In recent years, 2D materials have been considerably developed for constructing nanochannel membranes. 2D materials are generally classified into the following categories: single-element 2D materials [
54-
57], transition metal sulfide [
47,
48,
58,
59], layered silicate materials [
50,
51], novel 2D materials [
60-
62] and other 2D materials [
63]. 2D material was proposed with the Geim's group at the University of Manchester in 2004 for successful isolation of single-atom layers of graphite material-graphene [
64]. Graphene, with single-atom layer thickness and high strength, whether in theoretical research or application fields, has aroused great interest, and it is also the earliest widely used 2D material utilized for constructing bionic nanochannels (
Fig. 2a) [
53]. Graphene and its derivatives, especially GO, have excellent modifiable sites such as hydroxyl and carboxyl. It can be modified with specific molecules to mimic receptor-based specific adsorption or selective transport of specific ions on the membranes of nerve cells. BP is another type of single-element 2D material, and its properties and structure are similar to graphite [
65]. Furthermore, it can be peeled off. The stripped BP will be oxidized when exposed to air and water. BP is the most stable allotrope in phosphorus elements. It has become a new material for the preparation of layered nanochannels. Zhang
et al. stripped BP and conducted controlled oxidation in water to produce charged phosphorus compounds. Then, they reconstructed the nanosheets as layered nanochannels for ion transport (
Fig. 2b) [
46]. Transition metal disulfide compounds are a major branch of 2D materials. These materials generally exhibit a sandwich structure of X-M-X, and the layers are connected by van der Waals forces, showing obvious anisotropy. Radenovic
et al. utilized molybdenum disulfide (MoS
2) to construct nanochannel and demonstrated more desirable water-transport performance in comparison to graphene because of the enriched hydrophilic surface sites [
47]. TMDs can be prepared for atomically thin nanopore membranes. Ultrathin nanopore membranes are considered an approach to achieve rapid and cheap DNA sequencing. Compared with traditional silicon nitride nanopore with thickness of about tens nanometers, it performs better sensitivity [
66]. Montmorillonite (MMT), a naturally occurring silicate mineral, is a kind of earth-like mineral composed of nanometer-thick negatively charged silicate sheets that are stacked together by electrostatic interaction between the layers [
67,
68]. The average thickness of the wafer is less than 25 nm after stripping and dispersing, purification and modification, ultrafine grading, and special organic composite (
Fig. 2c) [
69]. It has very strong adsorption capacity and cation exchange performance, and low cost. Kaolin is another layered silicate substance, which is the most abundant in soil [
70]. The difference between MMT and kaolin lies in the spatial structure [
71]. Kaolin is an aqueous aluminosilicate with no cations or water molecules between the structural layers and strong hydrogen bonds (O-strengthen the bonds between the structural layers) (
Fig. 2d) [
72]. However, montmorillonite is a silicate clay mineral with a lamellar structure and lamellar crystallization. There are cations or water molecules between the structural layers. The strong oxygen ion chain strengthens the connection between the structural layers. They are the appropriate layered materials for nanochannels.