Covalent organic frameworks-based microspheres with precisely designed recognition sites for selective adsorption of luteolin

Abstract

Global agricultural activities generate substantial flavonoid-rich waste streams, which presents both resource recovery opportunities and environmental challenges. The selective separation of high-value luteolin (LTL) from such complex matrices remains difficult due to structural similarities among flavonoids. Covalent organic frameworks (COFs) are promising separation materials due to their tunable structures and functionalities. However, COFs face limitations in accurately recognizing LTL within complex environmental matrices. Key issues include insufficient specific binding sites and low functionalization density. To overcome these challenges, we developed molecularly imprinted COFs microspheres (COFs-DVA-SH MIPMCs) through a novel emulsion-based synthesis and post-modification strategy. This approach involved constructing hollow vinyl-functionalized COFs microspheres via emulsion polymerization, followed by dithiol linker grafting through thiol-ene click reaction, and culminating in boronic acid affinity site imprinting. This yielded COFs microspheres with precise recognition capabilities. The COFs-DVA-SH MIPMCs combine boronate affinity with molecular imprinting advantages to enable selective LTL extraction. They demonstrate significant recognition capacity (67.97 mg g⁻¹), rapid mass transfer (180 min), and high selectivity (IF = 2.89) under alkaline conditions. The adsorbent also exhibits excellent stability, maintaining 93.7 % capacity after 5 cycles and robust thermal stability. This work provides a new strategy for specific separation of natural flavonoids using COFs, supporting sustainable valorization of agricultural waste through advanced separation technologies.