Adsorption of tetracycline antibiotics in water by hydrochloric acid modified biochar

In this study, waste poplar branches from landscaping were used as raw material to prepare pristine biochar (BC) via high-temperature pyrolysis, and hydrochloric acid-modified biochar (HBC) was obtained through chemical modification. The adsorption performance and mechanism of these biochars for tetracycline hydrochloride (TCH) in aqueous solutions were systematically investigated. Results indicated that hydrochloric acid modification effectively removed inorganic ash fractions (e.g., CaCO₃) from the biochar, significantly increased the pore size, and enriched surface oxygen-containing functional groups (such as C-O, -OH, and C=O), thereby enhancing its adsorption capacity. Under the optimal adsorption conditions (dosage = 2. 4 g/L, pH=3, temperature=35℃), the adsorption rate of TCH by HBC increased from 50.29% (for BC) to 82%, with a maximum adsorption capacity of 76.61 mg/g. The adsorption behavior followed the Langmuir isotherm model and pseudo-second-order kinetic model, suggesting that the process is monolayer chemisorption. The primary adsorption mechanisms include electrostatic attraction, hydrogen bonding, and π-π interactions. This study provides a feasible approach for the resource utilization of landscaping waste and the efficient removal of tetracycline antibiotics from water bodies, achieving both environmental and economic benefits.