Synergistic adsorption of norfloxacin by magnetic Fe-Mn modified biochar: mechanisms and role of surface functionalities

• An new material with high adsorption performance derived from agricultural waste. • Investigate the influence of microstructure and surface chemistry on NOR adsorption. • Analyzing the impact of different electrolytes and Cu 2+ on adsorption. • Achieving rapid magnetic separation and multi-cycle durability. • Revealing the synergistic mechanism of FMBC adsorption for NOR. Norfloxacin (NOR) is widely used in aquaculture; however, its overuse has been shown to cause water pollution. In this research, NOR was chosen as the target pollutant, and agricultural waste, specifically corn cobs, was used to prepare ferromagnetic iron-manganese composite modified biochar (FMBC) for adsorbing NOR from aquaculture wastewater. The adsorption mechanism was explored using various characterization techniques and evaluating the adsorption performance. The results indicate that the optimal modification conditions for FMBC include an iron source concentration of 0.3 M, the iron-manganese ratio is 3:1, with a calcination temperature of 350°C. At pH 6, FMBC achieved an adsorption capacity of 31.17 mg/g for NOR, which is approximately 85.5% and 49.14% higher than that of pristine biochar (BC) and iron-modified biochar (FBC), respectively. The adsorption process obeyed pseudo-second order kinetics and the Langmuir isotherm model. As the temperature increased, the adsorption capacity of FMBC for NOR decreased. The adsorption capacity of FMBC for NOR increased at low concentrations of Cu 2+ (maximum 25 mg/L), but at higher concentrations, it was inhibited. FMBC demonstrated the capacity to maintain NOR removal performance at a rate of greater than 50% following five cycles. The adsorption processes of FMBC for NOR are driven by several factors: pore filling, electrostatic adsorption, hydrogen bonding, surface complexation, π-π interactions, and hydrophobic bonding. In summary,this novel composite material offers promising prospects for mitigating water pollution in aquaculture, making it a cost-effective and sustainable alternative.