Two‐Dimensional Covalent Organic Framework Membranes: Multi‐Scale Design and Forward‐Looking Perspectives

Two-dimensional covalent organic frameworks (2D COF) are attracting considerable attention as an emerging platform for membrane materials due to their well-defined nanochannels, exceptional structural designability, high stability, and versatile synthesis routes. This review aims to establish a multiscale design framework to accelerate the advancement of 2D COF membranes. First, we systematically discuss engineering principles ranging from molecular-scale monomer design, crystallinity control, transport-channel engineering, and stacking modulation to macroscopic membrane processing. Second, we summarize and highlight recent progress in 2D COF membranes for various separation-related applications, including gas separation, liquid purification, ion sieving, and energy storage and conversion. Finally, we identify key scientific and technological challenges and propose a roadmap to bridge laboratory innovations with industrial deployment. The outlined multiscale design principles and forward-looking perspectives are expected to guide the rational development of 2D COF membranes for diverse environmental and energy applications.