Engineering Nanochannel Structure and Chemistry in Covalent Organic Framework Membranes ^†

Comprehensive Summary Covalent organic frameworks (COFs), characterized by their reticular chemistry with covalent bonds between organic building blocks, have emerged as the state‐of‐the‐art membrane materials in numerous applications. Compared to conventional polymer membranes, COF membranes hold superior capacities in pushing the boundary of separation performance with high permeability and selectivity, due to their merits of highly tunable and ordered crystalline pore structure, programmable chemistry, high porosity, and excellent stability. Over the past decade, substantial advances in material design and application exploration of COF membranes have sparked ever‐increasing research attention. To offer insightful implication for researchers from different fields, it is highly valuable to systematically summarize the recent advancements of COF membranes from the perspective of nanochannel structure and chemical property, two of the most important indicators to dictate their separation performance. In this review, we discuss recent progress in the mainstream fabrication methods of COF membranes, mainly including interfacial polymerization, in‐situ growth, and nanosheets assembly and stacking. Then, we emphasize how to engineering nanochannel structure and chemical property of COF membranes in these three kinds of fabrication methods, as well as highlight their potential application in many areas such as ion/molecule sieving, gas separation and osmatic energy harvesting. Finally, some unsolved challenges and future perspectives in this field will be discussed, inspiring for the design and synthesis of advanced COF membranes. Key Scientists In 2011, Dichtel and coworkers achieved in‐situ growth of highly ordered COF thin films via solvothermal methods, marking the emergence of COF membrane materials. [1] In 2017, Banerjee's group reported liquid‐liquid interfacial polymerization of COF membranes via Schiff‐base condensation. [2] In 2018, Wang's group leveraged polymer membrane design principles to construct COF separation layers on porous polymeric substrates through interfacial polymerization. [3] In 2020, Jiang's group developed monolayer NUS‐9 nanosheets and assembled COF membranes. [4] They subsequently developed multiple strategies for fabricating COF separation membranes, focusing on precise regulation of nanostructure to enhance separation performance. In the same year, Zhao's team reported the fabrication of two‐dimensional COF membranes for gas separation. [5] Then they advanced the development of high‐performance responsive membranes. In 2021, Sun's research focused on mass transport mechanisms in COF nanofluidic membranes, investigating the relationship between structure and separation performance. [6] In 2022, Tang's research group proceeded to develop ultrathin COF membranes for the osmotic energy conversion through interfacial polymerization. [7] In 2023, Liu's group began preparing COF membranes through modulated interfacial polymerization, primarily for separation in water environments or organic solvents with smart responsiveness. [8] In the same year, Wang developed a solid‐liquid interfacial method for highly oriented COF membranes, contributing to the design of COF membranes with tunable properties for applications in electronics and energy applications. [9] Given the abundance of distinguished studies on COF separation membranes, this timeline aims to highlight representative breakthroughs instead of providing an exhaustive historical record. These breakthroughs have collectively established a foundational framework for the design and synthesis of next‐generation high‐performance COF separation membranes.