A Green Biobased Aerogel Scaffold Functionalized with Boronate Covalent Organic Framework for the Precision Separation of Bioactive Flavonoids

The efficient and selective extraction of flavonoids from complex plant sources remains challenging, primarily due to their structural diversity and trace presence in natural matrices. To address this, we developed a novel biobased aerogel functionalized with boronic acid grafted covalent organic frameworks (BCOFs), which enables precise and tunable flavonoid recognition via dynamic boronate affinity. The hybrid aerogel (TOCN@CS@BCOF) was synthesized through a green sol–gel process combined with freeze-drying, incorporating TEMPO-oxidized cellulose nanocrystals (TOCN) and chitosan (CS) as sustainable structural scaffolds. The composite exhibits a hierarchical porous structure (BET surface area: 119.28 m2/g) and exhibits outstanding adsorption capacities for quercetin (216.52 mg/g) and luteolin (195.36 mg/g), surpassing conventional adsorbents by 2.1–9.0-fold. The adsorption kinetics follow a pseudo-second-order kinetic model, driven by a reversible boronate esterification reaction, thereby achieving pH-responsive selectivity. For instance, at pH 8.0, the selectivity ratio between quercetin and naringenin reaches 5.21. The aerogel demonstrates excellent regenerability, retaining over 90% of its adsorption capacity after six consecutive cycles, alongside robust performance in dynamic adsorption settings. This study introduces a sustainable and scalable platform for the highly selective separation of bioactive flavonoids, merging the precision of covalent organic frameworks with the environmental benefits of biopolymer aerogels.