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Biochar (BC) is widely used in the remediation of soil and wastewater polluted by heavy metals, but there are few reports on the characteristics of biochar derived via pyrolysis from different traditional Chinese medicine residues (TCMRs). In this study, biochars were prepared by slow pyrolysis of five common Chinese medicine residues, namely, Salvia miltiorrhiza (DNS), Ligusticum striatum (CX), Angelica sinensis (DG), Codonopsis pilosula (DGS), and Astragalus membranaceus (HQ). The biochars were systematically investigated by determining their physicochemical properties and using common characterization techniques. The Spearman correlation matrix between factors was used to examine relationships between properties of different biochars. Batch adsorption experiments were carried out to investigate the adsorption characteristics of biochar on Pb(II) and the mechanisms involved. The results showed that the physicochemical properties and adsorption performance of biochar were related to the type of its pharmaceutical residue. Biochar produced from materials with higher lignin content showed a better adsorption of the heavy metal Pb(II). All biochars were alkaline, with yields ranging from 29.30 to 38.65 %, and the main structure comprised of mesopores and macropores. The FT-IR and Boehm experiments revealed that the various TCMR biochars contained comparable functional groups, but their content varied. XRD and TEM results show that all biochar is amorphous with a crystalline structure, with the surface dominated by cellulose crystals and graphitic carbon. The O/C ratio ( 0.99), and their isotherms were consistent with the Langmuir model (R2 > 0.99), indicating a monolayer chemisorption process. The biochar samples exhibited varying adsorption capacities for Pb(II), with the highest capacity observed for BDNS (36.42 mg/g). The adsorption mechanism mainly involved precipitation, complexation with oxygen-containing functional groups, and ion exchange. This study indicates that biochars from herbal residues exhibit promising potential for adsorbing heavy metal Pb(II), suggesting biochar production as a viable method for recycling herbal residues.

In recent years, the quality and safety issues of Chinese medicinal herbs have received great attention worldwide. Thereinto, heavy metal contamination has been one of the most serious concerns. Compared to the wide research in the analysis of heavy metals in medicinal herbs, the studies on the removal of heavy metals are relatively limited. In this study, polyethylene glycol functionalized Fe3O4@MIL-101(Cr) (Fe3O4@MIL-101(Cr)@PEG) was designed and synthesized to remove heavy metals from the decoction of Ligusticum chuanxiong Hort. The in-house fabricated Fe3O4@MIL-101(Cr)@PEG was characterized by a porous structure and a large specific surface area. Then, the efficiency of the material for the removal of five heavy metals was tested under optimal adsorption conditions. Meanwhile, the content of Senkyunolide A, Senkyunolide I, and Ferulic acid, the solid content, and the HPLC fingerprints similarity were used as the quality monitoring indicators of Ligusticum chuanxiong Hort decoction before and after the heavy metal removal. Results showed that the magnetic nanomaterial had excellent removal efficiency for As5+ (81.4 %), Cd2+ (88.19 %), and Pb2+ (83.79 %) and certain removal efficiency for Ni2+ (51.59 %) and Zn2+ (55.4 %) under the spiked concentration of 50 μg/mL. The content of Senkyunolide A, Senkyunolide I, and Ferulic acid were decreased by less than 8.00 % after the removal of heavy metals. Besides, the loss rate of solid content was only 0.18 %, and the fingerprints similarity was over 99.9 %. The results indicated that Fe3O4@MIL-101(Cr)@PEG could efficiently and selectively remove heavy metals from Ligusticum chuanxiong Hort without affecting its effective components. Due to the advantages of low-cost, simple manipulation, and good efficiency, the material can be recommended for heavy metals removal from the aqueous solutions of medicinal herbs, providing a new and promising application for the removal of exogenous contaminants in medicinal herbs.