Two-step synthesis of nano-biochar and its adsorption performance for tetracycline hydrochloride

Although significant progress has been made in using biochar for the removal of antibiotics such as tetracycline hydrochloride, challenges remain in improving its dispersion, surface reactivity, and adsorption efficiency,highlighting the need for nanoscale engineering. In this study, monodisperse nano-biochar was synthesized from corn straw via a two-step precipitation-pyrolysis method and employed for the removal of tetracycline hydrochloride from aqueous solutions. The effects of material type, contact time, reaction temperature, and tetracycline hydrochloride concentration on the adsorption performance of nano-biochar were systematically investigated. The experimental results revealed that the nano-biochar prepared by the two-step method exhibited significantly enhanced removal efficiency of tetracycline hydrochloride compared to conventional biochar. Under optimized conditions (25 ℃, initial tetracycline hydrochloride concentration of 200 mg/L, and 0.5 g/L nano-biochar dosage), the maximum adsorption capacity reached 141.4 mg/g. Mechanistic analysis revealed that the adsorption process was primarily driven by the synergistic effects of physical and chemical adsorption. Compared to conventional biochar, the smaller particle size of nano-biochar enabled stable dispersion in aqueous solutions, thereby improving contact efficiency with pollutants. Additionally, the nano-biochar surface is rich in functional groups and active sites, which facilitates the formation of stable chemical bonds, further enhancing adsorption capacity and binding stability.