Closed-Loop Utilization of Sophora tonkinensis Gagnep.: Nanocellulose from Non-Medicinal Parts into Magnetic Imprinted Polymers for Targeted Quercetin Separation of Medicinal Parts

Emphasizing the use of biomass resources is a vital step in advancing green chemistry and environmental protection, significantly contributing to the reduction of carbon emissions and the promotion of carbon neutrality. Converting agricultural waste into biomass resources, such as nanocellulose, is of great significance for a low-carbon economy. Furthermore, the challenge of environmentally friendly and selective separation of natural active plant ingredients still needs to be addressed. In this study, drawing inspiration from the wisdom of “Pods burned to cook peas”, the biomass of the nonmedicinal portion of the herbal medicine (Sophora tonkinensis Gagnep.) was processed to obtain nanocellulose for the preparation of a magnetic molecularly imprinted composite, which was used to separate quercetin from the medicinal portion of this herbal medicine. The stacked complex of magnetic Fe₃O₄ nanoparticles and nanocellulose particles served as the carrier, and the magnetic nanocellulose molecularly imprinted polymer (MIPs/MCNC) was prepared through surface imprinting. It exhibited a strong adsorption capacity (Q_e = 50.64 mg/g) and imprinting factor (IF = 2.55) as well as specific selectivity (K_s’ = 3.48) against structurally similar compounds (naringenin). The regeneration capability remained at 75% after 5 adsorption-elution cycles. It was also successfully applied in a complex solvent environment to selectively separate quercetin from the deep eutectic solvent (DES, choline chloride─acrylic acid) extract of S. tonkinensis Gagnep. Additionally, an interdisciplinary approach was integrated into the design process of MIPs/MCNC, utilizing density functional theory (DFT) to effectively guide the design of functional monomers. This work presented a concept with significant potential for reusing the nonmedicinal parts waste of herbal medicine as nanocellulose and for the environmentally friendly and selective separation of active components.