Enhancing norfloxacin removal from water using nitrogen-doped biochar synthesized via solvent-free ball milling

Nitrogen-doping has proven to be a highly effective technique for modifying biochar to enhance its adsorption capacity. The synthesis of N-doped biochar by solvent-free ball milling has earned significant attention due to its convenient, environmentally friendly, and energy-efficient nature. In this study, traditional Chinese herbal medicine ( Astragali radix , AR) was used as the raw material, with urea as the nitrogen source. A novel approach combining ball milling and in-situ pyrolysis was employed to prepare nitrogen-doped biochar for the removal of norfloxacin (NOR). At 298 K, the maximum adsorption capacity of NOR was 501 mg/g. The S BET of the prepared N-doped biochar (ACB 1000 ) is 779 m 2 /g, and the V Total reaches 0.938 cm 3 /g, significantly higher compared to biochar produced without ball milling and N-doping treatment Both pseudo-second-order (PSO) and Elovich models effectively describes the kinetic data, while the Langmuir model is appropriate for analyzing NOR adsorption on ACB 1000 , which is spontaneous and exothermic. The NOR removal efficiency by ACB 1000 remains unaffected by coexisting ions at 10–100 mg/L. The superior pore structure and nitrogen doping of ACB 1000 are the primary factors contributing to its high adsorption efficiency. Among the numerous mechanisms driving adsorption, the pore-filling effect and π-π interactions are the most significant, while hydrogen bonding and electrostatic interactions also play contributory roles. An economic analysis of the biochar indicates an investment return rate of 1.63 $/kg. More importantly, even after 5 cycles, ACB 1000 still has a high NOR removal rate (over 81 %), indicating its great potential for application in wastewater treatment.