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 m 2  g −1 ) and HAR@ZnCl 2 (1896 m 2  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 (a Chinese medicine residue) biochar, a biowaste-derived product, were demonstrated in its ability to remove antibiotics from water, showing great potential in wastewater treatment application.