The adsorption behavior and mechanism of Cu(Ⅱ), Fe(Ⅱ) and Co(Ⅱ) on straw biochar and their Fenton-like performance for ciprofloxacin decontamination.

In this study, the adsorption of aqueous Cu(Ⅱ), Fe(Ⅱ), and Co(Ⅱ) on biochars at diverse synthesized temperatures was evaluated. The optimal sample BC-800 achieved superior adsorption performance of Cu(Ⅱ), Fe(Ⅱ), and Co(Ⅱ) at 10-50 mg L^-1 initial concentration. Due to the larger surface area (349.6 m²/g), total pore volume (0.24 cm³/g), average pore diameter (6.4 nm), higher degree of graphitization (I_G/I_D = 1.00) and stable aromatic carbon structure, BC-800 achieved excellent adsorption of Cu(Ⅱ), Fe(Ⅱ), and Co(Ⅱ) through multilayer chemical adsorption, corresponding to the pseudo-2nd-order and Freundlich model (Q_{m Cu(Ⅱ)} = 433.4 mg g^-1, Q_{m Fe(Ⅱ)} = 472.0 mg g^-1 and Q_{m Co(Ⅱ)} = 301.0 mg g^-1). After then, the adsorbed biochars with Cu(Ⅱ), Fe(Ⅱ), and Co(Ⅱ) were directly used as heterogeneous catalysts in Fenton-like reaction for ciprofloxacin (CIP) degradation. Compared with Co-BC-800/peroxymonosulfate (PMS) system, Co-BC-800/H₂O₂ system exhibited the 56.6% decontamination of CIP with lower ions leaching (0.53 mg/L) within 70 min. The 97.9% of CIP was finally removed by Co-BC-800/H₂O₂ under optimized conditions: initial pH = 6.94, catalyst dosage = 1.0 g L^-1, H₂O₂ concentration = 0.44 g L^-1. Furthermore, Co-BC-800 exhibited superior acid-base adaptability (2.94-10.94) and anti-anion interference ability. The removal of CIP was achieved by the synergistic effect of adsorption and oxidative degradation. This study proposes some insights into the behavior and mechanism of metal ions adsorption on biochar and hazardous waste treatment.