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

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, Fe 3 O 4 @SiO 2 @COF and Fe 3 O 4 @SiO 2 @COF-DMSA, possess abundant binding sites that enhance adsorption capacities, rapid kinetics, and remarkable regeneration performance for gold recovery. Significantly, the Fe 3 O 4 @SiO 2 @COF exhibits a lower gold adsorption capacity (898 mg g −1 ), whereas Fe 3 O 4 @SiO 2 @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 Fe 3 O 4 @SiO 2 @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.