Selective Capture of Scandium Ions by Designing Chelation Sites in Covalent Organic Framework Membranes

The rational design of adsorbents capable of efficiently and selectively capturing target metal ions from complex matrices remains a significant challenge in the field of materials science. Herein, it is demonstrated that atomic-level design of chelation sites within covalent organic frameworks (COFs) is a feasible strategy for achieving selective metal ion capture. This study presents a comprehensive approach that integrates theoretical predictions, structural design, and experimental validation to develop targeted metal ion-specific absorbents. The synthesized β-ketoenamine-linked COFs, with tailored chelation sites, exhibit exceptional selectivity and enhanced adsorption capacities for scandium ions (Sc³⁺), an important rare metal, and selective separation of Sc³⁺ from complex multi-metal ion solutions are realized using Janus membranes prepared from these tailored COFs. Mechanistic analysis reveals the critical roles of chelation coordination and electrostatic interactions in the selective adsorption process. This work represents a significant methodological advancement in utilizing chelating coordination for the structural design of COFs targeting metal ion capture, addressing the specific challenge of Sc³⁺ recovery and providing valuable insights into the development of selective adsorbents for other critical metal ions. These findings are promising for solving longstanding issues in resource recovery and environmental remediation.