Covalent organic framework membranes for selective ion separation

Ion-selective membranes play a crucial role in addressing water scarcity, environmental security, and energy utilization. Conventional microphase separation membranes suffer from trade-off limitation between permeability and selectivity due to the poor dimensional stability of ion-conductive regions. Microporous membranes utilize rigid polymer backbones to mitigate the trade-off effect, yet their tortuous pore connections hinder efficient ion separation. Covalent organic frameworks (COFs), known for their regular pore structures with permanent porosity and facilely tailored functionality, are anticipated as new-generation membrane materials. In this review, we elaborate on the potential and challenges of COF membranes from structural design, preparation protocols, and separation applications. Furthermore, we propose future opportunities and research trends for COF membranes, particularly in the scale-up fabrication, demanding ion separation system and genuine selective ion transport mechanism. Ion-selective membranes are essential for tackling water scarcity, environmental security, and energy challenges, yet conventional designs face a trade-off between permeability and selectivity. In this Review, the authors explore covalent organic frameworks as promising membrane materials, highlighting their structural advantages and proposing future research directions for enhanced ion separation and scalability.