Rod-structured phytic acid-functionalized covalent organic frameworks for enhanced uranium extraction from seawater

The uranium extraction from seawater (UES) by adsorption is considered to be a promising method. However, current adsorbents suffer from insufficient exposure of active sites, limiting their accessibility for uranyl ion (UO₂ 2+ ) binding. In this work, a phytic acid-functionalized covalent organic framework (COF-PA) was successfully synthesized for highly efficient uranium extraction from seawater. COF-PA surfaces exhibited numerous rod-like protrusions, exposing additional active sites. Furthermore, the incorporation of phytic acid endowed the material with abundant phosphate groups, which exhibited strong coordination ability with uranyl ions, leading to a remarkable adsorption capacity (Q m  = 645.6 mg g −1 ). The adsorption capacity achieved in natural seawater over a 15-day period was 2 mg g −1 . Additionally, the COF-PA demonstrated exceptional selectivity for UO 2 2+ over competing metal ions and maintained over 70 % of its initial adsorption capacity after four regeneration cycles, highlighting its robust reusability. Furthermore, mechanistic investigations, including X-ray photoelectron spectroscopy, X-ray absorption fine structure spectroscopy and density functional theory calculations, revealed that the adsorption process is driven by chemisorption, where phosphate groups act as bidentate ligands to form stable equatorial coordination bonds with uranium. This work provides a novel strategy for designing functionalized COFs with natural, eco-friendly ligands for UES.