Extreme Ion‐Transport Inorganic 2D Membranes for Nanofluidic Applications

Abstract

Inorganic 2D materials offer a new approach to controlling mass diffusion at the nanoscale. Controlling ion transport in nanofluidics is key to energy conversion, energy storage, water purification, and numerous other applications wherein persistent challenges for efficient separation must be addressed. The recent development of 2D membranes in the emerging field of energy harvesting, water desalination, and proton/Li‐ion production in the context of green energy and environmental technology is herein discussed. The fundamental mechanisms, 2D membrane fabrication, and challenges toward practical applications are highlighted. Finally, the fundamental issues of thermodynamics and kinetics are outlined along with potential membrane designs that must be resolved to bridge the gap between lab‐scale experiments and production levels.

Selective Ion Transport in Two‐Dimensional Lamellar Nanochannel Membranes

“…[2,3] The substantial progress achieved in two-dimensional (2D) materials during the last decade has fostered research on ion transport behavior under nanoconfinement and brought new possibilities for the development of advanced ion separation technology (Figure 1). [20,21] Membranes with extraordinary separation performance derived from singlelayer graphene with uniformly perforated nanopores were first proposed. [22] Although atom-thick membranes could minimize the transport resistance and subsequently maximize the permeability, the effective strategy to scale an integrated 2D nanosheet with large angstrom-precise pores into industrial devices is still a great obstacle to its industrial application.…”

Efficient photo-driven ion pump through slightly reduced vertical graphene oxide membranes

“…Two-dimensional (2D) nanofluidic membranes, constructed using 2D nanomaterials like graphene oxide (GO), [13][14][15] graphene derivatives, [16][17][18] transition metal carbides and nitrides (Mxenes), [19][20][21] transition metal dichalcogenides (TMDs), 22,23 black phosphorus (BP), 24 and caly, 25 offer ideal platforms for nanofluidic ion transport due to their high selectivity and ultrafast permeation. [26][27][28][29] Consequently, physical ion pumps based on 2D nanofluidic membranes have become the focus of extensive research. One noteworthy example is the generation of a transmembrane ionic flow along GO membranes (GOMs) under asymmetric light illumination, following a diffusion-based charge separ-ation mechanism.…”

Ionic Sieving at Sub-Angstrom Precision Enabled by Metal Organic Frameworks

“…16−22 Among them, the porous organic framework is an emerging class of nanomembrane materials, and metal−organic framework (MOF) is one of their representatives. 23,24 The structure of MOF materials can be precisely designed and constructed by the precursors, i.e., metal nodes and organic linkers, 25,26 and the pore size can be further tuned by chemical modification with specific functional groups. 27 With their narrow pores, MOFs have shown potential for the selective separation of ionic species such as F − /Cl − , Br − /NO 3 − , Na + /K + , and Na + /Ca 2+ , mimicking the transport behavior of biological channels.…”

“…Utilizing traditional polymer membrane synthesis routes, it is often difficult to precisely regulate the pore structure since the fabrication process involves random cross-linking reactions, , thereby giving rise to broad pore size distribution and low ion selectivity. Advances in nanotechnology have brought intriguing techniques, including top-down and bottom-up synthesis approaches, for creating membranes composed of more defined pore structures. − Among them, the porous organic framework is an emerging class of nanomembrane materials, and metal–organic framework (MOF) is one of their representatives. , The structure of MOF materials can be precisely designed and constructed by the precursors, i.e., metal nodes and organic linkers, , and the pore size can be further tuned by chemical modification with specific functional groups . With their narrow pores, MOFs have shown potential for the selective separation of ionic species such as F – /Cl – , Br – /NO 3 – , Na + /K + , and Na + /Ca 2+ , mimicking the transport behavior of biological channels. ,− This prompts further development of these materials in a variety of ion separation scenarios.…”