Synergistic Effects of Nitrogen and Oxygen Active Sites in Covalent Organic Frameworks for Highly Efficient Gold Recovery

Developing efficient adsorbents for precious metals, especially gold recovery, necessitates the integration of multiple critical properties, including high adsorption capacity, rapid adsorption kinetics, and exceptional selectivity, posing significant scientific challenges with substantial economic and environmental implications. Herein, we report a strategy to achieve highly efficient gold adsorption through synergistic effects of nitrogen and oxygen active sites into covalent organic frameworks (COFs). Two β-ketoenamine-linked COFs (NKCOF-77 and -78) with high-density nitrogen/oxygen active sites are rationally designed and synthesized via a Michael addition-elimination reaction approach. Notably, the comprehensive gold recovery performance for NKCOF-77 is among the best in the COF field, with the third highest adsorption capacity (up to 3225 mg g^-1), ultrafast adsorption kinetics (<5 min), and near-perfect selectivity (>99.9% with 10 competitive cations and anions). Moreover, the COFs show exceptional ability for gold recovery from real e-waste solutions, demonstrating tremendous practical application potential. Various experimental characterization and density functional theory calculations reveal that strategically incorporating high-density nitrogen and oxygen active sites is crucial in significantly enhancing the gold adsorption capacity. This work provides a novel strategy for designing COFs as precious metal adsorbents, highlighting their promising potential for industrial applications.