Bio-inspired solid-state one-dimensional nanochannels for molecule/ion selective separation

In the past decades, an increasing number of works about nanostructured materials were designed by mimicking natural biological structures or biological functions. These biomimetic nanostructured materials with specifically designed properties show promising potential in the field of industry, agriculture, and biomedicine. As one type of functional protein embedded in cell membranes, biological channel proteins are mainly devoted to achieving fast transport of specific molecules or ions across cell membrane, and they play a significant role in regulating various physiological functions of the cell life processes. Inspired by biological channel proteins, scientists have been committed to developing diverse artificial nanochannels with selective molecule/ion transport capabilities to mimic the functions of biological channel proteins, as well as to explore the mechanisms of molecular/ion selective transport in biological channel proteins. At the same time, scientists have attempted to optimize artificial nanochannels for applications in the fields of filtration, biosensing, and energy harvesting and conversion. Up to now, scientists have successfully fabricated a variety of artificial nanochannels with different dimensions, and investigated the molecule/ion-selective transport mechanisms of these nanochannels, including size sieving, charge effects, wettability as well as channel-guest interactions. In artificial nanochannels, solid-state 1D nanochannels with a diameter or length less than 100 nm is possessed of a single-dimensional molecule/ion transport path that is similar to biological channel proteins. Moreover, the geometry and surface functional groups of solid-state 1D nanochannels are adjustable and designable, showing unique advantages in the field of rapid and selective molecule/ion transport or separation. Consequently, a diversity of bottom-up and top-down approaches are adopted to fabricating solid-state 1D nanochannel materials with selective molecule/ion transport capabilities, such as carbon nanotubes (CNTs) by chemical vapor deposition (CVD), covalent organic frameworks (COFs) by self-assembly strategies, as well as polymer nanochannels and nanopores fabricated by electron/ion beam etching. The bottom-up approach is suitable for preparing solid-state 1D nanochannels with accurate subnanometer size and ordered channel structure. The top-down approach not only could be applied for fabricating nanochannels with diameters ranging from atomic size to a few hundred nanometers, but also shows great advantages in controllably regulating the selective transport behavior of 1D nanochannels through post-processing. In view of the excellent molecule/ion selective transport capability of solid-state 1D nanochannels, their successful applications in the field of selective separation have been achieved. Among which, COFs, CNTs and nanoporous graphene have been proven to possess remarkable separation performance and practical application potential in the fields of gas separation and desalination. However, it is difficult to achieve large-scale preparation of separation membranes based on solid-state 1D nanochannels with existing explored preparation methods. In addition, diverse selective separation mechanisms play different roles in the selective molecule/ion transport. Thus, a thorough understanding of the exact selective separation mechanisms is of great importance to assist the design of solid-state 1D nanochannels with improved separation performance. In this paper, several methods for the preparation of solid-state 1D nanochannels were introduced and the selective molecule/ion transport mechanisms of these nanochannels were analyzed in detail. Several solid-state 1D nanochannel-based materials, including COFs, CNTs, as well as nanoporous graphene, were highlighted for specific applications in the fields of gas separation and desalination. Finally, the challenges and future development opportunities of solid-state 1D nanochannels in the field of selective separation were discussed. This work provides a guideline for the design of solid-state 1D nanochannels and the study of molecule/ion selective separation mechanism.