Identification of oxygen sites in β-ketoenamine-linked covalent organic frameworks for highly efficient uranium adsorption through experimental and theoretical studies

Abstract

Anthropogenic activities involving unintended uranium leakage from nuclear accidents, large-scale uranium mining, or nuclear weapon production have caused health and environmental concerns. The increasing demand for highly efficient materials to dispose of uranium may facilitate the sustainable development of nuclear power plants. Herein, a β-ketoenamine-linked covalent organic framework (COF) material, named DQTP COF, was solvothermally synthesized by an imine condensation of 1,3,5-triformylphloroglucinol (TFP) and 2,6-diaminoanthraquinone (DAAQ). The chemical and physical properties of the synthesized DQTP COF were analyzed using various advanced techniques. Additionally, the adsorption behaviors of DQTP COF for U(VI) were optimized by varying parameters, such as pH, ionic strength, contaminant concentration, and reaction temperature. The produced DQTP COF showed an enhanced adsorption capacity of 517.62 mg g⁻¹ at pH 6.0 towards U(VI), outperforming most of the currently reported COF-based materials. Moreover, DQTP COF exhibited favorable thermodynamics and excellent anti-ion interference properties as well as good reusability. Experimental analysis and theoretical DFT calculations revealed that UO₂²⁺ ions were bound exclusively by carbonyl groups via intramolecular coordination and electrostatic interaction in DQTP COF. This work paves the way to rationally develop functionalized COFs and highlights the potential of COFs for environmental remediation.