Highly Efficient Adsorption of Norfloxacin by Low-Cost Biochar: Performance, Mechanisms, and Machine Learning-Assisted Understanding

Abstract

This study employed potassium carbonate (K₂CO₃) activation using ball milling in conjunction with pyrolysis to produce biochar from one traditional Chinese herbal medicine <i>Atropa belladonna</i> L. (ABL) residue. The resulting biochar KBC₈₀₀ was found to possess a high specific surface area (<i>S</i> _BET = 1638 m²/g) and pore volume (1.07 cm³/g), making it effective for removing norfloxacin (NOR) from wastewater. Batch adsorption tests confirmed its effectiveness in eliminating NOR, along with its excellent resistance to interference from impurity ions or antibiotics. Notably, the maximum experimental NOR adsorption capacity on KBC₈₀₀ was 666.2 mg/g at 328 K, surpassing those of other biochar materials reported. The spontaneous and endothermic adsorption of NOR on KBC₈₀₀ could be better suited to the Sips model. Additionally, KBC₈₀₀ adsorbs NOR mainly by pore filling, with electrostatic attraction, π-π EDA interactions, and hydrogen bonds also contributing significantly. The machine learning model revealed that NOR adsorption on the biochar was significantly affected by the initial concentration, followed by <i>S</i> _BET and average pore size. Based on the random forest model, it is demonstrated that biochar is able to adsorb NOR effectively. It is noteworthy that the use of low-cost pharmaceutical wastes to produce adsorbents for emerging contaminants such as antibiotics could have greater potential for future practical applications under the ongoing dual carbon policy.