Preparation for a Novel N-Doped Magnetic Sludge-Based Biochar and Application for Norfloxacin Removal from Wastewater

Nowadays, the use of antibiotics is widespread which is causing great pressure on the ecological environment. Incorporation of nitrogen source in biochar can improve its adsorption performance, which is widely used as an adsorbent due to its high efficiency and low-cost. In this study, municipal sludge and red mud were used as raw materials, urea as nitrogen source and KOH and ammonium oxalate as activators to prepare N-doped sludge-based magnetic biochar (NBC) by co-pyrolysis for adsorption of norfloxacin (NOR) in wastewater. The experiment was conducted using 50 mL of NOR wastewater with a concentration of 100 mg/L. The optimal adsorption conditions were identified as 1.6 g/L dosage, pH 5, and temperature 25 °C. The actual adsorption capacity of NBC reached a maximum of 160.25 mg/g. The maximum adsorption capacity of NBC was 388.82 mg/g, which was measured by Langmuir isothermal modelling. The adsorption kinetics are consistent with a pseudo-second order model, while the adsorption isotherms are consistent with the Langmuir and Freundlich models. The characterization demonstrates that NBC is a rough and porous material, with a specific surface area of 192.8397 m2/g and a surface functional group composition including -OH/NH, C = C, C = N, C-O. The main mechanisms of this research include pore filling, π-π interactions, H-bonding and electrostatic interactions. The introduction of a nitrogen source to sludge-based magnetic biochar (BC) has improved its performance in various aspects of adsorption. This paper demonstrates the excellence of NBC by comparing the adsorption performance of NOR with that of BC, which has great potential for future practical applications. Graphical Abstract