From waste to resource: TCM herb residue-derived biochar as a multifunctional material for environmental remediation

The massive generation of traditional Chinese medicine herb residues (TCMHR), a direct consequence of industry expansion, presents a dual challenge: significant waste disposal burdens, and untapped resource potential. Concurrently, the remediation of heavy metal and organic contaminants in aqueous and soil matrices requires innovative, sustainable materials. This review systematically synthesizes recent advancements in the strategic conversion of TCMHR into engineered biochar (BC), and BC-based composites for environmental decontamination. Synthesis protocols (e.g., pyrolysis, hydrothermal carbonization, activation) and their direct influence on critical physicochemical properties are evaluated, such as hierarchical pore architecture, specific surface area (often exceeding 500 m2/g), and tailored surface chemistry. The inherent lignocellulosic and bioactive composition of TCMHR facilitates biochar production with exceptional adsorption capacities, documented here for pollutants including Pb(II) (up to 599.40 mg/g), and tetracycline (up to 930.3 mg/g). The dominant remediation mechanisms are detailed: for heavy metals, a combination of surface complexation, ion exchange, and reduction-precipitation; for organic contaminants, synergistic effects involving π–π stacking, electrostatic attraction, and hydrogen bonding. Furthermore, how engineered modifications—such as magnetic Fe3O4 impregnation for separation or the creation of heteroatom-doped carbon matrices for catalytic processes (e.g., peroxymonosulfate activation)—enhance functionality, reusability, and pollutant degradation efficiency are analyzed. Moreover, well-designed preparation techniques can transform active constituents from TCMHR into functional biochar while retaining core pharmacological components during carbonization, offering potential medical applications. Despite promising laboratory results, key obstacles impede scalable application. These include performance in complex, multi-pollutant systems, long-term environmental stability, and potential secondary leakage of modified BCs, and a need for full life-cycle and ecotoxicity assessments. Addressing these research gaps is essential to transform TCMHR-derived biochar from a promising valorization concept into a viable, circular economy solution that contributes to environmental sustainability and carbon neutrality goals.