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Xing et al. Microstructures 2023;3:2023031 https://dx.doi.org/10.20517/microstructures.2023.11 Page 25 of 35

Table 3. Summary of gas separation membranes

Membrane Base material Assembly method Pore size Gas Selectivity
[191]
Graphene/NPC/MWNT Graphene Spin-coating 20-30 nm H /CH 11-23
2 4
[192]
pCN Carbon nitride Low-pressure chemical vapor deposition N/A H /CO 6.58
2 2
[193]
Zn/Co-HDS Bimetallic MOF nanosheet Vapor phase transformation 0.21 nm H /CO 54.1
2 2
[194]
β-ketoenamine-type COF membrane β-ketoenamine-type COF Hot-drop coating 0.6 nm H /CO 22
2 2
(LDH/FAS)n-PDMS hybrid membranes LDHs Vacuum filtration/layer-by-layer assembly N/A H /CO 43
2 2
[195]
BN membrane Boron nitride Vacuum filtration 0.33 nm Ethylene/Ethane 128
[196]
Printed GO-based membranes GO Printing 0.89 nm CO /N 2 70
2
Yang et al. prepared a metal-organic framework as a multifunctional ionic sieve membrane for aqueous zinc–iodide batteries, greatly extending the battery
lifespan . The recovery of rare metals has become increasingly popular due to the rising popularity of electric vehicles and electronic products. Efficient
[169]
screening of metal ions is the key to recovering rare metals. Xu et al. developed a special lithium ion sieving UiO-67/AAO membrane, which achieved an ultra-

high Li permeability of 27.01 mol m h and a Li /Mg selectivity of up to 159.4 [Figure 10F] . For a better comparison of related membranes, a summary of
2+
[170]
+
-2
-1
+
ion sieving membranes is shown in Table 4.
Important factors to consider when selecting a 2D nanochannel membrane for separation are the object to be separated, expected performance, ideal structure,
cost-effectiveness, and environmental impact. In various application scenarios, choosing the appropriate membrane fabrication and modification process is the
precondition for the membrane to ensure the ideal performance. Taking these factors into account can lead to the successful development of efficient and

environmentally friendly separation processes.

CONCLUSION AND OUTLOOK
In summary, the emergence of a family of 2D materials with atomic-level thickness and excellent physical and chemical properties has brought significant

development opportunities to nanochannel membranes. Over decades of development, 2D-materials-based membranes have made a preliminary
breakthrough from raw materials to laboratory-level applications.

A s o u t l i n e d i n Figure 11, t h i s r e v i e w s u m m a r i z e d i n d e t a i l s t r a t e g i e s f o r c o n s t r u c t i n g n a n o c h a n n e l s i n s e c t i o n

CONSTRUCTING NANOCHANNELS WITH 2D NANOSHEETS. The extensive research on the swelling mechanism of 2D-material-based membranes has

provided effective guidance for researchers to synthesize 2D nanosheets with ideal properties via “top-down” and “bottom-up” strategies, i.e., from a “clay” to
“bricks” process. The appearance of various types of perforation methods (e.g., focused ion beam, plasma etching, chemical etching, etc.) has facilitated the
transition from “bricks” to “porous bricks”, providing more options for the next step of nanochannel formation. The membrane assembly process is analogous