Covalent/metal–organic framework membranes with tailored pore functionality for accurate ion separation
Penglin Cheng, Tiantian Chen, Tiantian Liu, Yuhan Wei, Miaomiao Tian, Xueli Cao, Shi‐Peng Sun, Yatao Zhang, Bart Van der Bruggen, Junyong Zhu
Abstract
Ion-selective membranes present a promising solution for efficient ion extraction, a critical need addressing both water resource cycling and critical metal supplies. Conventional polymer membranes often exhibit an intrinsic permeability-selectivity trade-off, stemming from their disordered and random pore architecture. This structural limitation further complicates the understanding of how diverse ion species are transported within their non-uniform sub-nanochannels. Covalent organic frameworks (COFs) and metal-organic frameworks (MOFs) stand out as a promising solution for ion separation due to their ordered pore architecture, designable topological configuration, and tunable pore microenvironment. Herein, recent advancements in ion-selective membranes fabricated using these advanced COF and MOF materials are critically reviewed. We begin by unravelling the currently dominant ion-differentiation mechanisms within their sub-nanochannels, including size exclusion, electrostatic interactions, and chemically specific binding. Particular emphasis is placed on the pore engineering design principles of these crystalline framework materials, highlighting the role of specific ion-binding moieties, pore dimensions and charge, and asymmetric structures in selective ion transport. Advanced fabrication methods and ion-related applications of crystalline framework-based membranes are subsequently described. We conclude by presenting fundamental prospects and challenges for the on-demand design of next-generation ion-selective framework membranes.