shell of dipolar water molecules, which means that dehydration inevitably occurs in ion trans-membrane processes since the membrane pore size is usually smaller than the hydrated ion, further impacting the selective transport of different ions. , However, most dehydration mechanisms in previous research have been discussed by theoretical simulation or analyzed based on size relationships and retention rates, while experimental evidence is lacking due to the difficulty of finding adequate techniques. , Therefore, systemic investigations on dehydration in ion-selective transport are needed for a thorough understanding of ion trans-membrane mechanisms, which can facilitate the design of solute–solute selective membranes needed for precise separations.…”