Selective Ion Transport in Two‐Dimensional Lamellar Nanochannel Membranes

Abstract

Precise and ultrafast ion sieving is highly desirable for many applications in environment-, energy-, and resource-related fields. The development of a permselective lamellar membrane constructed from parallel stacked twodimensional (2D) nanosheets opened a new avenue for the development of next-generation separation technology because of the unprecedented diversity of the designable interior nanochannels. In this Review, we first discuss the construction of homo-and heterolaminar nanoarchitectures from the starting materials to the emerging preparation strategies. We then explore the property-performance relationships, with a particular emphasis on the effects of physical structural features, chemical properties, and external environment stimuli on ion transport behavior under nanoconfinement. We also present existing and potential applications of 2D membranes in desalination, ion recovery, and energy conversion. Finally, we discuss the challenges and outline research directions in this promising field.

Selective Ion Transport in Two-Dimensional Ti3C2Tx Nanochannel Decorated by Crown Ether

“…We also investigated the impacts of salt concentration and membrane composition on ion sieving. Prior research has often shown reduced cation or anion selectivity as a result of the diminished range of the surface charge under high-concentration conditions, according to the Poisson–Boltzmann theory. ,, However, we confirmed relatively stable ion sieving performance when the chloride salt concentration was varied between 0.05 and 0.2 M, as illustrated in Figure d. This indicated that selective ion transport based on specific binding interactions with the crown ether molecules was not significantly affected by the ion concentration.…”

“…SEM observations of the CTM surface morphology (Figures a and S3) showed an intact membrane surface without structural defects such as cracks and holes. However, as with other 2D lamellar membranes, a typical wrinkled morphology was formed due to irregular stacking during the preparation process . Moreover, SEM observations of the cross-section (Figure b,c) clearly showed a layered structure, indicating that the Ti 3 C 2 T x nanosheet skeleton was not destroyed by the introduction of crown ether rings.…”

“…However, as with other 2D lamellar membranes, 39 a typical wrinkled morphology was formed due to irregular stacking during the preparation process. 11 Moreover, SEM observations of the cross-section (Figure 3b,c) clearly showed a layered structure, indicating that the Ti 3 C 2 T x nanosheet skeleton was not destroyed by the introduction of crown ether rings. Furthermore, energy-dispersive spectroscopy (EDS) (Figure S4) was used to confirm the distributions of carbon, nitrogen, oxygen, and titanium in the CTM structure and its surface, which indicated uniform intercalation of the ACE molecules into the Ti 3 C 2 T x nanosheets.…”

“…To address the challenges in developing high-performance ion-selective membranes, two-dimensional (2D) nanochannels fabricated through layer-by-layer stacking of nanosheets have been developed. The primary advantage of such 2D nanochannels lies in the abundant functional groups on the nanosheet surface, which allow for precise control of both channel size and surface properties to regulate ion transport behavior. − While graphene derivatives were initially used as the building blocks for 2D layered membranes, other materials such as transition metal carbon/nitrides (MXenes), , transition-metal dichalcogenides, , MOFs, , hexagonal boron nitride, , and vermiculite , have been reported to date. Among these materials, MXenes have attracted considerable attention due to their unique physical and chemical properties.…”

“…Among these materials, MXenes have attracted considerable attention due to their unique physical and chemical properties. Notably, Ti 3 C 2 T x , a prominent representative of the MXene family, exhibits a remarkably higher Young’s modulus of 0.33 TPa in comparison to GO and MoS 2 . , Moreover, Ti 3 C 2 T x membranes have demonstrated remarkable antibacterial properties, , excellent hydrophilicity, , and an abundance of functional groups on their surfaces, offering promising opportunities for further functionalization to enhance ion selectivity . As a result of these advantages, Ti 3 C 2 T x has become a critical building block for constructing nanochannel membranes in the field of ion sieving.…”