Unlocking the potential of Chinese herbal medicine residue-derived biochar as an efficient adsorbent for high-performance tetracycline removal.

This study employed hydrothermal carbonization (HTC) in conjunction with ZnCl 2 activation and pyrolysis to produce biochar from one traditional Chinese medicine astragali radix (AR) residue. The resultant biochar was evaluated as a sustainable adsorbent for tetracycline (TC) elimination from water. The adsorption performance of TC on two micropore-rich AR biochars, AR@ZnCl 2 (1370 m2 g−1) and HAR@ZnCl 2 (1896 m2 g−1), was comprehensively evaluated using adsorption isotherms, kinetics, and thermodynamics. By virtue of pore diffusion, π-π interaction, electrostatic attraction, and hydrogen bonding, the prepared AR biochar showed exceptional adsorption properties for TC. Notably, the maximum adsorption capacity (930.3 mg g−1) of TC on HAR@ZnCl 2 can be achieved when the adsorbent dosage is 0.5 g L−1 and C 0 is 500 mg L−1 at 323 K. The TC adsorption on HAR@ZnCl 2 took place spontaneously. Furthermore, the impact of competitive ions behavior is insignificant when coexisting ion concentrations fall within the 10–100 mg L−1 range. Additionally, the produced biochar illustrated good economic benefits, with a payback of 701 $ t−1. More importantly, even after ten cycles, HAR@ZnCl 2 still presented great TC removal efficiency (above 77%), suggesting a good application prosperity. In summary, the effectiveness and sustainability of AR biochar, a biowaste-derived product, were demonstrated in its ability to remove antibiotics from water, showing great potential in wastewater treatment application. • Chinese herbal medicine residues could be converted into value-added products. • HAR@ZnCl 2 has a micropore-rich structure. • The maximum adsorption capacity of TC on HAR@ZnCl 2 can reach 930.3 mg g−1 at 323 K. • HAR@ZnCl 2 displays a good adsorption effect on TC across a wide pH range (pH 2–12). • The removal rate of TC on HAR@ZnCl 2 maintains above 77% after 10 regeneration cycles. [ABSTRACT FROM AUTHOR]