Efficient adsorption mechanism of ciprofloxacin by Zn-enriched hyperaccumulator derived biochar

Zn-doped biochar has gained significant attention due to its excellent antibiotic adsorption performance. The Zn content in the phytoremediation residue of Sedum plumbizincicola (SP) reached 18.515 mg/g, possesses both resource and pollutant characteristics. This research is the first attempt to prepare biochars (PBCx, where x represents the pyrolysis temperature) from the Zn-enriched SP for ciprofloxacin (CIP) adsorption. PBC500 demonstrated an exceptional adsorption capability, reaching 254.14 mg/g, which outperforms the majority of traditional biochars modified with Zn salts. The pseudo-second-order kinetic model and the Freundlich isotherm model provided the most accurate description of the adsorption process. Further analysis of FTIR and XPS elucidated that the effective adsorption was attributable to an intricate interplay of forces, not only involved the conventional roles of pore filling, electrostatic adsorption, hydrogen bonding, π-π interactions, and reduction reaction but also benefited from the Zn-N/O coordination. Across a wide pH range (4-11), the concentrations of Zn leached into the solution post-adsorption complied with the strict drinking water safety standards. Research indicates that biochar produced from Zn-enriched SP, serves as an effective and environmentally benign material for the remediation of water contaminated with CIP.