Construction of magnetic covalent organic frameworks based on the monomer-mediated in situ layer-by-layer growth strategy for efficient gold recovery

Abstract

Creating uniform magnetic covalent organic framework (MCOF) adsorbents for effectively capturing and separating gold presents a considerable challenge. However, achieving this uniformity is crucial for resource recycling and environmental protection. This study introduces a monomer-mediated in situ layer-by-layer growth strategy employing a timed injection method for fabricating magnetic covalent organic frameworks. The hybrid MCOFs produced, Fe3O4@SiO2@COF and Fe3O4@SiO2@COF-DMSA, possess abundant binding sites that enhance adsorption capacities, rapid kinetics, and remarkable regeneration performance for gold recovery. Significantly, the Fe3O4@SiO2@COF exhibits a lower gold adsorption capacity (898 mg g−1), whereas Fe3O4@SiO2@COF-DMSA exhibits an improved Au (III) selectivity and a larger capacity for adsorption (1116 mg g−1). The capturing mechanism of Au (III) by Fe3O4@SiO2@COF-DMSA is predominantly attributed to coordination and reduction, as identified through XPS analysis. This study motivates conceptualizing molecular/ionic capture strategies using core–shell NP/COF hybrid materials to retrieve precious metals.