Standardization and micromechanistic study of tetracycline adsorption by biochar

Modification serves as an excellent approach to enhancing the adsorption performance of biochar for tetracycline. Selective modification further allows the attainment of biochar materials that are not only more efficient but also cost-effective. However, the key structural factors influencing the adsorption of tetracycline by biochar remain unclear at present, hindering the effective guidance for modification strategies. This study established the relationship between carbonization degree and adsorption capacity, constructed a standardized microscopic model for biochar adsorption of tetracycline, and explored potential reaction mechanisms. The results indicated that with increases in the degree of carbonization, the tetracycline adsorption capacity of biochar increased from 16.08 mg L-1 to 98.35 mg L-1. The adsorption energy exhibited a strong correlation with the aromatic condensation of biochar at p <= 0.01, with a linear relationship (r2 >= 0.94). For low carbonization degrees, the adsorption of tetracycline by biochar was primarily driven by chemical bonds (69.21%) and complemented with electrostatic interactions, weak van der Waals forces or pi-pi interactions. For high carbonization degrees, the synergistic effects of hydrogen bonding, van der Waals forces, and pi-pi interactions determined the adsorption of tetracycline on biochar (91.1%). Additionally, larger carbon clusters resulted in stronger and more stable adsorption interactions. Furthermore, carboxyl-functionalized highly carbonized biochar displayed the highest reaction energy of - 1.8370 eV for adsorption of tetracycline through electrostatic interactions. This study suggests that a high degree of aromatic condensation in the carbon structure of biochar is crucial for the efficient adsorption of tetracycline. Low-carbonized biochar primarily adsorbs tetracycline through chemical bonds.High degree of aromatic condensation facilitates biochar adsorption of tetracycline.-COOH provides the highest binding affinity for tetracycline adsorption by high-carbonized biochar.