Engineering Dual‐Active N and O Sites in Covalent Organic Frameworks for Ultrahigh and Selective Thorium Removal

ABSTRACT Developing high‐efficiency adsorbents for the selective capture of thorium from uranium and rare earth elements necessitates integrating multiple critical functions, including strong adsorption ability, exceptional selectivity, and acid‐resistance performance, posing a technically challenging task. Herein, guided by the hard‐soft acid‐base (HSAB) principle, a series of imine‐linked covalent organic frameworks (COFs) functionalized by oxygen‐rich groups is designed and synthesized. The abundance of high‐affinity dual‐active N and O sites on the COF skeleton enables rapid adsorption kinetics and superior Th(IV) uptake. Particularly, TPT‐PA‐COOH and TPT‐PA‐SO 3 H exhibit record‐breaking saturated adsorption capacity and Th/U separation selectivity, making them the most efficient Th(IV) adsorbent reported to date. Especially, the introduction of –COOH or –SO 3 H groups renders the 2D COFs highly acid‐resistant, while keeping good Th(IV) adsorption capacity and selectivity even under harsh acidic conditions. These findings provide insight into the coordination mechanism between thorium and functional binding sites, thus advancing applications of COFs in the separation of thorium from radioactive wastewater.