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Xing et al. Microstructures 2023;3:2023031 https://dx.doi.org/10.20517/microstructures.2023.11 Page 27 of 35

allows the membrane to obtain the desired properties (e.g., defined size nanochannels, specific ionic or
electronic conductivity, etc.) to meet the requirements for the corresponding applications.

Although researchers have tried a variety of membranes for liquid molecular separation, gas separation, and
ion sieving applications (e.g., wastewater treatment, desalination, CO capture, ion recovery, etc.), as we
2
summarized in section APPLICATIONS OF 2D-MATERIAL-BASED NANOCHANNEL MEMBRANES,
the vast majority of these applications are only at the laboratory level (“trial residence” stage), and the
research and development of high-performance 2D-material-based nanochannel membranes are still at an
early stage with both opportunities and challenges. To speed up the eventual commercialization of
membranes and make them better serve the development of society, we propose an outlook on the future
development of membranes from the following three aspects.

(1) Transport Mechanism. The current research has well explained the mechanism of the swelling problem
and the construction and modification of nanochannels. Moreover, there is a large amount of work using
theoretical calculations and simulations to try to make theoretical explanations for the differences in the
filtration performance of various membranes. However, mechanisms during filtrations (e.g., the behavior
mechanism of nanofluid in the channel, the rejection and passage mechanism of nanochannel to various
filtrates, the force mechanism of nanochannel, the interaction mechanism between nanochannel and
various filtrates, etc.) still need to be studied in depth. The emergence of various advanced characterization
tools (e.g., cryoelectron microscopy, in-situ electron microscopy, in-situ Raman, etc.) provides new
possibilities to investigate these mechanisms in depth. Mechanistic studies of the dynamic behavior of
nanochannel membranes (including nanofluids and membranes themselves) will significantly advance
mechanical innovation in the membrane field and accelerate the development of the new generation of
high-performance membranes and industrial applications.

(2) Large-scale preparation. Rapid advances in chemistry and materials science have given rise to thousands
of 2D materials. Yet, the mainstream “top-down” and “bottom-up” strategies are often only suitable for
small-scale production in the laboratory. While there have been reports of kilogram-scale yields, this
remains insufficient to meet the industrial demand of tens or even hundreds of kilograms. To overcome this
challenge, it is crucial to develop new reliable methods for the preparation of 2D materials and reliable
related manufacturing equipment. Notably, corresponding membrane assembly and modification
technologies are also growing rapidly. Similarly, most methods, such as vacuum filtration, spin coating, and
cross-linking, are more suitable for small-scale laboratory production and modification. Therefore, large-
scale preparation is inevitable to apply advanced nanochannel membranes in the industry successfully. This
calls for deep collaboration between the scientific and industrial communities to develop simple and
scalable membrane fabrication methods, and relevant pilot experiments are necessary.

(3) Applications. Although almost all studies reported outstanding application performance, such as high
selectivity, high permeability, and long membrane lifespan, these properties may be overestimated due to
the limited membrane operating area, mild test conditions, and relatively short test durations in the
laboratory. To truly reflect membrane capabilities, scaled-up application experiments under harsh
conditions close to real-world applications (e.g., the effects of biochemical contaminants, sudden changes in
water temperature and flow rate, etc.) are needed, which may pose additional challenges to researchers but
will significantly facilitate the eventual commercialization of the membranes.

By addressing these challenges, the development of membranes with optimized nanochannels has the
potential to transcend the limitations of traditional separation methods. Advances in membrane technology,