Transform waste into profit: Extract licorice residue fiber to load Zr-MOF as a promising adsorbent

The research on the reuse of resources is crucial for achieving high-value utilization of traditional Chinese medicine (TCM). In this study, licorice residues were selected to extract fibers by alkaline hydrogen peroxide oxidation because of their high cellulose content and widespread use. The cellulose, hemicellulose and lignin content of obtained fibers were found to be 55 %, 8.2 % and 18.8 %, respectively. Immobilizing MOF-808 onto licorice residue fibers yields a composite material exhibiting enhanced adsorption capabilities. The synthesized material was employed to adsorb ketoprofen, naproxen and diclofenac sodium. The characterization results confirmed the successful modification. Adsorption performance experiments indicate that the adsorption behavior follows pseudo-second-order kinetic models and Langmuir isotherm. The adsorption is a process of rapid adsorption and slow equilibrium, showing satisfactory adsorption capacity. X-ray photoelectron spectroscopy and density functional theory calculation revealed that the sustained adsorption attributed to the synergy of π-π stacking, hydrogen bonding and coordination interaction. This study emphasizes the potential for reusing licorice residues and paves the way for the treatment of TCM residue after extracting active ingredients.