Characteristics of poplar leaf biochar and its synergistic purification mechanism for ofloxacin in wastewater

To explore the application potential of waste biomass valorization in the treatment of antibiotic pollution in water bodies, poplar leaf litter was used as the feedstock to prepare biochar (labeled BC300-BC700) at different pyrolysis temperatures (300-700 ℃). By evaluating the adsorption performance of biochar prepared at different temperatures for ofloxacin (OFX) in wastewater, the optimum pyrolysis temperature was identified. Scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) specific surface area analysis, X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations were employed to investigate the relationship between the adsorption performance of poplar leaf biochar for OFX and its structural characteristics. The results showed that the pyrolysis temperature significantly affected the pore structure and surface chemical properties of the biochar. As the pyrolysis temperature increased from 300 ℃ to 600 ℃, the specific surface area of the prepared biochar increased from 22.711 m²/g to 379.656 m²/g, the total pore volume increased from 0.036 0 cm³/g to 0.368 2 cm³/g, with the micropore volume reaching 0.187 cm³/g and the average pore diameter increasing to 2.734 4 nm. The comprehensive performance of BC600 was the best. In the simulation system, compared with BC300, the removal rates of OFX at 50 and 100 mg/L by BC600 increased from 42.2% and 36.7% to 78.4% and 66.5%, respectively. In actual wastewater, the removal efficiencies of BC600 for OFX, COD, \mathrmNH_4^+ -N, \mathrmNO_3^- -N, TN, and TP reached 73%, 91%, 82%, 78%, 88%, and 94%, respectively. The adsorption isotherms of OFX onto poplar leaf biochar were well described by the Langmuir model (R²>0.97), and the maximum adsorption capacity at 35 ℃ was 80.9 mg/g. Adsorption kinetic analysis indicated that the process was jointly controlled by physical diffusion and chemical adsorption. DFT-calculated adsorption energies further demonstrated that hydroxyl and carboxyl groups on the biochar enhanced OFX adsorption by strengthening hydrogen bonding, π—π stacking, and electron donor–acceptor interactions. These findings indicate that poplar leaf biochar has promising potential for the treatment of antibiotic pollution in actual wastewater.