High-Crystallinity Covalent Organic Framework Synthesized in Deep Eutectic Solvent: Potentially Effective Adsorbents Alternative to Macroporous Resin for Flavonoids

A critical challenge in the enrichment of active ingredients in natural medicines is the design of adsorbents with high selectivity and adsorption capacity. Covalent organic frameworks (COFs), which have adjustable pores and high specific surface areas, could be effective as adsorbents for active ingredients. This study used an environmentally friendly deep eutectic solvent (DES) instead of organic solvents as the reaction solvent, and high-crystallinity COF-DES was successfully prepared. The COF-DES fabricated using 1,3,5-tris(4-aminophenyl)benzene and 2,5-dihydroxyterephthalaldehyde as building blocks showed good dispersibility, large surface area (444.56 m2·g–1), and suitable pore size (25.9 Å). Owing to its unique structure and functional group properties, COF-DES can prevent interferences from other compounds such as alkaloids, resulting in outstanding selective adsorption performance for flavonoids. Furthermore, under optimized adsorption conditions, the adsorption effects of the COF-DES on flavonoids were much better than those of the effects of macroporous resins, indicating the potential of the COF-DES as a selective adsorbent for flavonoids. Finally, a flavonoid-possessing rich natural medicine, Abelmoschus manihot (Linn.) Medicus flower, was used as a sample to study the application potential of the COF-DES. The results showed that the COF-DES had good adsorption and selection capability for flavonoids in actual samples. Moreover, compared with solid-phase extraction (SPE) columns based on macroporous resins, a COF-DES based SPE column showed superior adsorption performance for an actual complex sample, indicating the potential to COF-DES as an effective adsorbent alternative to macroporous resins. Additionally, the COF-DES had great commercial value as an adsorbent for SPE flavonoid columns.