Adsorption performance of zero-valent iron-loaded biochar for tetracycline antibiotics

Tetracycline hydrochloride (TCH) and oxytetracycline hydrochloride (OTC) are widely used tetracycline antibiotics in global livestock production and the medical field. However, due to their strong chemical stability and resistance to degradation, these antibiotics can cause severe environmental pollution. Adsorption technology is an effective method for removing these drugs from wastewater. In this study, hexahydrate ferric chloride (FeCl₃·6H₂O), 2-methylimidazole (C₄H₆N₂), and potassium hydroxide (KOH) were used to modify biochar (BC) derived from Camellia seed shells, enhancing its adsorption performance for the TCH and OTC. The adsorption process primarily involves chemical adsorption and multilayer adsorption mechanisms. Solution pH significantly affects adsorption efficiency, with an optimum pH of 3. The maximum adsorption capacity for the TCH is 62.07 mg g^-1, while for the OTC it is 41.28 mg g^-1. An elevation in the operating temperature leads to a reduction in the adsorption capacity of TCH, while the adsorption capacity of OTC exhibits an initial decline followed by a subsequent increase. The adsorption mechanisms include π-π interactions, electrostatic forces, and hydrogen bonding between the biochar and the antibiotics.