Enhanced ciprofloxacin removal from water by chitosan/Mn-modified biochar: Synergistic adsorption at multi-site active centers

The widespread contamination of water resources by ciprofloxacin (CIP) necessitates efficient remediation technologies. While biochar (BC) is a promising adsorbent, its practical application is hindered by limited adsorption capacity. To bridge this gap, this study presents a novel chitosan-manganese co-modified biochar (CS-MBC) engineered through a coupled impregnation-pyrolysis method. This strategic modification significantly enhanced the adsorption performance, with CS-MBC achieving a maximum CIP capacity of 167.08 mg·g^-1, vastly outperforming pristine BC. The novelty of this work lies in the synergistic integration of chitosan biopolymer and manganese oxides, which created multiple active sites for CIP binding. Crucially, CS-MBC demonstrated exceptional robustness and practicality in complex environments, maintaining high efficiency across varying ionic strengths, in the presence of humic acid, and in real water matrices. A combination of advanced characterization and theoretical calculations (DFT and MD) elucidated the enhanced adsorption mechanisms: (1) coordination between Mn species and the piperazine group of CIP, (2) optimized π-π electron donor-acceptor interactions, and (3) hydrogen bonding and electrostatic interactions facilitated by surface amino/hydroxyl groups. This work not only provides a highly effective and sustainable adsorbent for antibiotic removal but also offers deep mechanistic insights that can guide the future design of advanced functionalized materials for environmental remediation.