Magnetic Rod-Shaped Covalently Connected MOFs@COFs Imprinted Adsorbents with Ultrahigh Adsorption Capacity for Highly Specific Adsorption of Flavonoids

Naringin (NRG) is a bioactive substance with important pharmaceutical and industrial value. However, the major challenges in the separation of NRG arise from the complexity and low concentration of crude extracts. In this work, by integrating the advantages of magnetic separation, MOFs@COFs composite materials, and surface molecular imprinting strategy, a new kind of magnetic MOF@COF-based boronate-affinity molecular imprinted adsorbent (NH2-MIL-68-Fe3O4@COFs@BA-MIPs) was constructed. Magnetic NH2-MIL-68 substrates were prepared by the solvothermal method, aldehyde-functionalized by surface modification with 2,4,6-triformylphloroglucinol (Tp). Then, a covalent organic framework shell was grown on the surface of substrates via the Schiff base reaction. Finally, a boronate-affinity imprinted polymer was prepared via surface-initiated atom transfer radical polymerization (SI-ATRP). The as-prepared adsorbent features rapid magnetic separation. In addition, the high-density boronate-imprinted recognition sites and porous structure endow the material with a fast adsorption rate (reaching equilibrium about 60 min), a high adsorption capacity (57.29 μmol g–1), and good retention performance (92.79%) after six adsorption–desorption cycles at 308 K under pH 8.0. Moreover, the extraction rate of crude NRG by NH2-MIL-68-Fe3O4@COFs@BA-MIPs reached 93.61%. This study provides a design strategy for constructing NRG adsorbents with rapid magnetic response and has important application value in the specific separation and purification of flavonoids.